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PubMed1995

Microevolution and the genetic structure of parasite populations.

The development of polymerase chain reaction-based methods for assessing the genotypes of small individual organisms will promote groundbreaking investigations of the genetic architecture of parasite populations. Both quantitative genetic models and general knowledge of parasite natural history are useful for making general predictions about the distribution of genetic variation over geographic space. However, designing experimental studies to assess relationships between specific life history variables and patterns of genetic structure in natural populations will be challenging. Traditional biochemical-genetic methods have already been used to study a limited number of parasite populations, and inferred patterns of genetic structure are distinctly different between certain species. Some of these differences in genetic architecture may be explained by parasite or host factors that either promote or retard the dissemination of life cycle stages over geographic space. Many additional empirical studies are needed to characterize basic features of parasite populations, including the spatial distribution and group size of random mating populations and levels of gene flow among parasite subpopulations.

Animals↗
PubMed1994

Parasitic infection among children living in two orphanages in Cairo.

Children living in institutions as orphanages are more exposed to intestinal parasitism, since crowding and behavioral pattern contribute greatly to the spread of parasitic infection. The present study was conducted on 100 children living in Ain-Shams and El-Mowassa orphanages, Cairo. Twenty children living under appropriate health conditions were studied as controls. Ages of both groups ranged from 6-12 years. The results of this study revealed that 69/100 (69%) orphanage children were positive for parasitic infection, while 8/20 (40%) control subjects were positive for parasitic infection; the difference was statistically significant. Enterobius vermicularis was the commonest parasite among both groups. Other parasitic infections detected were; Giardia lamblia, Entamoeba histolytica, Hymenolepis nana and Entamoeba coli with a prevalence of 10%, 9%, 2% and 9% respectively in the study group compared to 15%, 10%, 0% and 5% in the control group; the differences were statistically not significant. Cryptosporidium oocysts were not detected in both groups.

Child↗
PubMedDate not supplied

Parasitic agents in childhood diarrhoea and malnutrition.

In a prospective survey, 1130 children were studied for parasitic infections associated with acute diarrhoea and/or protein energy malnutrition at the Jos University Teaching Hospital, Jos, Nigeria. Intestinal parasites were isolated in 29.2% of the children with E. histolytica, S. mansoni, Hookworm and A. lumbricoides predominating. Children with diarrhoea marginally harbour parasites more frequently than those without diarrhoea, particularly the diarrhoeagenic parasites. The prevalence and pattern of parasitic infections was similar between the malnourished children and their controls reflecting similar environmental influence. We therefore conclude that significant number of children are infected with intestinal parasites and these contribute to morbidity and mortality by precipitating or aggravating diarrhoeal disease or malnutrition. The need for improving sanitation, community awareness, and periodical mass treatment of pre-school and school age children with antiprotozoal and anti-helminthic drugs is advocated.

Acute Disease↗
PubMed1997

[Intestinal parasitic infections and schistosomiasis in the valley of the Senegal river in the Islamic Republic of Mauritania].

An epidemiological survey was carried out in the Trarza and Brakna regions of the Senegal River valley in Mauritania prior to implementation of a program to control intestinal parasitic infection and schistosomiasis. A total of 1297 school children between the ages of 5 and 12 years from a randomized selection of villages in the region were examined to determine the prevalence and intensity of intestinal parasitic infections and schistosomiasis. Overall prevalence was 38.1% for intestinal parasitic infection, 7.1% for intestinal schistosomiasis, and 17.1% for urinary schistosomiasis. Analysis of weight and height as indicators of nutritional status indicated that 40.9% of the children examined were under the 10th percentile of the weight-for-height indicator and that there was a statistically significant correlation between malnutrition, diarrhea, and intestinal parasitic infection (p < 0.0001). Measurement of hemoglobin levels showed that 50.4% of children were anemic (hemoglobin level < 11 g/dl) and that there was a correlation between anemia and infection by Schistosoma haematobium. This is the first epidemiological survey on intestinal parasitic infections in Mauritania and the first study on Schistosoma mansoni on the Mauritanian side of the Senegal River. Findings suggest not only that implementation of a program to control intestinal parasitic infection and schistosomiasis is needed in the region but also that it should be associated with a food/iron supplementation program and growth monitoring.

Anemia↗
PubMed1997

[Prevalence of intestinal parasitism in the public laboratories of Martinique: development from 1988 to 1995].

This survey drew up the epidemiological situation of intestinal parasitism in Martinique in 1994-1995. 13,978 stool specimens collected in 1994-1995 were tested by parasitologic examination. Stool specimens were from patients hospitalised in the 3 principal hospitals of Martinique or coming to the Laboratoire départemental d'hygiène. The parasitism rate was 8.73%. This study showed a significant reduction of intestinal parasitism between results of 1988 and results of 1994-1995. The oro-faecal parasitism was not very important that reflected the good economic and sanitation level of Martinique. On the other hand, regarding the important prevalence of parasitism with Strongyloïdes stercoralis and hookworm, it would be good to improve detection, sanitary education and know better local contamination factors to decrease the prevalence of this parasitism.

Amebiasis↗
PubMedDate not supplied

[Intestinal parasitic infections in Serbia].

To determine the public health significance of intestinal parasitism in Serbia today, systematic parasitologic examination of 16 regions (Kragujevac, Luchani, Zhagubica, Bor, Sjenica, Novi Pazar, Valjevo, Aleksandrovac, Pirot, Bosilegrad, Ivanjica, Golubac, Uzhice, Kladovo, Negotin, Beograd) in central Serbia were carried out over the period 1984-1993. The study involved a total of 5981 schoolchildren (2887 F, 3094 M), 7-11 years old representing 10% of the total age-matched population (N = 58,228) of the examined regions, residing in 91 settlements. Field parasitological examinations included the examination of perianal swabs for E. vermicularis and Taenia sp., and examination of a single feces sample by direct saline smear and Lugol stained smear for intestinal protozoa, and the Kato and Lörincz methods for intestinal helminths. Nine species of intestinal parasites were detected, of which five protozoan: Entamoeba histolytica (0.02%), Entamoeba hartmanni (0.02%), Entamoeba coli (1.3%), Iodamoeba bütschlii (0.02%), Giardia lamblia (6.8%), and four helminthic: Hymenolepis nana (0.06%), Enterobius vermicularis (14.7%), Ascaris lumbricoides (3.3%), Trichuris trichiura (1.8%). The overall prevalence of intestinal parasite infections amounted to 24.6% (1207/4913), with a highly significant difference (p < 0.001) between particular sites (range 14.4%-43.8%) (Figure 1). Helminthic infections (810) were significantly more frequent (p < 0.001) as compared to both protozoan (296) and combined helminthic-protozoan infections (101). Of these, two species (G. lamblia, E. vermicularis) were found in all examined regions, three (E. coli, A. lumbricoides, T. trichiura) were detected in two or more, while four species (E. histolytica, E. hartmanni, I. bütschlii, H. nana) were each found in a single region (Figure 2). The predominant species (E. coli, G. lamblia, E. vermicularis, A. lumbricoides, T. trichiura) were distributed at considerably different prevalence rates, with a significant difference between the minimal and maximal values (p < 0.01). Of 91 settlements examined, intestinal parasites were found in all but one. However, the prevalence rates in 90 settlements varied significantly (p = 0.0004), from a low of 5.9% to a high of 66.7%. Thus, according to the World Health Organization criteria [19], infections with the four clinically relevant species (G. lamblia, E. vermicularis, A. lumbricoides, T. trichiura) ranged from sporadic to endemic and hyperendemic (Figure 3). The results obtained provide the basic epidemiological data about intestinal parasite infections in Serbia, and indicate their significance in terms of both the number of species and their respective prevalence rates. Given the significant differences obtained in the frequency and distribution of particular parasite infections in different regions, a programme for the control of these infections in Serbia should obviously include a wide variety of measures.

Adolescent↗
PubMed2005

Parasite prevalence and richness in sympatric colobines: effects of host density.

Factors that influence proximity and the number and duration of contacts among individuals can influence parasite transmission among hosts, and thus parasite prevalence and species richness are expected to increase with increasing host density. To examine this prediction we took advantage of a unique situation. Following the clearing of a forest fragment that supported red colobus (Piliocolobus tephrosceles) and black-and-white colobus (Colobus guereza), the animals moved into a neighboring fragment that we had been monitoring for a number of years and for which we had described the primate parasite community. After the animals immigrated into the fragment, the colobus populations more than doubled and colobus density became almost twice that found in Kibale National Park, Uganda. Despite this increase in host density, the richness of the parasite community did not increase. However, in both colobus species the prevalence of Trichuris sp., the only commonly occurring gastrointestinal parasite, increased. Over the next 5 years the prevalence and intensity of infection of Trichuris sp. in red colobus declined and their population numbers slowly increased. In contrast, the prevalence and intensity of infection of Trichuris sp. increased in black-and-white colobus and remained high following the immigration, and their population size declined. While Trichuris sp. infections are typically asymptomatic, we consider it a possibility that they contributed to the decline of the black-and-white colobus, and that the red colobus may be serving as a reservoir for Trichuris, thereby increasing the infection risk for black-and-white colobus.

Animals↗
PubMed2000

Using parasites as biological tags of fish populations: a dynamical model.

A simple model of macro-parasitic infections has been used to evaluate the potential use of parasites as biological tags of fish populations. In the model, the parasite-host interaction is regulated by a birth-death process, and parasites can only be acquired by the non-specific migratory host population in a particular area of the space domain. In this case, we show that parasites can be successfully used for stocks identification and to describe the migratory routes taken by some marine fish species.

Animals↗
PubMed2000

The evolution of parasite virulence and transmission rate in a spatially structured population.

If the transmission occurs through local contact of the individuals in a spatially structured population, the evolutionarily stable (ESS) traits of parasite might be quite different from what the classical theory with complete mixing predicts. In this paper, we theoretically study the ESS virulence and transmission rate of a parasite in a lattice-structured host population, in which the host can send progeny only to its neighboring vacant site, and the transmission occurs only in between the infected and the susceptible in the nearest-neighbor sites. Infected host is assumed to be infertile. The analysis based on the pair approximation and the Monte Carlo simulation reveal that the ESS transmission rate and virulence in a lattice-structured population are greatly reduced from those in completely mixing population. Unlike completely mixing populations, the spread of parasite can drive the host to extinction, because the local density of the susceptible next to the infected can remain high even when the global density of host becomes very low. This demographic viscosity and group selection between self-organized spatial clusters of host individuals then leads to an intermediate ESS transmission rate even if there is no tradeoff between transmission rate and virulence. The ESS transmission rate is below the region of parasite-driven extinction by a finite amount for moderately large reproductive rate of host; whereas, the evolution of transmission rate leads to the fade out of parasite for small reproductive rate, and the extinction of host for very large reproductive rate.

Animals↗
PubMed2005

Comparative studies on goby (Teleostei) parasite communities from the North and Baltic Sea.

The parasite communities of three goby species from the marine North and the brackish Baltic Sea were compared. The samples of summer 1992/93 from Helgoland, Lubeck and Kiel Bight comprised a parasite spectrum of 4-5 in Pomatoschistus microps, 2-3 in P. pictus or 3-8 parasite species in Gobiusculus flavescens. The highest numbers were found in Kiel Bight whereas those of Helgoland and Lubeck Bight differed between 3 and 7, respectively. In comparing the species identity of the studied localities the value was intermediate in P. microps, low in P. pictus and zero in G. flavescens. Values of prevalence and abundance were clearly lower in Helgoland than in Baltic localities. The prey of Helgoland goby populations comprised meio- and macrobenthos in P. microps, predominantly macrobenthos but also meiobenthos and some plankton in P. pictus, and predominantly plankton and some benthos in G. flavescens. Former studies (Zander in J Zool Syst Evol Res 32:220 1994) revealed a greater variability of prey choice in the Baltic. The greater parasite richness in the Baltic compared with that of Helgoland, may lie on better adaptations of genuine brackish components, lower defence mechanisms of hosts as a consequence of lower salinity, and greater variability in habitat choice. The effect of several filters on the colonisation of parasites in hosts is submitted here in a model.

Animals↗
PubMed1994

The disposition of antiparasitic drugs in relation to the development of resistance by parasites of livestock.

The kinetic and dynamic disposition of endo- and ectoparasiticides in livestock in relation to development of resistance is examined. Based on the modes of action of antiparasitic drugs, maximum activity necessitates that the parasite be exposed to 'toxic' concentrations for as great a duration as possible. In contrast, exposure to non-lethal discriminating drug concentrations has a significant potential to promote the development of resistance. Orally administered anthelmintics quickly associate with particulate digesta in the rumen; their subsequent desorption from particulate matter as it vacates the rumen maintains the duration of metabolite availability. The flow rate of digesta increases with feed intake and the presence of gastrointestinal parasites, and together with other parasite-induced physiological changes to the gut, contributes to reduced duration of drug availability. The potential for orally administered drugs to bypass the rumen, due to closure of the oesophageal groove, exacerbates the effect. Once absorbed, the metabolite concentration with time profile progressively decreases, the rate depending upon the chemical nature of the drug and the type and condition of the host into which it was administered. The greater hepatic activity of goats speeds drug elimination, the lower dose equivalent availability increases the potential for generation of drug resistance in parasites of goats as compared to sheep. Parasites whose resistance is generated in goats may be then transferred to sheep. Similar distribution/elimination kinetics apply to topically administered insecticides of sheep. The progressively reducing concentrations expose ectoparasites to discriminating drug levels, again contributing to the development of resistance. It is anticipated that a greater understanding of the physiological/pharmacological effects which are described in this review will permit the more efficient use of existing and future antiparasitic drugs.

Administration, Oral↗
PubMed1994

Parasite control in transhumant situations.

Transhumance is defined as 'seasonal moving of livestock to regions of different climate'. It is an integral part of livestock production in many parts of the world and takes several forms including moving of livestock from lowland to mountainous pastures or from dry to humid areas. The impact of transhumance on parasite populations of livestock and on parasite control is described, mainly using examples from Europe. The epidemiology of trichostrongylidosis of cattle, mainly caused by Ostertagia ostertagi and Cooperia oncophora, is characterised by prolonged survival of overwintered infective larvae until the end of June. Cattle moved to such contaminated pastures in a transhumant grazing system are exposed to these larvae and may be protected, during the second half of the grazing season until autumn, by a late application (June/July) of an intraruminal drug-release device. Community pastures used in a transhumant system with mixed grazing of young cattle originating from various farms may enhance transmission of dictyocaulosis. Therefore, specific prophylactic measures are required. Hill sheep nematode populations may differ from those in lowland sheep in that Haemonchus contortus generally plays a minor role in hill sheep in which Ostertagia circumcincta and Nematodirus spp. predominate. Infections with Fasciola hepatica and Dicrocoelium dendriticum can be acquired on mountainous pastures by cattle, sheep and other livestock grazing in a transhumant system as intermediate hosts of these parasites may find suitable habitats in these regions. There is evidence that in the prealpine and alpine area both parasites are mainly transmitted in two-season cycles. Further examples for the impact of transhumance on parasite-host inter-relationships include cysticercosis in cattle, echinococcosis, psoroptic manage in sheep, tick-borne fever of cattle, and hypodermosis in cattle. These are described and discussed.

Animal Husbandry↗
PubMed2005

Coevolutionary interactions between host and parasite genotypes.

More than 20 years after Dawkins introduced the concept of "extended phenotype" (i.e. phenotypes of hosts and parasites result from interactions between the two genomes) and although this idea has now reached contemporary textbooks of evolutionary biology, most studies of the evolution of host-parasite systems still focus solely on either the host or the parasite, neglecting the role of the other partner. It is important to consider that host and parasite genotypes share control of the epidemiological parameters of their relationship. Moreover, not only the traits of the infection but also the genetic correlations among these and other traits that determine fitness might be controlled by interactions between host and parasite genotypes.

Alleles↗
PubMed1997

Mathematical models of parasite responses to host immune defences.

We examine the evolution of microparasites in response to the immune system of vertebrate hosts. We first describe a simple model for an acute infection. This model suggests that the within-host dynamics of the microparasite will be a 'race' between parasite multiplication and a clonally expanding response by the host immune system, resulting either in immune-mediated clearance or host death. In this very simple model, in which there is only a single parasite and host genotype, maximum transmission is obtained by parasites with intermediate rates of growth (and virulence). We examine how these predictions depend on key assumptions about the parasite and the host, and consider how this model may be expanded to incorporate the effect of additional complexities such as host-parasite co-evolution, host polymorphism, and multiple infections.

Animals↗
PubMed2006

The evolution of parasite manipulation of host dispersal.

We investigate the evolution of manipulation of host dispersal behaviour by parasites using spatially explicit individual-based simulations. We find that when dispersal is local, parasites always gain from increasing their hosts' dispersal rate, although the evolutionary outcome is determined by the costs-to-benefits ratio. However, when dispersal can be non-local, we show that parasites investing in an intermediate dispersal distance of their hosts are favoured even when the manipulation is not costly, due to the intrinsic spatial dynamics of the host-parasite interaction. Our analysis highlights the crucial importance of ecological spatial dynamics in evolutionary processes and reveals the theoretical possibility that parasites could manipulate their hosts' dispersal.

Adaptation, Physiological↗
PubMed2000

The coevolution of parasites with host-acquired immunity and the evolution of sex.

Here I present a deterministic model of the coevolution of parasites with the acquired immunity of their hosts, a system in which coevolutionary oscillations can be maintained. These dynamics can confer an advantage to sexual reproduction within the parasite population, but the effect is not strong enough to outweigh the twofold cost of sex. The advantage arises primarily because sexual reproduction impedes the response to fluctuating epistasis and not because it facilitates the response to directional selection-in fact, sexual reproduction often slows the response to directional selection. Where the cost of sexual reproduction is small, a polymorphism can be maintained between the sexuals and the asexuals. A polymorphism is maintained in which the advantage gained due to recombination is balanced by the cost of sex. At much higher costs of sex, a polymorphism between the asexual and sexual populations can still be maintained if the asexuals do not have a full complement of genotypes available to them, because the asexuals only outcompete those sexuals with which they share the same selected alleles. However, over time we might expect the asexuals to amass the full array of genotypes, thus permanently eliminating sexuals from the population. The sexuals may avoid this fate if the parasite population is finite. Although the model presented here describes the coevolution of parasites with the acquired immune responses of their hosts, it can be compared with other host-parasite models that have more traditionally been used to investigate Red Queen theories of the evolution of sex.

Animals↗
PubMed1985

Prevalence of some internal parasites recovered at necropsy of Thoroughbreds born in 1982 in Kentucky.

A total of 89 Thoroughbreds, 14 to 333 days old (born in 1982), were examined at necropsy for certain internal parasites during a 1-year-period, Mar 1, 1982, to Feb 28, 1983. The eyes of 73 of the horses and the cranial mesenteric arteries of 71 were examined. Specific interest was on prevalence of parasites according to month of the year and age of the horses at necropsy. Parasites recovered (first month-last month infected horse found) were as follows: Thelazia lacrymalis (eyes) immature and mature (June - February); Habronema/Draschia (lungs) immature (May - September); Habronema muscae (stomach) immature (July - February) and mature (September - February); Draschia megastoma (stomach) immature (August - December), mature (August - February), and lesions (September - February); Gasterophilus intestinalis (stomach) 2nd instars (July - February) and 3rd instars (August - February); Gasterophilus nasalis (stomach) 2nd instars (August - November) and 3rd instars (August - February); Parascaris equorum (lungs) immature (March - November), P equorum (small intestine) immature (March - February), and mature (July - February); Strongyloides westeri (small intestine) mature (March - September); Anoplocephala perfoliata (cecum) immature and mature (August - February); Strongylus vulgaris (cranial mesenteric artery) immature and mature (May - February). Other parasites recovered, but only from 1 or 2 horses each (months found in infected horses) were: Thelazia skrjabini (eyes) (October), Dictyocaulus arnfieldi (lungs) (January); Trichostrongylus axei (stomach) (October); Anoplocephala magna (small intestine) (October, November); S vulgaris (cecum) (November); Strongylus edentatus (cecum) (January); Setaria spp (abdominal cavity) (January). Influence of probable chemotherapy of the horses on prevalence of the parasites is discussed.

Age Factors↗
PubMed1996

Control of intestinal parasitic infections in Seychelles: a comprehensive and sustainable approach.

Intestinal parasitic infections have been perceived as a public health problem in Seychelles for decades. A comprehensive strategy to reduce morbidity and, in the long term, transmission of intestinal parasites has been implemented successfully since 1993. Management of the programme is integrated into the well established primary health care system, with control activities being undertaken through existing health facilities. The strategy is based on periodic chemotherapy of schoolchildren, intense health education and improvement of sanitation and safe water supply. The initial objectives of the control programme were met after 2 years of activities, with an overall reduction in prevalence of intestinal parasitic infections of 44%. The intensity of infection with Trichuris trichiura, the commonest parasite, was halved (from 780 to 370 eggs per g of faeces). The programme's integrated approach, in concert with political commitment and limited operational costs, is a warranty for the future sustainability of control activities. The programme can be seen as a model for other developing countries, even where health and socioeconomic conditions are different and the control of parasitic infections will need a much longer-term commitment.

Adolescent↗