Avian malaria: clinical and chemical pathology of Plasmodium gallinaceum in the domesticated fowl Gallus gallus

Abstract

Data on the effects of Plasmodium gallinaceum on domesticated fowl are sparse, justifying a full investigation of its pathology. Clinical signs following blood-induced infections with the Wellcome line of strain 8A included depression, fever, anorexia, reduced weight gain, poor feed conversion, anaemia, green faeces and often death. After administration of 106 erythrocytic parasites, mortality 5 to 10 days after infection was 10% to 93% in chickens 7 to 84 days old. The older the birds, the lower the mortality and the longer the time to death. Onset of detectable parasitaemia occurred mostly during the second day after infection (59% of birds). Peak parasitaemia (∼70%) occurred on the sixth day in 85% of surviving birds. The patent period was usually 7 to 19 days. Abnormally low haematocrit values of ≤24% and high colonic temperatures of ≥42°C were recorded. A febrile response is demonstrated conclusively here in P. gallinaceum malaria for the first time. Weight gain of malarious birds was reduced by ∼18% to 51%, and feed conversion efficiency was often reduced by ∼12% to 41%. Growth reduction was due entirely to anorexia. Liver weight relative to body weight (normally ∼2% to 3%) increased to ∼4.5% by 8 days, and relative spleen weight (normally ∼0.2%) increased to 1.6% by 12 days. Specific gravities of livers and spleens in healthy and infected birds were ∼1.09. Gall bladder volume in malarious birds 8 days after infection was approximately four times that of normal birds. Statistically significant changes occurred in the proportions of plasma proteins in malarious birds 8 days after infection; albumin and α2-globulin were reduced, while γ1-globulin and γ2-globulin were increased. Those changes coincided with significant increases in concentrations of plasma total protein and the enzymes aspartate aminotransferase, glutamate dehydrogenase and γ-glutamyltransferase, and a decrease in creatinine. Green (biliverdin) colouration of the faeces was a consistent sign of malaria. Birds acquired non-sterile immunity after a single primary infection. The quantitative data presented facilitate selection of the most useful criteria for field diagnosis, estimation of potential economic losses, and assessment of potential avian antimalarial drugs.