5 key points on fever in international travellers (clinical problem)

• a travel history should be obtained from anyone with a febrile illness
• malaria should be excluded in anyone with a fever who has been in a malaria-endemic area recently
• then consider dengue & other arbovirus infections if there has been mosquito exposure
• do not forget the neglected bacterial tropical infections: enteric fever, leptospirosis, scrub typhus & melioidosis
• do not forget to ask about potential risk for sexually-transmitted infections & HIV/AIDS

The μGnome got out his set of paintbrushes today to refresh a set of disease maps for the forthcoming tropical medicine breakfast session at Sir Charles Gairdner Hospital.

Gone are the neat little red outlines carefully added to world map outlines. This is the genuine graffiti version in block colour – world distribution of scrub typhus and melioidosis, as of May, 2010.

The stand-alone maps will appear on the Priobe Net shortly.

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Some of the best descriptions of infectious diseases come from before the antibiotic era.

Tropical infectious diseases are no exception, and where better to go than Manson-Bahr’s Synopsis of Tropical Medicine? A little more succinct than Manson’s Tropical Diseases. Some years ago I found a copy of the 1946 edition that had been used by a member of staff at the British Military Hospital in Hong Kong.

The entry on what we now call scrub typhus is instructive, once you get past the vocabulary of a bygone era:

IV. TSUTSUGAMUSHI. MITE TYPHUS

“Scrub typhus”, acute endemic typhus; initial eschar at site of bite of mite, Trombicula akamushi.

Geographical distribution and epidemiology. – Japan, Formosa, Korea, Malaya, Ceylon, New Guinea, Pescadores, Philippines, Indo-China, Queensland. Men more commonly affected than women, especially labourers, cane-cutters and workers on palm plantations in malaya, particularly after floods and rainy season. In Formosa, April-November.

Ætiology.- Rickettsia orientalis develops in leptotrombicula – larval stage of mite (Trombicula akamushi – in Sumatra, T. deliensis) Infection conveyed in bite through salivary glands.

Reservoir host.- Wild rats, local varieties found infected with R. orientalis and mite is parasitic on them. R.orientalis transmitted to guinea-pigs and rabbits by intra-ocular inoculation.

Transmission.- Trombidiidae-velvet mites-burrow under skin (harvest bugs). Adult Trombicula in soil of infected fields, 0.9mm by 0.5mm; pale grey or red with rudimenrary yeyes, four pairs of legs, anterior pair stout, two pairs of suckers on ventral surface. Larva leptotrombicula (microtrombidium), 0.4 by 0.25mm.; resembles harvest mite in appearance; has three pairs of legs (hexapod) covered with minute plumose hairs. Larva of T.akamushi : bright vermilion, of T.deliensis : plae ochre.

Pathology.- Lesion at site of bite : coagulation necrosis, other lesions resemble those of I, except that widespread thrombotic lesions of peripheral blood vessels do not occur. Histologically, chief change is perivascular inflammation ; intima secondarily attacked.

Clinical.- Bite of mite at first not noted ; larvae easily seen by magnifying glass with heads and bodies in skin. Incubation period : 4-10 days ; malaise, frontal and temporal headache, then pain and tenderness in lymphatic glands of groin, axilla and neck. Eschar, 2-4mm, surrounded by red areola, some lymphangitis. T., 104-105°F. Conjunctivae injected. Bronchitis. Splenomegaly. Rash : 6-7th day, dark red papules on forearms, legs, trunk – roseolar on face ; less pronounced on upper arms, thighs, neck and palate ; more pronounced than in I. Delirium, deafness. Primary ulcer heals in second week ; temperature falls by crisis or lysis on 14th day. Complications and sequelae as in I ; pregnant women usually abort. Mortality : 20-30 per cent. in Japan ; in Sumatra 15 per cent. N.B. uninfected mite bites may give rise to irritation at site and mild constitutional phenomena.

Diagnosis.- As in I ; Weil-Felix reaction OXK (Kingsbury strain). Intradermal test with OXK also employed. Initial necrotic ulcer and lymphadenitis characteristic. Differentiate from other forms of typhus, measles and dengue.

Treatment.- Site of bite cauterized or excised. Lumbar puncture for delirium ; otherwise symptomatic.

Prophylaxis.- Mite-proof suiting for workers in infected fields ; mite bites treated with disinfectant (Vleminckx’s solution- sulphide of calcium). Prophylactic inoculation in Malaya ; results inconclusive.

[spelling and punctuation as in original version; I is a reference to epidemic typhus]

What’s the connection between Ena Sharples; the hairnet helmeted doyenne of Coronation St and tropical medicine? Coronation St afficionados would be hard pressed to place the sullen rows of back-to-back brick terraces with the humid tropics.

The explanation will be unveiled during next Tuesday’s tropical medicine breakfast in the Emergency Department seminar room at Sir Charles Gairdner Hospital.

You may glean a shrew idea if you take a look at the lecture notes before Tuesday.

Download (PDF, 830.79KB)

For those following the FACTM pt 1 series, the next instalment is just around the corner, if you’re planning your diary for next week. The face-to-face session will take place at the later time of  7:30am next Tuesday (25th May) in the ED seminar room at Sir Charles Gairdner Hospital, and will run for an hour in its usual two topic format.

Next week’s session is open to junior medical staff and there will be a light breakfast as usual. The MicroGnome apologises for not having the unit notes ready in time for this post, owing to an encounter with arboviruses in Queensland earlier this week. He assures you that the lecture material will meet the usual standard, and was inspired by recent fieldwork in tropical Australia.

Tuesday’s units will cover Leptospirosis, Melioidosis and Scrub Typhus; three infections prevalent in the Australian tropics. Reading for this unit includes:

• Leptospirosis – Oxford Handbook of Tropical Medicine p694
• Manson’s Tropical Diseases p1161 ff;
• Melioidosis – Oxford Handbook p700, Manson p1127 ff
• Scrub Typhus – Oxford Handbook p687, Manson p 885 ff.