Biology of the Malaysian Strain of Plasmodium juxtanucleare Versiani and Gomes, 1941. I. Description of the Stages in the Vertebrate Host

Plasmodium juxtanucleare was first described from domestic fowl in Brazil. Since that time similar parasites have been reported from Mexico, Uruguay, and Ceylon. Recently a morphologically similar form has been found widely distributed in the domestic fowl of Malaysia. The Malaysian strain of P. juxtanucleare is described and illustrated. The Asian strains are morphologically quite similar. However, some differences are noted between the Malaysian and the Brazilian strains. Versiani and Gomes (1941) described a malarial parasite from the domestic fowl (Gallus gallus) in Minas Gerais, Brazil which they named Plasmodium juxtanucleare. In the same year Beltran isolated a similar parasite from the same genus of fowl in Huixtla, Chiapas, Mexico. More detailed descriptions of this parasite along with observations on the frequently fatal course of experimental infections in chickens were published by the same authors 2 years later (Versiani and Gomes, 1943; Beltran, 1943). In 1945 Cassamagnaghi reported this parasite from domestic chickens in Uruguay. Ishiguro (1957) described a new species of malaria from Japanese domestic fowl which he named Plasmodium japonicum. This parasite had morphological characters similar to P. juxtanucleare but it was relatively nonpathogenic. Later, Dhanapala (1962) reported what he considered to be P. juxtanucleare from Ceylonese chickens. This latter parasite also produced a low mortality rate in chickens. Recently a parasite, indistinguishable from Dhanapala's Ceylon strain of P. juxtanucleare, has been found widely distributed as a generally nonlethal infection in the domestic fowl of the Malay states. This parasite has also been identified as P. juxtanucleare. The present paper describes and illustrates the Malaysian strain of this parasite. MATERIALS AND METHODS Source of the parasite During March-April of 1963, mosquitoes caught in monkey-baited net traps in the canopy of the Received for publication 1 March 1966. * Present address: Ontario Research Foundation, 43 Queen's Park, Toronto 5, Ontario, Canada. coastal mangrove swamp near Rantau Panjang, approximately 5 miles NW of Klang, State of Selangor, Malaysia, were examined for malarial parasites. In April, a Culex (Culex) sitiens Wiedmann, caught in one of the traps, was dissected and the salivary glands found to contain numerous sporozoites. Approximately one-half of the sporozoites were inoculated subcutaneously into a canary, the remainder intravenously into a chick. The former inoculation failed to produce an infection. The latter produced a patent parasitemia at 14 days. This parasite has subsequently been maintained in this laboratory by a succession of blood and sporozoite transfers. In June 1963 a Culex (Culex) annulus Theobald, taken in a hill forest region (Ulu Gombak) near Kuala Lumpur, was found to be infected with sporozoites morphologically similar to those mentioned above. When injected into a chick a patent infection resulted on day 12. The blood parasites were morphologically indistinguishable from those obtained at Rantau Panjang. On further study, various aspects of the biology of this parasite were found to be identical with those of the Rantau Panjang isolate and both isolations were considered to be the same parasite. Hatchery-reared chickens from the local market were used throughout the study. All birds were housed in mosquito-proof cages for a period of at least 2 weeks prior to their use. Their parasitefree status was confirmed by blood examinations prior to use. No natural infections with malaria were found in chickens from this source. Blood films were taken daily from either the brachial artery or vein. Routine preparations were stained with Giemsa stain at pH 7.2, and all descriptions, unless specifically noted, were made from these films. Pigment granules were more readily observed by staining alcohol-fixed films with thiazine red (5% thiazine red, 1% acetic acid in distilled water) for 3 min. Nuclear elements of both the host cell and the parasite remained unstained whereas the c toplasm of both stained light red. Pigment granules stood out clearly as blackish brown clumps. Measurements in the text are presented in the following way: average (range)/number of measurements. For example, the length of the schizonts is presented as 2.7 u (2 to 4)/39.