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More than half of the Hawaiian honeycreepers (Drepanidinae) known from historical records are now extinct. Introduced mosquito-borne disease, in particular the avian malaria Plasmodium relictum , has been incriminated as a leading cause of extinction during the 20th century and a major limiting factor in the recovery of remaining species populations. Today, most native Hawaiian bird species reach their highest densities and diversity in high elevation (1,800 m above sea level) forests. We determined the thermal requirements for sporogonic development of P. relictum in the natural vector, Culex quinquefasciatus , and assessed the current distribution of native bird species in light of this information. Sporogonic development was completed at constant laboratory and mean field temperatures between 30 and 17 C, but development, prevalence, and intensity decreased significantly below 21 C. Using a degree-day (DD) model, we estimated a minimum threshold temperature of 12.97 C and a thermal requirement of 86.2 DD as necessary to complete development. Predicted (adiabatic lapse-rate) and observed summer threshold isotherm (13 C) correspond to the elevation of high forest refuges on the islands of Maui and Hawai'i. Our data support the hypothesis that avian malaria currently restricts the altitudinal distribution of Hawaiian honeycreeper populations and provide an ecological explanation for the absence of disease at high elevation.

Measures of parasitemia by intraerythrocytic hematozoan parasites are normally expressed as the number of infected erythrocytes per n erythrocytes and are notoriously tedious and time consuming to measure. We describe a protocol for generating rapid counts of nucleated erythrocytes from digital micrographs of thin blood smears that can be used to estimate intensity of hematozoan infections in nonmammalian vertebrate hosts. This method takes advantage of the bold contrast and relatively uniform size and morphology of erythrocyte nuclei on Giemsa-stained blood smears and uses ImageJ, a java-based image analysis program developed at the U.S. National Institutes of Health and available on the internet, to recognize and count these nuclei. This technique makes feasible rapid and accurate counts of total erythrocytes in large numbers of microscope fields, which can be used in the calculation of peripheral parasitemias in low-intensity infections.

Isospora manchacensis n. sp. is described from ground skinks, Scincella lateralis (Say, 1823) from Louisiana. Overall prevalence at 6 sites near Lake Ponchartrain was 43.1% (59/137) and ranged from 8% (1/13) to as high as 60% (6/10). Endogenous stages develop inside the nuclei of epithelial cells in the small intestine. Infected hypertrophic nuclei migrate from the basal lamina of the host cell to the luminal striated border. Oocysts in freshly passed fecal pellets usually contain a single contracted sporont that divides to form 2 sporoblasts. These undergo a brief pyramid stage followed by sporulation within 45-50 hr. Sporulated oocysts have a single- layered wall and measure 25.0 x 22.6 (20.0-28.9 x 18.6-26.0) Am. The lemon-shaped sporocysts measure 12.8 x 10.2 (11.1-15.2 x 9.0-11.0) Am and contain a Steida body, a spherical to oval substeida body, and a dispersed, granular sporocyst residuum. Prepatent periods in skinks fed 700 and 1,400 oocysts ranged from 24 to 32 days. Experimentally infected skinks produced large numbers of oocysts continuously during the 3-4 wk they were monitored after the onset of patency, but exhibited no signs of disease. Experimental doses of 200 oocysts failed to produce infections in skinks monitored for as long as 7 wk.

Postembedding immunoelectron microscopy, using pooled serum samples from a recent vaccination experiment involving Aotus monkeys, was used to localize immune targets in Plasmodiumfalciparum-infected erythrocytes and free merozoites. Serum samples from Aotus monkeys, protected completely by immunization with the P. falciparum merozoite surface coat precursor protein, identified immune targets on the surface of free and intracellular merozoites as well as the cytoplasm, plasma membrane, and parasitophorous vacuole membrane of immature schizonts. Serum samples from unprotected monkeys, which had been immunized with a complex of 143-kDa, 132-kDa, and 102-kDa polypeptides reacted specifically with the rhoptries of immature schizonts and mature merozoites.

Trypanosoma thamnophis from Thamnophis sirtalis in eastern Canada is the only previously known trypanosome from a North American snake. Trypanosoma yaegeri n. sp. and Trypanosoma hydrae n. sp. are described here from a cottonmouth Agkistrodon piscivorus leucostoma and a broad-banded watersnake Nerodia fasciata confluens, respectively, from southern Louisiana. Trypanosoma hydrae easily infects other colubrid snakes, but not cottonmouths, turtles, or the lizard Anolis carolinensis. There are only a few scattered records of try- panosome infections in Nearctic reptiles, with two named species from lizards, one from turtles, and one from snakes. We describe here two new trypanosomes found in swamp dwelling snakes from Louisiana's Mississippi River delta region, and summarize the earlier observations on try- panosomes of North American reptiles (Table I), with some revised host identifications.

Ookinetes of Haemoproteus meleagridis were structurally similar to kinetes of other apicomplexan parasites and possessed a polar ring complex (PRC) composed of an electron-lucent polar ring with 25 supporting tines. Fifty subpellicular microtubules were anchored in a circle to the inner surface of the polar ring. A bilayered electron-dense canopy was continuous with the inner layer of the pellicle and formed a caplike cover over the PRC. Embedded rings of actin-sized microfilaments completely encircled each layer of the canopy. Numerous micronemes, 2 smaller preconoidal rings, and a conoid composed of approximately 6 spirally wound, electron-dense tubules were also present. Other organelles were similar to those reported in previous studies of haemosporidian ookinetes. Mature ookinetes of H. meleagridis developed in the midguts of engorged specimens of Culicoides edeni (Diptera: Ceratopogonidae) within 24 hr after a blood meal. Most parasites were found beneath, or embedded within, a peritrophic membrane composed of fine granules and fibrils. The observation of actin-sized microfilaments within the canopy is a previously unrecognized modification of the pellicle that probably supports the anterior end of ookinetes during penetration of the peritrophic membrane.

The fate and disposition of the circumsporozoite (CS) protein of Plasmodium falciparum was investigated during hepatoma cell invasion with several sera raised against defined CS peptides, including both repeat and nonrepeat regions spanning approximately 60% of the P. falciparum CS gene product. Distribution of the protein, as revealed by immunoelectron microscopy, was limited to the surface of the sporozoite both before and after invasion. In particular, no CS protein antigen was detected in association with either the parasitophorous vacuole membrane or the host cell surface.

Sporozoite-induced experimental infections of Haemoproteus meleagridis produced a moderate to severe myositis and significant effects on weight gain and growth in domestic turkey poults. Pathological effects occurred in both low- and high-dose infections (4,400 and 57,500 sporozoites, respectively). Low-dose birds weighed significantly less than controls at 3 wk postinfection (PI) when peripheral parasitemia reached a peak and had significantly shorter tarsometatarsal lengths at both 1 and 3 wk PI. High-dose birds were significantly lighter and smaller than control and low-dose birds throughout the course of the 8-wk study. Infected birds were not anemic in spite of high parasitemias that often exceeded 50% of circulating erythrocytes. The most serious pathological effects occurred prior to patency and were associated with development of megaloschizonts in skeletal muscle. Microscopic lesions in 4 high-dose birds that died between 19 and 22 days PI were characteristic of a severe, acute hemorrhagic myositis. Megaloschizonts were surrounded by a hemorrhagic inflammatory infiltrate composed of macrophages, heterophils, giant cells, and red blood cells. Muscle fibers adjacent to megaloschizonts were swollen, hyaline, and contained prominent calcium deposits. Other observations included enlargement of the spleen, deposition of pigment in macrophages of the lung and spleen, and secondary bacterial and fungal infections in the intestine and lungs. Necrotic and calcified muscle fibers and degenerating megaloschizonts were still present at 8 wk PI when the experiment ended. Our results demonstrated significant pathological changes in H. meleagridis-infected domestic turkeys that were associated primarily with preerythrocytic stages of development.