Differences In Parasite Burden Research Articles

Treatment of ichthyophthiriasis after malachite green. I. Concrete tanks at salmonid farms

Since the use of malachite green was banned in many European countries, new alternative treatments have been tested to prevent white spot disease caused by Ichthyophthirius multifiliis. We tested formalin, potassium permanganate (KMnO4), chloramine-T, hydrogen peroxide (H2O2) and Per Aqua or Desirox alone or in combinations of 2 chemicals, one of which was always formalin, in 50 m2 concrete tanks at 2 farms producing salmon Salmo salar smolt in 2001 and 2002. Both Per Aqua and Desirox are combinations of peracetic acid, acetic acid and hydrogen peroxide. The alternative chemicals or their combinations can be used successfully to lower the parasite burden to such a level that no high mortality occurs during the first 4 wk after the start of an infection. This period of time allows the fish to develop immunity against these ciliates, and treatments can be reduced and stopped in due course. I. multifiliis decreased in number 3 to 4 wk after the beginning of the infection in all the treatments. Large differences in parasite burden and mortality occurred among the replicates in all except the Desirox-formalin tanks, which means that they are not as reliable as the malachite green-formalin used previously. It was also evident that the chemicals and their concentrations must be planned carefully to suit the conditions on each farm.

Differential species‐specific ectoparasitic mite intensities in two intimately coexisting sibling bat species: resource‐mediated host attractiveness or parasite specialization?

Summary The mechanisms underlying host choice strategies by parasites remain poorly understood. We address two main questions: (i) do parasites prefer vulnerable or well‐fed hosts, and (ii) to what extent is a parasite species specialized towards a given host species? To answer these questions, we investigated, both in the field and in the lab, a host–parasite system comprising one ectoparasitic mite (Spinturnix myoti) and its major hosts, two sibling species of bats (Myotis myotis and M. blythii), which coexist intimately in colonial nursery roosts. We exploited the close physical associations between host species in colonial roosts as well as naturally occurring annual variation in food abundance to investigate the relationships between parasite intensities and (i) host species and (ii) individual nutritional status. Although horizontal transmission of parasites was facilitated by the intimate aggregation of bats within their colonial clusters, we found significant interspecific differences in degree of infestation throughout the 6 years of the study, with M. myotis always more heavily parasitized than M. blythii. This pattern was replicated in a laboratory experiment in which any species‐specific resistance induced by exploitation of different trophic niches in nature was removed. Within both host species, S. myoti showed a clear preference for individuals with higher nutritional status. In years with high resource abundance, both bat hosts harboured more parasites than in low‐resource years, although the relative difference in parasite burden across species was maintained. This pattern of host choice was also replicated in the laboratory. When offered a choice, parasites always colonized better‐fed individuals. These results show first that host specialization in our study system occurred. Second, immediate parasite choice clearly operated towards the selection of hosts in good nutritional state.

Role of steroid hormones in Trichinella spiralis infection among voles.

Males are generally more susceptible to parasite infection than females. This sex difference may reflect the suppressive effects of testosterone and enhancing effects of estradiol on immune function. This study characterized the role of circulating steroid hormones in sex differences after infection with the nematode Trichinella spiralis. Because testosterone suppresses immune function and because polygynous males have higher circulating testosterone concentrations than monogamous males, sex differences in parasite burden were hypothesized to be exaggerated among polygynous meadow voles compared with monogamous prairie voles. As predicted, sex differences in response to T. spiralis infection were increased among meadow voles; males had higher worm numbers than females. Male and female prairie voles had equivalent parasite burden. Overall, prairie voles had higher worm numbers than meadow voles. Contrary to our initial prediction, differences in circulating estradiol concentrations in females, testosterone concentrations in males, and corticosterone concentrations in both sexes were not related to the observed variation in T. spiralis infection. Taken together, these data suggest that not all sex differences in parasite infection are mediated by circulating steroid hormones and that adaptive-functional explanations may provide new insight into the causes of variation in parasite infection.

Mosquito-PlasmodiumInteractions in Response to Immune Activation of the Vector

Lowenberger, C. A., Kamal, S., Chiles, J., Paskewitz, S., Bulet, P., Hoffmann, J. A., and Christensen, B. M. 1999. Mosquito-Plasmodiuminteractions in response to immune activation of the vector.Experimental Parasitology91,59–69. During the development ofPlasmodiumsp. within the mosquito midgut, the parasite undergoes a series of developmental changes. The elongated ookinete migrates through the layers of the midgut where it forms the oocyst under the basal lamina. We demonstrate here that ifAedes aegyptiorAnopheles gambiae, normally susceptible toPlasmodium gallinaceumandP. berghei, respectively, are immune activated by the injection of bacteria into the hemocoel, and subsequently are fed on an infectious bloodmeal, there is a significant reduction in the prevalence and mean intensity of infection of oocysts on the midgut. Only those mosquitoes immune activated prior to, or immediately after, parasite ingestion exhibit this reduction in parasite development. Mosquitoes immune activated 2–5 days after bloodfeeding show no differences in parasite burdens compared with naive controls. Northern analyses reveal that transcriptional activity for mosquito defensins is not detected in the whole bodies ofAe. aegyptifrom 4 h to 10 days after ingestingP. gallinaceum, suggesting that parasite ingestion, passage from the food bolus through the midgut, oocyst formation, and subsequent release of sporozoites into the hemolymph do not induce the production of defensin. However, reverse transcriptase-PCR of RNA isolated solely from the midguts ofAe. aegyptiindicates that transcription of mosquito defensins occurs in the midguts of naive mosquitoes and those ingesting an infectious or noninfectious bloodmeal. Bacteria-challengedAe. aegyptishowed high levels of mature defensin in the hemolymph that correlate with a lower prevalence and mean intensity of infection with oocysts. Because few oocysts were found on the midgut of immune-activated mosquitoes, the data suggest that some factor, induced by bacterial challenge, kills the parasite at a preoocyst stage.

Energy Restriction and Zinc Deficiency Impair the Functions of Murine T Cells and Antigen-Presenting Cells during Gastrointestinal Nematode Infection ,

This study examined whether the impaired immune responses in zinc deficient- and/or energy-restricted mice exposed to a challenge infection of Heligmosomoides polygyrusmight be associated with reduced numbers of spleen cells, altered proportions of spleen cell subpopulations and/or altered function of the T cells or antigen-presenting cells (APC). Female BALB/c mice were given free access to either a zinc-sufficient (60 mg zinc/kg diet, Zn+) or a zinc-deficient diet (0.75 mg zinc/kg diet, Zn−) or were pair-fed (PF) the zinc-sufficient diet. Significant differences in parasite burdens were observed. Worm numbers were lowest in Zn+ mice, intermediate in the PF mice and highest in the Zn− mice, showing that both zinc deficiency and energy restriction reduced protective immunity against the gastrointestinal nematode H. polygyrus.Although the absolute numbers of spleen cells were reduced in both Zn− and energy-restricted (PF) mice, neither deficiency altered the phenotypic distribution of the subpopulations of positive marker cells in the spleen. In vitro functional assays using a 1:1 ratio of APC:T cells showed that T-cell proliferation in response to parasite antigen (Ag) was impaired by a dietary effect of zinc deficiency on T cells and of energy restriction and zinc deficiency on APC function. Consequences of the nutritional deficiencies on cytokine production in response to parasite antigen were more complex: zinc deficiency reduced T-cell function [interleukin-4 and interleukin-5 (IL-4 and IL-5) production], and both nutritional deficits depressed APC functions [IL-4, IL-5, and interferon-γ (IFN-γ) production] and T-cell function (IFN-γ production). Thus, this study showed that zinc deficiency and energy restriction played identifiably distinct roles in regulating host immune responses against the gastrointestinal nematode H. polygyrus.

The effect of salinity on transovarial transmission of a microsporidian infecting Gammarus duebeni

This is an investigation of the impact of salinity on transovarial transmission and burden of a microsporidian sex ratio distorter in the inter-tidal crustacean Gammarus duebeni. Exposure of parasitized mothers to increased salinity during the gonotrophic cycle caused an increase in parasite burden in the follicle cells and a decrease in burden in the oocytes. It appears that salinity impedes parasite transmission from the follicle cells to the oocytes during host oogenesis. A lower proportion of the young were infected in broods from elevated salinity and, in infected offspring, parasite burden was lower than in control embryos. Parasite replication occurred during embryogenesis. However, the pattern of parasite growth did not differ between salinities, indicating that differences in parasite burden could be attributed to a reduction in the initial parasite burden transmitted to the gamete, rather than to a reduction in parasite replication during host embryogenesis. We discuss our findings with respect to parasite/host dynamics and the ecology of the host.

Taenia taeniaeformis: Evasion of complement-mediated lysis by early larval stages following activation of the alternative pathway

Activation of the alternative pathway of complement by T. taeniaeformis oncospheres and early stage metacestodes, although a factor in host defense against primary infection, does not directly lead to the killing of the parasite larvae observed prior to day 6 post-infection in innately resistant BALB/cByJ inbred mice. Immunogold labelling techniques clearly demonstrated tegument-associated C3 on vitro-activated oncospheres incubated with non-immune mouse sera. However, C5, a protease necessary for the assembly of the membrane attack complex, was not detected. Early stage larvae cultured from in vitro-activated oncospheres escaped membrane damage and survived incubation in non-immune sera from both BALB/cByJ and taeniid-susceptible C3H/HeDub mice. Comparisons of cobra venom factor-treated and untreated C5-deficient B10.D2osn mice revealed no significant differences in parasite burden and local eosinophil infiltration at 6 days post-infection, suggesting that the terminal arm of the complement system is necessary for the previously reported role of complement in resistance to primary infection in BALB/cByJ and C3H/HeDub mice. An in vivo test of chemotaxis indicated that although both complement-intact mouse strains examined responded to intraperitoneal injections of inulin, there were lower numbers of eosinophils in C3H/HeDub mice than in BALB/cByJ mice, perhaps pointing to possible mouse strain differences in C5a generation/catabolism or eosinophil ability to respond to C5a. Lectin-binding studies showed an affinity of PNA for the exposed surface of taeniid oncospheres and 4-day post-infection metacestodes; however, binding of lectin to the carbohydrate moiety did not inhibit complement activation.

Laboratory Studies on Mansonella marmosetae in the Squirrel Monkey, Saimiri sciureus

gether, and it is more probable that they are exposed equally to parasite propagules. Given the mixed-age, mixed-sex groups in which bobwhites live during the winter, differences in parasite burdens may be rare. We are grateful for the assistance of personnel of the Southeastern Cooperative Wildlife Disease Study, The University of Georgia, which was provided under the Federal Aid in Wildlife Restoration Act (50 Stat. 917) and through contract Nos. 14-16-0009-82-500, 14-16-0004-83004, and 14-16-0004-84-005, Fish and Wildlife Service, U.S. Department of the Interior. We appreciate the field assistance of J. Atkinson and B. Mueller (Tall Timbers Research Station) and the technical assistance of S. Forster and J. Liberatos (Florida State University). Dr. R. Short (FSU) provided laboratory space and Colorado State University provided computer time. This study was funded by NSF BSR-8210218 to J. Moore, D. Simberloff, and R. Short and NSF BSR-8452076 to J. Moore.

Participation of natural killer cells in the recovery of mice from visceral leishmaniasis

After infection with the protozoan parasite Leishmania donovani, C57BL/6J bg/bg (beige) mice, which are deficient in natural killer (NK) activity, were unable to control splenic parasite loads relative to phenotypically normal C57BL/6J bg/+ and +/+ mice, particularly beyond 21 days of infection. When beige mice were injected intravenously with 2 or 3 × 10 6 syngeneic, cloned NK cells (NKB61B10 cell line), they displayed splenic parasite burdens which did not differ significantly from those of normal controls. In C57BL/6 +/+ mice rendered NK deficient by split-dose irradiation (four weekly, 200-rad doses of γ irradiation beginning at 4 weeks of age) splenic and hepatic parasite levels were significantly higher than those in nonirradiated controls at 15 days of infection and beyond. In both sets of experiments, relative degrees of hepato- and splenomegaly were not sufficient to account for differences in parasite burdens among NK-deficient and normal mice. Taken together, the results of these experiments suggest that NK cells may contribute to parasite elimination during the acquired-resistance phase of L. donovani infection in mice.

Helminth parasites of the muskrat (Ondatra zibethicus (L.)) in Newfoundland

One hundred and fourteen muskrats (Ondatra zibethicus (L.)), collected between September 1977 and January 1979 in three areas of insular Newfoundland, were examined for helminths, with 11 species being found (7 Digenea, 2 Cestoda, and 2 Nematoda). Diplostomum mergi was recovered from a mammal for the first time. Distribution along the alimentary tract was examined and all helminths recovered preferred the proximal 60% of the small intestine, except Quinqueserialis quinqueserialis and Trichostrongylus calcaratus, which preferred the caecum. Adult and immature muskrats showed differences in the prevalence and intensity of infection and the adults also had larger concurrent infections. In only one case, namely Hymenolepis evaginata, was a parasite species more prevalent in one sex (the males). Small seasonal differences in prevalence and (or) intensity of infection were noted for some parasites and were related to differences in parasite burden of adult and immature hosts and water temperature. A difference in the occurrence of Digenea between sample areas was related to water pH and hardness.