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At least 937 records · Page 52Linked to original sources
PubMed2006

Parasitism by Cotesia plutellae alters the hemocyte population and immunological function of the diamondback moth, Plutella xylostella.

Cotesia plutellae, a solitary endoparasitoid wasp, parasitizes the diamondback moth, Plutella xylostella, and induces host immunosuppression and lethality in the late larval stage. This study focused on changes of cellular immunity in the parasitized P. xylostella in terms of hemocyte composition and cellular functions. In third and fourth instar larvae of nonparasitized P. xylostella, granular cells represented the main hemocyte type (60-70%) and plasmatocytes were also present at around 15% among the total hemocytes. Following parasitization by C. plutellae, the relative proportions of these two major hemocytes changed very little, but the total hemocyte counts exhibited a significant reduction. Functionally, the granular cells played a significant role in phagocytosis based on a fluorescence assay using fluorecein isothiocyanate-labeled bacteria. The phagocytic activity of the granular cells occurred as early as 5 min after incubation with the bacteria, and increased during the first 40 min of incubation. The parasitism by C. plutellae significantly inhibited phagocytosis of the granular cells. Plasmatocytes also exhibited minor phagocytic activity. Moreover, plasmatocyte phagocytosis was not inhibited by parasitism. On the other hand, hemocyte-spreading behavior in response to pathogen infection was significant only for plasmatocytes, which exhibited a characteristic spindle shape upon infection. A significant spreading of the plasmatocytes was found as early as 5 min after pathogen incubation and their ratio increased during the first 40 min. An insect cytokine, plasmatocyte-spreading peptide 1 (PSP1) from Pseudoplusia includens, was highly active in inducing plasmatocyte-spreading behavior of P. xylostella in a dose-dependent manner. P. xylostella parasitized by C. plutella was significantly inhibited in plasmatocyte-spreading in response to an active dose of PSP1. An in vivo encapsulation assay showed that the parasitized P. xylostella could not effectively form the hemocyte capsules around injected agarose beads. This research demonstrates that the parasitism of C. plutellae adversely affects the total hemocyte populations in number and function, which would contribute to host immunosuppression.

Animals↗
PubMed2005

Influence of the stage of pregnancy on Neospora caninum distribution, parasite loads and lesions in aborted bovine foetuses.

In the present work we have studied in Neospra caninum aborted bovine foetuses the influence of foetal age (first, second and third gestational periods) on parasite distribution by nested PCR, parasite loads by real-time PCR and N. caninum associated lesions. For this purpose, a total of 220 aborted foetuses were analysed and detection of N. caninum infection was accomplished by nested-PCR in brain, heart and liver, detecting the presence of the parasite in 72 (32.7%) bovine foetuses. When the different age classes were compared, parasite DNA-detectability in heart and liver was reduced over time of gestation (P < 0.05, Fisher F-test). N. caninum distribution, parasite loads and lesions were studied on 34 out of 72 N. caninum-infected foetuses selected according to the stage of pregnancy and organs recovered. A higher number of positive-PCR tissue samples were observed in the foetuses corresponding to the first and second pregnancy periods. In the last trimester, the parasite could only be detected in the brain and, sporadically, in the diaphragm, heart and lymph nodes. The parasite loads decreased during pregnancy and the foetuses from the first period had higher parasite burdens in brain, heart, kidney and lung (P < 0.05, Kruskal-Wallis H-test) than in those corresponding to the other two trimesters of pregnancy. In addition, the observed lesions were more severe in foetuses from the first and second pregnancy periods than those from the third period (P > 0.05, Kruskal-Wallis H-test). Our results confirm the influence of N. caninum foetal age on pathogenesis in natural N. caninum infections.

Abortion, Veterinary↗
PubMed2005

In vitro recrudescence of Plasmodium falciparum parasites suppressed to dormant state by atovaquone alone and in combination with proguanil.

We studied the viability of Plasmodium falciparum parasites reappearing in long-term cultures after repetitive exposure to atovaquone and proguanil. Parasites (F32 and FCR3) exposed to 100-5000 nM atovaquone for 96 hours were reduced to <5% of initial parasitaemia but recrudesced after 9-15 days. Also, parasites exposed to 1000 nM atovaquone for 48, 72, 96 and 144 hours recrudesced after 9, 14, 21 and 23 days respectively. Immediately after removal of the drug, only 1-3 schizonts per 10000 red blood cells were found consistently, apparently unable to produce trophozoites and thus, possibly, adopting a "dormant state". Parasites (F32 and FCR3) exposed to 500 nM atovaquone for 72 hours reappeared after 14 days. These recrudescing parasites were then re-exposed and suppressed by atovaquone in three consecutive follow-up experiments. They reappeared after 12, 11 and 9 days respectively. No known point mutations in cytochrome b gene (cytb), associated with atovaquone resistance, were detected in any recrudescing parasites. Finally, parasites (F32) exposed to various concentrations of atovaquone and proguanil in combination for 72 hours reappeared after 9-17 days. The baseline susceptibilities of the parasites to individual drugs were similar before and after recrudescence in all experiments.

Animals↗
PubMed2003

In vitro culture of Echinococcus multilocularis and Echinococcus vogeli metacestodes: studies on the host-parasite interface.

The larval stage of Echinococcus multilocularis causes alveolar echinococcosis (AE) in various mammalians including humans, while Echinococcus vogeli larvae cause a related disease which is also occasionally found in man. Traditionally, Echinococcus metacestodes have been maintained in the laboratory by serial transplantation passages into susceptible animals such as mice or gerbils, enabling the parasite to proliferate asexually. These experimental animal models have been used extensively to investigate host-parasite interactions and to study immunological events occurring at the host-parasite interface. However, with the use of laboratory animals it has always been difficult to investigate in more detail those factors modulating metacestode differentiation, and investigations on gene expression and respective regulation have been hampered by the complexity of the host-parasite interplay. There has been a need for an in vitro culture model which would enable researchers to dissect specific parasite compartments involved in the host-parasite relationship in more detail. This review summarises the studies leading to the development and application of a suitable in vitro culture model for the maintenance and proliferation of E. multilocularis and E. vogeli metacestodes, including the formation of protoscoleces, in a chemically defined medium devoid of host influence. These culture models have been used to study the basic parameters of metacestode in vitro proliferation and differentiation, and for the dissection of the ultrastructure and composition of the acellular laminated layer, the structure of which is predominantly involved in the physical interaction between the parasite and host immune and non-immune cells and tissues. For E. multilocularis, in vitro cultured parasites have been more extensively employed to study the localisation of several antigens, and to generate defined antigens for immunological studies. Although in vitro culture will not completely eliminate the need of animal experimentation, a wider application of this technique could significantly reduce the use of animals, and thus the costs and time required for respective experimental investigations.

Animals↗
PubMed2000

Effects of environmental change on emerging parasitic diseases.

Ecological disturbances exert an influence on the emergence and proliferation of malaria and zoonotic parasitic diseases, including, Leishmaniasis, cryptosporidiosis, giardiasis, trypanosomiasis, schistosomiasis, filariasis, onchocerciasis, and loiasis. Each environmental change, whether occurring as a natural phenomenon or through human intervention, changes the ecological balance and context within which disease hosts or vectors and parasites breed, develop, and transmit disease. Each species occupies a particular ecological niche and vector species sub-populations are distinct behaviourally and genetically as they adapt to man-made environments. Most zoonotic parasites display three distinct life cycles: sylvatic, zoonotic, and anthroponotic. In adapting to changed environmental conditions, including reduced non-human population and increased human population, some vectors display conversion from a primarily zoophyllic to primarily anthrophyllic orientation. Deforestation and ensuing changes in landuse, human settlement, commercial development, road construction, water control systems (dams, canals, irrigation systems, reservoirs), and climate, singly, and in combination have been accompanied by global increases in morbidity and mortality from emergent parasitic disease. The replacement of forests with crop farming, ranching, and raising small animals can create supportive habitats for parasites and their host vectors. When the land use of deforested areas changes, the pattern of human settlement is altered and habitat fragmentation may provide opportunities for exchange and transmission of parasites to the heretofore uninfected humans. Construction of water control projects can lead to shifts in such vector populations as snails and mosquitoes and their parasites. Construction of roads in previously inaccessible forested areas can lead to erosion, and stagnant ponds by blocking the flow of streams when the water rises during the rainy season. The combined effects of environmentally detrimental changes in local land use and alterations in global climate disrupt the natural ecosystem and can increase the risk of transmission of parasitic diseases to the human population.

Animals↗
PubMed2002

Host adaptation and host-parasite co-evolution in Cryptosporidium: implications for taxonomy and public health.

To assess the genetic diversity and evolution of Cryptosporidium parasites, the partial ssrRNA, actin, and 70kDa heat shock protein (HSP70) genes of 15 new Cryptosporidium parasites were sequenced. Sequence data were analysed together with those previously obtained from other Cryptosporidium parasites (10 Cryptosporidium spp. and eight Cryptosporidium genotypes). Results of this multi-locus genetic characterisation indicate that host adaptation is a general phenomenon in the genus Cryptosporidium, because specific genotypes were usually associated with specific groups of animals. On the other hand, host-parasite co-evolution is also common in Cryptosporidium, as closely related hosts usually had related Cryptosporidium parasites. Results of phylogenetic analyses suggest that the Cryptosporidium parvum bovine genotype and Cryptosporidium meleagridis were originally parasites of rodents and mammals, respectively, but have subsequently expanded their host ranges to include humans. Understanding the evolution of Cryptosporidium species is important not only for clarification of the taxonomy of the parasites but also for assessment of the public health significance of Cryptosporidium parasites from animals.

Actins↗
PubMed1997

Molecular methods for diagnosis and epidemiological studies of parasitic infections.

Direct microscopy is widely used for the diagnosis of parasitic infections although it often requires an experienced microscopist for accurate diagnosis, is labour intensive and not very sensitive. In order to overcome some of these shortcomings, molecular or nucleic acid-based diagnostic methods for parasitic infections have been developed over the past 12 years. The parasites which have been studied with these techniques include the human Plasmodia, Leishmania, the trypanosomes, Toxoplasma gondii, Entamoeba histolytica, Giardia, Trichomonas vaginalis, Cryptosporidium parvum, Taenia, Echinococcus, Brugia malayi, Wuchereria bancrofti, Loa loa and Onchocerca volvulus. Early methods, which involved hybridisation of specific probes (radiolabelled and non-radiolabelled) to target deoxyribonucleic acid (DNA), have been replaced by more sensitive polymerase chain reaction (PCR)-based assays. Other methods, such as PCR-hybridisation assays, PCR-restriction fragment length polymorphism (PCR-RFLP) assays and random amplified polymorphic DNA (RAPD) analysis have also proved valuable for epidemiological studies of parasites. The general principles and development of DNA-based methods for diagnosis and epidemiological studies will be described, with particular reference to malaria. These methods will probably not replace current methods for routine diagnosis of parasitic infections in developing countries where parasitic diseases are endemic, due to high costs. However, they will be extremely useful for genotyping parasite strains and vectors, and for accurate parasite detection in both humans and vectors during epidemiological studies.

Animals↗
PubMedDate not supplied

Molecular analysis of recrudescent parasites in a Plasmodium falciparum drug efficacy trial in Gabon.

Recrudescent Plasmodium falciparum parasites were sampled from 108 children taking part in a drug efficacy trial in Gabon. A finger-prick blood sample was taken from each child before treatment, and a post-treatment sample taken of the recrudescent parasites. Sample deoxyribonucleic acid was amplified by the polymerase chain reaction using primers specific to the P. falciparum antigen genes MSP-1, MSP-2 and GLURP. Seventy-seven children had identical parasites in their pre- and post-treatment samples, indicating genuine recrudescences of resistant parasites. Fourteen children had completely different parasites in their pre- and post-treatment samples, indicating either a fresh infection from a mosquito or growth of a population of parasites not detected in the pre-treatment sample, perhaps due to sequestration. The remaining 17 children had a mixture of pre-treatment and new parasites in their post-treatment samples. This study demonstrated the use of polymorphic markers to confirm whether parasites in patients with clinical recrudescences after drug treatment are genuinely resistant.

Adolescent↗
PubMedDate not supplied

The occurrence and mechanisms of innate immunity against parasites in fish.

Parasitic infections in teleost fish are limited by constitutive innate defence mechanisms that render the host refractory or reduce the severity of infection. Controlled challenge trials using naive animals provide indirect evidence of innate immunity as well as identifying the host range or specificity of a parasite, often when specific details of defence mechanism(s) are lacking. Examples of parasites for which innate immunity may be inferred from cross-infectivity studies include Gyrodactylus spp., Lepeophtheirus salmonis, Cryptobia spp., Trypanosoma spp., Ceratomyxa shasta, Myxobolus cerebralis and Kudoa thyrsites. Recent studies however, have begun to clarify the relative roles of innate and acquired immunity against parasitic infection in teleosts by recognizing the presence and significance of specific innate effector mechanisms. The physico-chemical characeristics of skin mucus, the presence of bioactive substances including lysozyme, complement, C-reactive protein, haemolysins and lectins and the epidermal migration of inflammatory cells and their secretions may affect the establishment and proliferation of ectoparasitic copepods, ciliates or monogenea. Similarly in refractory species, haematozoic parasites are lysed via the alternative complement pathway and in susceptible and refractory hosts, protease inhibitors associated with the plasma neutralize proteolytic virulence factors. Detailed knowledge of innate resistance mechanisms against histiozoic parasites are lacking although non-specific cytotoxic lymphoid cells and macrophages probably play a role. The demonstration in certain disease models that innate resistance traits are under genetic control and may be inherited in a simple Mendelian fashion suggests opportunities for selective breeding for resistance against parasitic disease. Beyond a small number of well-described models however, research programs focussing on innate immunity against parasites in fish are lacking. Given the relative importance of innate immunity in fish, particularly as disease losses continue to have an economic impact in aquaculture, this area deserves considerable attention.

Animals↗
PubMed1990

Behavioral adaptations to pathogens and parasites: five strategies.

The ever present threat of viral, bacterial, protozoan and metazoan parasites in the environment of wild animals is viewed as responsible for the natural selection of a variety of behavioral patterns that enable animals to survive and reproduce in this type of environment. Several lines of research, some quite recent, point to five behavioral strategies that vertebrates utilize to increase their personal or inclusive fitness in the face of parasites (broadly defined to include pathogens). These are: 1) avoidance of parasites; 2) controlled exposure to parasites to potentiate the immune system; 3) behavior of sick animals including anorexia and depression to overcome systemic febrile infections; 4) helping sick animals; 5) sexual selection for mating partners with the genetic endowment for resistance to parasites. The point is made that to consider a behavioral pattern as having evolved to serve a parasite control function the parasite or causative agent should be shown to adversely impact the animal's fitness and the behavior in question must be shown to help animals, or their offspring or group mates, in combating their exposure, or reducing their vulnerability, to the parasite.

Adaptation, Psychological↗
PubMed1999

Parasite infection and Japanese cedar pollinosis in monkeys.

To evaluate the relationship between helminthic parasite infection and sensitization to Japanese cedar (Cryptomeria japonica; CJ) pollen allergens in Japanese monkeys (Macaca fuscata), we examined the parasite infection, presence of anti-pollen allergen IgE and development of pollinosis. Serum samples and fecal specimens were taken from 169 monkeys in five troops, and the presence of IgE antibody for CJ pollen allergen and of helminthic parasite eggs in their feces was examined. Of the 169 monkeys, helminthic parasite eggs from 138 monkeys were detected. The frequency of anti-CJ IgE (19%) and the level of total IgE did not differ significantly between the monkeys with and without parasite eggs. We examined the presence of anti-CJ IgE and pollinosis symptoms in 31 monkeys of a troop; six of the monkeys demonstrated anti-CJ IgE and pollinosis symptoms. Five of these six monkeys had parasite eggs. We found that the monkeys that demonstrated anti-CJ IgE and pollinosis symptoms had helminthic parasite infections. These data suggest that helminthic parasite infection does not reduce the development of clinical signs of CJ pollinosis in Japanese monkeys.

Allergens↗
PubMed1999

The immunoepidemiology of nematode parasites of farmed animals: a mathematical approach.

The population dynamics of farmed animals are controlled by humans, and often involve high host densities, which encourage higher parasite burdens than would be usual in wild animals. As a result, the immunity to reinfection acquired by the host is an important determinant of parasite population dynamics. For example, lambs are highly susceptible to gastrointestinal nematodes as they begin to graze, but develop an immunity that accounts for the observed within-year variation in parasite load and pasture contamination. In the longer term, control measures are compromised by the development of parasite strains resistant to chemotherapy, focusing attention on the development of 'natural' measures, including the selection for resistant hosts and the development of antiparasite vaccines. Mick Roberts here considers the immunoepidemiology of parasites of farmed animals on three levels: the interaction between the parasite and the host's immune system determining the individual's level of protection; the development of acquired immunity determining the within-year parasite population dynamics; and the long-term effects of control measures on the between-year parasite population dynamics.

Animal Husbandry↗
PubMed2001

Control of anthelmintic resistant endoparasites in a commercial sheep flock through parasite community replacement.

An effort was undertaken to replace a community of sheep endoparasites that had been classified as resistant to levamisole and albendazole with a community of more susceptible parasites using a dilution approach that could be integrated into the management of a commercial flock. For this study, pastures on this sheep farm were divided into two areas: north and south. Strategically timed anthelmintic treatments combined with pasture management reduced to nondetectable levels the endemic community of anthelmintic resistant parasites in this flock and on these pastures by early summer. A group of 102 ewes, lambs, and rams were experimentally infected with third stage larvae from the more susceptible community of parasites. These sheep then seeded the south pastures with the new parasite community, while sheep on the north pastures maintained the endemic resistant community. Despite its insensitivity as a technique for detecting anthelmintic resistance, fecal egg count reduction tests at the end of the grazing season indicated that the more susceptible parasites were present on the south pastures while resistant parasites were present on the north. The following grazing season, similar protocols were used to introduce the more susceptible parasites onto the north pastures. At the end of the grazing season, fecal egg count reduction tests indicated that the new community of parasites had become established on both groups of pastures of the farm.

Albendazole↗
PubMed2001

Host responses against the fish parasitizing ciliate Ichthyophthirius multifiliis.

Recent studies have shown that fish are able to mount protective immune responses against various parasites. One of the best characterized parasite-host system in this context is the ciliate Ichthyophthirius multifiliis (Ich) parasitizing a range of freshwater fishes. Both specific and non-specific host defence mechanisms are responsible for the protection of fish against challenge infections with this ciliate. The specific humoral components comprise at least specific antibodies. The non-specific humoral elements included are the alternative complement pathway and probably lectins. Cellular factors involved in the specific response are B-cells and putative T-cells. The non-specific effector cells recognized are various leukocytes. In addition, goblet-cells and mast cells (EGC-cells) may have a function. The NCC-cell (suggested analogue to NK-cells in mammals) seems to play a role in the non-specific response. This well documented protective response in freshwater fishes against Ich has urged the development of anti-parasitic vaccines. Indeed, such products based on formalin killed parasites have been developed and found to offer the vaccinated host a satisfactory protection. However, the collection of parasites for vaccine production is extremely laborious. It involves keeping infected fish due to the fact that in vitro propagation of the parasite is still insufficiently developed. Gaining knowledge of amino acid sequences and its encoding DNA-sequences for the protective antigens (i-antigens) in the parasite was a major breakthrough. That achievement made it possible to produce a recombinant protein in E. coli and preliminary results indicated a certain protection of fish vaccinated with this product. Recent work has shown that the free-living and easily cultivated ciliate Tetrahymena can be transformed and express the i-antigen. This path seems to be promising for future development of vaccines against Ich. A novel approach in fish is the development of DNA-vaccines. Successful DNA-vaccination trials have been conducted in fish against viral infections and the technology also makes it possible to develop a DNA-vaccine against Ich. Other approaches to immuno-protection against Ich have been the use of heterologous vaccines. Thus, both bath and injection vaccination using live or killed (un-transformed) Tetrahymena has been reported to offer treated fish a certain level of protection. Such protection could be explained by non-specific reactions and the efficacy and duration of this vaccination type should be further evaluated.

Animals↗
PubMed2002

Virulence in rodent malaria: host genotype by parasite genotype interactions.

In an effort to understand what limits the virulence of malaria parasites, we infected inbred mice of three genotypes (C57Bl/6J, CBA/Ca and DBA/2) with one of two parasite lines of the rodent malaria Plasmodium chabaudi. One of these parasite lines had been serially passaged through C57Bl/6J mice and had evolved higher asexual growth rate, virulence and transmission in the process. The other parasite line was the unadapted ancestral line which had low virulence. In all three host genotypes, the C57Bl/6J-adapted parasite line was more virulent than the ancestral line thus indicating that trade-offs in virulence between alternative host genotypes had not placed strong constraints on the evolution of high virulence in this system. By examining the infection dynamics for fitness-related components-asexual parasite population growth, transmission and virulence-we revealed alternative possible explanations for what sets the upper limit to virulence in nature. The total number of transmission forms (gametocytes) produced during the infection, a measure of parasite Darwinian fitness, was four-fold higher in mice that survived the infection than those which died. Among mice that survived, total gametocyte production was greatest in the host genotype that suffered intermediate levels of morbidity (anaemia and weight loss). Thus, there were transmission costs of high virulence that were partly due to host death (as most theoretical models of virulence evolution assume), but perhaps partly due to some factor related to high morbidity. Both mortality and morbidity-related factors might therefore influence the upper limit on virulence of malaria parasites.

Animals↗
PubMed1981

Thymidine uptake by chicken kidney cells parasitized by Eimeria tenella: evidence for a diffusable mediating substance.

The pattern of DNA synthesis in chicken kidney (CK) cells parasitized by Eimeria tenella was altered; a 2-fold increase in the uptake of [3-H]-thymidine occurred in these cells compared with that shown by the controls. This difference was significantly different at 16 h post-inoculation (p.i.) and reached a peak at 20 h p.i. Non-parasitized cells in co-culture with parasitized cells showed a level of incorporation intermediate between that of the parasitized and non-parasitized monocultures. It was shown that this stimulation was due to a factor released into the medium by the parasite or the parasitized cell. A possible course of events leading to induced and prolonged DNA synthesis by the host cell and the significance of this change in the life-cycle of the parasite is discussed.

Animals↗
PubMed2001

Parasite richness and abundance in insular and mainland feral cats: insularity or density?

Hosts living on islands carry few parasite species, and the prevalence and intensity of directly transmitted parasites are often higher in insular than in mainland populations. However, it is unclear whether density or other features of insular populations can be responsible for the pattern observed. We compared the parasite richness, prevalence and intensity of parasites between 2 feral populations of cats living either at low density on an island (Kerguelen) or at high density on the mainland (Lyon). Parasite richness was higher in Lyon than in Kerguelen, where only Toxocara cati was found. T. cati egg prevalence was higher in Kerguelen (71.1%) than in Lyon (58.0%). Because cat density cannot explain this pattern, we propose that the low number of parasite species, the diet and/or immunity of cats act to increase prevalence in Kerguelen. Moreover, prevalence, intensity and variance-to-mean ratio increased with age and body mass in Kerguelen whereas, in Lyon, prevalence decreased with age and body mass. We hypothesize that the pattern of exposure differs between populations, and that density-dependent parasite mortality is lower in Kerguelen than in Lyon. We discuss the consequences concerning the influence of parasites on insular host populations.

Age Factors↗
PubMed2003

The influence of malaria parasite genetic diversity and anaemia on mosquito feeding and fecundity.

Studies of invertebrate-parasite interactions frequently report that infection reduces host fecundity. The extent of the reduction is likely to be determined by a wide range of host and parasite factors. We conducted a laboratory experiment to evaluate the role of parasite genetics and infection genetic diversity on the fecundity of mosquitoes carrying malaria parasites. The malaria vector Anopheles stephensi was infected with either of 2 different genotypes of the rodent malaria parasite Plasmodium chabaudi, or by a mixture of both. Mixed genotype infections reduced mosquito fecundity by 20%, significantly more than either of the 2 single genotype infections. Mixed genotype infections were associated with high gametocyte densities and anaemia in mice, both of which were correlated with reduced bloodmeal size in mosquitoes. Bloodmeal size was the most important predictor of mosquito fecundity; the presence and number of parasites had no direct effect. Parasite density influenced the propensity of mosquitoes to feed on infected mice, with a higher percentage of mosquitoes taking a meal as asexual parasite and gametocyte density increased. Thus mosquitoes may preferentially feed on hosts who will most impair their fecundity.

Anemia↗