Micrognome

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]