An explanation was sought for the disparity between the low reported incidence of scrub typhus and the high prevalence of antibody to Rickettsia tsutsugamushi in the rural population of Malaysia. A combination of isolation of the organism, titration of antibody by indirect immunofluorescence, and the Weil-Felix test was used to confirm infections. Scrub typhus was found to be very common, causing 23% of all febrile illnesses at one hospital. The infection was particularly prevalent in oil-palm workers, causing an estimated 400 cases annually in a population of 10,000 people living on one plantation. The clinical syndrome, whether mild or severe, was difficult to distinguish from that due to other infections. Eschars, rashes and adenopathy were uncommon. When used to examine early sera, the Weil-Felix test failed to confirm the diagnosis in most infections.20
Tropical canine pancytopenia (TCP) is a newly recognized infectious disease of dogs in diverse tropical and subtropical areas. The disease is characterized by hemorrhage, pancytopenia, severe emaciation and persistent infection. Dogs with TCP are often presented with epistaxis, which is the most dramatic sign of the disease; however, a large number of affected dogs develop severe pancytopenia and die without manifesting clinical signs of hemorrhage. The disease has been reported most frequently in the German Shepherd. Pathological findings consist of petechial and ecchymotic hemorrhages on serosal and mucosal surfaces of numerous organs. The most prominent histological finding is a perivascular plasma cell infiltrate in most organs. Disease, indistinguishable from the natural disease, has been produced in laboratory dogs inoculated with whole blood from affected dogs. Ehrlichia canis has been consistently recovered from all experimentally infected dogs. Attempts to transmit the disease to other laboratory animals and to propagate the agent in cell cultures and embryonating eggs have been unsuccessful. The tick is the probable vector of the disease.
An indirect fluorescent-antibody test for detection and titration of antibodies to Ehrlichia canis, the causative agent of tropical canine pancytopenia, has been described. The organism propagated by an in vitro technique in canine blood monocytes served as an antigen in the test. The specificity of the test was revealed by absence of cross-reactivity between the antigen and sera from dogs infected with various common pathogens and specific sera against eight rickettsial species. The accuracy of the test was ascertained by isolation of the organism from reactor dogs located in and outside the United States. Histopathological examination of nine reactor dogs revealed plasmacytosis of meninges and kidneys in eight of them.
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