A myopathy associated with elongated intramuscular protozoan schizonts of uncertain classification was observed in chickens in commercial farms. Of 152 affected fowls originating from 21 flocks in 12 farms, 149 were 24 weeks of age or older and 136 were broiler breeder birds. Both sexes were affected. The disease was only observed during the months of October, November and December, 1976 and 1977. The monthly mortality rate in affected adult flocks rose by 0.5% to 4% and the egg production declined by 5% to 15% during this period. Most affected birds were in good body condition or overweight. Gross lesions were usually present in all skeletal muscles and the cardiac muscle. They resembled nutritional myopathy, sarcosporidiosis, leucocytozoonosis or haemorrhagic syndrome. Microscopically visible elongated schizonts were demonstrated in skeletal muscles and the cardiac muscle in 49 of 55 birds examined histologically. The possible aetiology with respect to known parasites of muscles in fowls is discussed.
Plasmodium knowlesi poses a health threat throughout Southeast Asian communities and currently causes most cases of malaria in Malaysia. This zoonotic parasite species has been studied in Macaca mulatta (rhesus monkeys) as a model for severe malarial infections, chronicity, and antigenic variation. The phenomenon of Plasmodium antigenic variation was first recognized during rhesus monkey infections. Plasmodium-encoded variant proteins were first discovered in this species and found to be expressed at the surface of infected erythrocytes, and then named the Schizont-Infected Cell Agglutination (SICA) antigens. SICA expression was shown to be spleen dependent, as SICA expression is lost after P. knowlesi is passaged in splenectomized rhesus. Here we present data from longitudinal P. knowlesi infections in rhesus with the most comprehensive analysis to date of clinical parameters and infected red blood cell sequestration in the vasculature of tissues from 22 organs. Based on the histopathological analysis of 22 tissue types from 11 rhesus monkeys, we show a comparative distribution of parasitized erythrocytes and the degree of margination of the infected erythrocytes with the endothelium. Interestingly, there was a significantly higher burden of parasites in the gastrointestinal tissues, and extensive margination of the parasites along the endothelium, which may help explain gastrointestinal symptoms frequently reported by patients with P. knowlesi malarial infections. Moreover, this margination was not observed in splenectomized rhesus that were infected with parasites not expressing the SICA proteins. This work provides data that directly supports the view that a subpopulation of P. knowlesi parasites cytoadheres and sequesters, likely via SICA variant antigens acting as ligands. This process is akin to the cytoadhesive function of the related variant antigen proteins, namely Erythrocyte Membrane Protein-1, expressed by Plasmodium falciparum.