BackgroundRapid diagnostic tests play a pivotal role in the early diagnosis of malaria where microscopy or polymerase chain reaction are not immediately available.Case presentationWe report the case of a 39 year old traveler to Canada who presented with fever, headache, and abdominal pain after visiting friends and relatives in India. While in India, the individual was not ill and had no signs or symptoms of malaria. Laboratory testing upon his return to Canada identified a false positive malaria rapid diagnostic (BinaxNOW® malaria) result for P. falciparum with coincident Salmonella Typhi bacteraemia without rheumatoid or autoimmune factors. Rapid diagnostic test false positivity for malaria coincided with the presence or absence of Salmonella Typhi in the blood.ConclusionsClinicians should be aware that Salmonella Typhi infection may result in a false positive malaria rapid diagnostic test. The mechanism of this cross-reactivity is not clear.
SUMMARYTwo temperature-sensitive mutants of the Ukg 27/72 strain of swine vesicular disease virus were isolated in tissue culture and a third was derived following adaptation in mice. All three were found to have similar growth restrictive temperatures, but varied considerably in their virulence when administered to pigs. The route of inoculation appeared to exert a considerable influence on the apparent degree of attenuation, the antibody titre engendered and the transmission of disease to pigs held in contact with inoculated animals. One strain appeared almost totally attenuated when inoculated into pigs but spread to animals in contact causing severe disease. Virus re-isolated from one such animal was found to have retained its temperature sensitive phenotype, suggesting that virulence in this case was not directly related to temperature sensitivity. Pigs with high antibody titres were found to be susceptible when placed in contact with challenge animals, although the lesions which developed were mild.
Qualitative and quantitative laboratory tests on small and large plaque variants of the foot-and-mouth disease virus type SAT1Nig10/75 revealed an antigenic similarity which was confirmed by vaccine potency tests in guinea pigs. $ Virus preparations used for vaccines have often been shown to be heterogeneous in terms of the size of plaque they can elicit when plated on to cell monolayers. Where such plaque variants have been found to be stable, they have in many cases been linked with other changes in the virus population, e.g. attenuation (7, 10) and antigenic shift (6,12). COWA~ et al. (3) have suggested that plaque heterogeneity may be of importance in the production of vaccine antigens by showing the large plaque (LP) variant, of a type Asia, t foot-and-mouth disease virus to be four times more potent than the small plaque (SP) variant, when used to vaccinate small groups of cattle.Plaque size variants have been observed for six of the seven serot)~pes of footand-mouth disease (FMD) viruses when grown under various cultural conditions (8). To date, in most reported eases of plaque variants in FMD viruses, the large plaque variant is considered to be the "wild type" parent producing natural disease in animals (5).In the light of other workers' data, it was decided to investigate this phenomenon further, using a different serotype of FMD virus, and also paying particular attention to (1) the mass of antigen used to formulate vaccines and (2) the use of controlled vaccine trials :in guinea pigs to produce reliable data.During the growth of FMD virus strain SAT 1 Nig10/75 in BHK suspension cells in this laboratory, virus was assayed for infectivity by a plaque assay technique. Observations of the assay plates showed two different plaque types, one large (5--6 ram), and other small (1 mm). Both variants were isolated, plaque purified twice and given three BHK suspension {SP) or monotayer (LP) passage
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