The purpose of this chapter is to provide an overview of tropical diseases that most commonly affect the skin.
This will be useful for health workers who may not be familiar with tropical diseases and also as a guide to help those who are already working in the tropics and who see them all the time. Skin disease is extemely common in the tropics, affecting up to 50% of the population.
Most are infections or infestations such as impetigo, ringworm, and scabies.
These can easily be treated but continue to be common because of overcrowding, poverty, and the lack of resources given to health care (training of health personnel and lack of basic medicines).
To a large extent such diseases can be controlled with very simple measure suitable for use by those with minimal training.
Atopic eczema is just as common in urban areas in the tropics as in the west.
Skin cancers are uncommon in those with a black skin because of the protective effect of melanin, but are common in albinos.
The spectrum of tropical dermatology
All the common inflammatory dermatoses occur in the tropics but may have a different appearance in pigmented skin.
Erythema, readily visible in Caucasians, will not be so apparent in black skin.
Infections and infestations occurring in the tropics produce distinctive skin changes
These may be due to the presence of the organism, ova, or larvae in the skin.
In other diseases a reaction to the organism produces a rash. Bacterial infections
Impetigo is particularly prone to occur in the tropics and may complicate any area of minor trauma to the skin.
It is characterised by erythema, and exudative lesions forming crusts. Bullae may develop.
If possible swabs should be taken for bacteriology and the appropriate antibiotics given.
Erysipelas is a localised streptococcal infection with erythema and tenderness accompanied by fever and malaise.
Treatment is with penicillin.
Leprosy
Leprosy is a chronic infection of the skin and nerves by Mycobacterium leprae.
It is spread by droplet infection and has a long incubation period (anything from two months to 40 years). There is a spectrum of clinical disease depending on the patient’s cell mediated immunity to the organism.
Diagnosis
• Typical clinical findings:
(a) In tuberculoid leprosy (TT) there is a single anaesthetic patch or plaque with a raised border.
(b) In lepromatous leprosy (LL) there are widespread symmetrical shiny papules, nodules, and plaques which are not anaesthetic.
(c) In borderline leprosy (BT, BB, BL) there are varying numbers of lesions, few in BT and numerous in BL.
They may be widespread but are asymmetrical.
(d) Palpably enlarged cutaneous nerves (great auricular nerve in the neck, the superficial branch of the radial nerve at the wrist, the ulnar nerve at the elbow, the lateral popliteal nerve at the knee, and the sural nerve on the lower leg).
(e) Glove and stocking sensory loss causing blisters, ulcers or both on anaesthetic fingers or toes.
(f) Deformity due to invasion of the peripheral nerves with leprosy bacilli, a leprosy reaction or recurrent trauma to anaesthetic limbs.
• Slit skin smears measure the numbers of bacilli in the skin (Bacterial Index (BI)) and the % of these that are living (Morphological Index (MI)).
Treatment
Paucibacillary leprosy (BI of 0 or 1+): Rifampicin 600 mg once a month (supervised), Dapsone 100 mg daily [for six months] Multibacillary leprosy (BI of 2+ or more): Rifampicin 600 mg once a month (supervised), Clofazamine 300 mg once a month (supervised), Clofazamine 50 mg/day, Dapsone 100 mg/day [for two years]
Cutaneous leishmaniasis
Cutaneous leishmaniasis is due to the protozoa
Leishmania tropica, and is transmitted by the bite of a sandfly.
There is a spectrum of disease depending on the patient’s immunity.
Acute leishmaniasis
A red nodule like a boil occurs at the site of the bite.
It enlarges, may or may not ulcerate, and heals spontaneously after about one year leaving a cribriform scar.
Chronic leishmaniasis
In a patient with good cell mediated immunity, after the acute leishmaniasis has healed, new granulomata appear at the edge of the scar; these do not heal spontaneously.
Diffuse cutaneous leishmaniasis
This is leishmaniasis in a patient with no immunity to the organism (equivalent to lepromatous leprosy).
Extensive skin nodules occur that are full of organisms.
Treatment
Intramuscular injections of sodium stibogluconate 10mg/kg body weight daily until healing occurs.
Superficial fungal infections
The same fungal infections of the epidermis occur in the tropics as in temperate climates only more so heat and occlusion of clothing leading to maceration of the skin in which fungi thrive, so expect to see more florid lesions.
There are also many fungal infections that are specifically found in the tropics.
These include tinea imbricata, tinea nigra, piedra, and favus. Suspect a dermatophyte fungal infection in any chronic, itching, scaling, slowly developing lesion with epidermal changes.
Tinea imbricata due to Tricophyton concentricum is characterised by superficial concentric scaling rings spreading across the trunk.
It occurs mainly in Asia but also in other tropical areas.
Tinea nigra occurs in the tropical areas of America, Asia, and Australia. Brown or black macules are seen on the palms and soles.
It is due to Cladosporium werneckii.
Piedra is a fungal infection of the hair producing hard nodular lesions on the hair shaft.
The lesions may be black (due to Piedra hortai) or white piedra (due to Trichosporum beigelii).
Favus is widespread throughout the Mediterranean, the Middle East, and tropics, but is rare in Africa.
It is due to an endothrix fungus Trichophyton schoenleinii which causes a thick yellow crust with an unpleasant odour.
Erythematous areas of scarring occur that must be differentiated from lichen planus and other causes of scarring alopecia.
Deep fungal infections
In these conditions there is chronic inflammation in the subcutaneous tissues leading to granulomatous and necrotic nodules.
Mycetoma (Madura foot)
This is a chronic infection of the dermis and subcutaneous fat caused by various species of fungus (eumycetoma) or bacteria (actinomycetoma).
Both types look the same with a swollen foot and multiple discharging sinuses, but it is important to differentiate between them because the treatment is different.
Diagnosis
• Examination of the discharging grains (colour will give a clue as to the cause).
• Culture of the grains to identify the causative fungus or bacteria.
• If no grains can be found a skin biopsy will show them.
Treatment
Eumycetoma:
• Itraconazole 200mgtwice daily for at least 12 months if it is affordable.
If not
• Surgical excision of affected tissue if disease is limited.
• Amputation if extensive.
Actinomycetoma:
• Sulfamethoxazole-trimethoprim mixture 960mgtwice daily for up to two years.
Blastomycosis
This condition is caused by the invasion of lymphatic system, lungs, and skin by Paracoccioddes brasiliensis.
The widespread cutaneous lesions, which vary in appearance and distribution, must be differentiated from tuberculosis and other mycoses such as sporotrichosis, chromomycodis, and coccidiomycosis. It occurs in central and south America.
Chromomycosis
This chronic granulomatous condition mainly affects the legs and results from infestation by a variety of parasitic fungi. Large verrucous plaques may require surgical removal.
Histoplasmosis
This occurs in West Africa with nodules, ulcers, and bone lesions developing due to infection with Histoplasma duboisii. Treatment is with aphotericin B.
Infestations
Tungiasis
Invasion of the skin by sand fleas (Tunga penetrans) causes tungiasis in tropical areas of Africa, America, and India.
It is most common on the feet, especially under the toes and toenails.
The condition looks a bit like plantar warts, but if you watch for a while you will see the eggs being squirted out.
Prevention
Wear shoes.
Treatment
• Carefully winkle the fleas out with a pin (most patients know how to do this themselves).
• If the fleas are very extensive, soak the feet in kerosene or treat with a single dose of ivermectin 200 micrograms/kg body weight.
Subcutaneous myiasis
Invasion of the skin by the larvae of the tumbu (mango) fly (Cordylobia anthropophaga) in central and southern Africa causes this condition. The fly lays her eggs on clothes layed out to dry on the ground.
The eggs hatch out two days later on contact with the warm skin when the clothes are put on.
The larvae burrow into the skin causing a red painful or itchy papule or nodule, predominantly on the trunk, buttocks, and thighs. Other flies that cause miyasis are:
• Dermatobia hominis tropical bot fly, in Mexico, central, and south America with tender nodules developing on the scalp, legs, forearms, and face.
• Aucheronia sp. Congo floor maggot, in central and southern Africa. Bites of the larvae cause intense irritation.
• Callitroga sp. in central
America causing inflamed lesions with necrosis.
Prevention
Iron the clothes before wearing them.
Treatment
Cover the nodule with petroleum jelly or other grease; the larva will be unable to breath and will crawl out.
Filariasis
This is an infestation with thread-like helminths (Latin “Filum” a thread).
They are widely distributed in many species and live in the lymphatics and connective tissue.
Fertilised eggs develop into embryonic worms microfilariae.
These are taken up by insect vectors that act as intermediate hosts in which further development occurs.
They are then inoculated into a human host when next bitten by the insect.
Three diseases are caused by filarial worms:
• Lymphatic filariasis due to Wuchereria bancrofti, which liberate microfilariae into the blood stream.
• Onchocerciasis due to Onchocera volvulus.
The microfilariae are liberated into the skin and subcutaneous tissues.
• Loiasis due to Loa loa, in which microfilariae are found in the blood.
Lymphatic filariasis affects 120 million people in 73 countries (34% in sub-Saharan Africa).
It causes lymphoedema of the legs, genitalia, and breasts.
It may be asyptomatic for a long period and the adult worms live for four to six years in the lymphatic vessels and lymph nodes producing thousands of microfilaria each day.
These are picked up by mosquitoes when they take a blood meal and are passed on to the next victim when they feed again.
Treatment
• In endemic areas the whole community should be treated with a single dose of two of the following three drugs once a year for four to six years:
(a) Ivermectin 400 micrograms/kg body weight
(b) Diethylcarbamazine (DEC) 6 mg/kg body weight
(c) Albendazole 600 mg.
• The chronic lymphoedema can be improved by keeping the legs moving, raising the legs when sitting, and prevention of secondary bacterial infection by regular washing and moisturising of the skin.
Onchocerciasis
Onchocerciasis (river blindness) occurs in Africa south of the Sahara and in Central America.
It is due to Onchocerca volvulus transmitted by the bite of black flies Simuliidae which breed by fast flowing rivers.
The inoculation of microfilariae by the bite of a black fly causes intense local inflammation and is followed by an incubation period of many months.
The adult worms live in nodules around the hips and cause no harm in themselves.
They produce thousands of microfilaria each day which travel to the skin and eyes.
In the skin they produce a very itchy rash which looks like lichenified eczema.
On the lower legs there is often spotty depigmentation.
Involvement of the eyes causes blindness.
Risk factors for being infected
• Living, working, or playing near fast flowing rivers.
• Not wearing enough clothes so that the skin is exposed to insect bites.
• The construction of dams leads to less breeding of black flies in the dam itself but increased breeding in the dam spillways.
Diagnosis
• Demonstrate the microfilaria in the skin by skin snips.
• Remove a skin nodule and see the adult worms inside it.
• Polymerase chain reaction to show parasite DNA not much use in the field.
Treatment
• Spray the breeding areas with insecticides.
• Annual dose of ivermectin 400 micrograms/kg body weight for four to six years.
This stops the release of microfilaria from the adult worms.
Loiasis
Loiasis occurs in the rain forests of central and west Africa.
It is transmitted by mango flies (Chrysops). The adult worms live in the subcutaneous tissues where they can be seen in the skin and under the conjunctiva.
The microfilaria are only found in the blood. A hypersensitivity to the worms shows itself as swelling of the skin, particularly of the wrists and ankles (calabar swellings).
Dracontiasis
This condition is due to infestation by Draculus medinensis in the connective tissue.
It is acquired from drinking water containing the intermediate host, a crustacean, Cyclops.
Localised papules develop on the lower legs containing the female worm and numerous microfilariae.
Treatment consists of very carefully extracting the worm by winding it onto a stick over several weeks.
Symptomatic treatment of secondary infection and allergic reactions is also required.
