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PubMed1988

Immunoparasitology: its contribution to development of new parasite vaccines.

Immunoparasitology--the study of the immunology of host-parasite relationships--can post some notable research successes over the past decade. Progress towards prophylactic molecularly-defined vaccines against human parasitic diseases such as falciparum malaria, schistosomiasis mansoni and cutaneous leishmaniasis, as well as economically-important veterinary parasites, has been good. However, new vaccines are not coming as easily as might be hoped mainly because of several deficiencies in knowledge on the immunology of host-parasite relationships and the unknown relevance of well-characterized model systems to real-life parasitic diseases. In some models, the immunology of resistance and the immunology of disease are understood in broad outline. The availability of isolated antigens and their epitopes has improved quantitation of host immune responses to various life cycle stages of parasites and enabled vaccination efficacy or diagnostic potential to be assessed. One of several major challenges facing the immunoparasitologist interested in vaccine development is overcoming genetically-based unresponsiveness to "oligoepitope", defined-antigen vaccines particularly at the level of helper TH and cytotoxic (Tc) T cells.

Animals↗
PubMed1979

Food-borne parasitic infections--old stories and new facts.

A review is presented of food-borne parasitic infections. Parasitic infections with public health hazards both from conventional slaughter animals and from seafood (fish and shellfish) are discussed. The former category includes cysticercosis, echinococcosis, and trichinosis, the latter category covers various trematode, cestode, nematode, and possibly also protozoan infections. Examples of trematode infections are heterophyidiasis, transmitted to man by marine fish, and Paragonimus spp parasites, transmitted by crustaceans. Cestode infections include diphyllobothriasis transmitted by both fresh water fish and fish from brackish waters. Special attention is drawn to the condition known as sparganosis. Of the nematode infections, the eosinophilic granulomatous enteritis due to the genera Anisakis, Phocanema, and Contracaecum, transmitted to man by either marine fish or crustaceans, is mentioned. Two other nematode infections. Angiostrongylus cantonensis and Capillaria philippinensis, can also be transmitted to man by marine fish. Free living amoebae (a.o. Naegleria) may be transmitted to man via shellfish as vehicles. Apart from a possible direct effect of these parasites, chemical alterations in seafood resulting from the presence of parasites may also be deleterious to the consumer. Special attention is drawn to a newly developed serological detection method, the enzyme-linked immunosorbent assay, which makes detection of infection possible not only at the slaughterhouse but also at the farm or in large herds. Strategies to control parasitic infections both in conventional slaughter animals and in seafood are discussed.

Animals↗
PubMed1985

Research needs and priorities for swine internal parasites in the United States.

The swine industry in the United States is increasing in the Southeast. The proportion of pigs raised in confinement has increased to 25% and the trend is expected to continue. Changes in geographic origin and in management have affected the swine parasite fauna. A few parasites have almost disappeared and others have gained new prominence. Prevention and control of parasites are accomplished by feed additives and routine therapeutic treatments. Knowledge of the epizootiologic factors governing parasite transmission, in relation to climate and management systems, may lead to improvements in the prevention and control of swine parasites. Opportunities exist for developing biological, chemical, and managerial practices that can be integrated economically into management systems to control parasites and improve performance through decreases in mortality and morbidity and increases in daily gain and feed conversion efficiency.

Animal Husbandry↗
PubMed1972

The development, clinical signs and economic losses of gastrointestinal parasitism in feeder cattle on irrigated and non-irrigated dikeland and upland pastures.

Investigations were carried out over three grazing seasons with parasitized and treated (control) steers on irrigated and non-irrigated upland and dikeland pastures. The stocking rate in each paddock was adjusted by either adding or removing animals so as to maintain as uniform a sward and rate of grazing as possible. Animals were weighed on and off the pastures and fortnightly during the grazing seasons. During the first grazing season clinically normal steers shedding low numbers of gastrointestinal worm eggs contaminated the parasite-free pastures sufficiently to give rise to large residual pasture infections and clinical parasitic gastroenteritis in grazing stock during the second grazing season. Worm burdens of 100,000 to 200,000 Ostertagia ostertagi and Cooperia oncophora were established in several steers showing marked clinical signs. In spite of treatments with high dosages of thiabendazole in attempts to keep worm burdens at a minimum, there was a slow but gradual buildup of pasture infections in the paddocks grazed by the control steers over the three year period. During the second and third grazing seasons there were significant differences in the daily rate of gain between the parasitized and control animals on both upland and dikeland pastures. The parasitized groups of steers had daily rates of gain ranging from 0.29 to 0.80 pounds less than their comparable control groups. Under Maritime conditions, irrigation did not have a consistent effect on weight gains and development of parasitism.

Animals↗
PubMed1982

Prevalence of parasitism diagnosed by fecal examination in Louisiana dogs.

The prevalence of canine intestinal parasitism was evaluated by fecal examination of 4,058 dogs admitted to the Louisiana State University Veterinary Teaching Hospital and Clinics from March 1977 to March 1980). One or more species of parasites was identified in 2,048 (50.5%) dogs. Hookworms were encountered in 38.5% of the dogs examined, whipworms in 14.9%, ascarids in 8.5%, coccidia in 2.6%, tapeworms in 2.2%, and giardia in 0.8%. Single parasitic infection was present in 1,456 (35.9%) dogs. For hookworm and whipworm infections, male dogs were significantly (P less than .05) more often affected, compared with females or spayed females. Ascarid, coccidia, and giardia infections were more prevalent in pups than in mature dogs, whereas whipworm infections were detected less often in dogs less than 6 months of age. Hookworms were the most prevalent parasites in male (39.2%) and female (35.7%) dogs less than 6 months of age and maintained high prevalence in mature dogs. Tapeworm infections were diagnosed sporadically in all age groups. In female dogs greater than 24 months of age, significantly less parasitism was present as compared with younger females. In male dogs, the prevalence of parasitism diminished less markedly with increasing age.

Age Factors↗
PubMed1977

Effect of age and sex on the prevalence of intestinal parasitism in dogs.

The effects of age, sex, and neutering on the prevalence of canine intestinal parasitism were evaluated by fecal examination of 1,468 pet dogs admitted to the University of Missouri Veterinary Teaching Hospital during 1975. Evidence of hookworm infection was encountered in 35.8% of the dogs examined, whipworms in 18.5%, ascarids in 17.9%, tapeworms in 5.2%, and coccidia in 4.5%. Evidence of intestinal parasitism was not detected in 653 (44.4%) dogs. Whipworm infections were detected less often in young dogs than in older ones, whereas ascarid and coccidial infections were more prevalent in pups that in mature dogs. In dogs more than 6 months old, hookworm infections were the most common parasitism. Tapeworm infections were diagnosed sporadically in all age groups. For most of these parasites, castrated males and spayed females had decreased prevalence of infection, compared with their respective intact counterparts. There were significant (P less than 0.05) differences in the prevalence of both ascarid and hookworm infections between intact and spayed female dogs. Also, there were significant (P less than 0.001) differences between age categories for all parasites observed. Overall, parasitism tended to decrease with age.

Age Factors↗
PubMed1996

Prevalence of intestinal parasites in adult patients with enteropathic AIDS in north-eastern Tanzania.

A six month study was conducted in north-eastern Tanzania to determine the prevalence of pathogenic intestinal parasites among adult patients with enteropathic AIDS. A total of 352 patients were recruited of whom 158 (45%) had chronic diarrhoea. Of the 352 patients, 123 (35%) had intestinal parasites. Of the 123, 77 (62.6%) patients had chronic diarrhoea. The types of parasites detected were Cryptosporidium, Isospora belli, Strongyloides stercoralis, Schistosoma mansoni, Trichuris, trichiura, Ascaris lumbricoides, hookworm and Entamoeba histolytica. The prevalence of intestinal parasites was significantly higher in patients with chronic diarrhoea than in those without (P < 0.05). Cryptosporidium and Isospora belli were only detected in patients with chronic diarrhoea and were thus the most likely cause of the diarrhoea. This study has established that coccidian parasites are the most important gut opportunistic infections in Tanzanian patients with enteropathic AIDS. The fact that a high proportion of patients with chronic diarrhoea (51.3%) had no identifiable parasitic agents, suggests that other infectious agents or alternative mechanisms other than infections are responsible for the diarrhoea.

Adult↗
PubMed1997

Quantitative aspects of evaluating the consequences of pollution for parasite populations and communities.

The utility of parasites as indicators of environmental health depends upon scientists' ability to understand how environmental stress may cause changes in parasite populations and communities. Predicting the changes due to pollution calls for dynamic models and experimentally determined knowledge of the consequences of pollution on the parameters of the model. Through an interplay of modeling, laboratory experiments, and field comparisons scientists can develop a theory of pollution and parasites and perhaps use it to assess the impact of pollution. To develop a theoretical framework for the effects of pollution on host-parasite relationships will require an identification of the appropriate scale and a determination of whether the host and parasite populations should be treated as open and recruitment-driven or closed and reproduction-driven. A theory can then be developed using epidemiology models. Those models are divided into prevalence models that track the prevalence of infection and abundance models that track the number of parasites per host. Whether a deterministic model or a stochastic counterpart should be used depends upon the scale but generally a stochastic model will give a more realistic picture. Mimicking the variability inherent in natural systems is the goal of stochastic models. The models emphasize that field tests of their predictions can only be made by studies designed with extensive replication of samples from reference and stressed sites.

Animals↗
PubMed2004

Veterinary parasitic vaccines: pitfalls and future directions.

Most available antiparasitic drugs are safe, cheap and highly effective against a broad spectrum of parasites. However, the alarming increase in the number of parasite species that are resistant to these drugs, the issue of residues in the food chain and the lack of new drugs stimulate development of alternative control methods in which vaccines would have a central role. Parasite vaccines are still rare, but there are encouraging signs that their number will increase in the next decade. The modern paradigm is that an understanding of parasite genes will lead to the identification of useful antigens, which can then be produced in recombinant systems developed as a result of the huge investment in biotechnology. However, we should also continue to devote efforts to basic research on the host-parasite interface.

Animals↗
PubMed1997

Deer and their parasites: disease or coexistence?

The occurrence of different parasites in roe (Capreolus capreolus), and red deer (Cervus elaphus) were examined during the period 1972-1995. Deer shot at random or found dead were examined and parasitological status of a farmed red deer herd has been observed regularly. Age, carcass weight, physical condition and pathological features were checked or measured. Of the parasites, 38 species in roe and 18 in red deer were identified and at least 11 of them were shared by both hosts. None of them seems to be pathogenic for these hosts, not considerating local alterations. Disease or mortality together with excessive parasite burden were found only in specimens or herds living in captivity. Beside lungworms, protozoans as well as hair louse may occur in high intensity due to the stress-related diathesis of the host organism. Therefore the relation of deer and their native parasites can be considered as a coexistence rather than a harmful impact of the latter. Parasites of direct development can serve as bioindicators, monitoring the health status of the host individuals, herds or their habitat quality. Finally, the indigenous parasitofauna of roe and red deer and the large variety of their other intermediate and final hosts represent a colourful example of biodiversity.

Adaptation, Physiological↗
PubMed1994

Antibacterial peptides in insect vectors of tropical parasitic disease.

The induction and characterization of immune peptides in two groups of medically important insects, the mosquitoes and blackflies, is currently an important research area. Mosquitoes transmit a variety of viral and parasitic diseases including yellow fever, dengue, malaria and lymphatic filariasis. Simuliid black flies are vectors of river blindness. The diseases are together responsible for death and morbidity in millions of people each year. The relationship between inducible peptides and bacterial and parasitic infections in these insects is proving to be a complex one. The identification of an insect defensin (4 kDa) in Aedes aegypti, the yellow fever mosquito, has proved to be the first peptide characterized in a vector of human disease. This inducible molecule appears in the haemolymph in response to bacterial and to a lesser extent filarial infection. The characterization of inducible blackfly peptides has revealed potent inducible anti-Gram-positive as well as anti-Gram-negative activity. In addition, non-self recognition molecules such as phenoloxidase may play a part in differentiating one species of eukaryotic pathogen from another of the same genus. The interactions between the peptides and these other proteins are likely to be important in the establishment of a successful immune response against a parasitic pathogen, particularly as we now know these peptides to have anti-eukaryotic activity (against a range of parasite species). As well as being of fundamental interest in our understanding of host-parasite relationships, the indication that antibacterial peptides are toxic to parasitic organisms has implications for their possible use in the disease vector control strategies of the future. It may also mean that a revision in our understanding of their mode of action, loose as it is, has to take place.

Aedes↗
PubMed1983

Cell biology of host-parasite membrane interactions in leishmaniasis.

Molecular interactions at the host-parasite interface are crucial for the outcome of microbial infection, particularly in infection by intracellular parasites, such as Leishmania donovani and Leishmania mexicana, whose natural transmission begins with the delivery of the promastigote stage by the sandfly vector into the susceptible host. The ensuing event is intracellular parasitism of macrophages in the host by the amastigote stage. The establishment of this event in leishmaniasis must follow the sequence: (1) Leishmania-macrophage attachment; (2) entry of Leishmania species into macrophages; (3) intra-macrophage survival and differentiation of Leishmania species; and (4) intracellular multiplication of Leishmania species. This sequence precedes all clinical symptoms and pathological consequences in different forms of the disease. Study of these cellular events in Leishmania-macrophage systems in vitro indicates that host-parasite membrane interactions dictate many of the cellular events. Some morphological and functional changes of macrophages in response to leishmanial infection are related to their membrane activities, i.e. endocytosis and exocytosis. Leishmania parasites undergo profound plasma membrane-related changes, on entry into macrophages, at the morphological, antigenic and molecular levels. Most of these changes probably reflect necessary steps for the transition of Leishmania species from an extracellular to an intracellular life. The remarkable ability of Leishmania species subsequently to live in the secondary lysosome of the macrophage may also be due to certain intrinsic structures and dynamic properties of the parasite plasma membrane. Further analysis of leishmanial surface molecules and their interactions with macrophages is essential in any attempt to understand the pathogenic mechanism in leishmaniasis.

Animals↗
PubMed1985

Trypanosoma cruzi: modulation of parasite-cell interaction by plasma fibronectin.

Treatment of either rat peritoneal macrophages (RPM), cloned 3T3 fibroblasts (3T3FR) or Trypanosoma cruzi trypomastigote culture forms with human plasma fibronectin (huFN) enhanced their association with the untreated counterpart and this related to the concentration of huFN used. When treatment was performed at 4 degrees C, the enhancing effect of huFN on parasite-cell interaction was greater than that observed at 37 degrees C. This observation could be related to the indirect immunofluorescence antibody assay showing that a significant increase of fibronectin staining was observed on the cell and parasite surfaces upon incubation with huFN and that the extent of fibronectin staining was greater at 4 degrees C. Incubation of huFN-treated or nontreated parasites or cells with anti-huFN antibodies exerted an inhibitory effect on the parasite-cell association. The region of fibronectin that interacts with the trypomastigote surface is unknown. Inhibition experiments suggested that the domain of fibronectin which interacts with parasite surface receptors would probably be localized close to the NH2-terminal region of the molecule. Taken together, these results suggest that fibronectin may play a role in the binding of parasites to the vertebrate host cell surface.

Animals↗
PubMed1996

Host-parasite arms race in mutation modifications: indefinite escalation despite a heavy load?

If constantly changing genotypes are favorable in host and parasite coevolution, an indefinite escalation of mutation rates would result despite heavy mutational loads. We theoretically study this possibility by examining the mutation modifier dynamics of host and parasite that engage in genotype-specific epidemiological interaction. In the first model, we study the evolutionarily stable (ESS) mutation rate or switching rate if two alleles in a single locus are subjected to frequency-dependent selection favoring the rarer of the two. Mutation modifier locus is either tightly linked or unlinked to the selected locus. Sufficiently strong frequency-dependent selection may cause cycles in allele frequencies and a modifier with higher mutation rate enjoys the long-term advantage by randomizing the genotype of their offspring. Through the repeated events of invasion and replacement of mutation modifiers, the mutation rate continues to increase until the allele frequencies are stabilized. If some fraction of mutations are deleterious, there is no longer a pure ESS mutation rate: the evolutionarily stable population then consists of multiple strains concerning mutation modifier, typically one with a very high mutation rate and the other with a very low rate, stably coexisting and fighting off invasion by any other modifiers. These results are almost independent of the linkage between the selected and the modifier loci. In the second model, we consider the joint evolution of host and parasite mutation modifiers, assuming that a specific pair of host and parasite genotype densities change following the Nicholson-Bailey type model. If there is no cost of deleterious mutations, mutation rates of both species are escalated indefinitely by modifier evolution until they completely suppress the fluctuation of genotype densities. However, a small cost of deleterious mutation is enough to collapse this coevolutionary equilibrium of inflated mutations. Typical coevolutionary outcome is that the parasite mutation rate is accelerated to a high level; whereas the host mutation rate is driven to zero. Extension of our results to host-parasite coevolution of recombination modifier evolution is discussed.

Animals↗
PubMed2000

Population dynamics of plant-parasite interactions: thresholds for invasion.

Thresholds are derived for the invasion of plant populations by parasites. The theory is developed for a generic model that takes into account two features characteristic of plant-parasite interactions: a dual source of inoculum (infection from primary or externally introduced inoculum and secondary infection from contact between susceptible and infected host tissue) and a host response to infection load. Each of the threshold criteria is shown to be the sum of the individual components for primary and secondary infection. This indicates that if parasite invasion is not possible through primary or secondary infection alone, when the two modes of transmission are combined, the parasite may be able to invade. The invasion criteria demonstrate that there is a threshold population of susceptible hosts below which the parasite is unable to invade. If there are nonlinearities in the population dynamics (arising through either the transmission process or the host response), there are also threshold densities for the infected hosts and parasite populations below which invasion does not occur. The implications of the results for the control of plant disease are discussed.

Animals↗
PubMed1989

Host-parasite relationship of Trypanosoma corvi in Ornithomyia avicularia.

The first description of an electron microscopic study of Trypanosoma corvi in the vector Ornithomyia avicularia is reported. There is a close association between vector and parasite in the midgut, ileum and rectum of the vector. The midgut distribution of parasites is determined by the peritrophic membrane, which confines the early infection to the endoperitrophic space. Parasites escape from the ruptured region of the peritrophic membrane at the pylorus to gain access to the ectoperitrophic space, where intense multiplication occurs. The resulting, smaller epimastigotes attach to the cuticle in the pylorus, ileum and rectum, where they continue multiplying to give rise to mature, short, stumpy trypomastigotes (metacyclics) that are not attached. Attachment to these cuticularly lined regions occurs by the formation of dense, hemidesmosome-like plaques at the extremities of the expanded flagella. A fibrous matrix surrounds the parasites in the ileum. For the first time, intracellular midgut forms are reported for T. corvi in O. avicularia. These parasites enter the cells between the microvilli and penetrate deeply between the folds of the midgut. In the midgut of O. avicularia, the cells of a mycetome region are packed with Rickettsia-like organisms. The significance of these intracellular parasites in the relationship of T. corvi in O. avicularia remains unknown.

Animals↗
PubMed1998

Maternal malaria and parasite adhesion.

Malaria during pregnancy continues to be a major health problem in endemic countries, with clinical consequences, including death, for both mother and child. Just as cerebral malaria results from parasite sequestration in the brain, maternal malaria results from parasite sequestration in the placenta, and a distinct subpopulation of parasites which bind chondroitin sulfate A but not CD36 causes the syndrome. Women have little or no immunological experience with this parasite prior to first pregnancy, making primigravid women particularly vulnerable to infection. Parasites adhere to the surface of trophoblastic villi, eliciting the accumulation of inflammatory leukocytes in the intervillous space, and the necrosis of adjacent placental tissue. Maternal malaria results in poor pregnancy outcomes, although the responsible mechanisms have not been defined. In holoendemic areas both placental infection and poor outcome decrease in frequency with successive pregnancies; protection may result from control of parasite adhesion, suggesting an attractive target for new therapies.

Animals↗
PubMed2004

The distribution of Echinococcus granulosus in moose: evidence for parasite-induced vulnerability to predation by wolves?

The role of parasites in influencing the trophic dynamics of hosts is becoming increasingly recognized in the ecological literature. Echinococcus granulosus is a tapeworm that relies on the predator-prey relationship between the definitive host (wolf, Canis lupus) and the intermediate host, (moose, Alces alces) to complete its life cycle. Heavy infection by E. granulosus may predispose moose to increased risk of predation by wolves. Theory predicts that parasite-induced vulnerability to predation will reduce the degree of aggregation of parasites in a host population. We tested for different levels of aggregation of E. granulosus in moose in areas of low, moderate, and high levels of wolf predation using Green's coefficient of dispersion. Parasite aggregation was lower in an area with high predation rate, thus we hypothesize that heavy infection by E. granulosus predisposes moose to predation by wolves. This increase in predation rate due to parasite infection may influence the role of wolves in regulating moose populations. We discuss alternative explanations for the negative correlation between predation rate and parasite aggregation.

Age Factors↗