Richard L. Beaudoin

Plasmodium berghei: immunization of mice against the ANKA strain using the unaltered sporozoite as an antigen.

Abstract Mice were immunized with normal sporozoites of Plasmodium berghei. Test mice were placed on suppressive doses of chloroquine throughout the immunization period and were given curative courses of primaquine prior to challenge. All mice survived sporozoite challenge but succumbed to challenge with infected erythrocytes. It is concluded that the normal infective sporozoite is immunogenic and will stimulate a degree of protection against sporozoite challenge comparable to that obtained by immunization with X-ray irradiated sporozoites. A biphasic density gradient for separating sporozoites from mosquito tissue is described.

A Model For The Ecology Of Avian Malaria

Although studies on Plasmodium infections of wild birds have been reported frequently in the literature, our knowledge of the ecology of these parasites remains incomplete. A synthesis of data and ideas from these field studies, and recent experimental work led to the construction of the following hypothetical model for the ecology of avian malaria: During the late spring, summer, and early fall susceptible birds (young of the year or previously uninfected adults) contract the infection from the bite of an infected mosquito on the breeding ground. The birds migrate or remain in the area and infections become latent over the winter. In the spring, migratory birds return to the breeding area and all birds commence reproductive activity. With the onset of migration and breeding activity, parasite populations become elevated in the birds. This relapse of malarial infections coincides with emergence of vectors. The mosquitoes obtain the parasite, passing it on to susceptibles in the population (whose numbers are simultaneously increasing as the result of reproduction), and the cycle continues. Under favorable conditions, transmission rates equal or exceed a level needed to replace mortality of infected birds. Under unfavorable conditions the parasite is maintained by the bird reservoir, the population of susceptibles increases, and transmission is postponed until favorable conditions return and transmission to the expanded population of susceptibles replenishes the supply of infected adults. Such a cycle, in which the parasite, vector, and susceptible host populations reach a maximum in an apparently favorable sequence, with provision for occasional failure of transmission, has obvious survival value. A more complete understanding of the ecology of avian malaria will be achieved with the investigation of specific problem areas defined in this model. The model may prove of additional value in suggesting an ecological approach to our understanding of the epidemiology of human malarias. It may also have applicability in other disease systems where bird-mosquito relationships are similar, such as certain of the arboviruses.

Primaquine-Induced Changes in Morphology of Exoerythrocytic Stages of Malaria

Exposure to primaquine for 48 hours caused lesions in the exoerythrocytic stages of Plasmodium fallax grown in cultivated cells derived from embryonic turkey brain. The lesions appeared in the form of cytoplasmic vacuoles when viewed under the light microscope. The electron microscope revealed these vacuoles as swollen mitochondria readily identifiable by their typical protozoan cristae. Mitochondria of the host cell were unaffected.

Plasmodium berghei berghei: ectopic development of the ANKA strain in Anopheles stephensi.

Abstract Sporogonic development of Plasmodium berghei berghei is frequently ectopic, occurring deep within the tissue of the midgut with oocysts expelling sporozoites into its lumen. Inocula containing oocysts and sporozoites defecated with blood during the mosquito blood meal produced infections when introduced into mice. The fine structures and pellicle of luminal parasites appeared normal in all respects.

Plasmodium falciparum: Freeze-fracture of the gametocyte pellicular complex

Freeze-fracturing has been used to study the architecture of the pellicular complex of the gametocytes of Plasmodium falciparum. The gametocyte is surrounded by three membranes and a layer of subpellicular microtubules. During freeze-fracturing, each of the three membranes is split along its hydrophobic interior to yield a total of six fracture faces. The most obvious feature of each fracture face is the presence of globular intramembranous particles on their surfaces. The six fracture faces differ from one another in arrangement, size, and density of these intramembranous particles. In gametocytes, unlike in sporozoites, the intramembranous particles are always distributed randomly and lack any definite pattern or orientations. A unique feature of gametocytes revealed by the freeze-fracturing technique is the presence of several transverse sutures on the middle membrane that encircle the gametocyte and give it a segmented appearance.

Plasmodium fallax: high-resolution autoradiography of exoerythrocytic stages treated with Primaquine in vitro.

Abstract The distribution of 3 H-primaquine within cultures of the exoerythrocytic stages of Plasmodium fallax was studied using electron microscope autoradiography techniques. 3 H-primaquine first becomes localized within the parasite mitochondria where it is often associated with mitochondrial swelling. In advanced stages of treatment, mitochondria overlaid by silver grains are invariably swollen, although exposed grains can also be detected overlying the electron-dense paired organelles.

Plasmodium berghei: Architectural analysis by freeze-fracturing of the intraoocyst sporozoite's pellicular system

Abstract The technique of freeze-fracturing has been used to study the architecture of the pellicular complex of the intraoocyst sporozoite of Plasmodium berghei . The sporozoite is surrounded by three plasma membranes and a layer of subpellicular microtubules. During freeze-fracturing, each of the three membranes can split along its hydrophobic interior to yield a total of six fracture faces. The most obvious feature of each fracture face is the presence of globular intramembranous particles on the surface. The six fracture faces differ from one another in arrangement, size, and density of these intramembranous particles. Two of the fracture faces exhibit a unique arrangement of particles in well-organized parallel rows along the long axis of the sporozoite. This arrangement has not been reported in either the erythrocytic or the exoerythrocytic forms of Plasmodium spp. Another unique feature in the sporozoite revealed through freeze-fracturing is a single suture line that traverses the long axis of the inner two membranes of the parasite.

Antibodies to larval Taenia crassiceps in hibernating woodchucks, Marmota monax

Abstract An experiment was designed to study the effects of hibernation on the production and induction of antibody response to cysticerci of Taenia crassiceps in woodchucks ( Marmota monax ). Eight woodchucks were placed at 6 °C (hibernators) and eight at 20 °C (nonhibernators). The food was removed from all woodchucks to induce hibernation or lethargy. Four of each group were infected before hibernation and four after. Cysticerci were injected intraperitoneally. The response was judged by hemagglutination titration. The results showed no difference in antibody level among the four groups. Thus, it is concluded that antibodies to at least some helminths are produced during the period of hibernation. Whether or not production occurs only during the brief periods of arousal was not determined.

Plasmodium berghei berghei: Irradiated sporozoites of the ANKA strain as Immunizing Antigens in mice

Abstract Mice were protected against challenge with infective Sporozoites following immunization with X-ray irradiated Sporozoites. The immunity lasted at least 8 weeks. Mice immune against sporozoite challenge remained fully susceptible to challenge with erythrocytic stages. Immunization of mice with extracts of mosquito thorax failed to protect them, indicating that mosquito antigens were not directly responsible for the immunity observed in the basic experiments.

Plasmodium fallax and P. gallinaceum: Experimental resistance to primaquine☆

Abstract Primaquine-resistant strains of Plasmodium fallax and P. gallinaceum were produced by subjecting a large population of erythrocytic parasites to the selection pressure of continuous drug therapy. It was also demonstrated that the resistance acquired by drug pressure on the erythrocytic stages becomes a property of the exoerythrocytic parasite, that it is stable in the absence of drug, and that there is no cross resistance with pyrimethamine-resistant strains. An attempt to confirm asexual transfer of the property of drug resistance from one strain to another was unsuccessful.