Out of the history books

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]

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