Vector species-specific association between natural Wolbachia infections and avian malaria in black fly populations.

Artificial infection of mosquitoes with the endosymbiont bacteria Wolbachia can interfere with malaria parasite development. Therefore, the release of Wolbachia-infected mosquitoes has been proposed as a malaria control strategy. However, Wolbachia effects on vector competence are only partly understood, as indicated by inconsistent effects on malaria infection reported under laboratory conditions. Studies of naturally-occurring Wolbachia infections in wild vector populations could be useful to identify the ecological and evolutionary conditions under which these endosymbionts can block malaria transmission. Here we demonstrate the occurrence of natural Wolbachia infections in three species of black fly (genus Simulium), which is a main vector of the avian malaria parasite Leucocytozoon. Prevalence of Leucocytozoon was high (25%), but the nature and magnitude of its association with Wolbachia differed between black fly species. Wolbachia infection was positively associated with avian malaria infection in S. cryophilum, negatively associated in S. aureum, and unrelated in S. vernum. These differences suggest that Wolbachia interacts with the parasite in a vector host species-specific manner. This provides a useful model system for further study of how Wolbachia influences vector competence. Such knowledge, including the possibility of undesirable positive association, is required to guide endosymbiont based control methods.

Chickens treated with a nitric oxide inhibitor became more resistant to Plasmodium gallinaceum infection due to reduced anemia, thrombocytopenia and inflammation.

Malaria is a serious infectious disease caused by parasites of the Plasmodium genus that affect different vertebrate hosts. Severe malaria leads to host death and involves different pathophysiological phenomena such as anemia, thrombocytopenia and inflammation. Nitric oxide (NO) is an important effector molecule in this disease, but little is known about its role in avian malaria models. Plasmodium gallinaceum-infected chickens were treated with aminoguanidine (AG), an inhibitor of inducible nitric oxide synthase, to observe the role of NO in the pathogenesis of this avian model. AG increased the survival of chickens, but also induced higher parasitemia. Treated chickens demonstrated reduced anemia and thrombocytopenia. Moreover, erythrocytes at different stages of maturation, heterophils, monocytes and thrombocytes were infected by Plasmodium gallinaceum and animals presented a generalized leucopenia. Activated leukocytes and thrombocytes with elongated double nuclei were observed in chickens with higher parasitemia; however, eosinophils were not involved in the infection. AG reduced levels of hemozoin in the spleen and liver, indicating lower inflammation. Taken together, the results suggest that AG reduced anemia, thrombocytopenia and inflammation, explaining the greater survival rate of the treated chickens.

Plasmodium relictum as a cause of avian malaria in wild-caught magellanic penguins (Spheniscus magellanicus).

Avian malaria (Plasmodium relictum) caused significant mortality in wild-caught Magellanic penguins (Spheniscus magellanicus) in 1986 at the Blank Park Zoo in Des Moines, Iowa (USA). In early winter, wild birds were captured off the southern coast of Chile and flown to Detroit, Michigan for a 38 day quarantine. After quarantine, 18 birds were dispersed to Lansing, Michigan, six to a facility in Maine, and 46 to Des Moines, Iowa. Upon arrival in Des Moines, several penguins became weak and inactive, had to be force-fed, and died after 2 days. Gross lesions at postmortem included splenomegaly, hepatomegaly, and pulmonary edema. Histopathological examination revealed numerous intraendothelial schizonts in spleen, lung, liver, heart and kidney. Schizonts were generally 16 to 28 micron by 11 to 16 micron and contained merozoites of two distinct sized (macromerozoites, nuclei 1.0 micron; micromerozoites, nuclei 0.5 micron). Based on the morphology of the abundant exoerythrocytic forms, a tentative diagnosis of avian malaria (Plasmodium sp.) was made. Subsequent transmission electron microscopic examination of schizonts in formalized tissue revealed merozoites with tear-shaped rhoptries. Antimalarial therapy was initiated early but deaths continued for 5 mo. Mortality, which eventually totaled 83%, occurred in three distinct waves, each separated by a hiatus of approximately 1 mo. Despite examinations of repeated blood smears, intraerythrocytic Plasmodium relictum was not detected until late in the outbreak. Diagnosis was based on morphologic characteristics including schizonts with eight to 12 merozoites/segmenter and round gametocytes that displaced and turned the infected erythrocyte nucleus. In addition to malaria, penguins showed evidence of aspergillosis, bacterial enteritis (Escherichia coli; Proteus sp.; and Edwardsiella sp.), and helminthiasis (Contracaecum sp. and Tetrabothrius sp.). Based on gross and histological lesions, disease prevalence in this group of penguins was malaria 58%, aspergillosis 61%, enteritis 60%, helminthiasis 26%. Epidemiologic investigation including group transport history, disease prevalence in co-quarantined birds not sent to Des Moines and climatological data implicated Des Moines as the likely site for initial exposure, although information is not conclusive. Stress and concurrent disease certainly contributed to the severe mortality in this group of penguins infected with P. relictum.

The Plasmodium lophurae (avian malaria) ribosome.

Ribosomes were isolated from Plasmodium lophurae by Triton X-100 lysis and ultracentrifugation. Plasmodium lophurae ribosomal subparticles, produced by treatment of ribosomes with puromycin, were separated by sucrose gradient centrifugation. The nucleotide base composition of P. lophurae ribosomal RNA (rRNA) from intact ribosomes and subparticels was low in guanine-cytosine content (approximately 37% G + C) whereas the rRNA of the host cell (duck reticulocyte) was considerably higher (64% G + C). The rRNA of the malaria parasite was typically protozoan, with sedimentation values of 25S and 17S. In vitro, free parasites and malaria-infected red cells incorporated radioactive adenosine into both the large and the small plasmodial subparticles; label was also recovered in the 25S and 17S RNAs. These results suggest that host ribosomes do not contribute to ribosome biogenesis in this malaria, rather parasite rRNA is the transcription product of plasmodial cistrons.