Male-female interaction during breeding and non-breeding seasons in Akodon azarae (Rodentia, Muridae)

Dyad encounters between male and female adults of Akodon azarae (Fischer, 1829) were analyzed by means of observational techniques in a natural closure during the breeding and non-breeding seasons. The animals were held in observation during 21 days, with daily 15-minute recordings of interindividual separation distance, relative displacements, characteristics of the male-female interaction, copulation, and construction and exclusive or shared use of nests by each pair. The couples, which bred successfully, showed, on average, the longest separation distance between male and female allowed by the closure. During the first two weeks of gestation the females exhibited more displacements than their respective mates did. The male-pregnant female encounters were significantly more aggressive than those recorded between pairs which did not breed successfully. During the non-breeding season a shorter average distance between individuals and a frequent use of nests shared by the pair were recorded. The results obtained are discussed within the framework of the social system of A. azarae.

The interaction of Gram negative bacteria and S. mansoni in mice with experimental Schistosomiasis

Animals (122 mice) were infected each with eighty cercariae of S. mansoni and subsequently challenged intravenously eight weeks later with the following gram-negative organisms. S. typhi, E. coli, Klebsiella-enterobacter species, Proteus mirabilis and Pseudomonas aeruginosa. Enumeration of bacteria in the liver, spleen and blood and S. mansoni from the portal sistem was performed from one to four weeks later in infected animals. A significant difference between infection produced by S. typhi and other gram negative organisms was observed: S. typhi persisted longer in the spleen and liver and could be recovered from S. mansoni worms up to three weeks following bacterial infection. Other gram negative bacteria disappeared from S. mansoni worms after two weeks of initial challenge. Additional animals (51 mice) infected with S. mansoni were given S. typhi, E. coli or sterile saline. After two weeks, animals were sacrificed and the recovery rate of worms from the portal system, and the mesenteric and hepatic oogram were determined. in animals infected with E. coli a significant decrease in the number of worms was observed compared to the saline control group; thirty worms were recovered in the control group compared to two worms in e. coli infected animals. In addition, the patterns of oviposition was significantly different in these latter animals suggesting complete inhibition of this process. Following S. typhi infection the difference in recovery of worms and pattern of oviposition was minimal. These findings suggest a difference in the interaction of various gram negative bacteria and S. mansoni and are consistent with the clinical observation of prolonged salmonella bacteremia in patients with schistosomiasis.

Interaction of avirulent Leishmania species with rat peritoneal macrophages

An "in vitro" system has been developed for study of host cell-parasite interaction in visceral and cutaneous leishmaniasis. Avirulent promastigotes of L. brasiliensis and L. donovani, from strains originally isolated from human cases and mantained by serial culture in Davis' Medium were allowed to infect cultured macrophages from rat peritoneal exudate. Challenge of the macrophages by parasites took place in 199 medium, at 33ºC for L. brasiliensis and at 37ºC for L. donovani. Although the rat is resistant to infections by Leishmania spp., the promastigotes not only invaded the host cells, but transformed into amastigotes and later mutiplied, from 10 min after challenge to 24 hours later.

Effect of drugs on Trypanosoma cruzi and on its interaction with heart muscle cell in vitro

Megazol, nifurtimox, benznidazol and allopurinol were investigated, by light and electron µscopy, for their action on T. cruzi. Both the direct effect upon amastigote and trypomastigote forms and the effect upon the interaction of heart muscle cells (HMC) with bloodstream trypomastigotes were studied. The proliferation of amastigotes in Warren medium was inhibited in a dose-dependent manner by megazol, nifurtimox and benznidazol. Treatment of amastigotes (25-50 µM/24 h) and trypomastigotes (25 µM/24h) led to several ultrastructural alterations in the parasites. These three drugs also had a potent effect on the treatment of infected heart muscle cells when added at the beginning of the interaction or after one or three days of infection. The interiorized parasites showed a similar pattern of ultrastructural alterations as observed by the direct effect on the amastigotes. The primary heart muscle cell culture proved to be a suitable model for the study of drugs on intracellular parasites. Likewise, the amastigote proliferation in axenic medium was shown to be an adequate assay for an initial trial of drugs. These parameters seem very reliable to us for a systematic investigation of the mechanism of action of new drugs.

Trypanosoma cruzi: effect of phenothiazines on the parasite and its interaction with host cells

Phenothiazines were observed to have a direct effect on Trypanosoma cruzi and on its in vitro interaction with host cells. They caused lysis of trypomastigotes (50 uM/24 h) and,to a lesser extent, epimastigote proliferation. Treatment of infected peritoneal macrophages with 12.5 uM chlorpromazine or triflupromazine inhibited the infection; this effect was found to be partially reversible if the drugs were removed after 24 h of treatment. At 60 uM, the drugs caused damage to amastigotes interiorized in heart muscle cells. However, the narrow margin of toxity between anti-trypanossomal activity and damage to host cells mitigates against in vivo investigation at the present time. Possible hypothesis for the mechanism of action of phenothiazines are discussed.

Effects of azadirachtin on Rhodnius prolixus: immunity and trypanosoma interaction

The effects of azadirachtin, a tetranortriterpenoid from the neem tree Aradirachta indica J. on both immunity and Trypanosoma cruzi interaction within Rhodniusprolixus and other triatomines, were presented Given through a blood meal, azadirachtin affected the immune reactivity as shown by a significant reduction in numbers of hemocytes and consequently nodule formation follwing challenge with Enterobacter cloacae ß12, reduction in ability to produce antibacterial activities in the hemolymph when injected with bacteria, and decreased ability to destroy the infection caused by inoculation of E. cloacae cells. A single dose of azadirachtin was able to block the development of T. cruzi in R. prolixus if given through the meal at different intervals, together with, before or after parasite infection. Similary, these results were observed with different triatomine species and different strains of T. cruzi. Azadirachtin induced a permanent resistance of the vector against reinfection with T. cruzi. The significance of these data is discussed in relation to the general mode of azadirachtin action in insects.