1. Cross-protection tests between a strain of Sumatran mllite-fever and strains of the tsutsugamushi disease were done in the rabbit and monkev with the object of elucidating the inter-relation of these two diseases.
2. It is concluded that Sumatran mite-fever is not a disease sui qeneris, but is identical with the tsutsugamushi disease.
Scrub typhus is a common cause of febrile illness among children from rural regions in tropical countries. We described 2 cases of scrub typhus with an eschar localized in the genitalia that was missed during the routine medical examination of a febrile child.
A short description of the tsutsugamushi disease is given, followed by a note on the conditions under which it occurs in Sumatra and the Malay States. Abandoned agricultural land which has grown up in weeds is particularly dangerous. Small rodents are the reservoirs of the virus which is carried from them to man by larval mites. Trombicula akamushi is the carrier in Japan, and T. deliensis in Sumatra. The disease has been conveyed to monkeys by inoculation and also by the bites of infected mites. A description is given of four mites which are commonly found in the ears of rats in the Malay States, and a method for the examination of the mites is described. Black rats, to the number of 130, were examined. Sixteen were trapped in an abandoned portion of an oil-palm estate where three Europeans became infected with the tsutsugamushi disease, and T. deliensis, the Sumatran carrier, was found on ten of them. Thirty rats were caught in other parts of the estate, and T. deliensis was found on nine. Thirty rats were caught in other rural districts, where the disease was not known, and T. deliensis was found on only one. Fifty-four rats caught in the town of Kuala Lumpur were examined, with the result that T. deliensis was found in none. The conclusion is reached that T. deliensis is probably the carrier in the Malay States, as it is in Sumatra.
1. A strain of the rural form of tropical typhus has been established and maintained in guinea-pigs, and is now in its 97th generation. The history and characteristics of this strain are given. The clinical criterion of infection is a well-marked febrile reaction. Scrotal swelling does not occur. Ascites invariably follows intra-peritoneal inoculation of passage virus.
2. In more than one hundred other such attempts made in this laboratory it has proved impossible to maintain a strain beyond a few generations. Similarly all attempts to maintain the virus of the tsutsugamushi disease in guinea-pigs have failed. The guinea-pig must, therefore, be regarded as very insusceptible to the viruses of the rural typhus and tsutsugamushi group of fevers of Malaya.
3. Infection of rabbits by the intra-ocular inoculation of the virus of rural typhus and of the tsutsugamushi disease has been readily secured. The method, based on that of Nagayo et al., and the criteria of infection, are described in detail.
4. The white rat is readily infected with the virus of rural typhus, the infection being of the "inapparente" form. That the virus could be maintained with unabated virulence for 21 generations indicates, by the criterion of Nicolle, that rural typhus is a murine strain.
5. Monkeys have been successfully infected by the intradermal route with the virus of rural typhus and of the tsutsugamushi disease. At the sites of inoculation, in the case of both viruses, necrotic ulcers have developed that appear to be identical with one another, and with the initial lesion of the tsutsugamushi disease in man; in all other features the experimental infections in the monkey appear to be identical. Rabbits have been similarly infected.
6. The results of the Weil-Felix reactions of sera from rabbits and monkeys convalescent from experimental infection with rural typhus and the tsutsugamushi disease are summarized.
7. Methods of demonstration of Rickettsia from infected guinea-pigs and rabbits are described. In morphology, distribution and staining characteristics the Rickettsia demonstrable in material from animals infected with rural typhus and with the tsutsugamushi disease are identical, and do not appear to differ from the Rickettsia orientalis of Nagayo.
8. The experimental data secured indicate that, provided that intra-ocular inoculation is practised, the rabbit is the laboratory animal of choice in the case of the rural typhus and tsutsugamushi group of fevers (it being assumed that
expense and scarcity make extensive use of monkeys impracticable). Further, these data stress the remarkable similarity of the behaviour of these two viruses in experimental laboratory animals-a similarity that, as will be set forth in a later paper, is fully supported by cross-immunity experiments.
1. The results of the Weil-Felix reactions of sera from rabbits and monkeys inoculated with human virus or virus of laboratory strains of rural typhus, urban typhus or the tsutsugamushi disease are reported and discussed; as also are corresponding results in rabbits inoculated with the virus of two strains of tropical typhus recovered from wild rats.
2. Instances are given of a change in type of antibody response; in particular, an experience is described in which the agglutinogenic properties of a virus of a tropical typhus strain underwent a temporary change, while the immunogenic properties remained unchanged.
No focalization of rats (Rattus tiomanicus and R. argentiventer) infected with Rickettsia tsutsugamushi could be discerned over a 500 m trapping transect at the border between a forest and lalang grass (Imperata cylindrica). R. tiomanicus appeared to occupy 250 m of the transect on the average and had periods during which infections were observed which averaged 97 days. Calulations indicated that more than 50% of individuals become infected over their life-time. The high rate of infection in this and other areas described in earlier publications and the habits of the rats suggest that infected mites are densely and widely dispersed in the areas studied in Malaysia.
Serological surveillance for up to two years of 114 patients with laboratory confirmed scrub typhus showed that antibody to Rickettsia tsutsugamushi as demonstrated by the indirect fluorescent antibody test is short-lived. The mean reversion time from mean peak titre (1:499) was 48.9 weeks and the calculated annual reversion rate to a titre less than 1:50 was 61%. This can be used to estimate attack rates based on point prevalence of antibody. The relationship between antibody prevalence and attack rates observed by other workers was confirmed using this model. The possible uses of the finding and its implications in Malaysia are briefly discussed.
Scrub typhus is an endemic problem in Malaysia. Yet its diagnosis appears to depend heavily on the Wetl-Felix test as the more sophisticated diagnostic procedures are not available routinely. We therefore reviewed our experience with scrub typhus patients treated at the Melaka General Hospital from 1983 to April 1986, to identify those clinical features which are diagnostic of this rickettsial illness. Based on the clinical presentation of our patients and the dramatic response of scrub typhus to Doxycycline, we propose a clinical approach to diagnosis until more specific and cheap diagnostic procedures become available in our laboratories. Otherwise, this rickettsial illness will continue to be under-recognised.