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Birds and influenza H5N1 virus movement to and within North America.

Highly pathogenic avian influenza avian influenza: see influenza.  (HPAI HPAI Highly Pathogenic Avian Influenza
HPAI Hospital Pharmacists Association, Ireland
HPAI Hewlett Packard Associates International
) H5N1 expanded considerably during 2005 and early 2006 in both avian avian /avi·an/ (a´ve-an) of or pertaining to birds.

Of, relating to, or characteristic of birds.
 host species and geographic distribution. Domestic waterfowl waterfowl, common term for members of the order Anseriformes, wild, aquatic, typically freshwater birds including ducks, geese, and screamers. In Great Britain the term is also used to designate species kept for ornamental purposes on private lakes or ponds, while in  and migratory migratory /mi·gra·to·ry/ (mi´grah-tor?e)
1. roving or wandering.

2. of, pertaining to, or characterized by migration; undergoing periodic migration.


emanating from or pertaining to migration.
 birds are reservoirs, but lethality of this subtype (programming) subtype - If S is a subtype of T then an expression of type S may be used anywhere that one of type T can and an implicit type conversion will be applied to convert it to type T.  appeared to initially limit migrant effectiveness as introductory hosts. This situation may have changed, as HPAI H5N1 has recently expanded across Eurasia and into Europe and Africa. Birds could introduce HPAI H5N1 to the Western Hemisphere Western Hemisphere

Part of Earth comprising North and South America and the surrounding waters. Longitudes 20° W and 160° E are often considered its boundaries.
 through migration, vagrancy vagrancy, in law, term applied to the offense of persons who are without visible means of support or domicile while able to work. State laws and municipal ordinances punishing vagrancy often also cover loitering, associating with reputed criminals, prostitution, and , and importation by people. Vagrants and migratory birds are not likely interhemispheric introductory hosts; import of infected domestic or pet birds is more probable. If reassortment or mutation were to produce a virus adapted for rapid transmission among humans, birds would be unlikely introductory hosts because of differences in viral transmission mechanisms among major host groups (i.e., gastrointestinal for birds, respiratory for humans). Another possible result of reassortment would be a less lethal form of avian influenza, more readily spread by birds.


Avian influenza virus A refers collectively to a group of viruses within the family Orthomyxoviridae that has a worldwide distribution and causes a variety of diseases in birds. Classification of influenza viruses is based on 2 glycoproteins (antigens) characteristic of the group members: hemagglutinin hemagglutinin /he·mag·glu·ti·nin/ (-gloo´ti-nin) an antibody that causes agglutination of erythrocytes.

cold hemagglutinin  one which acts only at temperatures near 4° C.
, of which 16 forms are known; and neuraminidase neuraminidase /neu·ra·min·i·dase/ (-ah-min´i-das) an enzyme of the surface coat of myxoviruses that destroys the neuraminic acid of the cell surface during attachment, thereby preventing hemagglutination. , of which 9 forms have been described. In 1997, a virulent, highly pathogenic avian influenza (HPAI) A virus, identified as the H5N1 subtype, was identified in samples taken in Hong Kong Hong Kong (hŏng kŏng), Mandarin Xianggang, special administrative region of China, formerly a British crown colony (2005 est. pop. 6,899,000), land area 422 sq mi (1,092 sq km), adjacent to Guangdong prov.  (1,2). This virus has spread to several localities in Asia and, since late 2005, Europe (3) and Africa (4) (Table 1). HPAI HSN HSN Home Shopping Network
HSN High Speed Network
HSN Hereditary Sensory Neuropathy
HSN Highly Saturated Nitrile
HSN Healthy Schools Network, Inc.
HSN Hopping Sequence Number
HSN Historical Sample of the Netherlands
HSN Haiti Support Network
1 virus is found most commonly in domestic fowl, although as of late 2005, it has been found in migratory and resident birds of several orders (mainly Anseriformes) and in pigs, civets, house cats, tigers, leopards, and humans (3). This virus poses a potential danger to human populations; 224 human cases of HSN1 avian influenza have been reported as of May 29, 2006; 127 of these cases were fatal (17). Its discovery in migratory birds is especially troubling because of the potential for rapid dispersal of the virus across continents and hemispheres.

We review facts concerning outbreaks of H5N1; the species of birds, especially migrants, known to have been infected by this subtype; and available information on the ability of migrants to serve as reservoir or introductory hosts that move the virus from outbreak areas to new localities. On the basis of this information, we consider the avian pathways by which HPAI H5N1 might enter the Western Hemisphere and, once present, the likelihood that it will be able to disperse to new regions. We define migratory or migrant birds as those species that move annually between geographically separate breeding and wintering quarters. Migrating birds are those actually in the process of moving from 1 locality to another.

Ecology of Influenza A influenza A
Influenza caused by infection with a strain of influenza virus type A.

influenza A Infectious disease An avian virus, especially of ducks–which in China live near the pig reservoir and 'vector';

Avian influenza A viruses are common and widespread in birds. Most viruses in this family attack the intestinal tract of the host preferentially and are spread mainly by shedding in host feces (18,19). Waterfowl, e.g., ducks, geese, and swans (Anseriformes), and shorebirds (Charadriiformes) are particularly susceptible because they are exposed to water that may be contaminated contaminated,
v 1. made radioactive by the addition of small quantities of radioactive material.
2. made contaminated by adding infective or radiographic materials.
3. an infective surface or object.
 with infected fecal fecal /fe·cal/ (fe´k'l) pertaining to or of the nature of feces.

Relating to or composed of feces.


pertaining to or of the nature of feces.
 matter, especially at specific sites and seasons, when these birds congregate densely at relatively confined and shallow water See:
  • Shallow water blackout
  • Waves and shallow water
  • Shallow water equations
  • Shallow Water, Kansas
 bodies (Figure 1). A secondary mode of viral spread is consumption of infected avian host parts by predators, including captive carnivores, avian raptors, and carrion-feeding vertebrates. Infection by most avian influenza A strains appears to be asymptomatic for the host (18). Proportions of birds shedding active virus can be high (e.g., >30% in some Canadian duck populations) among juvenile waterfowl gathered in large flocks on lakes and ponds during the summer postbreeding molting molting, periodical shedding and renewal of the outer skin, exoskeleton, fur, or feathers of an animal. In most animals the process is triggered by secretions of the thyroid and pituitary glands.  period but decrease rapidly during southward south·ward  
adv. & adj.
Toward, to, or in the south.

A southward direction, point, or region.

 migration, falling to 1% to 2% during winter (18). Nevertheless, shedding of active virus can remain as high as 0.25% by individual birds among northbound spring migrants, sufficient to reinfect Re`in`fect´   

v. t. 1. To infect again.
 northern breeding populations (18).


Most birds appear to be more or less susceptible to [greater than or equal to] 1 strain of avian influenza A, but rates of infection and levels of susceptibility to the different viral subtypes vary among taxa taxa: see taxon. . For instance, H3 and H6 subtypes are common in ducks, geese, and swans (Anseriformes), while H4, H9, H11, and H13 subtypes are more prevalent in sandpipers, terns, and gulls (Charadriiformes) (20). The best opportunities for viral transmission among large numbers of anseriform hosts would likely be on lakes and ponds in summer, where large concentrations gather for weeks to undergo the postbreeding, premigratory molt (18). For charadriiformes, the greatest viral transmission opportunities would likely be at stopover sites during fall migration, where tens of thousands of individual birds congregate to feed and roost (20).

Avian Influenza in Humans

Humans and other mammals normally are not susceptible to infection by avian influenza A viruses. Nevertheless, several subtypes of avian influenza or bird-origin influenza viruses have infected humans; 3 of these subtypes have caused pandemics within the past century. At present, HPAI H5N1 is entirely an avian influenza subtype. Humans can become infected, but so far as is known, they must inhale in·hale
1. To breathe in; inspire.

2. To draw something such as smoke or a medicinal mist into the lungs by breathing; inspire.
 or ingest in·gest  
tr.v. in·gest·ed, in·gest·ing, in·gests
1. To take into the body by the mouth for digestion or absorption. See Synonyms at eat.

 massive viral doses from excreta excreta /ex·cre·ta/ (eks-kret´ah) excretion (2).

Waste matter, such as sweat or feces, discharged from the body.
 or tissues of infected birds to do so. Although clinically ill humans have high death rates, [approximately equal to] 50%, passage of H5N1 virus from human to human is rare (3).

The more humans infected with HPAI H5N1, the greater the probability that reassortment with a human influenza virus strain will occur and produce a lethal form that is spread readily between humans (18,19). However, viral interhost transmission strategies differ fundamentally for those viruses that primarily infect humans versus those that infect birds. Bird viruses have an affinity for the host's intestinal tract, and interhost transmission occurs mainly by fecal contamination of shared water bodies. Human viruses more often attack the respiratory system respiratory system: see respiration.
respiratory system

Organ system involved in respiration. In humans, the diaphragm and, to a lesser extent, the muscles between the ribs generate a pumping action, moving air in and out of the lungs through a
 and depend on shedding in respiratory effluvia for interhost transfer. If, or when, a reassortment or mutation of HPAI H5N1 produces a virus capable of efficient horizontal transfer among humans, the new virus would likely not be particularly effective in transfer among birds; migrants likely would play little role in spread of such a virus. Vaccines produced to prevent human infection by H5N1 might not be effective against a new virus produced by reassortment.

Birds as HPAI H5N1 Reservoirs and Introductory Hosts in the Old World

The main reservoirs and introductory hosts for avian sinfluenza A viruses in general are migratory waterfowl and domestic fowl (18,19). HPAI H5N1, however, causes high rates of disabling dis·a·ble  
tr.v. dis·a·bled, dis·a·bling, dis·a·bles
1. To deprive of capability or effectiveness, especially to impair the physical abilities of.

2. Law To render legally disqualified.
 illness and death in most avian species (21). High rates of illness would prevent migrants from being introductory hosts, since sick wild birds normally cannot move far and do not survive long. Thus, perhaps not surprisingly, no evidence exists that migrants were introductory hosts for H5N1 for several years after its initial appearance in Guangdong Province Noun 1. Guangdong province - a province in southern China
Guangdong, Kwangtung
, People's Republic People's Republic
A political organization founded and controlled by a national Communist party.
 of China, in 1996. In fact, no deaths or even infections of migrants were reported until December 2002, when several migrants and exotic birds The Exotic Birds was a pop music group formed in Cleveland, Ohio in 1983 by three Cleveland Institute of Music percussion students, Andy Kubiszewski, Tom Freer and Tim Adams. They wrote their own music and were described as synth pop, techno-pop and techno-dance.  were found dead at a Hong Kong park
This article is about a park in Central, Hong Kong. For general information on the parks in Hong Kong,
please refer to List of urban public parks and gardens of Hong Kong.
 and zoologic garden (10). Of 3,095 outbreaks of HPAI H5N1 reported from December 2003 through February 2005, all involved captive birds or domestic fowl (6). Until early August 2005, only 2 outbreaks of HPAI H5N1 had been confirmed in migratory birds presumed to be completely separate from domestic fowl: Qinghai Lake Qinghai Lake, often known by its Mongol name, Koko Nor or "The Blue Lake" (Tibetan: mTsho sngon po), is located in what was the former Tibetan province of Amdo, now part of the Chinese province of Qinghai.  and Xinjiang Province, China, (April, May 2005) (12) and Lakes Erhel and Khunt in northern Mongolia (August 2005) (15). However, that situation has changed, and several new outbreaks have been recorded in migrants that were presumably pre·sum·a·ble  
That can be presumed or taken for granted; reasonable as a supposition: presumable causes of the disaster.
 separate from domestic fowl within the last few months (online Appendix; available from http://www.cdc. gov/ncidod/EID/vol12no_10/05-1577_app.htm), perhaps signaling genetic modification of the virus (19).

Data based on observations of dead wild birds at sites where infections have broken out and negative results from subsequent extensive screening for seropositive seropositive /se·ro·pos·i·tive/ (-poz´i-tiv) showing positive results on serological examination; showing a high level of antibody.

 or infected migrants around outbreak sites have indicated that HPAI H5N1 was lethal for most wild birds, at least until recently. Nevertheless, some studies have demonstrated that chickens, domestic ducks, and geese infected under laboratory conditions, as well as some wild birds exposed under quasilaboratory conditions (e.g., birds fed, watered, and protected at zoologic parks or gardens), survive infection and shed the virus in active form (10,22,23). The work by Komar et al. (24) on wild birds exposed to West Nile virus West Nile virus, microorganism and the infection resulting from it, which typically produces no symptoms or a flulike condition. The virus is a flavivirus and is related to a number of viruses that cause encephalitis.  (WNV WNV West Nile Virus
WNV World Net Visions
) under laboratory conditions may be instructive in this regard. These researchers found that in species like the fish crow fish crow
A crow (Corvus ossifragus) native to the coastal regions and rivers of the eastern United States.
 (Corvus ossifragus), in which individual birds were known to have high death rates on exposure to the New York New York, state, United States
New York, Middle Atlantic state of the United States. It is bordered by Vermont, Massachusetts, Connecticut, and the Atlantic Ocean (E), New Jersey and Pennsylvania (S), Lakes Erie and Ontario and the Canadian province of
 99 subtype of WNV in the wild (on the basis of large numbers of birds found dead and failure to find free-flying birds captured that were seropositive), survival rates from exposure in the laboratory were 45%. When one considers that birds kept in a laboratory have ready access to food and water during their illness, as well as protection from inclement in·clem·ent  
1. Stormy: inclement weather.

2. Showing no clemency; unmerciful.

 weather and predators, this finding perhaps is not surprising. However, wild birds associating with free-ranging domestic fowl at farm ponds, or captive exotic birds at city parks or zoological gardens, may receive some of the same benefits as laboratory birds, experiencing conditions conducive to survival of infection by HPAI H5N1.

Recent detections of HPAI H5N1 in free-ranging migrants may be a result of heightened awareness and thus the virus could have been circulating in migrants, although undetected. This explanation is unlikely considering the extensive screening of blood and feces of migrants in the past several years in Europe, parts of Asia, and North America North America, third largest continent (1990 est. pop. 365,000,000), c.9,400,000 sq mi (24,346,000 sq km), the northern of the two continents of the Western Hemisphere. . These screenings have searched for birds seropositive for H5N1 and other avian influenza type A viruses. These searches have involved sampling thousands of birds of hundreds of species (25,26). The virus may also have changed to some degree (2,19), allowing higher survival rates among some species of migrants. Both explanations may have some relevance to the current situation. In any event, some migratory birds may now be able to move HPAI H5N1 in active form over considerable distances (online Appendix). Increasing numbers of recent reports document apparent movement of the virus, whereas before April 2005, no evidence existed of HPAI H5N1 in free-ranging migratory birds distant from domestic fowl, despite years of sampling of tens of thousands of migratory waterfowl of several species from wetland sites across the European continent (25).

Possible Role of Birds in Arrival of HPAI H5N1 Avian Influenza in New World

To date, HPAI H5N1 has not been recorded in the New World, although outbreaks of related avian influenza viruses lethal to domestic fowl have occurred in Ontario, Canada, in 1966 (H5N9); Pennsylvania, United States United States, officially United States of America, republic (2005 est. pop. 295,734,000), 3,539,227 sq mi (9,166,598 sq km), North America. The United States is the world's third largest country in population and the fourth largest country in area.  in 1983 (H5N2); Puebla, Mexico, in 1994 (H5N2); Chile in 2002 (H7N3); Canada in 2004 (H7N3); and Texas, United States, in 2004 (H5N2) (27). All of these outbreaks occurred in domestic poultry and were controlled without further diffusion. We see 3 possible modes by which HPAI H5N1 might gain entry to the New World if birds were the introductory host: 1) normal interhemispheric migration, 2) vagrancy, and 3) legal and illegal importation of birds as explained in the following section.

Normal Interhemispheric Migration

Few individual birds within few species undertake regular, interhemispheric migration. However, some do, and the waterfowl (Anseriformes, Charadriiformes, Ciconiiformes) could be introductory hosts for HPAI H5N1 to the New World (Table 2). Three pathways are used annually by a small number of waterfowl species to travel between the hemispheres: 1) Alaska-East Asia, in which birds that breed in Alaska winter in East Asia East Asia

A region of Asia coextensive with the Far East.

East Asian adj. & n.
; 2) East Asia-Pacific North America, in which birds that breed in northeast Asia Often used interchangeably with the term 'East Asia,' Northeast Asia is, as its name implies, in the geographic northeast region of Asia. Being a geographic, rather than a cultural term--as opposed to East Asia, which has varying definitions, some being cultural--Northeast Asia  winter along the Pacific Coast of North America; and 3) Europe-Atlantic North America, in which birds that breed in Iceland or northwestern Europe winter along the Atlantic Coast of North America (Figure 2, Table 2).


Two lines of evidence argue against normal, interhemispheric migration as a likely mode of entry for HPAI H5N1 into the Western Hemisphere. First, as discussed previously, data indicate that most infected individual birds of most species of migrants become extremely ill and either cannot migrate far in their weakened state or die at the place of infection. Second, investigation of the genetics of avian influenza viruses has shown that little natural interchange occurs between the Eastern and Western Hemispheres: each hemisphere appears to have an avian influenza virus community that is largely distinct (18). This fact is particularly noteworthy when one considers that most avian influenza A viruses appear to be asymptomatic, and migrants readily transport them in infectious form, in stark contrast to the situation for HPAI H5N1. Presumably, the distinct nature of the avian influenza A community in each hemisphere results from the fact that the main reservoir for these viruses is migrants, and few migrants move regularly between the hemispheres (32).


Perhaps a third or more of Eurasian waterfowl species have traveled into the Western Hemisphere as vagrants; some occur more regularly than others, including those listed in Table 2. However, all Eurasian vagrants are, by definition, extremely rare in the New World (a few birds per decade). One mode of interhemispheric vagrancy is tropical storm tropical storm
A cyclonic storm having winds ranging from approximately 48 to 121 kilometers (30 to 75 miles) per hour.

tropical storm 
 systems that originate off the West African West Africa

A region of western Africa between the Sahara Desert and the Gulf of Guinea. It was largely controlled by colonial powers until the 20th century.

West African adj. & n.
 coast during the Atlantic hurricane Atlantic hurricane refers to a tropical cyclone that forms in the Atlantic Ocean usually in the Northern Hemisphere summer or autumn, with one-minute maximum sustained winds of 74 mph (64 knots, 33 m/s, 119 km/h).  season, which lasts from June to November each year. These systems can, and occasionally do, sweep up Verb 1. sweep up - force into some kind of situation, condition, or course of action; "They were swept up by the events"; "don't drag me into this business"
drag in, embroil, tangle, drag, sweep
 and transport Old World birds, especially waterfowl, across the Atlantic to the New World (route 4, Figure 2). Vagrancy is much rarer (by several orders of magnitude) than normal interhemispheric migration and seems an even less likely mode of entry for HPAI H5N1.

Legal and Illegal Importations

Human traffic in birds and bird products is the sole documented means of HPAI H5N1 movement between geographically separate regions to date (19). While migratory birds have been suspected of involvement, particularly in cases in which no obvious human interchange of infected birds or products has occurred, these conclusions are inferred (19). Thus, if HPAI H5N1 is to be kept out of the Western Hemisphere, control of legal and illegal imports should be the primary focus of prevention efforts.

The legal importation of exotic birds has declined dramatically in the United States since enactment of the 1992 Wild Bird Conservation Act. Nevertheless, 2,770 birds entered the country through the New York port of entry in 1999, including 323 pet birds and 2,447 commercial birds. In addition, 12,931 birds passed through in transit (S. Kaman, US Department of Agriculture [USDA USDA, See United States Department of Agriculture.
], pers. comm.) Legal importations are controlled by USDA Animal and Plant Health Inspection Service and the US Fish and Wildlife Service. Most imported birds undergo a 30-day quarantine at USDA facilities located near each of the 3 allowed ports of entry: New York, Miami, and Los Angeles Los Angeles (lôs ăn`jələs, lŏs, ăn`jəlēz'), city (1990 pop. 3,485,398), seat of Los Angeles co., S Calif.; inc. 1850. . Quarantine procedures include isolation in indoor, air-filtered cages and standard testing for common poultry diseases, including avian influenza. The number of illegally imported birds is not known. These birds are not subject to quarantine and testing and could be a mode of entry for HPAI H5N1. Hawk eagles from Thailand infected with the virus were recently detected while being smuggled smug·gle  
v. smug·gled, smug·gling, smug·gles
1. To import or export without paying lawful customs charges or duties.

2. To bring in or take out illicitly or by stealth.
 into Belgium (11). Although these birds were detected and quarantined, they serve as an example of how such imports could spread the virus. Species commonly associated with the transhemispheric bird trade are listed in Table 2.

If birds turn out to be responsible for entry of HPAI H5N1 into the Western Hemisphere, illegal import of an infected bird or bird product seems the most likely mode of entry. We base this conclusion on the fact that illegally imported birds, unlike infected, free-flying migrants, are provided food and water ad libitum ad libitum

without restraint.

ad libitum feeding
food available at all times with the quantity and frequency of consumption being the free choice of the animal.
 and protected from predators, greatly increasing their chances of survival in an infectious state. Furthermore, these birds often end up in close association with other, similarly protected birds, sharing the same food or water, a situation that provides ample opportunity for viral transmission.

Possible Role of Birds in Movement of HPAI H5N1 in Western Hemisphere

Movement of HPAI H5N1 by sale of infected domestic fowl or poultry products in the United States and Canada is unlikely, given existing regulations. Thus, a major mode of HPAI spread available in much of Eurasia would be ruled out. Also, most domestic fowl are kept separate from wild migratory waterfowl in both countries, which would rule out a second major mode of introduction and cross-infection. Mixing of wild migratory birds with captive, exotic birds is relatively common, however, at North American North American

named after North America.

North American blastomycosis
see North American blastomycosis.

North American cattle tick
see boophilusannulatus.
 zoos. Birds in such exhibits should be screened regularly for H5N1 or whatever HPAI virus is in circulation during a given year.

The HPAI H5N1 subtype of avian influenza A causes high mortality rates in most wild birds, at least in its present form. The situation is similar to that found for the form of WNV introduced into the Western Hemisphere in 1999 (24,32-34). Even under conditions in which food, water, and protection from predators are provided, death rates are high. These kinds of death rates could result if the current form of HPAI H5N1 were introduced into New World bird populations. In such a scenario, migrants might not be capable of moving the virus far from its point of introduction, at least initially. Also, the die-offs occurring at the site of entry likely would be obvious to wildlife disease monitors, which would allow for rapid quarantine. However, if the H5N1 virus were introduced into the Western Hemisphere, migratory birds, particularly anseriforms (ducks, swans, geese), might serve as dispersal agents, especially if the virus were to change to a less lethal form through reassortment or mutation.

A key difference between mosquitoborne WNV and birdborne HPAI H5N1 is the virtual absence of effective reservoir hosts other than birds for the latter. WNV can be maintained without birds because infected mosquitoes can pass active virus to subsequent generations through vertical transmission (35). So far as is known, no alternative to birds exists as major reservoir hosts for HPAI H5N1.

An additional consideration concerning the future of HPAI H5N1, should it gain wide circulation in migratory birds, is the possibility of infection of a bird already infected with another form of avian influenza virus. Such infection could result in reassortment and production of a new virus, possibly less lethal than HPAI H5N1 but more readily spread.


HPAI H5N1 spread rapidly across Eurasia during 2005 for reasons that are not entirely understood. Despite this rapid movement, effective introduction (i.e., under conditions allowing its spread) of the virus to the New World through migratory or vagrant VAGRANT. Generally by the word vagrant is understood a person who lives idly without any settled home; but this definition is much enlarged by some statutes, and it includes those who refuse to work, or go about begging. See 1 Wils. R. 331; 5 East, R. 339: 8 T. R. 26.  birds seems unlikely. Few individual members of few waterfowl species migrate between hemispheres, and should a bird make the journey while shedding sufficient active virus to infect birds in the Western Hemisphere, newly infected birds would probably die before being able to transport the virus from the entry site. If spread of HPAI H5N1 to the New World occurs in its current form (e.g., through domestic or pet bird trade or smuggling smuggling, illegal transport across state or national boundaries of goods or persons liable to customs or to prohibition. Smuggling has been carried on in nearly all nations and has occasionally been adopted as an instrument of national policy, as by Great Britain ), it should be readily detectable because of the large number of dead native birds likely to result. However, the virus is changing (19), and a modified H5N1 virus introduced into the Western Hemisphere could be moved more readily by migratory waterfowl. If this event were to occur, the virus should be amenable to control through isolation and quarantine. If viral reassortment or mutation occurs to produce a new virus that is readily transmissible transmissible /trans·mis·si·ble/ (trans-mis´i-b'l) capable of being transmitted.

Capable of being conveyed from one person to another.
 to humans, the role of birds in general and migrants in particular may be moot because of the fundamentally different methods of infection favored by viruses infecting humans and birds. Viruses infecting birds preferentially attack the intestinal tract and are shed with the feces; by contrast, human viruses mainly attack the respiratory tract respiratory tract
The air passages from the nose to the pulmonary alveoli, including the pharynx, larynx, trachea, and bronchi.

Respiratory tract 
 and are shed with respiratory effluvia. If HPAI H5N1 were to gain wide circulation among migrants, it might infect a bird already infected with another form of avian influenza A and undergo reassortment to produce a low-pathogenic form that is more readily spread.


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1. a widespread epidemic of a disease.

2. widely epidemic.

Epidemic over a wide geographic area.

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(17.) World Health Organization (WHO). Cumulative number of confirmed human cases of avian influenza A/(H5N1) reported to WHO as of 29 May 2006 [article in French] [cited 2006 May 29]. Available from table_2006_05_29/en/index.html

(18.) Webster RG, Bean W, Gorman O, Chambers T, Kawaoka Y. Evolution and ecology of influenza A viruses. Microbiol Rev. 1992;56:152-79.

(19.) Webster RG, Peiris M, Chen H, Guan Y. H5N1 outbreaks and enzootic en·zo·ot·ic
Prevalent among or restricted to animals of a specific geographic area. Used of a disease.

An enzootic disease.


peculiar to or present constantly in a location. See also endemic.
 influenza. Emerg Infect Dis. 2006;12:3-8.

(20.) Kawaoka Y, Chambers T, Sladen W, Webster G. Is the gene pool of influenza viruses in shorebirds and gulls different from that in wild ducks? Virology. 1988; 163:247-50.

(21.) Perkins LE, Swayne D. Comparative susceptibility of selected avian and mammalian species to a Hong Kong-origin H5N1 high-pathogenicity avian influenza virus. Avian Dis. 2003;47:956-67.

(22.) Shortridge KF, Zhou N, Guan Y, Gao P, Ito T, Kawaoka Y, et al. Characterization of avian H5N1 influenza viruses from poultry in Hong Kong. Virology. 1998;252:331-42.

(23.) Hulse-Post DJ, Sturm-Ramirez K, Humberd J, Seiler P, Govorkova E, Krauss S, et al. Role of domestic ducks in the propagation and biological evolution of highly pathogenic H5N1 influenza viruses in Asia. Proc Natl Acad Sci U S A. 2005;102:10682-7.

(24.) Komar N, Langevin S, Hinten S, Nemeth E, Edwards D, Hettler B, et al. Experimental infection of North American birds <onlyinclude> This list of North American birds is a comprehensive listing of all the bird species known from the North American continent north of Mexico. </onlyinclude>  with the New York 1999 strain of West Nile virus. Emerg Infect Dis. 2003;9:311-22.

(25.) Munster VJ, Wallensten A, Baas C, Rimmelzwann G; Schutten M, Olsen B, et al. Mallards and highly pathogenic avian influenza ancestral viruses, northern Europe. Emerg Infect Dis. 2005; 11:1545-51.

(26.) Spackman E, Stallknecht D, Slemons R, Winker K, Suarez D, Scott M, et al. Pbylogenetic analyses of type A influenza genes in natural reservoir Natural reservoir or nidus, refers to the long-term host of the pathogen of an infectious disease. It is often the case that hosts do not get the disease carried by the pathogen or it is asymptomatic and non-lethal.  species in North America reveals genetic variation. Virus Res. 2005;114:89-100.

(27.) Werner O. Klassische Gefluegelpest--eine Uebersicht. Berl Munch munch - To transform information in a serial fashion, often requiring large amounts of computation. To trace down a data structure. Related to crunch and nearly synonymous with grovel, but connotes less pain.

Often confused with mung.
 Tierarztl Wochenschr. 2006;119:140-50.

(28.) Kessel B, Gibson D. Status and distribution of Alaska birds. Studies in Avian Biology. 1978;1:1-100.

(29.) Palmer R. Handbook of North American birds. Vol 2. New Haven New Haven, city (1990 pop. 130,474), New Haven co., S Conn., a port of entry where the Quinnipiac and other small rivers enter Long Island Sound; inc. 1784. Firearms and ammunition, clocks and watches, tools, rubber and paper products, and textiles are among the many  (CT):Yale University Yale University, at New Haven, Conn.; coeducational. Chartered as a collegiate school for men in 1701 largely as a result of the efforts of James Pierpont, it opened at Killingworth (now Clinton) in 1702, moved (1707) to Saybrook (now Old Saybrook), and in 1716 was  Press; 1976.

(30.) American Ornithologists' Union The American Ornithologists' Union (AOU) an ornithological organization in the USA. Unlike the National Audubon Society, its members are primarily professional ornithologists rather than amateur birders.  (AOU AOU American Ornithologists' Union
AOU Apparent Oxygen Utilization
AOU American Ornithological Union
AOU Arab Open University (Saudi Arabia)
AOU American Open University
AOU Arithmetic Output Unit
AOU Area Of Uncertainty
). The A.O.U. check-list of North American birds. 7th ed. Washington: American Ornithologists' Union; 1998.

(31.) Rasmussen P, Anderton J. Birds of South Asia The birds of South Asia include the species found in India, Pakistan, Nepal, Bangladesh, Bhutan, Sri Lanka and the Maldives.

This is not only a huge geographical area, but has a range of habitats extending from deserts to rainforest, and from the world's highest mountains to
: the Ripley guide. Barcelona: Lynx Ed.; 2005.

(32.) Rappole JH, Derrickson S, Hubalek Z. Migratory birds and spread of West Nile virus in the Western Hemisphere. Emerg Infect Dis. 2000;6:319-28.

(33.) Bernard KA, Maffei J, Jones S, Kauffman E, Ebel G, Dupuis A II, et al. West Nile virus infection in birds and mosquitoes, New York State, 2000. Emerg Infect Dis. 2001;7:679-85.

(34.) Brault AC, Langevin S, Bowen R, Panella N, Biggerstaff B, Miller B, et al. Differential virulence of West Nile West Nile may refer to:
  • West Nile virus
  • West Nile region in Uganda
 strains for American crows. Emerg Infect Dis. 2004;10:2161-8.

(35.) Nasci RS, Savage HM, White DJ, Miller JR, Cropp BC, Godsey MS, et al. West Nile virus in overwintering o·ver·win·ter·ing
The persistence of an infectious agent in its vector for an extended period, as in the cooler winter months, during which the vector has no opportunity to be reinfected or to infect another host.
 Culex Culex /Cu·lex/ (ku´leks) a genus of mosquitoes found throughout the world, many species of which are vectors of disease-producing organisms.

 mosquitoes, New York City New York City: see New York, city.
New York City

City (pop., 2000: 8,008,278), southeastern New York, at the mouth of the Hudson River. The largest city in the U.S.
, 2000. Emerg Infect Dis. 2001;7:742-7.

Address for correspondence: John H. Rappole, 1500 Remount re·mount  
tr.v. re·mount·ed, re·mount·ing, re·mounts
1. To mount again.

2. To supply with a fresh horse.

A fresh horse.

Noun 1.
 Rd, Front Royal, VA 22630, USA; email:

John H. Rappole * and Zdenek Hubalek ([dagger])

* Smithsonian Institution Smithsonian Institution, research and education center, at Washington, D.C.; founded 1846 under terms of the will of James Smithson of London, who in 1829 bequeathed his fortune to the United States to create an establishment for the "increase and diffusion of , Washington, DC, USA; and ([dagger]) Academy of ciences, Valtice, Czech Republic Czech Republic, Czech Česká Republika (2005 est. pop. 10,241,000), republic, 29,677 sq mi (78,864 sq km), central Europe. It is bordered by Slovakia on the east, Austria on the south, Germany on the west, and Poland on the north.

Dr Rappole is a research scientist with the Smithsonian National Zoological Park's Conservation and Research Center. His principal research interests are migratory bird ecology and evolution, sub-Himalayan ornithogeography, and avian conservation.

Dr Hubalek is a scientist at the Academy of Sciences of the Czech Republic The Academy of Sciences of the Czech Republic Czech: Akademie věd České republiky, abbr. AV ČR . He is interested in the ecology of arthropodborne human pathogenic viruses and bacteria.
Table 1. Geographic spread of highly pathogenic avian influenza H5N1
subtype since 1996

Date                                       Event

1996                 1st isolation, domestic geese, southern China (5)
1997-1998            Chickens, Hong Kong, 18 humans (6 deaths) (6)
1999                 Geese, Hong Kong (7)
2001                 Geese from China in Vietnam (8)
Nov 2002             Hong Kong poultry, other bird species in or near
                     zoologic parks (7)
Feb 2003             Human travelers from Fujian Province (China) (9)
Dec 2003-Nov 2005    Poultry (mainly chickens) and humans: South Korea,
                     Vietnam, Thailand, Hong Kong, Cambodia, Laos,
                     Indonesia, China, and Malaysia (6)
Jan 2004             Wild birds: Hong Kong (10)
Feb 2004             Birds in a zoo collection: Cambodia (10)
Mar 2004             Wild bird: South Korea (10)
Oct 2004             Bird smuggled from Thailand into Belgium (11)
Apr-Jun 2005         Migratory birds: Qinghai Lake and Xinjiang
                     Province, China (12)
Jul-Oct 2005         Poultry and wild waterfowl: Novosibirsk, Altai,
                     Kurgansk, Omsk, and Tyumen regions, Asian Russia
                     (13, 14)
Aug 2005             Geese and other poultry: northern Kazakhstan,
                     Tibet (13)
Aug 2005             Migratory waterfowl: northern Mongolia (15)
Aug-Oct 2005         Poultry and pigeons: Ural Territory, Russia (13)
Aug 2005             Wild waterfowl: Kalmykia, European Russia (13)
Oct 2005             Domestic turkeys: Western Asian turkey (13)
Oct-Nov 2005         Poultry and wild migratory birds: Romania, Ukraine
Oct 2005             Wild birds: Thailand (15)
Oct-Nov 2005         Poultry, wild birds, some humans: 7 Chinese
                     provinces (15)
Oct 2005             Migratory waterfowl: Croatia (13)
Oct 2005             Poultry: Tula and Tambov regions, European Russia
Oct 2005             Quarantined birds from Taiwan in United Kingdom
Jan 2006             Humans: Iraq (15)
Jan 2006             Poultry: Nigeria, India (Maharashtra) (15)
Feb 2006             Migratory waterfowl: Bulgaria, Greece, Italy,
                     Slovenia, Bosnia, Azerbaijan, Iran, Georgia,
                     Germany, Switzerland, Austria, Hungary, France,
                     Croatia, Slovakia, Bosnia (15)
Feb 2006             Poultry: Egypt, Cameroon, Niger, Ethiopia (15)
Mar 2006             Migratory birds: Sweden, Denmark, Serbia, Poland,
                     Czech Republic (15)
Mar 2006             Poultry: Afghanistan, Pakistan, Albania, Israel,
                     Jordan, Lebanon (15)
Apr 2006             Poultry: Burkina Faso, C6te d'Ivoire, Myanmar,
                     Nigeria, Palestinian Autonomous Territories (15)
May 2006             Poultry: Sudan; migratory birds: United Kingdom

Table 2. Known interhemispheric movement by migratory or vagrant
waterfowl (Ciconiiformes, Anseriformes, Charadriiformes), domestic
bird trade (Galliformes), or exotic bird trade (Galliformes,
Psittaciformes) from Eurasia to North America *

Species                                      Likely mode of entry

Bean goose (Anser fabalis)                   Migration ([dagger])
Greylag goose# (A. anser) (domestic)    Exotic and domestic bird trade
Whooper swan# (Cygnus cygnus)                Migration ([dagger])
Falcated duck (Anas falcata)           Migration ([dagger]) exotic bird
                                             trade, zoos, vagrant
Eurasian wigeon# (A. penelope)               Migration ([dagger])
                                        ([double dagger]) exotic bird
                                                 trade, zoos
Mallard# (A. platyrhynchos)
  (domestic and wild)                   Exotic and domestic bird trade
Garganey (A. querquedula)                    Migration ([dagger])
                                        ([double dagger]) exotic bird
                                                 trade, zoos
Green-winged teal (A. crecca)                Migration ([dagger])
                                              ([double dagger])
Common pochard# (Aythya ferina)              Migration ([dagger])
Tufted duck# (Aythya fuligula)               Migration ([dagger])
                                              ([double dagger])
Smew# (Mergellus albellus)                   Migration ([dagger])
Jungle fowl# (Gallus gallus)
  (domestic)                                 Domestic bird trade
Pheasants# (Phasianidae)                   Exotic bird trade, zoos
Quail# (Coturnix coturnix)                   Domestic bird trade
Wild turkey# (Meleagris gallopavo)
  (domestic)                                 Domestic bird trade
Red-faced cormorant (Phalacrocorax
  urile)                                    Migration ([section])
Gray heron# (Ardea cinerea)                        Vagrant
Little egret# (Egretta garzetta)                   Vagrant
Cattle egret (Bubulcus ibis)                       Vagrant
Eurasian kestrel (Falco tinnunculus)               Vagrant
Northern lapwing (Vanellus vanellus)               Vagrant
Mongolian plover (Charadrius
  mongolus)                                  Migration ([dagger])
Common ringed plover (C. hiaticula)         Migration ([section])
Eurasian dotterel (C. morinellus)           Migration ([section])
Spotted redshank (Tringa erythropus)         Migration ([dagger])
Wood sandpiper (T. glareola)                 Migration ([dagger])
Gray-tailed tattler (Heteroscelus
  brevipes)                                  Migration ([dagger])
Bar-tailed godwit (Limosa lapponica)        Migration ([section])
Red-necked stint (Calidris
  ruficollis)                               Migration ([section])
Little stint (C. minuta)                           Vagrant
Sharp-tailed sandpiper (C.
  acuminata)                           Migration ([dagger]) ([section])
Ruff (Philomachus pugnax)                    Migration ([dagger])
                                              ([double dagger])
Little gull (Larus minutus)              Migration ([double dagger])
Black-headed gull# (L. ridibundus)           Migration ([dagger])
                                              ([double dagger])
Black-tailed gull (L. crassirostris)               Vagrant
Yellow-legged gull (L. cachinnans)                 Vagrant
Slaty-backed gull (L. schistisagus)          Migration ([dagger])
Common tern (Sterna hirundo)                       Vagrant
Rock pigeon# (Columba livia)
  (domestic)                                  Exotic bird trade
Oriental turtle-dove (Streptopelia
  orientalts)                                 Exotic bird trade
European turtle-dove (S. turtur)              Exotic bird trade
Eurasian collared-dove (S. decaocto)          Exotic bird trade
Parrots# (Psittacidae)                        Exotic bird trade

Note: Species shown indicated with # are known to have been infected
with highly pathogenic avian influenza H5N1.

* Species shown in bold are known to have been infected with highly
pathogenic avian influenza H5N1. Sources for information on migrant or
vagrant status are Kessel and Gibson (28), Palmer (29), and the
American Ornithologists' Union (30). Nomenclature follows the American
Ornithologists Union checklist (30) to the degree possible.
Supplementary source: Rasmussen and Anderton (31).

([dagger]) Route 2. See Figure 2.

([double dagger]) Route 3. See Figure 2.

([section]) Route 1. See Figure 2.
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Author:Hubalek, Zdenek
Publication:Emerging Infectious Diseases
Geographic Code:100NA
Date:Oct 1, 2006
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