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Parasites and the skin: parasitic infections may be confined to the skin or may have skin involvement as part of their pathology.

This article seeks to familiarise readers with the management of those conditions that are encountered in daily practice and to remind you of those rare and wonderful infestations that you might never see. I will focus on and deal with parasitic infestations and the skin. Skin pathology often provides important clues to systemic infections. This article will discuss common clinical presentations and tabulate the rarer diseases.

Parasitic infestations are common in the tropics due to a combination of heat, humidity and ultimately poor socioeconomic and health care conditions.

Parasitic infections can be solely confined to the skin, as seen with human scabies, cutaneous larva migrans, the chigger flea, cutaneous myiasis and cutaneous leishmaniasis. Parasites not confined to the skin include onchocerciasis, loiasis, the guinea worm, schistosomiasis, cutaneous amoebiasis and the cutaneous involvement in trypanosomiasis.

Common scenarios


The common scenario of a child brought to a busy rural outpatient department or public hospital is shown in Figs 1 and 2. The history is that of severe pruritis persisting for a few weeks, worse at night and there are family members or friends with the same affliction as shown in Fig. 1. The diagnosis is scabies until proven otherwise, and treatment consists of topical scabicides.



Human scabies is caused by the host-specific mite Sarcoptes scabie var. hominis. A hypersensitivity reaction to the mite is responsible for the intense pruritis experienced by infested individuals. This burrowing mite lives its entire life cycle within the epidermis of the skin. Secondary infection with group A Streptococcus pyogenes or Staphylococcus aureus may occur. Transmission occurs by direct contact and sometimes spreads through fomites. Drug resistance to topical scabicides is occurring.

The diagnosis is confirmed by direct microscopy of skin scraping from a burrow, mounted on a glass slide. The findings are demonstrated in Fig. 3. Dermoscopy, epiluminescence microscopy and skin biopsy are other diagnostic aids. Treatment is shown in Table I.

Table I. Treament of scabies

Drug                             Dose                    Comment

Gamma-bezenehexachloride:  Apply and leave on for  Contraindicated
Lindane 1% lotion          8 hours; repeat 1 week  during pregnancy and
                           later                   in children <2 years
                                                   of age

                                                   Resistance is

                                                   Aplastic anaemia
                                                   recently reported in
                                                   children treated with
                                                   Gambex shampoo

Precipated sulphur 5 -     Apply for 3             Safe in children and
10%: Tetmosol soap 5%      consecutive days, then  in pregnancy
                           wash off                Preparations include
                                                   Tetmosol soap 5%
                                                   Useful for
                                                   Ineffective in
                                                   infestation Sulphur
                                                   ointments in soft
                                                   white paraffin
                                                   effective in children

Crotamiton: Eurax          Apply on 2 consecutive  Eurax not as
                           days, repeat in 5       effective as the
                           days                    others

Benzyl benzoate 10%        Apply for 24 hrs then   Dilute in water for
lotion: Ascabiol emulsion  wash off May need to    children Safe in
25%                        repeat                  pregnancy Rare
                                                   side-effects Skin

Ivermectin 200             Stat dose Can repeat    Highly effective,
[micro]g/kg                after a week            especially in
                                                   Norwegian crusted

                                                   Can be obtained on a
                                                   named-patient basis
                                                   from MSD with
                                                   permission from the

Pyrethroids: Spregal       Spray entire body       Esdepallethrin is a
aerosol                    except the face; leave  pyrethroid pesticide,
                           on overnight and        which is scabicidal
                           repeat one week later

                           Repeated sprays may be  Piperonyl butoxide
                           needed in HIV+          acts by blocking the
                           patients                defense system that
                                                   the parasite uses to
                                                   counteract the latter

                           All persons affected    Contraindicated in
                           in same household to    children <2 years and
                           treat at the same       during pregnancy

                           Do in well-ventilated
                           room and avoid any

                           Disinfect clothes and
                           bed linen

Treatment of scabies

Effective management of scabies requires the following:

* Treat all contacts.

* Apply scabicides from the neck down over the entire body, especially unaffected intertriginous areas of the skin.

* Avoid using antiseptic such as dettol and savlon.

* Avoid overuse of tetmosol soap, which may worsen existing pruritis.

* Disinfect towels, clothing and bedding.

* Use systemic antibiotics and/or systemic antihistamines in severe cases.

* Short courses of topical or systemic steroids may be effective in treating post-scabetic pruritis, which is common. Avoid the continuous use of topical antiseptics.

* Use sulphur-based ointments in neonates, infants and in pregnancy.

Norwegian scabies

The second clinical scenario of Norwegian scabies is commonly seen in HIV-positive patients. Fig. 4 shows the eczematous, psoriasiform rash reminiscent of psoriasis.


Diagnosis will be assisted by considering the following:

* One or more skin biopsies may be required to confirm the diagnosis.

* This illness is highly contagious and often health care workers become afflicted after contact.

* Norwegian scabies is commonly seen in old age homes and psychiatric facilities.

* The most effective treatment for Norwegian scabies is oral ivermectin, which requires permission for use from the Medicines Control Council.

* Several applications and prolonged use of stronger concentrations of sulphur ointments, Ascabiol or Spregal spray need to be used in these patients to obtain cure.

* Keratolytics and occasionally anti-proliferative agents are needed to clear the hyperkeratosis that is teeming with mites before using the above agents.


Scenario 3 demonstrates a typical case of myiasis. A backpacker ventured into rural Zimbabwe for a few months and subsequently returned to Johannesburg with numerous boils on his back (Fig. 5). These irritating lesions persisted for approximately 3 weeks and did not respond to topical antiseptics and systemic antibiotics.


Myiasis is caused by the larvae of flies, which lay their eggs on skin or clothing. The eggs hatch and the larvae penetrate the skin. Worldwide the most common flies that cause human infestation are Dermatobia hominis (human botfly) and Cordylobia anthropophaga (tumbu fly).

The route of transmission differs with different flies. The botfly lays her eggs on mosquitoes, which in turn deposit them on warm-blooded mammals. The tumbu fly deposits its eggs on moist clothing, soiled blankets and in sand. In endemic areas people usually iron their clothes after hanging them out to kill the fly eggs.

There are essentially two types of myiasis:

* Furuncular myiasis (Fig. 6), which is what the patient described in our scenario has, usually caused by the botfly.


* Wound myiasis (Fig. 7), where larvae are deposited in suppurating wounds or on decomposing flesh. Cochliomyia hominovorax is the causative fly in the Americas and Chrysomia in Africa.


The main aim of treatment is literally to suffocate the larvae. Occlusive ointments such as vaseline are effective as they interfere with the larva's respiration and force it to extrude itself. Alternatively, surgical nicking of the furuncle followed by extraction of the larvae can be curative (Fig. 6).

Topical and systemic antibiotics may be needed to cure any secondary infection. The approach in wound myiasis would be surgical debridement and the principles of surgical management.

Cutaneous larva migrans

In the fourth scenario a young child is brought for a rash on his foot, as shown in Fig. 8. The family had just returned from a coastal holiday. This is typical of cutaneous larva migrans or 'creeping eruption'. The latter term is being used because of the slow crawling movement of the worm, which is visible. This condition is due to the incomplete development of hookworm larvae, whose natural hosts are cats and dogs, in man. The larvae are found in damp soil contaminated by dog and cat faeces. Invasion of human skin usually takes place on beaches, where shoes are seldom worn.


Treatment of larva migrans

Spontaneous cure can take place over months. Do not try to catch, freeze or surgically clip the worm. The treatment of choice is a single dose or 3-day course of albendazole.

Alternatively, a 500 mg tablet of thiabendazole is ground up in 25 g of vaseline and applied once a day for 2 days.

Chigger fleas or tungiasis

In scenario 5 a child from a rural, economically poor area of KZN is brought to you. Fig. 9 demonstrates the clinical picture. The primary lesions are black dots, papules, nodules and burrowing excoriations. There is some resemblance to a minor abscess with a central punctum. The child complains of mild discomfort. The differential diagnosis includes infected warts or scabies but the primary lesions of these are fairly typical ofchigger fleas, therefore always consider tungiasis or chiggers in this setting.


This is common in the tropics (endemic in Central and South America, the Caribbean, tropical Africa, India and Pakistan), and is caused by the wingless flea Tunga penetrans. The condition is called tungiasis.

The flea's eggs are found in clusters in soil, from which infestation of the bare-footed patient occurs. The impregnated female burrows itself into the skin of the foot, the toe webs, around the nails and on the heels. The flea's abdomen expands rapidly, forming a large white sphere like a mistletoe berry. Rare complications include gangrene, tetanus and auto-amputation.

Treatment of tungiasis

* Maintaining a high index of suspicion for this condition.

* Removal of the flea with a sterile needle.

* Surgical curettage and electrodessication.

* Topical thiabendazole or ivermectin.

* Systemic thiabendazole or ivermectin.

* Systemic antibiotic cover.

* Tetanus prophylaxis.


In this scenario, a 26-year-old medical doctor visited Israel over a period of a month and returned with a small sore on his upper lip. This increased in size with time. He took an empiric dose of a broad-spectrum antibiotic in addition to a topical antibiotic for 2 weeks, with no response. He had no associated constitutional symptoms. Fig. 10 shows the ulcerating plaque, which is clinically non-diagnostic.


The differential diagnoses include:

* furunculosis resistant to antibiotics

* an actinic cheilitis (this would occur on the lower lip)

* granulomatous conditions which may be fungal such as sporotrichosis, or mycobacterial such as tuberculosis

* atypical mycobacteria

* syphilis or other sexually transmitted infections

However, his visits to the Middle East would make one consider leishmaniasis.

Diagnosis requires the mandatory performance of an adequately sized deep skin biopsy.

The presence of amastigotes in neutrophils is in keeping with leishmaniasis. This doctor had the oriental sore of cutaneous leishmaniasis.

Leishmaniasis is a genus of flagellate protozoa found in Africa, the Mediterranean basin, the Caribbean and Latin America. It is transmitted by the bite of the phlebotomus sandfly.

Dogs and rodents are the intermediate hosts.

There are three forms of leishmaniasis:

* cutaneous leishmaniasis, which is restricted to the skin and is seen more often in the old world, as seen in our patient

* mucocutaneous leishmaniasis, which affects the skin and mucous surfaces and occurs exclusively in the so-called new world (Fig. 11)


* visceral leishmaniasis, which affects the organs of the mononuclear phagocytic system, such as the lymph nodes and spleen.

There are various species and subspecies of Leishmania. The commonest old-world form is L. major or L. tropica.

The clinical picture begins with a small papule at the inoculation site, which enlarges into a nodule or plaque. This may become verrucous or ulcerate. The lesions are often solitary but may be multiple, with the formation of satellites in a lymphatic or sporotrichoid spread. These lesions can resolve spontaneously in people living in endemic areas or may become chronic and disseminate. The latter occurs more often in immunosuppressed patients with poor cell-mediated immunity.

Diffuse cutaneous leishmaniasis develops in the setting of infections with L. aethiopica and L. amazonensis. After a prolonged time period of years and decades some patients develop mucocutaneous disease. Additional forms of cutaneous leishmaniasis are L. recidivans, which follows a sporotrichoid pattern with dry erythematous plaques. L. recidivans is characterised by recurrences at the site of an original ulcer, generally within 2 years and often at the edge of a scar.

Diagnosis of leishmaniasis

The diagnosis is confirmed by tissue or skin histology which demonstrates the presence of amastigotes in dermal macrophages. This is sometimes found in dermal scrapings or fine-needle aspirate (FNA) of affected tissue--so-called Leishman-Donovan bodies in large histiocytes. However, in older lesions parasites may not be found. Here the delayed skin reaction test (Montenegro test or Leishman reaction), which uses leishmania antigens to induce a cell-mediated (CMI) response can be an important diagnostic tool.

This test is positive in 50% of patients with cutaneous and mucocutaneous leishmaniasis. It is negative in diffuse leishmaniasis. Another drawback is that the test does not distinguish between past and current infection. Other adjunctive tests are tissue culture, ELISA and PCR.

Treatment of cutaneous leishmaniasis

Treatment depends on the type and severity of infection. Old-world disease is often self-limiting. Severe cases of L. tropica and L. major can be treated with pentavalent antimonials. New-world disease, e.g. L. brazilienzes, can progress to mucocutaneous disease. Treatment of choice is pentavalent antimonials, e.g. sodium stiboglutamate or meglumine antimonials.

Adjunctive treatments for cutaneous and mucocutaneous lesions include heat and cryotherapy, and drugs such as itraconazole, amphotericin B, ketaconazole and allopurinol. Prevention measures include insect repellants, insecticides and destruction of animal reservoirs.

Parasites not confined to the skin include onchocerciasis, loiasis, the guinea worm, schistosomiasis, cutaneous amoebiasis and the cutaneous involvement in trypanosomiasis. These are listed in Table II and depicted in Figs 12 - 14.



Table II. Summary of parasitic diseases not confined to the skin

Disease          Pathogen        Vector          Geographic

Onchocerciasis   Onchocerca      Blackflies      Equatorial
(Fig. 12)        volvulus        Simulium        Africa,
                                 Along           Central and
                                 free-flowing    South
                                 rivers Larvae   America,
                                 develop well    Yemen
                                 in aerated

Loiasis (Fig.    Loa loa         Chrysops        West and
13)                              flies           Central

Dracunculosis    Guinea worm     Ingest larva    Africa, Latin
(Fig. 14)        Dracunculous    in              America,
                 medinensis      contaminated    India

Cutaneous        S. haematobium  Humans are      Haematobium
schistosomiasis  S. mansoni      infected by     North Africa
                 S. japonicum    contact with    Middle east
                                 fresh water     Sub-Sahara
                                 The parasite    Mansoni
                                 penetrates      Sub-Saharan
                                 intact skin     Africa Middle
                                 Water snails    East Brazil
                                 are             Caribbean
                                 intermediate    Japonicum
                                 hosts           China

Trypanosomiasis  American T.     American:       Tropical
                 cruzi           Reduviid bug    America
                 (Chagas'        Occasionally    Tropical
                 disease)        contaminated    Africa
                 African T.      blood Tsetse
                 rhodesiense     fly
                 (acute) T.      (Glossina)

Filarial         Wuchereria      Mosquitoes      Africa, West
elephantiasis    bancrofti,      Genus: Aedes    Indies

Disease          Diagnostic        Disease and
                 tests             complications

Onchocerciasis   Skin snips for    Chronic pruritis
(Fig. 12)        unsheathed        and excoriations
                 microfilaria      Eye involvement
                   DEC             with gradual
                 (Mazotti test      impairment of
                                   vision and
                                   blindness (river

Loiasis (Fig.    Microscopy of     Calabar swellings
13)              day blood for     (migrating
                 microfilaria      swelling) Transient
                                   nodules often on
                                   the arm Irritation
                                   of eye as an adult
                                   worm traverses the

Dracunculosis    Clinical: see     Ingested larva
(Fig. 14)        adult worm        reach the skin,
                 stringing out of  where adult worm
                 skin ulcer        literally breaks

Cutaneous        Identification    Papules, nodules
schistosomiasis  of viable eggs    Cercarial
                 Microscopy of     dermatitis
                 terminal urine    (swimmer's itch)
                 in S.             Main pathology is
                 haematobium       granuloma formation
                 Stool in S.       around eggs
                 mansoni and S.    Katayama fever:
                 japonicum Eggs    development of
                 from all on       adult worms and the
                 rectal biopsy     early stages of egg
                 Serology: does    deposition, days to
                 not distinguish   weeks after
                 acute from past   infection May cause
                 infection         severe systemic
                                   reaction including
                                   fevers, rigors,
                                   myalgia, urticaria,
                                   lymphadenopathy and
                                   High eosinophilia
                                   Chronic established
                                   disease affecting
                                   all organs

Trypanosomiasis  American: In      Clinical includes a
                 acute stage       necrotic chancre at
                 stage micro exam  the site of
                 for               inoculation,
                 trypomastigotes   pruritis in the
                 in blood specs    later stage, and
                 Thereafter: PCR   'trypanides', more
                 African:          or less discoid or
                 Detection of      annular
                 trypanosomes in   erythematous
                 blood film,       eruptions African
                 chancre, lymph    Trypanides Cervical
                 node aspirate,    lymphadenopathy In
                 buffy coat, bone  American Tryp
                 marrow or CSF     Affects ANS, GIT
                 PCR               and CVS systems
                                   Myocarditis is
                                   critical in these
                                   patients When
                                   conjunctiva is the
                                   portal of entry
                                   oedema of the
                                   palpebral and
                                   periocular tissue
                                   is seen--Romana's
                                   sign Chagoma:
                                   painful nodule at
                                   site of

Filarial         Microfilaria in   Thickened
elephantiasis    peripheral blood  oedematous skin
                 at night

Disease          Treatment

Onchocerciasis   Ivermectin
(Fig. 12)        effective against
                 sterilises female
                 worm Add systemic
                 steroids in cases
                 of eye involvement
                 Suramin for adult

Loiasis (Fig.    Oral DEC 1 - 6 tabs
13)              dly for 2 weeks
                 Repeated courses
                 are necessary

Dracunculosis    Excision and
(Fig. 14)        extraction
                 more than
                 Wound care

Cutaneous        Praziquantel 40
schistosomiasis  mg/kg/day stat
                 Sometimes repeated
                 Systemic steroids
                 in Katayama fever
                 Avoidance of water
                 in endemic areas
                 Snail control

Trypanosomiasis  Nifurtimox (with
                 gamma interferon
                 Eflornithine WHO
                 control measures

Filarial         Ivermectin
elephantiasis    Adjunctive

DEC = diethylcarbamazine; ANS = autonomic nervous system; GIT =
gastrointestinal; CVS = cardiovascular system; CSF = cerebrospinal
fluid; PCR = polymerase chain reaction.

RELATED ARTICLE: In a nutshell

* Skin pathology often provides important clues to systemic infections.

* Parasitic infestations are common in the tropics due to a combination of heat, humidity and ultimately poor socioeconomic and health care conditions.

* Parasitic infections can be solely confined to the skin, as seen with human scabies, cutaneous larva migrans, the chigger flea, cutaneous myiasis and cutaneous leishmaniasis.

* Parasites not confined to the skin include onchocerciasis, loiasis, the guinea worm, schistosmiasis, cutaneous involvement in trypanosomiasis.

DEEPAK MODI, MB BCh, DTM &H (RCP Lond), MSc (Lond), FFDerm (SA)

Professor and Academic Head, Division of Dermatology, University of the Witwatersrand, Johannesburg

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Article Details
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Author:Modi, Deepak
Publication:CME: Your SA Journal of CPD
Article Type:Disease/Disorder overview
Geographic Code:6SOUT
Date:Jan 1, 2010
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