Chapter 15: Tropical medicine and the returned traveller

Doctors in western countries—including Australia, with its own tropical diseases in the far north—are more likely to encounter tropical diseases in the traveller returning from countries where these disorders are endemic. Many of these diseases are likely to be encountered in newly arrived refugees (see CHAPTER 135). The diseases include bacterial infections such as tuberculosis (a huge problem), plague, melioidosis, leprosy, typhoid/cholera, zoonoses. Other infections to be considered are parasitic, Rickettsia and myriad viral infections including haemorrhagic fevers, various types of encephalitis, yellow fever, polio, trachoma, hepatitis, lyssavirus such as rabies and bat bite infections, dengue and influenzas.

It is worth reviewing the various protozoal and helminthic parasitic infections that need to be considered in the sick returned traveller.¹ The helminths (worms) include cestodes (tapeworms), trematodes (flukes) and nematodes (roundworms).

• Protozoal infections: African trypanosomiasis (sleeping sickness), American trypanosomiasis (Chagas disease), amoebiasis, babesiosis, coccidiosis and microsporodiosis, cryptosporidiosis, giardiasis, leishmaniasis—cutaneous and visceral (kala-azar), malaria, toxoplasmosis, trichomonas

• Cestodes (tapeworms): Cysticercosis (Taenia solium, T. saginata), echinococcus (hydatid disease)

• Trematodes (flukes): Schistomiasis (bilharziasis), clonorchiasis, paragonimiasis

• Nematodes (roundworms): Ascariasis, enterobiasis (pinworm), Dracunculus medinensis (Guinea worm), filariasis, hookworm, larva migrans (cutaneous and visceral), strongyloidiasis, trichinosis (Trichinella spiralis), trichuriasis (whipworm)

• Most will present within 2 weeks except HIV seroconversion infection.

• Common infections encountered are dengue fever, giardiasis, hepatitis A and B, gonorrhoea or Chlamydia trachomatis, malaria and helminthic infestations.

• An important non-infection problem requiring vigilance is deep venous thrombosis (DVT) and thromboembolism.

• The asymptomatic traveller may present for advice about exposure (without illness) or about an illness acquired such as rabies, malaria, schistosomiasis and STIs.

Gastrointestinal symptoms

Mild diarrhoea

• Stool microscopy and culture

• Look for and treat associated helminthic infestation (e.g. roundworms, hookworms)

Moderate or prolonged (>3 weeks) diarrhoea

Usually due to Giardia lamblia, Entamoeba histolytica, Campylobacter jejuni (especially South-East Asia), Salmonella, Yersinia entero-colitica or Cryptosporidium.²

• Stool examination (three fresh specimens):

  • – microscopy

  • – wet preparation

  • – culture

• Faecal Multiplex PCR (if available)

• Treat pathogen (see guidelines under diarrhoea in CHAPTERS 14 and 44)

Non-pathogens such as Escherichia coli and Endolimax nana are often reported but do not treat specifically.

Note: Consider exotic causes such as schistosomiasis, strongyloidiasis and ciguatera in unusual chronic post-travel ‘gastroenteritis’.

Persistent abdominal discomfort

This common syndrome includes bloating, intestinal hurry and borborygmi, and often follows an episode of diarrhoea. Usually no pathogens are found on stool examination. However, giardiasis can be difficult to detect and an empirical course of tinidazole (2 g statim) is worthwhile. Any persistent problem then is a type of postinfective bowel dysfunction or irritable bowel. Reassurance is important.

Rash/other skin lesions

• Maculopapular: consider dengue, HIV, typhus, syphilis, arbovirus infections, leptospirosis, Q fever

• Petechiae: viral haemorrhagic fevers, leptospirosis, dengue

• Rose spots: typhoid

• Eschar: typhus (tick and scrub), anthrax

• Chancre: African trypanosomiasis, syphilis

Fever

• Causes range from mild viral infections to potentially fatal cerebral malaria (see TABLE 15.1) and meningococcal septicaemia.

• An Australian study of fever in returned travellers³ revealed the most common diagnosis was malaria (27%) followed by respiratory tract infection (24%), gastroenteritis (14%), dengue fever (8%) and bacterial pneumonia (6%). The commonness of malaria was supported by results from the GeoSentinel Surveillance Network.⁴

• The common serious causes are malaria, typhoid, hepatitis (especially A and B), dengue fever and amoebiasis.

• Most deaths from malaria have occurred after at least 3 or 4 days of symptoms that may be mild. Death can occur within 24 hours. Factors responsible for death from malaria include delayed presentation, missed or delayed diagnosis (most cases), no chemoprophylaxis and old age.

• Refer immediately to a specialist unit if the patient is unwell.

• Be vigilant for meningitis and encephalitis.

• Be vigilant for amoebiasis—can present with a toxic megacolon, especially if antimotility drugs are given.

• If well but febrile, first-line screening tests:

  • – full blood examination and ESR

  • – thick and thin films

  • – liver function tests

  • – urine for micro and culture

• Refer immediately if malaria is proven or if fever persists after a further 24 hours.

Malaria

See FIGURE 15.1.

• Incubation period: P. falciparum 7–14 days; others 12–40 days

• Most present within 2 months of return

• Can present up to 2 or more years

• Can masquerade as several other illnesses

See CHAPTER 14.

• High fever, chills, rigor, sweating, headache

• Usually abrupt onset

• Can have atypical presentations (e.g. diarrhoea, abdominal pain, cough)

• Beware of modified infection.

• Must treat immediately. Delay may mean death.

• Typical relapsing patterns often absent.

• Thick smear allows detection of parasites (some laboratories are poorly skilled with thick films).

• Thin smear helps diagnose malaria type.

• If index of suspicion is high, repeat the smear (‘No evidence of malaria’ = 3 negative daily thick films). Newer tests (e.g. polymerase chain reaction [PCR] tests and immune chromatographic test [ICT] card tests for PFM) show promise. Cerebral malaria and blackwater fever are severe and dramatic. The Para check V test (a desktop test) is accurate and needs to be positive before prescribing artemether in some areas.

• Admit to hospital with infectious disease expertise. Rule out G6PD deficiency

• Supportive measures, including fluid replacement

• Avoid the same drugs used for prophylaxis

• P. vivax, P. ovale, P. malariae⁵

  artemether + lumefantrine 20 mg + 120 mg (Riamet)

  4 tablets with food at 0, 8, 24, 36, 48, 60 hours (i.e. 24 tablets) in 60 hours

  +

  primaquine dose by weight to achieve a total dose of 6 mg/kg

• P. falciparum⁵ uncomplicated

  Riamet (as above)

  or

  atovaquone + progunail

  or

  quinine sulphate 600 mg (o) 8 hourly, 7 days +

  doxycycline 100 mg (o) 12 hourly, 7 days

  or

  clindamycin 300 mg (o) tds, 7 days (children, pregnancy)

  complicated (severe):

  artesunate 2.4 mg/kg IV statim, 12 hours, 24 hours, then once daily until oral therapy (Riamet) is possible

  or

  quinine dihydrochloride 20 mg/kg up to 1.4 g IV (over 4 hours) then after 4-hour gap 7 mg/kg IV 8 hourly until improved (ECG/cardiac monitoring)

  then

  quinine (o) 7 days

  Note: Check for hypoglycaemia. Beware if antimalarial use in previous 48 hours.

Typhoid fever

Incubation period 10–14 days

Clinical features

• Insidious onset

• Headache prominent

• Dry cough

• Fever gradually increases in ‘stepladder’ manner over 4 days or so

• Abdominal pain and constipation (early)

• Diarrhoea (pea soup) and rash—rose spots (late)

• ± splenomegaly

Diagnosis

• On suspicion—blood and stool culture

• Serology not very helpful

Treatment

• Azithromycin l g (o) for 7 days

  • or

• Ciprofloxacin 500 mg (o) bd for 7–10 days

Cholera

Incubation period a few hours–5 days

Clinical features

Variable

• Subclinical

• Mild, uncomplicated episode of diarrhoea

• Fulminant lethal form with severe water and electrolyte depletion, intense thirst, oliguria, weakness, sunken eyes and eventually collapse

Diagnosis

Stool microscopy and culture (Vibrio cholerae)

Treatment

• In hospital with strict barrier nursing

• IV fluid and electrolytes

• Doxycycline

VIRAL HAEMORRHAGIC FEVERS

These include: yellow fever, Lassa fever, etc., plus dengue fever and chikungunya.

Yellow fever

Milder cases may present with flu-like symptoms and relative bradycardia (Faget's sign) and albuminuria. Severe cases experience these symptoms with abrupt fever then prostration, jaundice and abnormal bleeding from the gums and possibly haematemesis. Diagnosis is by ELISA testing.

Lassa fever, Ebola virus, Marburg virus, Hanta virus

These rare but deadly tropical diseases usually commence with a flu-like illness, gastrointestinal symptoms with thrombocytopenia, anaemia and, if severe, findings consistent with disseminated intravascular coagulation leading to bleeding and possibly shock and frank haemorrhage. Hanta virus tends to cause respiratory symptoms, including cough, progressing to respiratory difficulty. Seek urgent expert help.

• Incubation period: 2–16 days

• Transmission: direct body contact (body fluids, esp. blood, vomit from affected or dead person), infected animals, contaminated objects (needles, medical equipment)

• Early symptoms: constitutional (fever, malaise, headache), upper respiratory (flu-like, cough, etc.), abdominal (pain, nausea, vomiting, diarrhoea)

• May progress to severe symptoms as above then multiorgan failure

• Diagnosis: PCR, histopathology

• Treatment is supportive, esp. IV fluids

Dengue fever⁷

Also known as ‘breakbone’ fever, it is widespread in the south-east Pacific and endemic in Queensland. A returned traveller with myalgia and fever <39°C is more likely to have dengue than malaria. It is commonly misdiagnosed.

• Mosquito-borne (Aedes aegypti) viral infection

• Incubation period 5–6 days

• Abrupt onset fever, malaise, headache, nausea, pain behind eyes, severe backache, prostration

• Sore throat

• Severe aching of muscles and joints

• Fever subsides for about 2 days, then returns

• Maculopapular rubelliform rash on limbs → trunk (hand pressure for 30 seconds causes blanching)

• Petechial rash common (even in absence of thrombocytopenia)

• Generalised erythema with ‘islands of sparing’

• ± Diarrhoea

• The rare haemorrhagic form is very severe; may present with shock, which is usually fatal

• Later severe fatigue and depression (prone to suicide)

Note: A large-scale survey of dengue patients showed the symptoms as fever 100%, myalgia 79%, rash 74%, headache 68%, nausea 37%.

• Dengue-specific IgM serology—best on day 5

• PCR

• FBE: leukopenia; thrombocytopenia in haemorrhagic form

• Symptomatic with rest, fluids and analgesics (paracetamol). Avoid antibiotics, aspirin, NSAIDs and corticosteroids

• Avoid mosquito bites—no vaccine available

Zika virus

Also transmitted by Aedes aegypti, it is more common in Central and South America. Most infections are asymptomatic but common symptoms are fever, rash, arthralgia and conjunctivitis with a dengue-like syndrome. Can cause a Guillain–Barré-like syndrome or cerebral damage (microcephaly) in infants of infected mothers. Diagnosis is confirmed by serology and PCR. Treatment is symptomatic.

Chikungunya

This is an alpha-viral mosquito-borne infection with a similar clinical picture to dengue fever; it can cause haemorrhagic fever. It is encountered in tropical South-East Asia, Indian Ocean islands and parts of Africa.

• Positive serology

Encephalitis

Encephalitis presents with fever, nausea and vomiting then progressing to stupor, coma and convulsions. Mosquito-borne cases include Japanese B encephalitis and West Nile fever.

Consider mosquito-borne encephalitis and meningococcal meningitis in a patient presenting with headache, fever and malaise before neurological symptoms such as delirium, convulsions and coma develop.

Melioidosis

This serious disease with a high mortality is caused by the Gram-negative bacillus Burkholderia pseudomallei, a soil saprophyte that infects humans mainly by penetrating through skin wounds, especially abrasions. It is mostly acquired while wading in rice paddies. It is mainly a disease of third world countries and occurs between 20° North and 20° South of the equator, mainly in South-East Asia and including northern Australia. It may manifest as a focal infection or as septicaemia with abscesses in the lung, kidney, skin, liver or spleen. It is called the ‘Vietnamese time bomb’ because it can present years after the initial infection, as seen in Vietnamese war veterans.

• Fever, headache, cough, pleuritic pain and generalised myalgia

• Blood culture, swabs from focal lesions, haemagglutination test

• Ceftazidime 2 g IV, 6 hourly

  • or

• Meropenem 1 g IV, 6 hourly

  • or

• Imipenem 1 g IV, 6 hourly

• All for at least 14 days, followed by oral cotrimoxazole ± doxycycline bd + folic acid for 3 months

• Traumatised people with open wounds (especially diabetics) in endemic areas (tropical South-East Asia) should be carefully nursed.

Plague

Plague (Black Death), which is caused by the Gram-negative bacterium Yersinia pestis, is endemic in parts of Asia, Africa and the Americas. It has been presumed to be transmitted by the flea: ‘the flea bites the infected rat and then bites the human’, but spread from person to person is now considered more likely.

There are basically two forms:

1. bubonic plague—painful suppurating inguinal or axillary lymphadenitis (buboes) (see FIG. 15.2)

2. pneumonic plague—flu-like symptoms with haemoptysis, septicaemia and a fatal haemorrhagic illness (± buboes)

There is a rapid onset of high fever and prostration with black patches of skin due to subcutaneous haemorrhage.

• Serology and smear/culture of buboes

• Streptomycin and doxycycline

Rabies

Rabies is a rhabdovirus acquired by bites from an infected mammal, for example, a dog, cat, monkey, fox or bat.

Prodromal symptoms can include malaise, headache, abnormal behaviour including agitation and fever. It progresses to either paralytic ‘dumb rabies’ or encephalitic ‘furious rabies’, which involves excessive salivation and excruciating spasms of the pharyngeal muscles on drinking water (in particular). The patient is terrified of drinking water despite a great thirst (hydrophobia).

• Viral testing

• Post-bite prophylaxis (endemic area)

Wash the wound immediately then clean it. Administer rabies vaccine (if unimmunised) and rabies immune immunoglobulin ASAP (within 48 hours).

Ciguatera

This is a type of food poisoning caused by eating tropical fish, especially large coral trout and large cod, caught in tropical waters (e.g. the Caribbean and tropical Pacific). The problem is caused by a type of poison that concentrates in the fish after they feed on certain micro-organisms around reefs. Ciguatera poisoning presents within hours as a bout of ‘gastroenteritis’ (vomiting, diarrhoea and stomach pains) and then symptoms affecting the nervous system, such as muscle aching and weakness, paraesthesia and burning sensations of the skin, particularly of the fingers and lips. There is no cure for the problem but it can be treated with IV fluids and possibly mannitol infusion or gammaglobulin. It is unwise to eat large predatory reef fish, especially their offal (mainly the liver).

Hansen's disease (leprosy)

Hansen's disease (Gerhard Hansen, 1869) is caused by the acid-fast bacillus Mycobacterium leprae. It is a disorder of tropical and warm temperate regions, especially South-East Asia. It is considered to be transmitted by nasal secretions with an incubation period of 2–6 years. It affects the skin and nerves, especially of the extremities.

(WHO 1999)

Diagnosis is one or more of:

• Skin lesions—usually anaesthetic; hypopigmented or reddish maculopapules or annular lesions (see FIG. 15.3)

• Thickened peripheral nerves with loss of sensation, e.g. ulnar (elbow), median (wrist), common peroneal (knee) and greater auricular (neck); also peripheral neuropathy or motor nerve impairment

• Demonstration of acid-fast bacilli in a skin smear or on biopsy

• It can be localised (tuberculoid) or generalised (lepromatous)

• Diagnosis is by biopsy, the lepromin test, cultivation of the organisms or by PCR tests.

• Referral to specialists or a specialist centre is advisable for shared care.

• WHO treatment recommendations are multiple drug therapy, e.g. rifampicin, clofazimine and dapsone, but therapy is constantly being evaluated (see www.who.int/lep).

Scrub typhus

Scrub typhus is found in South-East Asia, northern Australia and the western Pacific. It is caused by Rickettsia tsutsugamushi, which is transmitted by mites.

• Abrupt onset febrile illness with headache and myalgia

• A black eschar at the site of the bite with regional and generalised lymphadenopathy

• Short-lived macular rash

• Can develop severe complications (e.g. pneumonitis, encephalitis)

• Serological assays

• Doxycycline 100 mg bd for 7–10 days

Queensland tick typhus

Queensland tick typhus, which is caused by Rickettsia australis, is directly related to a tick bite. The symptoms are almost identical to scrub typhus, although less severe, and the treatment is identical.

Travellers to tropical or subtropical areas are at risk of more unusual infections. Most of these infections are contracted through contaminated food and water, insect bites and walking barefoot on contaminated soil. The risk of such infections is highest in rural areas of countries other than Europe, North America and Australasia. Parasitic infections other than malaria include the following.

African trypanosomiasis (sleeping sickness)

Clinical features

Stage 1 (haemolymphatic)

• Incubation period about 3 weeks

• Fever, headache and a skin chancre or nodule

• Lymphadenopathy, hepatosplenomegaly

Stage 2 (meningoencephalitic)

• weeks or months later

• cerebral symptoms including hypersomnolence

Diagnosis

• Demonstrating trypomastigotes in peripheral blood smear or chancre aspirate

Treatment

• Suramin IV

• Infectious disease consultation essential

Prevention

• Avoid bites of the tsetse fly. If visiting areas of East, Central and West Africa, especially the safari game parks, travellers should use insect repellent and wear protective light-coloured clothing, including long sleeves and trousers.

Leishmaniasis

Visceral leishmaniasis (kala-azar)

The parasitic Leishmania which is transmitted by bites of sand flies and by blood transfusions and IV drug use, is endemic in 88 countries.

Clinical features

• The haemopoietic system is targeted and presenting features include fever; wasting; ulceration of the skin, mouth and nose; hepatosplenomegaly; and lymphadenopathy

• Among other signs is hyperpigmentation of the skin, hence the Hindu name kala-azar (‘black fever’)

• Most cases are subclinical

Diagnosis

• Serology and tissue biopsy

Cutaneous leishmaniasis

This may be encountered in travellers and servicemen and servicewomen returning from the Middle East, especially the Persian Gulf, and also travellers returning from Central and South America. The protozoa is transmitted by a sandfly and has an average incubation period of 9 weeks.

Clinical features

The key clinical finding is an erythematous papule (see FIG. 15.4).

Diagnosis

• Performing a punch biopsy and culturing tissue in a special medium

Treatment

• Treatment for extensive lesions is with high-dosage ketoconazole for 1 month.

• Smaller lesions should be treated topically with 15% paromomycin and 12% methyl benzethonium chloride ointment applied bd for 10 days.⁹

• A special vaccine is available in some Middle Eastern countries (e.g. Israel).

Schistosomiasis (bilharzia)

The infestation is caused by parasite organisms (schistosomes) which target the vasculature of the GIT or genitourinary tract. Its eggs are passed in human excreta, which contaminates watercourses (notably stagnant water) and irrigation channels in Egypt, other parts of Africa, South America, some parts of South-East Asia and China. Freshwater snails are the carriers (vectors).¹⁰

Clinical features

• The first clinical sign is a local skin reaction at the site of penetration of the parasite (it then invades liver, bowel, vulva and bladder). This site is known as ‘swimmer's itch’.

• Within a week or so there is a generalised allergic response, usually with fever, malaise, myalgia, abdominal pain and urticaria.

• A gastroenteritis-like syndrome can occur (nausea, vomiting, diarrhoea) and respiratory symptoms, particularly cough.

• Clinical findings, such as in trypanosomiasis, include lymphadenopathy and hepatosplenomegaly.

Diagnosis

• Serology

• Detecting eggs in the stools, the urine or in a rectal biopsy

Treatment

• Praziquantel (may need retreatment)

Prevention

• Travellers should be warned against drinking from, or swimming and wading in, dams, watercourses or irrigation channels, especially in Egypt and other parts of Africa.

Amoebiasis

Amoebiasis (Entamoeba histolytica) can be diagnosed in a sick traveller returning from an endemic area with severe diarrhoea characterised by blood and mucus. Complications include fulminating colitis, amoebomas (a mass of fibrotic granulation tissue) in the bowel and liver abscess. Acute amoebic dysentery is treated with oral tinidazole or metronidazole.

Amoebic liver abscess

Clinical features

• High swinging fever

• Profound malaise and anorexia

• Tender hepatomegaly

• Effusion or consolidation of base of right chest

There is often no history of dysentery, and jaundice is unusual.

Diagnosis

• Serological tests for amoeba and by imaging (CT scan)

Treatment

• Metronidazole and by percutaneous CT-guided aspiration

Giardiasis

Giardia lamblia infection is usually acquired from contaminated drinking water.

Clinical features

• Often asymptomatic

• Symptoms include abdominal cramps, bloating, flatulence and bubbly, foul-smelling diarrhoea, which may be watery, explosive and profuse.

Diagnosis

• Three specimens of faeces for analysis (cysts and trophozoites): ELISA/PCR

Treatment

• Scrupulous hygiene: metronidazole or tinidazole

Cutaneous myiasis

Myiasis, which refers to the infestation of body tissues by the larvae (maggots) of flies, often presents as itchy ‘boils’. Primary myiasis invariably occurs in travellers to tropical areas such as Africa (Tumbu fly) and Central and South America (bot fly), whereby the fly can introduce the larvae into the skin, or it can be due to secondary invasion of pre-existing wounds. All cutaneous bot fly lesions look like an unusual boil but with a small circular hole. Close inspection of lesions may reveal part or all of the larva. The simplest treatment is lateral pressure and tweezer extraction or place paraffin jelly (Vaseline) or thick ointment over the lesion to induce emergence by restricting oxygen, then apply a topical antibiotic.

Worms (helminths)

Worms that inhabit the human intestine can be classified into nematodes (roundworms), cestodes (tapeworms) and trematodes (flukes).

The roundworms, which include pinworm (Enterobius vermicularis), whipworm (Trichuris trichiura), human roundworm (Ascaris lumbricoides), human threadworm (Strongyloides stercoralis), hookworm (Ankylostomiasis), filariasis and larva migrans are the most prevalent worldwide and are usually asymptomatic in infected people.

Pinworm

Also known as ‘threadworm’, this is a ubiquitous parasite infesting mainly children of all social classes. They are tiny white worms about 1 cm long that multiply profusely and are spread readily between individuals by close contact (see FIG. 15.5). Virtually all children have been infected by the time they reach high school but at any one time approximately 50% of the 5–10 years age group will harbour pinworms.

Clinical features (usually asymptomatic)

• Pruritus ani (in about 30% of cases)

• Diarrhoea (occasionally)

• Abdominal pain, mimicking appendicitis

Diagnosis

• Inspect anus in child about 1 hour after going to sleep (see FIG. 15.5)

• Collect eggs with adhesive tape on perianal skin early morning—send to laboratory

Treatment

Management (troublesome cases)

• Scrupulous hygiene by family

• Hands should be washed thoroughly after toileting and before handling food

• Clip fingernails short (eggs lodge under nails)

• Patient should wear pyjamas (not nightgowns) and shower each morning

• Bed linen, nightwear and underwear changed and washed in very hot water daily for several days

• Vacuum room of affected person daily

• Have a veterinarian check any pets, especially dogs

Medication

• Any one of pyrantel, albendazole or mebendazole—as single dose orally

  pyrantel 10 mg/kg up to 750 mg

  or

  mebendazine 100 mg (child <10 kg: 50 mg)

  or

  albendazole 400 mg (child <10 kg: 200 mg)

• Repeat in 2–3 weeks—both patient and household contacts

Human roundworm

Adult worms are about 20–40 cm long and are usually acquired from contaminated food and water overseas. Many cases are asymptomatic but come to notice when they emerge from the anus, mouth or nostril (causing anxiety in the family!). Some will present with abdominal discomfort, failure to thrive, intestinal obstruction, cough, anaemia or biliary disease. They may be seen in radiological contrast examinations.

Diagnosis

• By finding eggs in the faeces. The worm is very sensitive to any of the three agents used for pinworm. May give positive faecal occult blood test.

Treatment

• A first-line option is pyrantel 20 mg/kg up to 750 mg orally, as a single dose—to be repeated after 7 days if a heavy infestation.

Whipworm

These used to be common in Indigenous communities, possibly causing failure to thrive, anaemia, abdominal pain and diarrhoea and rectal prolapse with heavy chronic infestation. The worms are about 1–2 cm long.

Diagnosis

• Faecal microscopy

Treatment

• Single large doses of mebendazole or albendazole

Hookworm

These are found in humid tropical regions but are now uncommon in northern Australia. About 1–1.5 cm long, the parasites are acquired by walking barefoot (or wearing thongs or sandals) on earth contaminated by faeces. The larvae penetrate the skin, travel through the lungs and settle in the small intestine.

Clinical features

The first sign is local irritation or ‘creeping eruption’ at the point of entry, known as ‘ground itch’, which is often unnoticed. This subsides within 2 days or so followed 1–2 weeks later by respiratory symptoms, which may be associated with bronchitis and bronchopneumonia. They can cause iron/protein deficiency anaemia in chronic infestation. Hookworm infection is the commonest cause of iron deficiency anaemia in the world.

Diagnosis

• As with other helminths, diagnosis is by finding eggs on microscopy of faeces

Treatment

• A single dose of mebendazole 100 mg bd for 3 days or 400 mg single dose pyrantel

Prevention

• Travellers should be warned to wear shoes and socks in endemic areas to prevent the entry of the larvae into the skin of the feet.

Human threadworm (Strongyloides)

These are tiny parasites (2 mm or so) and have a worldwide distribution. Infestation can cause symptoms such as recurrent abdominal pain and swelling and diarrhoea, skin and respiratory symptoms, with blood eosinophilia. Strongyloides can live and reproduce in the body for many years. The problem is aggravated by corticosteroid therapy and may present with a severe infection, such as septicaemia. High-risk people include migrants and refugees from tropical developing countries, returned soldiers, former prisoners of war from South-East Asia and workers or residents in northern Indigenous communities.

Diagnosis

• Detecting faecal larvae or duodenal biopsy

• ELISA: highly specific, sensitive

Treatment

• Ivermectin 200 mcg/kg (o) two doses 2 weeks apart (not in children < 5 years) or albendazole 200 mg bd for 3 days

Adverse effects are common. Beware of these drugs in pregnancy and children.

Cutaneous larva migrans

Cutaneous larva migrans (creeping eruption) (see FIG 15.6) should be suspected in any pruritic, erythematous lesion with a serpiginous eruption on the skin, especially the hands, legs and feet of a person from a subtropical or tropical area. It is caused by the larvae of dog or cat hookworms penetrating and migrating throughout human skin, the larva always being just ahead of the lesion it causes. The diagnosis is based on the classic clinical appearance and by eosinophilia. Biopsy is usually not indicated. The problem is usually self-limiting.

Diagnosis

• Clinical (characteristic appearance), eosinophilia (biopsy usually not indicated)

Treatment

• Ivermectin (single dose)

  or

  Albendazole

  Antihistamines for pruritus

  Note: This is usually a self-limiting problem.

Prevention

• As for hookworm. Moist sandy soil contaminated with dog or cat faeces is a common source.

Filariasis

This nematode infection has three main forms which are spread by mosquitoes, biting black flies and tabanid flies respectively.

1. Lymphatic filariasis causes acute adenolymphangitis and chronic lymphoedema with obstruction of lymph flow. The latter can manifest as a hydrocele, scrotal oedema or elephantiasis, especially of the extremities, genitals and breasts. Diagnosis is by blood film and serology.

2. Onchocerciasis (river blindness) starts as a nodule at the bite site followed by chronic skin disease and eye lesions such as uveitis and optic atrophy. It is the second leading cause of blindness worldwide. Diagnosis is by PCR testing, treatment by ivermectin.

3. Loiasis (tropical eye worm) due to the Loa loa worm causes conjunctivitis, localised angiooedema and Calabar swellings. Diagnosis is by microscopic examination—microfilariae in blood.

Hydatid disease

Hydatid disease is acquired by ingesting eggs of the dog parasite Echinococcus granulosus, which is found in sheep farming areas here and in several countries in Asia. The parasites can migrate anywhere but usually form hydatid cysts in the liver and lungs.

Clinical features

There may be no symptoms although the patient may complain of abdominal discomfort or cystic lesions on the skin and other sites. Rupture of a cyst (usually hepatic) can cause severe anaphylaxis with possible death.

Diagnosis

• Serological tests and ultrasound

Treatment

• Usually surgical removal of a cyst and albendazole

Dracunculus medinensis (Guinea worm)

This is the longest nematode. It is transmitted by tiny crustaceans in water.

Clinical features

• Local symptoms include pain and intense itching at the skin ulcer or blister as the worm emerges into the skin

Treatment

• Slow extraction of pre-emerging worms as they exit the skin

• Metronidazole ± corticosteroids