Nematode intestinal parasites of children in rural Guinea, Africa: prevalence and relationship to geophagia.
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BACKGROUND: Intestinal parasitism is common among children in developing countries, but the risk factors for infection are not well characterized. METHODS: A stool examination was performed on 286 randomly selected children aged 1-18 years from three rural villages in Guinea, Africa. Information collected by questionnaire was used to examine the relationship between geophagia and infection with intestinal nematodes acquired by ingestion versus skin penetration. RESULTS: Fifty-three per cent of children were infected by at least one type of soil-transmitted nematode. Geophagia was reported by parents to occur in 57%, 53%, and 43%, of children ages 1-5, 6-10, and 11-18 years, respectively. The pattern of geophagia by age and gender of the children more closely resembled the infection pattern for the two orally acquired and soil-transmitted nematodes (Ascaris lumbricoides, Trichuris trichiura) than it did the infection pattern for the two soil-transmitted nematodes that infect by skin penetration (hookworm, Strongyloides stercoralis). CONCLUSIONS: These findings demonstrate that geophagia is an important risk factor for orally acquired nematode infections in African children. Education regarding geophagia prevention should be an integral component of any soil-transmitted parasite control programme. (+info)
Cost of school-based drug treatment in Tanzania. The Partnership for Child Development.
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It has been argued that targeting delivery of anthelmintics to school-children by taking advantage of the existing education infrastructure and administrative system can be one of the most cost-effective approaches in minimizing the intensity of infections with both schistosomiasis and major intestinal nematodes in many developing countries. The study was conducted in January 1997, shortly after the completion of the drug intervention programme. This paper provides an analysis of the costs of providing age-targeted treatment of school-children for urinary schistosomiasis using praziquantel and for intestinal nematodes using albendazole as an integral part of the School Health Programme in Tanga Region, Tanzania. The analysis shows that the total financial cost of the intervention programme in 1996 prices was US$54 252.28 (exchange rate: TSH 573 = US$1). Of this amount, the cost of drugs constitutes 80.6%, while the delivery cost appears relatively low, representing just below 20%. Even when the opportunity cost of unpaid days of labour input is included, the cost of drugs still remains the highest cost component of the intervention (55.8%). In the current epidemiological and logistic setting of Tanzania, the financial cost per child treated using praziquantel, which involved prior screening at the school level, was US$0.79, while treatment using albendazole was as low as US$0.23, of which US$0.20 was drug purchase cost. It is concluded that the base cost of delivering a universal, standard, school-based health intervention such as albendazole can be as low as US$0.03 per child tested, but even a very slight increase in the complexity of delivery can have a very significant impact on the cost of intervention. (+info)
Effects of continuous ivermectin treatment from birth to puberty on growth and reproduction in dairy heifers.
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The effect of continuous ivermectin treatment from birth to puberty on growth and reproductive performance was studied in Holstein heifer calves grown on pastures in comparison to naturally nematode-infected, untreated animals. Ivermectin effectively abated the presence of nematode eggs in feces. Eggs per gram (EPG) in parasitized animals increased rapidly from wk 12 to 18 of age and then decreased. Animals treated with ivermectin grew faster than untreated ones, and differences in body weight became significant at 6 wk of life, even before eggs appeared in the feces of either treatment group. Ivermectin-treated heifers reached puberty 3 wk earlier than infected ones as assessed with serum progesterone concentrations (ivermectin, 30.4 +/- .8 vs untreated, 33.7 +/- 1.3 wk of age). This delay was not directly related to body weight. In addition, pelvic area at 39 wk and at 15 mo of age was increased in treated heifers (8 and 11%, respectively) compared with parasitized animals. No differences in the wither heights were observed. We conclude that ivermectin treatment in dairy heifers may increase growth rate during development, advance the onset of ovarian function, and positively affect yearling pelvic area. (+info)
Heritable variation in resistance to gastro-intestinal nematodes in an unmanaged mammal population.
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The impact of parasites on natural populations has received considerable attention from evolutionary biologists in recent years. Central to a number of theoretical developments during this period is the assumption of additive genetic variation in resistance to parasites. However, very few studies have estimated the heritability of parasite resistance under field conditions, and those that have are mainly restricted to birds and their ectoparasites. In this paper, to our knowledge, we show for the first time in a free-ranging mammal population, Soay sheep (Ovis aries) living on the islands of St Kilda, that there is significant heritable variation in resistance to gastrointestinal nematodes. This result is consistent with earlier studies on this population which have indicated locus-specific associations with parasite resistance. We discuss our results in the context of current studies examining heritable resistance to parasites in domestic sheep and the possible mechanisms of selective maintenance of genetic variation for resistance to gastrointestinal nematodes in the St Kilda Soay sheep population. (+info)
Wild rodents as experimental intermediate hosts of Lagochilascaris minor Leiper, 1909.
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A total of 25 specimens of Cavia porcellus (guinea pig), 5 Dasyprocta agouti (agouti), and 22 Calomys callosus (vesper mice) were inoculated with infective eggs of Lagochilascaris minor. The inoculum was prepared with embryonated eggs and orally administered to each individual animal through an esophagus probe. In parallel, 100 specimens of Felis catus domesticus were individually fed with 55-70 nodules containing 3rd-stage larvae encysted in tissues of infected rodents. Animals were examined and necropsied at different time intervals. The migration and encystment of L3 larva was observed in viscera, skeletal muscle, adipose and subcutaneous tissues from all rodents. Adult worms localized at abscesses in the cervical region, rhino, and oropharynx were recovered from domestic cats inoculated with infected rodent tissues. Through this study we can conclude that: (1) wild rodents act as intermediate hosts, characterizing this ascarid heteroxenic cycle; (2) in natural conditions rodents could possibly act as either intermediate hosts or paratenic hosts of Lagochilascaris minor; (3) despite the occurrence of an auto-infecting cycle, in prime-infection of felines (definite hosts) the cycle is only completed when intermediate hosts are provided; and (4) in the wild, rodents could serve as a source of infection for humans as they are frequently used as food in regions with the highest incidence of human lagochilascariasis. (+info)
The eosinophilic response and haematological recovery after treatment for Plasmodium falciparum malaria.
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To examine a possible relationship between the immune response and haematological recovery after acute falciparum malaria, we followed peripheral blood eosinophil counts and haemoglobin concentrations for 4 weeks after starting effective treatment in 70 adult Thai patients. Eosinophils are induced by Th-2 cytokines as well as other stimuli. Eosinophil counts were elevated in only 8 (11%) of the subjects at presentation, but were increased in 65 (93%) by day 7. Eosinophil counts then decreased markedly by day 14, followed by a second increase until day 28. A significant positive correlation was found between peak eosinophil counts on day 7 and the haemoglobin concentration on day 28, both in 16 subjects without stool parasites (r = 0.65, P = 0.006) and in 54 patients with stool parasites (r = 0.32; P = 0.0019). These results suggest that a robust eosinophilic response shortly after completing antimalarial therapy predicts a good recovery from malaria-associated anaemia. (+info)
Evaluation of Streck tissue fixative, a nonformalin fixative for preservation of stool samples and subsequent parasitologic examination.
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We undertook a study to evaluate Streck tissue fixative (STF) as a substitute for formalin and polyvinyl alcohol (PVA) in fecal preservation. A comparison of formalin, PVA, (mercuric chloride based), and STF was done by aliquoting fecal samples into each fixative. Stool specimens were collected in Haiti, and parasites included Cyclospora cayetanensis, Giardia intestinalis, Entamoeba coli, Iodamoeba butschlii, Endolimax nana, Ascaris lumbricoides, Trichuris trichiura, Strongyloides stercoralis, and Necator americanus. Preserved stools were examined at various predetermined times (1 week, 1 month, and 3 months) to establish the quality of the initial preservation as well as the suitability of the fixative for long-term storage. At each time point, stool samples in fixatives were examined microscopically as follows: (i) in wet mounts (with bright-field and epifluorescence microscopy), (ii) in modified acid-fast-, trichrome-, and safranin-stained smears, and (iii) with two commercial test kits. At the time points examined, morphologic features remained comparable for samples fixed with 10% formalin and STF. For comparisons of STF- and 10% formalin-fixed samples, specific findings showed that Cyclospora oocysts retained full fluorescence, modified acid-fast- and safranin-stained smears of Cryptosporidium and Cyclospora oocysts were equal in staining quality, and results were comparable in the immunofluorescence assay and enzyme immunoassay commercial kits. Stool fixed in STF and stained with trichrome showed less-than-acceptable staining quality compared with stool fixed in PVA. STF provides an excellent substitute for formalin as a fixative in routine examination of stool samples for parasites. However, modifications to the trichrome staining procedures will be necessary to improve the staining quality for protozoal cysts fixed in STF to a level comparable to that with PVA. (+info)
Immunogenic glycoconjugates implicated in parasitic nematode diseases.
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Parasitic nematodes infect billions of people world-wide, often causing chronic infections associated with high morbidity. The greatest interface between the parasite and its host is the cuticle surface, the outer layer of which in many species is covered by a carbohydrate-rich glycocalyx or cuticle surface coat. In addition many nematodes excrete or secrete antigenic glycoconjugates (ES antigens) which can either help to form the glycocalyx or dissipate more extensively into the nematode's environment. The glycocalyx and ES antigens represent the main immunogenic challenge to the host and could therefore be crucial in determining if successful parasitism is established. This review focuses on a few selected model systems where detailed structural data on glycoconjugates have been obtained over the last few years and where this structural information is starting to provide insight into possible molecular functions. (+info)