SUMMARYNine serological techniques were compared by monitoring the response to infection with Rift Valley fever (RVF) virus in three sheep. Antibodies were monitored daily for the first 14 days after infection, then weekly and later fortnightly up to week 24. The earliest antibody response was detected in one sheep on day 3 by a plaque reduction neutralization test, and by day 6 antibodies were demonstrable in all three sheep by haemagglutination-inhibition, reversed passive haemagglutination-inhibition, immunodiffusion, indirect immunofluorescence (IF), enzyme-linked immunosorbent assay and neutralization ofcytopathic effect in cell cultures. Antibodies were demonstrable by complement fixation on day 8 at the earliest. IF and the two neutralization techniques produced the highest titres, but all tests could be used satisfactorily for the serological diagnosis of RVF. Inactivated antigen could be used for all except the neutralization tests. A radioimmunoassay technique using l251-labelled staphylococcal protein A detected antibodies on day 8 at the earliest and produced lower mean titres than some of the other techniques. This was probably because sheep immunoglobulins bind protein A poorly.
SUMMARYIn order to determine the way in which vertebrates infected with CrimeanCongo haemorrhagic fever (CCHF) virus and potential ixodid tick vectors interact in nature, immature and adult ticks of several species were fed on viraemic mammals and then assayed for virus content at varying times after feeding. CCHF virus was not isolated from ticks of six species tested after feeding as adults and immature forms on sheep with viraemia of 102 -32 LD 50/ml, nor from larval ticks fed on guinea-pigs and white-tailed rats with viraemia of 1019-27 LD 50/ml. In contrast, virus was isolated from 10 of 152 pools of engorged adult ticks of 5 species that fed on cattle with viraemia of 101'-27 LD 50/ml and from 3 of 137 female ticks after oviposition. Infection was transmitted to larval and nymphal Hyalomma truncatum and H. marginatum rufipes, but not to Rhipicephalus evertsi evertsi, from a scrub hare with viraemia of 1042 LD 50/ml but only nymphal H. truncatum and H. m. rufipes became infected from scrub hares with viraemia of 102 6-2 7 LD 50/ml. Infection was transmitted trans-stadially in H. m. rufipes and H. truncatum infected as nymphae, and adult H. m. rufipes transmitted infection to a sheep. No evidence of transovarial transmission was found in larval progeny of ticks exposed to CCHF virus as adults on sheep and cattle or as immatures on scrub hares.
In November 1984 a case of Crimean-Congo haemorrhagic fever (CCHF) occurred in a worker who became ill after slaughtering ostriches (Struthio camelus) on a farm near Oudtshoorn in the Cape province of South Africa. The diagnosis was confirmed by isolation of CCHF virus from the patient's serum and by demonstration of a specific antibody response. It was suspected that infection was acquired either by contact with ostrich blood or by inadvertently crushing infected Hyalomma ticks while skinning ostriches. Reversed passive haemagglutination-inhibition antibody to CCHF virus was detected in the sera of 22/92 ostriches from farms in Oudtshoorn district, including 6/9 from the farm where the patient worked, but not in the sera of 460 birds of 37 other species. In pathogenicity studies domestic chickens proved refractory to CCHF infection, but viraemia of low intensity (maximum titre 2.5 log10 mouse ic LD50/ml) followed by a transient antibody response occurred in blue-helmeted guinea fowl (Numidia meleagris). These results offer the first direct evidence that some bird species are susceptible to CCHF virus infection.
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