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Consequences for host-parasitoid interactions of grazing-dependent habitat heterogeneity.
1. Environmental heterogeneity can produce effects that cascade up to higher trophic levels and affect species interactions. We hypothesized that grazing-dependent habitat heterogeneity and grazing-independent host plant heterogeneity would influence directly and indirectly a host-parasitoid interaction in a woodland habitat. 2. Thistles were planted randomly in 20 birch woodlands, half of which are grazed by cattle. The abundances of two species of seed herbivore and their shared parasitoid were measured, and related to habitat and host-plant heterogeneity. 3. The presence of cattle grazing created a structurally and compositionally distinct plant assemblage from the ungrazed seminatural situation. Grazing did not affect the number or dispersion of the host plant underpinning the host-parasitoid interaction. 4. The density of one insect herbivore, Tephritis conura, and its parasitoid Pteromalus elevatus was significantly increased by the presence of cattle; but another herbivore, Xyphosia miliaria, was unaffected. The percentage of parasitism of T. conura was increased in grazed habitat occurring at twice the rate found in ungrazed habitat. 5. The increase in T. conura abundance was correlated with increased species richness and cover of forbs in grazed sites. This effect of grazing-dependent habitat variation on host insect density cascaded up to parasitoid density and percentage of parasitism. Habitat heterogeneity had a further direct, positive effect on parasitoid density and percentage of parasitism after controlling for host-insect density. 6. Independent of grazing, heterogeneity in host-plant flowering, architecture and stature further affected T. conura and its parasitoid's densities. Parasitoid density was also affected by the dispersion of the host plant. 7. A combination of habitat and host-plant scale environmental heterogeneity influenced a host-parasitoid interaction indirectly and directly, providing a rare example of an anthropogenic disturbance positively affecting a tertiary trophic level. This finding highlights the need to consider not only the importance of bottom-up effects for top-down processes, but also the role of environmental heterogeneity arising from anthropogenic disturbance for trophic interactions such as parasitism.
Secrets of PDA's pioneering dynamism.
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HIV--Leishmania infantum co-infection: humoral and cellular immune responses to the parasite after chemotherapy.
Specific serum antibodies, peripheral blood T-cell subsets, cellular response in vitro to soluble Leishmania antigens, phenotype of stimulated cells, and serum levels of tumour necrosis factor (TNF)-alpha and transforming growth factor (TGF)-beta 1 were studied in Spain in 17 patients co-infected with HIV and Leishmania infantum who had been previously treated with pentavalent antimony. Both humoral and cellular responses to Leishmania sp. appeared diminished, 8 out of 17 patients were positive by indirect immunofluorescence, and immunoblotting detected heterogeneous antibody-binding pattern in 11 out of 13 subjects. A blastogenesis test was positive in 4 cases; 2 of them presented proliferation of CD4+ cells while CD8+ cells proliferated in the other 2 patients. Serum levels of TNF-alpha were similar to those observed in patients infected with HIV only, while serum levels of TGF-beta 1 were significantly lower in the co-infected patients. The inability of antibody response to control the parasite and the absence of specific T-cell immunity to Leishmania sp. would explain the high frequency of relapses reported in these patients. The decreased levels of TGF-beta 1 could have an important role in the interaction between the 2 pathogens.
CD4+-dependent immunity to Onchocerca volvulus third-stage larvae in humans and the mouse vaccination model: common ground and distinctions.
Onchocerciasis is a major filarial disease and is the second most common cause of infectious blindness in the world. Disease development after infection with Onchocerca volvulus varies widely and is determined by the host's immune response to the parasite. Vector control and administration of ivermectin has reduced infection and disease rates significantly. However, limitations of these programmes, including ivermectin's selective activity on microfilariae, the need for 10-15 years of annual treatments, logistical obstacles and the potential emergence of drug-resistant strains demand alternative strategies. A vaccine that targets O. volvulus infective third-stage larvae (L3) could provide an additional tool to guarantee successful elimination of infection with O. volvulus. An essential step in the development of immunoprophylactic procedures and reagents is the identification of host immune responses toward antigens of O. volvulus L3 and L3 developing to the fourth-stage larvae that are associated with protection against these stages of the parasite. This review summarises the recent advancements in understanding the immune mechanisms in particular the CD4(+) responses to L3 stages in humans and in the mouse vaccination model. Comparison between the two uncovered common immunological elements in naturally exposed humans and mice vaccinated with radiation attenuated L3 or recombinant O. volvulus antigens, as well as significant differences. These studies promisingly suggest that the O. volvulus mouse model is a very useful adjunct to the studying of natural infection in humans and could provide us with the tools to identify the target molecules and the effector immune correlates of protection in humans responsible for attrition of L3 stages. Since some of these antigens may exist in other nematodes, any insight gained into the mechanisms of vaccine-induced anti-O. volvulus L3 protective immunity in both humans and mice could be applicable to the development of vaccines against other nematode infections.
Studies on the anthelmintic effect of a sustained release pre-grazing treatment with morantel in grazing cattle in Sweden.
The effect of a morantel sustained release bolus (MSRB) to control gastrointestinal parasitism in cattle grazing their first season was assessed under field conditions in Sweden. The MSRB was administered orally to calves immediately prior to turnout onto spring pastures in May 1978. The level of pasture contamination of infective larvae was decreased by 73 per cent in August and by 98 per cent in September. There was a 72 per cent reduction in worm burdens acquired over the entire grazing season. During the same period the mean improvement in weight gain was 21.5 kg per animal. Weight gains were also recorded during housing until slaughter in April 1979, i.e. 335 days after MRSB administration at which time the treated animals were on an average 17.1 kg heavier than controls.
Evolution of paradigms of child health in developing countries.
In 1982 Costa Rica had an infant mortality of 18 per 1000 live births and a life expectancy at birth of 76 years for women and 72 years for men. In the evolution of infant health in Costa Rica two paradigms were identified. One developed in the decades before 1970 and the other during the 1970s. The necessity of conceptualizing a third new paradigm compatible with health needs of the present and the immediate future is recognized. The first or "malnutrition paradigm" was orthodox in its derivation; it identified the lack of food as the underlying base for the major health problems and placed its emphasis on institutional medicine. The paradigm was influenced by foreign schools of nutrition and pediatrics and led to the development of an infrastructure for the delivery of medical services and the programs for food distribution. The "infectious disease paradigm" recognized infectious diseases as the main determinants of morbidity, mortality and malnutrition in childhood. The strategies derived from such a revolutionary paradigm aimed at the control and eradication of infectious diseases, and they resulted in a rapid improvement of child nutrition and health. However, the infectious disease paradigm does not seem to reduce infant mortality below the present level.(ABSTRACT TRUNCATED AT 250 WORDS)
A prospective study of the association between the human humoral immune response to Plasmodium falciparum blood stage antigen gp190 and control of malarial infections.
The human humoral immune response to the Plasmodium falciparum merozoite surface antigen gp190 was analyzed to determine the rate of reinfection by the parasite and the ability to control parasite density. The prospective study was carried out in a West African village where malaria is hyperendemic. No correlation between the antibody titers and protection against infection was observed within the group of children. Positive and negative associations of antibody specificities with protection against and/or control of parasitemia were, however, found for adolescents and adults, respectively. Thus, in adolescents, the presence of antibodies to gp190 fragment M6 correlates with a 50% reduced risk of P. falciparum infection and an increased ability to control parasitemia, whereas in adults, the humoral response to some of the polymorphic regions of gp190 associates with an increased risk of infection.
The toxicity of praziquantel against Mesocestoides vogae (syn. corti) tetrathyridia can be assessed using a novel in vitro system.
We recently standardised Mesocestoides vogae (syn. corti) tetrathyridia cultures in the presence of sodium taurocholate. Parasite clustering and segmentation were observed as taurocholate-dependent effects in biphasic and monophasic media, respectively, and both were inhibited by a specific minimum inhibitory concentration (m.i.c.) of the cestocidal drugs albendazol and praziquantel. In the present study, we analysed the relationship between clustering inhibition and drug toxicity using praziquantel and a mouse experimental infection. In an "in vitro-in vivo" trial, a significant (ANOVA, P<0.05) reduction was observed in the infectivity of tetrathyridia previously cultured with praziquantel m.i.c. (0.06 micro g/ml) for 10 days. In an "in vivo-in vitro" trial, the clustering of tetrathyridia recovered from mice treated with praziquantel was found to be markedly reduced: 22%, compared with 83% cluster-containing wells of parasites from control mice. These results show that the outcome of infection and the suppression of taurocholate-induced clustering provide consistent indications of praziquantel toxicity against M. vogae, an observation confirmed by histological studies. The easily recorded clustering inhibition of M. vogae tetrathyridia in biphasic medium is a potentially useful system for the assessment of drug toxicity against cestode larvae.
Environmental consequences of treating cattle with the antiparasitic drug ivermectin.
Ivermectin (22,23-dihydroavermectin B1) is a recently discovered, persistent, broad-spectrum, antiparasitic drug of unpredecented potency which is now routinely administered to cattle, horses, sheep and pigs in many countries. In cattle, it is an efficient control for parasitic gastrointestinal and respiratory tract nematodes, warble fly, mites, lice and ticks. However, most of the ivermectin dose is ultimately eliminated in the faeces of the treated animals where it has been shown to have an insecticidal effect on the larvae of economically important, dung-breeding, haematophagous Diptera. Nevertheless, the effects of excreted ivermectin on the cowpat fauna as a whole and the wider consequences of such effects have not previously been considered. In field trials reported here, the faeces of calves fitted with rumenal boluses delivering ivermectin at 40 micrograms per kg per day, failed to degrade in the normal way and this failure was associated with the absence of dung-degrading insects. Faeces from placebo-treated controls contained a characteristic dung-degrading invertebrate community and were largely degraded within 100 days. These results indicate that the increasing widespread use of ivermectin may have important environmental consequences for pastureland.
How the integrated project was promoted in Tanzania.
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The Integrated Family Planning Project in China. FP and health education: a successful combination.
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The Bangladesh experience in family planning and health.
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Epidemiology of parasitic gastrointestinal nematode infections of ruminants on smallholder farms in central Kenya.
In order to establish the infection pattern with gastrointestinal nematodes in ruminants in the central Kenya highlands, a study was carried out in 58 smallholder farms. The study involved monthly faecal examinations from sheep, goats and cattle and pasture sampling from eight communal grazing areas. Each month, six Dorper worm-free tracer lambs were introduced and four locally grazed cross-bred sheep were purchased for parasite recovery. The mean faecal egg counts (FEC) for cattle were low throughout the study period, whereas those for sheep and goats showed a seasonal pattern with high levels of infection occurring during the two main rainy seasons, especially in March, April and October. There were significant differences in egg counts over time and among farms. Haemonchus contortus was the most prevalent nematode in the tracer lambs whereas the previously exposed locally grazed sheep had significantly lower numbers of H contortus but significantly higher numbers of Trichostrongylus species The highest levels of infection in the tracer lambs occurred in November 1995 and January, May and June 1996. Based on this study, it is now possible to explore the possibility of using strategic treatments for the control of parasitic gastroenteritis in this area of Kenya.
Paving the way to better health through IEC.
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