Cryptosporidium and Giardia spp. are parasitic protozoa localized in the alimentary tract of many animal species and humans. Each of these parasite species produces very resistant invasive forms (cysts and oocysts) excreted to the environment with feces of infected hosts. Water contaminated with cysts/oocysts constitutes one of the main transmission routes and is responsible for the majority of infections in humans. Cryptosporidium and Giardia spp. were found in many different species of animals, including livestock, pets and free living animals. The aim of our study was to determine the prevalence of these protozoa in selected species of semi-aquatic mammals and to estimate their role in water contamination. In years 1996-98 the prevalence of Cryptosporidium and Giardia infections was high in muskrats (Ondatra zibethicus)(58 and 87%, respectively). The origin of animals (farmed or free living) affected the prevalence of both parasites in European beavers (Castor fiber). The prevalence of infection increased in second period of study and was 4 and 19% for Cryptosporidium and 0 and 8% for Giardia spp. in the two studied periods, respectively. Both parasite species were also identified in water vole (Arvicola terrestris) and rat (Rattus norvegicus).

Wild brown rats (Rattus norvegicus) from 11 rural UK farmsteads were found to carry 13 zoonotic and 10 non-zoonotic parasitic species, many of which (e.g. Cryptosporidium, Pasteurella, Listeria, Yersinia, Coxiella and Hantavirus) have rarely or never been previously investigated for wild rats. The study suggests that wild brown rats, serving as vectors of disease, represent a serious risk to the health of humans and domestic animals in the UK.

The effect of Toxoplasma gondii on neophobic behaviour (the avoidance of novel stimuli) was assessed in four groups of wild rats with naturally occurring Toxoplasma infection. Two groups were placed in individual cages and tested in a series of experiments which examined the effect of Toxoplasma on the rat's reaction to 3 food-related novel stimuli (odour, food-container, food). A trappability study was performed on the other two groups to test whether Toxoplasma had an effect on probability of capture. The results show that low neophobia was significantly associated with positive Toxoplasma titres in 3 out of 4 groups. We suggest that differences between infected and uninfected wild rats arise from pathological changes caused by Toxoplasma cysts in the brains of infected rats. Such behavioural changes may be selectively advantageous for the parasite as they may render Toxoplasma-infected rats more susceptible to predation by domestic cats (the definitive host of Toxoplasma) and, as a side-effect, more susceptible to trapping and poisoning during post control programmes.

Tungiasis is a zoonotic ectoparasitosis caused by the sand flea Tunga penetrans L.(Siphonaptera: Tungidae). This disease is hyperendemic in poor communities of north-east Brazil, causing considerable morbidity in affected human populations, but the animal reservoirs have not been investigated previously in Brazil. To assess the prevalence and intensity of T. penetrans infection in domestic and peri-domestic animals, as well as in the human population, we surveyed two typical communities of north-east Brazil: an urban slum and a traditional fishing village. In the slum we examined 849 humans, 121 cats, 82 dogs, 2 pigs, 2 rabbits, 1 monkey and 56 rodents, comprising 34 rats (Rattus rattus L.) and 22 mice (Mus domesticus L). In the fishing village we examined 505 humans, 68 dogs, 37 cats, 7 donkeys, 4 cattle, 3 pigs and 1 monkey. Tungiasis was common among dogs and cats of both communities, with respective prevalence rates of 67.1%(95% CI: 55.8-77.1) and 30.9%(95% CI: 20.2-43.3) in dogs, 49.6%(95% CI: 40.4-58.8) and 32.4%(95% CI: 18.0-49.8) in cats. Slum rats were 41.2%(95% CI: 24.6-59.3) infested, but the other animals were not. Human prevalence rates were 54.4%(95% CI: 51.0-57.8) in the slum and 52.1%(95% CI: 47.6-56.5) in the fishing village. High prevalence rates (range 31-67%) of tungiasis in humans, pets and rats (but apparently not other animals) indicate the need for an eco-epidemiological approach to control of this anthropo-zoonotic problem.

Isolation of blood and intracellular forms of Trypanosoma cruzi was made mainly from rats (90-110 g) which had received 580 rad of whole-body gamma-irradiation not more than 24 h before subcutaneous inoculation with 10(7) trypomastigotes of the Sonya strain of T. cruzi. Unirradiated chinchillas (250-350 g) were, however, used for some experiments. Blood forms were isolated using a technique involving differential centrifugation to remove most of the erythrocytes and DEAE-cellulose chromatography to remove the remaining blood cells. Overall recoveries were usually in the range 30-70%. Parasites were mainly (approximately 98%) broad forms and were motile, metabolically active (as judged by respiratory and radio-tracer incorporation studies) and had lost none of their infectivity for mice. Intracellular forms were isolated from hind-limb muscle tissue. This was disrupted in an MSE tissue homogenizer and the homogenate incubated with DNase, collagenase and trypsin. Parasites, contaminated only by a few blood cells, were then obtained by differential centrifugation. For purer preparations, a terminal sucrose gradient step was used. Recoveries ranged between 40 and 70%. About 1-3% of the parasites isolated were epimastigotes and trypomastigotes; the remainder are probably best collectively termed 'amastigotes', though they were pointed and most had a short, free flagellum. They were undamaged as judged by light and electron microscopy and metabolically active as judged by respiratory and radio-tracer incorporation studies. However, the infectivity for mice of both these purified preparations and the initial cell homogenates could be accounted for by the epimastigotes and trypomastigotes present in them. Preliminary biochemical studies with isolated parasites have shown that blood, intracellular and culture forms of T. cruzi have a respiratory system which is in part sensitive to CN- and that all forms synthesize nucleic acids and proteins when incubated in vitro. There appears, however, to be a lack of DNA synthesis in blood stages, and thus it is not surprising that these forms do not divide.

After an outbreak in 2000 of eosinophilic meningitis in tourists to Jamaica, we looked for Angiostrongylus cantonensis in rats and snails on the island. Overall, 22%(24/109) of rats harbored adult worms, and 8%(4/48) of snails harbored A. cantonensis larvae. This report is the first of enzootic A. cantonensis infection in Jamaica, providing evidence that this parasite is likely to cause human cases of eosinophilic meningitis.

Adult Strongyloides ratti were expelled from the small intestine of rats starting 14-18 days after a primary infection. In a secondary infection very few adult worms developed and most of these were expelled before day 14. At the time of expulsion the worms migrated posteriorly in the intestine and their size decreased.

A light and electron microscopic study of Sarcocystis orientalis sp. n. was made. The life cycle of this parasite is in two hosts. Gametogony is in the intestinal epithelial cells of a predator, Python reticulatus. Isospora-like oocysts developed. Sporocysts average 9.1 by 7.7 mum. Rats (Rattus norvegicus) were infected with sporocysts and asexual stages developed. Ten days after infection large zoites (average 7.85 by 2.48 mum) were observed free in peripheral blood and within white blood cells. Small schizonts producing merozoites 2-3 mum long were seen in lung tissue. Tissue cysts developed in skeletal muscle and produced numerous cystozoites (average 5.53 by 1.38 mum). Fine structure was similar to previously described Sarcocystis spp.

Characterizing host and parasite population genetic structure and estimating gene flow among populations is essential for understanding coevolutionary interactions between hosts and parasites. We examined the population genetic structure of the trematode Schistosoma mansoni and its two host species (the definitive host Rattus rattus and the intermediate host Biomphalaria glabrata) using microsatellite markers. Parasites were sampled from rats. The study was conducted in five sites of the Guadeloupe Island, Lesser Antilles. Mollusks display a pattern of isolation by distance whereas such a pattern is not found neither in schistosomes nor in rats. The comparison of the distribution of genetic variability in S. mansoni and its two host species strongly suggests that migration of parasites is principally determined by that of the vertebrate host in the marshy focus of Guadeloupe. However, the comparison between genetic differentiation values in schistosomes and rats suggests that the efficacy of the schistosome rat-mediated dispersal between transmission sites is lower than expected given the prevalence, parasitic load and migration rate of rats among sites. This could notably suggest that rat migration rate could be negatively correlated to the age or the infection status of individuals. Models made about the evolution of local adaptation in function of the dispersal rates of hosts and parasites suggest that rats and mollusks should be locally adapted to their parasites.

Worm-conditioned saline (WCS) was prepared by incubating Hymenolepis diminuta from crowded infections for 12 hr in a balanced salt solution. The effect of the WCS on the incorporation of [3H] thymidine into DNA in the anterior regions of fresh H. diminuta was compared to effects produced by the cyclic nucleotides in the WCS. Cyclic AMP and cGMP were found in the WCS, and cGMP but not cAMP (at the concentration in WCS) caused some inhibition of DNA synthesis. For further study of the effects of cyclic nucleotides, worms were incubated with theophylline, caffeine, 3-isobutyl-1-methyl xanthine, 2-deoxy cGMP, and L-ascorbic acid, all of which produced some inhibition of [3H] thymidine incorporation. Treatment of WCS with 3',5' cyclic nucleotide phosphodiesterase abolished part of its inhibitory activity, i.e., that part presumed to be due to cGMP. When worms were incubated in the presence of succinate, acetate, D-glucosaminic acid, and cGMP simultaneously and in the concentrations each was found in the WCS, DNA synthesis was inhibited to a degree equal to that found in the WCS. Thus these substances apparently represent the putative crowding factors in the WCS. WCS prepared with worms from different population densities contained the same levels of cAMP but varied in content of cGMP, which decreased as the worm density increased. WCS prepared with patent worms contained high levels of cAMP, but the same amounts of cGMP as WCS prepared with 10-day-old worms. At least some inhibitors of cyclic nucleotide phosphodiesterase inhibited the secretion of cGMP by the worms. Levels of cGMP in the host intestine varied with the presence or absence of worms, number of worms, and area of the intestine.