The fear of tropical illness often worries those who have spent some time in the tropics, and many returnees express concern about harbouring diseases which may lead to health problems later in life. Even those who have had little illness during their stay are often keen to undergo screening on their return.

17.2  Screening asymptomatic returnees

Post-tropical screening is reassuring to the recipient and does produce a significant number of abnormal results. In most cases it can be done by the general practitioner, relatively few requiring referral to a specialist tropical diseases unit.

In one study, one in four asymptomatic people returning from at least three months in the tropics had an abnormality detected on screening. Three quarters of these were parasitic gut infections identified by stool examination for cysts, ova and parasites. Schistosomal serology was positive in nearly 11 per cent of those who had visited schistosomal areas, whether or not they gave a history of exposure. About eight per cent had an eosinophilia on the blood count, and further investigation resulted in a relevant tropical diagnosis in 40 per cent of these. Physical examination was of limited use in detecting tropical illness in these returnees, but picked up some non-tropical pathology. The yield from additional tests was small. Screening for schistosomiasis is recommended for all those who may have been exposed, even if asymptomatic. This should include schistosome ELISA and eosinophil count, and also microscopy of stool and terminal urine. Screening should start at least 12 weeks after exposure to allow time for seroconversion.

17.3  Investigation of symptomatic returnees

Management of those returning with symptoms depends on the nature of the problem, but many tropical diseases are best handled by a specialised tropical diseases unit where the necessary further investigations can be done and where there is access to a laboratory familiar with the tests involved. The incidence of individual diseases in tropical countries may change from year to year as epidemics occur and the last few years have seen notable instances of new or resurgent infections arising in the tropics. Tropical specialists are also more likely to be able to identify tropical skin diseases which may be unfamiliar to UK-based dermatologists. The travel history should be included on microbiology request forms, as unusual antimicrobial resistance patterns may occur.

17.3.1  Fever

The differential diagnosis of fever includes imported disease as well as conditions prevalent in the UK. Malaria must be excluded as a matter of urgency in all cases of febrile illness in those who have visited malaria endemic areas. (Malaria is a great mimic and should be considered in any patient who is unwell and has potentially been exposed.) Thick and thin blood films should be prepared without delay. Most cases of Plasmodium falciparum malaria imported into the UK present within the first three months, but presentation can be delayed for up to one year. Longer intervals have been recorded for the relapsing forms of malaria.

Enteric fever, dengue, pneumonia (including legionnaires' disease and other atypical pneumonias), hepatitis and acute schistosomiasis (Katayama fever) should also be considered. Early advice should be sought from a physician experienced in tropical and infectious diseases if the diagnosis is unclear.

17.3.2  Diarrhoea

Diarrhoea is frequent among returning travellers and many do not seek medical attention. A careful history is essential for correct diagnosis and should include a travel history, the time elapsed since returning to the UK and the duration of diarrhoea. This information should be included on the laboratory request form accompanying stool microscopy and culture.

Travellers' diarrhoea usually occurs during travel or very shortly after returning home. The longer the history, the more likely is a parasitic (eg Giardia, Entamoeba histolytica, Cyclospora) rather than a bacterial or viral cause. It should always be borne in mind that malaria can present as a diarrhoeal illness.

17.3.3  Pharyngitis

Throat swabs from patients with pharyngitis should include the history of recent travel so that culture for Corynebacterium diphtheriae is included where appropriate. Lassa fever should be considered in cases of fever and pharyngitis from rural West Africa.

17.3.4  Hepatitis

Hepatitis A and B together account for most cases of imported viral hepatitis. Less commonly hepatitis C and E, coxiella, cytomegalovirus, glandular fever or toxoplasma may be responsible for a hepatic illness. Malaria can present as hepatitis.

17.3.5  HIV infection

Where appropriate, tactful discussion of potential risk factors for HIV exposure abroad should form part of a post-travel consultation.

17.3.6  Skin conditions

Skin infections, from all groups of infectious agent including insects, are common in the tropics. Dermatophyte infections frequently occur. Pitfalls include cutaneous diphtheria and cutaneous leishmaniasis. Myiasis may be mis-diagnosed as furunculosis.

17.3.7  Systemic parasitoses

Helminth infections, eg onchocerciasis, loiasis, may present long after the patient has returned to the UK. Schistosomiasis may present acutely a few weeks or months after exposure, but presentation can be long-delayed and, in the case of genito-urinary involvement, may be overlooked or misdiagnosed.