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Chances are the next deadly pandemic will have originated among animals; We have lived with disease since the dawn of time. But where do diseases come from? Health Editor Madeleine Brindley spoke to the National Public Health Service for Wales.

Byline: Madeleine Brindley

INMID-March 2003 a US businessman died in a Hong Kong hospital - ordinarily such a death would have caused little attention beyond the usual tributes paid by family and friends in local newspapers.

The man had previously visited China and Vietnam before being admitted to hospital in the former British territory.

But the world sat up and took notice of his death, not least because hospital staff in the three Asian countries who had been in contact with the man subsequently became ill.

Suddenly the world was faced with a new and dangerous health threat, a new source of infection not seen before which had no cure and no treatment and the potential to spread easily and quickly among the human population, killing tens of thousands worldwide.

The businessman was one of the 800 or so people who died from this new disease - severe acute respiratory syndrome or Sars for short - during the 2002-03 global outbreak.

The disease is thought to have originated in China's southern Guangdong province in November 2002. When a Chinese professor of respiratory medicine treating people with the syndrome fell ill he travelled to Hong Kong, carrying the virus with him.

By February 2003 it had spread around the world, thanks to the ease and efficiency of air travel. Between March and July 2003, 8,400 probable cases of Sars had been reported in 32 countries.

Like the majority of new and emerging diseases, Sars originated in animals: it is a previously unknown type of coronavirus, which was found in Himalayan palm civets, a raccoon dog and a Chinese ferret badger.

It was also detected among people working in a live animal market in the southern Guangdong area where the outbreak first began. High levels of antibodies to the virus were also found in people trading masked palm civets, which are considered a delicacy in parts of China.

Dr Roland Salmon, director of the National Public Health Service for Wales' (NPHS) Communicable Disease Surveillance Centre, said: "It is thought that 60% to 70% of disease are zoonoses - animal diseases - although some people believe that is an underestimate."

History is littered with deadly examples of animal diseases crossing the species barrier, from plague, which originated in the Himalayan foothills and began to spread when it got into marmots; measles, which is closely linked to the dog distemper virus; HIV, which originated in great apes; to the current concerns about highly pathogenic avian flu H5N1, which has already killed a number of people working in close contact with infected birds.

"Often these diseases don't have any effect, or a minimal effect on the animals themselves," said Dr Rob Smith an NPHS clinical scientist. "But if it gets into a new host it can present differently. Humans pick up these infections through direct contact by touching the infected animals, by eating food which is contaminated with the animal pathogen - like E.coli O157 - or through another vector, like water."

Dr Salmon said: "There was a time when we lived very much more closely with animals: for example, in the Welsh longhouse, the family would live at one end of the building and the animals at the other. This increased opportunities for disease.

"If you look at avian flu H5N1, it is something that can affect humans if they are close enough to infected birds but it is not well adapted to humans."

There has been much speculation that H5N1 could become the source of the next flu pandemic. Its emergence in the animal world proved to be something of a catalyst for governments to start preparing detailed pandemic flu plans, amid predictions that a pandemic could kill anywhere between 50,000 and 750,000 people in the UK alone.

We are currently at phase three of the World Health Organization's (WHO) flu pandemic alert. This means that a new virus - H5N1 - has been identified in animals but there has been no, or very limited, human-to-human transmission.

But experts remain concerned that the H5N1 virus, which is currently circulating among birds in Africa, Asia and Europe, has demonstrated the ability to cross the species barrier to cause disease and death in humans.

Three new human cases of H5N1 were reported in the Hunan, Shanxi and Shandong provinces of China - a 27-year-old woman died - and a fourth in Egypt since the start of the year. To date there have been 397 cases around the world, of which 249 people have died, according to WHO figures.

But to become an effective human virus H5N1, like other zoonoses which are yet to fully cross the species barrier, needs to acquire the ability to transfer from one human to another, either by mutating or merging with an existing human virus.

"Successful diseases need a low infectivity rate so the host survives to carry the virus around or it needs to survive in the environment, either in animals or water," Dr Salmon said.

"Diseases which are relatively severe need to have an environmental source - in the case of flu, aquatic birds represent a reservoir when it is not circulating in humans."

Sars killed 800-plus people worldwide, although it was eventually isolated and contained. But WHO has warned that an epidemic could reoccur.

Dr Meirion Evans, a regional epidemiologist with the NPHS, said: "There is evidence in people working in the markets who handled animals of antibodies for Sars, which suggests past exposure to the virus.

"At least in that group of people they got infected but perhaps without any undue symptoms, but then something happened to trigger the spread of Sars. It mutated from a virus only acquired through contact with animals to a virus that could be transmitted from person to person.

"At the outset it was thought that this was the next pandemic flu before the virus was identified. It seemed to be behaving like influenza.

"In effect we had a completely new disease that we hadn't known about or recognised before; we had no easy way of diagnosing it, preventing it or treating it. It also had a high mortality rate in previously fit and healthy people.

"The key to bringing it under control was gathering information about it and beginning to understand the transmission of it - it was only infectious several days into the illness and if we caught it early enough and isolated the patient, it wouldn't spread."

But this is not to say that all emerging diseases, especially those that originate in animals, present a clear and present danger to humans.

There is a spectrum, with the highly pathogenic infections at the extreme end and relatively harmless diseases, such as the colourfully named simian foamy virus (SFV). No-one who has tested positive for SFV infection, which is common in chimpanzees, has become ill.

Dr Mark Temple, a consultant in public health medicine, also with the NPHS, said: "One of the great fortunes for humans was that every case of Sars was not the same, which meant that the isolation methods worked much better.

"Some people who had Sars did not have as serious an infection as others. If a disease has a uniform transmission it means that isolation is relatively less powerful because the one that gets away is likely to start a new outbreak.

"But with Sars, the one that got away was likely not to be very infectious. There was a case in Vancouver which was diagnosed only retrospectively.

The person had got better without infecting anyone else."

If the majority of new diseases originate in animals there is little doubt that the trappings of modern life have helped these new viruses and infections spread throughout the human population.

Dr Temple said: "Diseases travel much quicker than humans: it's quite feasible to transmit a disease across a continent without people physically carrying it across.

"I may be infected with something, I meet you, you go home and meet other people, they come into contact with others and the disease moves through the human chain. If you compare that to the 1918 outbreak of flu, it took three days for it to travel from New York to San Francisco. The only real mechanism then was by train."

And while improvements in sanitation may have all but eradicated diseases such as cholera and typhoid, in the western world at least - Zimbabwe is currently struggling with a large outbreak of cholera - improved hygiene conditions may, perversely, make us more susceptible to relatively new diseases and infections.

Legionella is regarded as a bug of the environment and yet the introduction of air conditioning in modern buildings has led to a relative explosion in cases of potentially lethal legionnaires' disease.

Likewise diseases that the affluent West has mastered still wreak havoc and bring large scale deaths in the Third World: acute respiratory disease, diarrhoea and malaria, all of which are relatively easy to treat, manage and even prevent, remain the biggest killers and the biggest causes of disability in sub-Saharan Africa.

Dr Evans said: "The difficulty is that as well as emerging diseases we also have re-emerging old diseases that can be just as effective at doing nasty things to people."

Dr Temple added: "Re-emerging diseases can be a real problem. For example, we know that we can treat and we can cure TB but because the treatment is tedious and long, ensuring that people take it properly can be a bit of a battle.

"If people don't take it properly, it comes back. There are quite a lot of diseases in that category where you take it for granted that the patient will get better but forget that there are 17 steps and if any one of those is missed, the patient won't get better.

"Since the Second World War we have been living in the lap of luxury, not least because we have a large range of successful antibiotics for bacterial infections - scarlet fever used to be a major killer.

"Diphtheria was also a major problem, but like other diseases is now vaccine preventable.

"They are controlled, but they are waiting to come back. We prevent them by eternal vigilance."

Infections that make the leap, from campylobacter to hydatid disease

The 2007 zoonoses report by the Department for Environment, Food and Rural Affairs, which was published in October 2008, reveals a number of "noteworthy" incidents of infections in animals and humans.

These include:

Campylobacter - in 2007, the number of recorded human cases throughout the UK increased by 10% compared to 2006.

A total of 57,590 cases were reported, but the level is below the peak of more than 65,000 cases reported in 2000.

Most cases of campylobacter infection are thought to be sporadic and the routes of transmission often remain unclear, although poultry meat may be an important source of infection;

Salmonella - the number of human infections showed a "moderate" decrease in 2007 in all parts of the UK compared with 2006.

A total of 13,213 cases were reported, a decrease of 6.2% compared to 2006.

There was also a reduction in reports of salmonella in cattle, sheep, pigs and poultry, which may in part have been due to the reduced number of diagnostic samples received, especially for cattle and sheep during the year;

E.coli O157 - human cases of infection in the UK fell by 9.8% in 2007 compared with the previous year;

Bovine tuberculosis - there was an increase in the number of new incidents of bovine tuberculosis in cattle during 2007 and a marginal increase in the number of herds tested;

Lyme borreliosis - there was an increase in reports of this disease, which is caused by infected tick bites, during 2007.

The proportion of reported travel-associated cases has declined and there have been a number of well-documented areas within the UK from which reports of the infection are received and a succession of relatively mild, wet winters have allowed ticks to survive and to continue feeding throughout the year.

Appropriate precautions should help to reduce the risk and available guidance should be followed;

Q fever - a cluster of cases was identified in the Cheltenham area, with likely exposures in late April and early May but no source was identified.

Q Fever is caused by the bacteria Coxiella burnetii and is a highly infectious zoonosis.

The main reservoirs for the bacteria are ticks or farm animals, such as cattle, sheep and goats, but pets and wild rats may also harbour the bacteria.

Humans become infected usually by inhaling the organism from domestic animals or occasionally from raw milk; Hydatid disease - a public awareness campaign was launched by the Welsh Assembly Government because of the potential for the re-emergence of hydatid disease in humans in South-East Wales.

The Assembly Government is also funding a 10-year programme to control hydatid disease in hot spot areas in Wales.

Hydatid disease - also known as Echinococcosis or cystic hydatid disease - results from infection with the larvae of the tapeworm Echinococcus granulosus.

The tapeworm is found most commonly in dogs which eat the organs or meat of infected sheep.

Humans can also become infected by the eggs shed in dog faeces.

The eggs hatch in the intestine, penetrate the gut wall and travel through the body where they lodge in the tissues.

An Assembly Government spokeswoman said: "Hydatid disease in humans appear to have become rare in the UK but it remains important to prevent transmission from dogs.

"The Assembly Government therefore launched the Hydatid Disease Campaign in May 2008 in order to raise awareness of the disease in dogs.

"As part of the campaign there is a pilot scheme under way in south Powys to explore the levels of hydatid in dogs and help raise awareness of the importance of regular worming and hygiene.

"The pilot phase is due to come to an end in May.

Results are being compiled and consideration will be given to the evidence and next steps."

Source: Zoonoses Report, United Kingdom 2007 published by Defra in October 2008; National Public Health Service for Wales

CAPTION(S):

AVIAN THREAT: A chicken infected with bird flu, a disease which has gone on to kill humans, but not in any great numbers PICTURE: AP/Suzanne Plunkett; PRECAUTIONS: Children attend ballet lessons wearing masks to protect themselves from severe acute respiratory syndrome, Sars
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Publication:Western Mail (Cardiff, Wales)
Date:Jan 26, 2009
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