Miodrag Ristic

Human Infection with Ehrlichia canis, a Leukocytic Rickettsia

RICKETTSIA that are pathogenic for humans include five main antigenic groups that cause, respectively, typhus, spotted fever, scrub typhus, Q fever, and trench fever.1 There is also a group of intr...

Heterologous strain immunity in bovine babesiosis using a culture-derived soluble Babesia bovis immunogen.

The cross-protective capacity of culture-derived soluble immunogens against heterologous Babesia bovis strains from different geographical locations of Latin America was examined. Susceptible yearling cattle were either immunized with immunogens derived from Venezuelan or Mexican strains, or were administered a multi-component immunogen containing antigens of the Australian, Mexican and Venezuelan strains. Cattle were challenged with virulent B. bovis organisms of the Argentinian, Colombian, Ecuadorean, Mexican and Venezuelan strains. The major parameters used to evaluate cross-protection were the following: presence, level and duration of parasitemia; maximal PCV reduction; level and duration of fever; determination of fibrinogen and cryofibrinogen; homologous and heterologous antibody levels; and net gains in body weight. Results showed good protection with a Venezuelan B. bovis immunogen after homologous and heterologous challenge exposures. A low degree of cross-immunity was observed when cattle vaccinated with the Mexican immunogen were challenged with each of the heterologous strains.

Methods of immunoprophylaxis against bovine anaplasmosis with emphasis on use of the attenuated Anaplasma marginale vaccine.

One of the major obstacles to the development of methods for immunoprophy-laxis against hemotropic diseases has been the lack of techniques for in vitro propagation of the causative agents (Anaplasma, Babesia), or the availability of similar systems for laboratory production of arthropod-associated “prototype” antigens (trypanosomes). A recent accomplishment in this direction has been the development of cell culture methods for Theileria parva, the causative agent of East Coast fever. While this step is considered an important breakthrough providing incentive for more optimistic future endeavors in the entire field, the accomplishment must not be viewed as an indication that this technique can be directly applied to other hemotropic agents. Theileria parva actively invades cellular elements of both the erythrocytic and lymphocytic series, the latter being adapted to in vitro propagation. Anaplasma, Babesia, and Plasmodium are considered to primarily affect the more inert circulating erythrocyte which, rather than offering replication ability in cell culture, continues its in vivo destiny of degeneration.

Isolation of Babesia spp. from asymptomatic human beings

Abstract Babesiosis is a worldwide tick-borne protozoan disease of a variety of wild and domestic animals. For decades, various babesia strains were considered host-specific. However, babesiosis has been diagnosed as the cause of acute illness in 13 human beings in recent years, three of whom died. Studies of babesiosis in domestic animals indicate that for every clinically demonstrable case, there are hundreds of cases of latent infection. In an effort to determine if human babesia infections might be present in Mexico, we selected as our testing ground an endemic rural area along the Gulf Coast where continuous epizootics of equine, bovine, ovine and canine babesiosis were known to occur. Of the 101 individuals examined serologically by the indirect hemagglutination (IHA) test using Babesia canis as antigen, 38 reacted at titers from 1 : 10 to 1 : 80. Blood from these reactors was injected into splenectomized hamsters. Hamsters inoculated with blood from three of the individuals showed babesia in their peripheral blood. The growth of the organism was established by subpassages into additional hamsters. The persons from whom the organisms were isolated were asymptomatic for babesiosis. None of the 29 individuals residing in Mexico City, which represented the urban population in the survey, reacted in the IHA test. This is the first documented finding of the latent form of human babesiosis.

Roles of the spleen in acute plasmodial and babesial infections in rats.

Abstract This investigation was conducted to elucidate the roles of the spleen in Plasmodium berghei and Babesia rodhaini infections of intact, splenectomized, and parabiotic rats. In addition, the function of splenectomy in altering the host-specific resistance of the rat to infection with P. gallinaceum was studied. Removal of the spleen resulted in delay of about a week before the peak of parasitemia, anemic crisis, erythrophagocytosis, and the appearance of agglutinins occurred. Splenectomized rats infected with P. berghei invariably died, while splenectomized rats infected with B. rodhaini all survived; other parameters of these two infections in splenectomized rats were very similar to each other. In parabiotic rats, the single spleen was able to moderate the course of the disease in the conjoined pair for nearly 2 weeks but was not able to overcome the deteriorating influence of the splenectomized animal, since both eventually died. Ordinarily regarded as highly host specific for avian species, P. gallinaceum successfully parasitized splenectomized rats; erythrocytic and probably, exoerythocytic stages, were observed. The morphologic features of the parasite were somewhat changed in the rat. Filaments attached to the parasite were observed and photographed. When parasitized rat blood was inoculated into chickens, the morphologic features of the organism returned to normal, but the peak of parasitemia was delayed in all and lowered in many chickens. Parasites were observed in the peripheral blood of rats between 3 and 13 days postinjection (DPI) and in the liver and bone marrow of rats up to 18 DPI. Results demonstrated the importance of the spleen in both general and specific-host resistance.

Autoimmune reactions in rats with Plasmodium berghei infection

Abstract An agglutinin for trypsinized autologous and homologous erythrocytes was demonstrated in rats with Plasmodium berghei infection. This agglutinin did not agglutinate nontrypsinized rat erythrocytes. The agglutinin was a cold type since it was eluted from erythrocytes of P. berghei infected rats at 37 °C. The antibody was susceptible to reductive cleavage by mercaptoethanol.

Babesia microti: Pathogenesis of parasite of human origin in the hamster

Abstract The pathogenesis of the disease in hamsters caused by the first human Babesia isolant, tentatively named Babesia microti , and the immunologic relationship of the organism to Babesia canis were studied. The patent phase of the disease was characterized by severe anemia and marked parasitemia which occurred between the 6th and 41st day following infection. An increase in total white cell count with a neutrophilia, eosinophilia, monocytosis, and lymphocytosis was observed during the patent phase. The patent phase was followed by development of a carrier state. This was demonstrated by relapse following splenectomy 113 days after infection. No statistically significant differences were observed between the serum profiles of infected and noninfected animals during the period monitored. A serologic relationship between B. microti and B. canis was revealed by the use of gel diffusion and indirect fluorescent antibody (IFA) tests. The IFA test was used to monitor serum antibody responses during the patent and carrier phases of the disease. Crossabsorption studies between B. canis and B. microti revealed that the two organisms possess common and specific antigens.

Bovine babesiosis: induction of protective immunity with culture-derived Babesia bovis and Babesia bigemina immunogens

The comparative protective efficacy of culture-derived Babesia bovis and B. bigemina immunogens against challenge exposure of susceptible crossbred cattle to heterologous strains was examined and correlated with the antigenic threshold requirements for induction of protective immunity. Strong protection was observed in animals vaccinated with 10 ml-equivalent doses of soluble, B. bovis exoantigen-containing supernatant fluids. Similar protective responses to B. bigemina exoantigens were evident even at 1 ml-equivalent dosages. In addition, the efficacy of a combined B. bovis-B. bigemina immunogen was assessed with a dose-response analysis in highly susceptible, purebred cattle. Vaccinated animals were protected against clinical babesiosis, and significant weight gains were recorded after challenge infection with virulent parasites.

Pathobiology of Borrelia theileri in the tropical cattle tick, Boophilus microplus

Abstract The development of Borrelia theileri infections in the tick Boophilus microplus was studied during all stages of the tick developmental cycle. Light microscopical examination of hemolymph and ovary smears from ovipositing females allowed identification and separation of infected and uninfected ticks. A Borreli-free tick colony was established. Small numbers of spirochetes were present in larvae, with numbers increasing through the nymphal and adult tick stages. Borreliae occurred in hemolymph, hypodermis, midgut, Malpighian tubules, ovary, Genes organ, and the central ganglion of engorging and ovipositing females and their eggs. The ovary, central ganglion, and hemolymph seemed to be preferred sites for the spirochete, with extensive multiplication occurring in hemocytes. No measurable effect of spirochete multiplication upon feeding and reproductive performance of ticks could be detected. Infections in cattle caused fever of short duration which coincided with the presence of spirochetes in blood smears. Morphology and size of blood and tick forms were consistent with those of B. theileri reported by other authors. B. theileri is important because infections of invertebrate and vertebrate hosts may interfere with the interpretation of data in various experimental designs, and because it is probably endemic in populations of one or more tick species and their hosts throughout the world.

Antigenic and immunogenic studies on cell culture-derived Babesia canis

Babesia canis antigens derived from cell culture reacted specifically with immune serum from dogs convalescing from babesiosis. The antigens were heterogenous as compared to antigens elaborated in vivo. The major antigenic moiety from cell culture eluted in the first peak of Sephadex G-200 is indicative of a molecular weight around 900 000. In contrast, in vivo-derived antigen coeluted with albumin and hemoglobin suggesting a molecular weight of 67 000. The major antigenic mass is proteinacious and contains disulfide bonds as indicated by thermolability and sensitivity to 2-mercaptoethanol. Both particulate and soluble B. canis antigens were immunogenic, particularly when emulsified in Saponin as an adjuvant. Such antigens conferred a considerable degree of protection in Saponin as an adjuvant. Such antigens conferred a considerable degree of protection in susceptible dogs and it suggested that immunoprophylaxis to B. canis may be feasible.