Oesophagostomum stephanostomum causing parasitic granulomas in wild chimpanzees (Pan troglodytes verus) of Taï National Park, Côte d'Ivoire.

Nematodes belonging to the genus Oesophagostomum frequently infect wild chimpanzees (Pan troglodytes) across widely separated field sites. Nodular lesions (granulomas) containing Oesophagostomum are commonly seen in the abdomen of infected chimpanzees post-mortem. At Taï National Park, Côte d'Ivoire, previous studies have identified larvae of a variety of Oesophagostomum spp. in wild chimpanzee stool, based on sequencing of larval DNA, and nodular lesions associated with Oesophagostomum, identified morphologically to the genus level but not sequenced. Here we present three recent cases of parasitic granulomas found post-mortem in chimpanzees at Taï. We complement descriptions of gross pathology, histopathology and parasitology with PCR and sequencing of DNA isolated from the parasitic nodules and from adult worms found inside the nodules. In all three cases, we identify Oesophagostomum stephanostomum as the causative agent. The sequences from this study were identical to the only other published sequences from nodules in nonhuman primates-those from the wild chimpanzees of Gombe, Tanzania.

Molecular method for the semiquantitative identification of gastrointestinal nematodes in domestic ruminants.

Standard diagnostic methods currently in use for the identification of helminth infections in ruminants are based on the morphological analysis of immature and adult stages of parasites. This paper describes a method for the semiquantitative identification of nematodes, mainly Trichostrongyloidea, at species-level resolution. The method is based on amplification and fragment analysis followed by minisequencing of the ITS-2 region (internal transcribed spacer 2) of the ribosomal DNA of parasite eggs or larvae. This method allows for the identification of seven genera (Chabertia, Cooperia, Haemonchus, Oesophagostomum, Ostertagia, Teladorsagia, and Trichostrongylus) and 12 species (Chabertia ovina, Cooperia curticei, Cooperia punctata, Cooperia oncophora/Cooperia surnabada, Haemonchus contortus, Haemonchus placei, Haemonchus longistipes, Oesophagostomum asperum, Oesophagostomum radiatum, Ostertagia ostertagi, Trichostrongylus axei, and Trichostrongylus colubriformis) of infectious nematodes of domestic ruminants. The concordance between the morphological and molecular analyses in the detection of genera ranged from 0.84 to 0.99, suggesting the proposed detection method is specific, semiquantitative, less laborious, and highly cost-efficient.

Oesophagostomiasis in non-human primates of Gombe National Park, Tanzania.

Oesophagostomum sp. is a parasitic nematode that frequently infects wild chimpanzees. Although nodular lesions are commonly associated with infection, some wild chimpanzee populations seem to tolerate Oesophagostomum nodular lesions while those at Gombe and other sites suffer from associated morbidity and mortality. From August 2004 to December 2013, we examined demographic (i.e., age, sex) and individual correlates (i.e., fecal consistency, Oesophagostomum egg production) to Oesophagostomum-associated pathology in 14 individually recognized chimpanzees at Gombe Stream National Park, Tanzania. In addition, we characterized Oesophagostomum-associated pathology in 14 individual sympatric primates including baboons, colobus, and cercopithecid monkeys. In five chimpanzees, there was no evidence of any significant underlying disease aside from oesophagostomiasis to explain the thin condition or diarrhea. All five of these chimpanzees had moderate to numerous parasitic nodules. In general, nodules were more numerous in older chimpanzees. Three of four chimpanzees with the highest average Oesophagostomum egg counts in feces collected during the year prior to their death had numerous parasitic nodules at necropsy. In contrast, the four chimpanzees with the lowest egg counts had only moderate numbers of nodules. No association (P = 0.74) was noted between frequency of diarrhea in the year prior to death and the number of nodules noted at necropsy. Nodules were also present in all baboons examined documenting pathology associated with Oesophagostomum infection in wild baboons. In contrast, no lesions were noted in colobus or cercopithecid monkeys, although it is uncertain if they are infected as no fecal studies have been completed in these species to date at Gombe. Sequence of DNA isolated from nodules in chimpanzees matched (99%) Oesophagostomum stephanostomum. Further research is needed to identify the types of Oesophagostomum causing lesions in baboons and to determine if baboons suffer from these infections. Am. J. Primatol. 80:e22572, 2018. © 2016 Wiley Periodicals, Inc.

Seasonal dynamics of endoparasitic infections at an organic goat farm and the impact of detected infections on milk production.

This study evaluated patterns and species composition of parasitic infections detected over a 1-year period at an organic goat farm. As a result of coprological examination, the overall prevalence of observed strongylids (99%), coccidia of the genus Eimeria (98%), and Muellerius capillaris lungworms (93%) was calculated. The most prevalent strongylids recovered from incubated fecal samples were Haemonchus contortus (42%), genera Trichostrongylus (23%), Oesophagostomum columbianum (13%), and Teladorsagia circumcincta (11%). A maximum intensity of coccidia infection 5150 oocysts per gram, strongylids infection 9900 eggs per gram and lungworm infection 867.26 larvae per gram were detected. The various effects (including environment, host, and parasites) on milk yield, lactose, protein, and fat were evaluated using generalized linear mixed models. Milk yield (P < 0.0001), milk fat (P < 0.01), and lactose (P < 0.0001) were affected by month, i.e., these parameters were influenced by the month of the year, regardless of the individual goat. With the intensity of infection detected in our study, only protein content was affected (P < 0.01) by parasitic infection (exclusively caused by strongylids). Correlation between measurements from one individual revealed that the goat itself can substantially decrease protein content but has much less of an effect on fat, milk yield, and lactose. Based on our results, we can conclude that a low intensity of parasitic infections does not significantly affect milk yield and the qualitative parameters of milk.

Study of the gastrointestinal parasitic fauna of captive non-human primates (Macaca fascicularis).

The aim of this study was to examine helminths and protozoans in cynomolgus macaques (Macaca fascicularis) imported from registered breeding facilities in China and their relation to health risks for non-human primate handlers in biomedical research centers and in breeding facilities. Fresh fecal samples were collected from a total of 443 M. fascicularis and analyzed by copromicroscopical analysis, immunoenzymatic, or molecular assays. As to helminths, whose eggs were shed in 2.03% of the samples, Trichuris and Oesophagostomum were the only two taxa found, with low prevalence and low eggs per gram (EPG) values. Protozoans were more frequently detected (87.40%), with Entamoeba coli (85.19%) and Endolimax nana (79.26%) as the most prevalent species shed. Other parasites found by fecal smear examination were uninucleated-cyst-producing Entamoebas (78.52%), Iodamoeba bütschlii (42.96%), and Chilomastix mesnili (24.44%), while cysts of Balantidium coli (22.2%) were only observed by sedimentation. No coproantigens of Giardia duodenalis, Cryptosporidium spp., and Entamoeba histolytica complex were detected. Blastocystis sp. infection was noticed in 87.63% of macaques by PCR. These cynomolgus monkeys were infected with many subtypes (ST1, ST2, ST3, ST5, and ST7), where the predominant Blastocystis sp. subtypes were ST2 (77.5%), followed by ST1 (63.5%). Data collected confirmed the presence of potentially zoonotic parasites and a high parasite diversity, suggesting the need for appropriate and sensitive techniques to adequately control them and related health risks for handlers of non-human primates in biomedical research centers and in breeding facilities.

Sequence variation in two mitochondrial DNA regions and internal transcribed spacer among isolates of the nematode Oesophagostomum asperum originating from goats in Hunan Province, China.

The present study examined sequence variability in two mitochondrial DNA (mtDNA) regions, namely cytochrome c oxidase subunit 1 (cox1) and NADH dehydrogenase subunit 1 (nad1), and internal transcribed spacer (ITS) of nuclear ribosomal DNA (rDNA) among Oesophagostomum asperum isolates from goats in Hunan Province, China. A portion of the cox1 (pcox1), nad1 (pnad1) genes and the ITS (ITS1+5.8S rDNA+ITS2) rDNA were amplified by polymerase chain reaction (PCR) separately from adult O. asperum individuals and the representative amplicons were subjected to sequencing from both directions. The lengths of pcox1, pnad1 and ITS rDNA were 366 bp, 681 bp and 785 bp, respectively. The A+T contents of gene sequences were 71.5-72% for pcox1, 73.7-74.2% for pnad1 and 58-58.8% for ITS rDNA. Intra-specific sequence variations within O. asperum were 0-1.6% for pcox1, 0-1.9% for pnad1 and 0-1.7% for ITS rDNA, while inter-specific sequence differences among members of the genus Oesophagostomum were significantly higher, being 11.1-12.5%, 13.3-17.7% and 8.5-18.6% for pcox1, pnad1 and ITS rDNA, respectively. Phylogenetic analyses using combined sequences of pcox1 and pnad1, with three different computational algorithms (Bayesian inference, maximum likelihood and maximum parsimony), revealed distinct groups with high statistical support. These findings demonstrated the existence of intra-specific variation in mtDNA and rDNA sequences among O. asperum isolates from goats in Hunan Province, China, and have implications for studying molecular epidemiology and population genetics of O. asperum.

Molecular identification of the strongyloid nematode Oesophagostomum aculeatum in the Asian wild elephant Elephas maximus.

The transmission of zoonoses by wildlife, including elephants, is a growing global concern. In this study, we screened for helminth infections among Asian wild elephants (Elephas maximus) of the Salakpra Wildlife Sanctuary, Kanchanaburi, Thailand. Elephant faecal samples (45) were collected from the sanctuary grounds during January through November 2013 and assayed individually using the tetranucleotide microsatellite technique. Microscopic examination indicated a high prevalence of strongylids (93.0%) and low prevalences of trichurids (2.3%) and ascarids (2.3%). To identify the strongylid species, small subunit (SSU) rDNA sequences were amplified from copro-DNA and compared with sequences in GenBank. The generated SSU-rDNA sequences comprised five distinct haplotypes that were closely related to Oesophagostomum aculeatum. A phylogenetic analysis that incorporated related nematodes yielded a tree separated into two main clades, one containing our samples and human and domestic animal hookworms and the other consisting of Strongyloides. The present results indicate that O. aculeatum in local elephants is a potential source of helminthiasis in human and domestic animals in this wild-elephant irrupted area.

High frequency of leaf swallowing and its relationship to intestinal parasite expulsion in "village" chimpanzees at Bulindi, Uganda.

Self-medication by great apes to control intestinal parasite infections has been documented at sites across Africa. Chimpanzees (Pan troglodytes) swallow the leaves of certain plant species whole, without chewing. Previous studies demonstrated a relationship between chimpanzee leaf swallowing and expulsion of nematode worms (Oesophagostomum sp.) and tapeworms (Bertiella sp.) in dung. We investigated the relationship between leaf swallowing and parasite expulsion in chimpanzees inhabiting a fragmented forest-farm mosaic at Bulindi, Uganda. During 13 months whole undigested leaves occurred in chimpanzee dung at a considerably higher frequency (10.4% of dungs) than at other sites (0.4-4.0%). Leaf swallowing occurred year-round and showed no pronounced seasonality. Chimpanzees egested adults of multiple species of Oesophagostomum (including O. stephanostomum) and proglottids of two tapeworms-Bertiella sp. and probably Raillietina sp. The latter may not be a true infection, but the byproduct of predation on domestic fowl. Compared to previous studies, the co-occurrence of whole leaves and parasites in chimpanzee dung was low. Whereas the presence of leaves in dung increased the probability of adult nematode expulsion, no association between leaf swallowing and the shedding of tapeworm proglottids was apparent. Anthropogenic habitat changes have been linked to alterations in host-parasite interactions. At Bulindi, deforestation for agriculture has increased contact between apes and people. Elevated levels of leaf swallowing could indicate these chimpanzees are especially vulnerable to parasite infections, possibly due to environmental changes and/or increased stress levels arising from a high frequency of contact with humans. Frequent self-medication by chimpanzees in a high-risk environment could be a generalized adaptation to multiple parasite infections that respond differently to the behavior. Future parasitological surveys of apes and humans at Bulindi are needed for chimpanzee health monitoring and management, and to investigate the potential for disease transmission among apes, people, and domestic animals.

Molecular identification of Oesophagostomum and Trichuris eggs isolated from wild Japanese macaques.

Natural habitat fragmentation and reducing habitat quality have resulted in an increased appearance of Japanese macaques, Macaca fuscata (Gray, 1870), in suburban areas in Japan. To investigate the risk of zoonotic infections, a coprological survey of helminth eggs passed by wild Japanese macaques was carried out in 2009 and 2010 in Shiga Prefecture, Japan. Microscopic examination found helminth eggs in high prevalence, and nucleotide sequencing of DNA extracted from the eggs identified Oesophagostomum cf. aculeatum and Trichuris trichiura. A fecal culture also detected infective larvae of Strongyloides fuelleborni. These zoonotic nematodes pose a potential health issue to local people in areas frequented by Japanese macaques.

Some aspects of nematode infection in pigs from small herds.

Two traditionally maintained, small herds from southern Poland, with 8 and 12 sows, respectively, were surveyed coprologically during 2006-2007. In one of the herds, while deworming a group of sows with levamisole, faecal samples were collected on Day -7, Day 0 (the day of treatment) and Day 10, in order to assess the therapeutic effect of the drug. Coprological investigation was performed also in 26 fatteners originating from other small farms and slaughtered in a local abattoir, with their intestines washed through for the presence of roundworms. In both herds examined, Ascaris suum and Oesophagostomum spp. were prevalent, whilst Trichuris suis appeared only very rarely. Mainly fatteners, replacement gilts and young sows were highly infected with A. suum. The roundworm occurrence in 2- 3-week-old piglets, with the intensity of 300 eggs per gram of faeces (EPG), indicated the possibility of parasite transmission to offspring very early in age. The highest level of Oesophagostomum spp. infection was observed in sows, but weaners were also much affected. For the group of dewormed sows, the mean faecal egg count reduction (FECR) was estimated to be 77.1- 80.4%, suggesting the presence of resistant nodular worms. A very high false-positive A. suum egg counts found in slaughtered animals (240 to 320 EPG) testified to a high contamination level of the environment of small piggeries, as well. Since the reciprocal transmission of parasites between pigs and poultry might occur, it implies that the flocks should be raised separately.

Diversity and prevalence of gastrointestinal parasites in two wild Galago species in Gabon.

In this study, we characterize the diversity and estimated infection levels of gastrointestinal parasites circulating in two galago species, Galago demidoff and G. thomasi in two sites situated in the Southeastern forests of Gabon. Our study reveals that eleven parasites including nine helminthes (Ascaris spp., Ankylostoma spp., Dicrocoelium spp., Gongylonema spp., Oesophagostomum spp., Lemuricola spp., Strongyloides spp. Trichostrongylus spp. and Trichuris spp.) and two protozoans (Balantidium spp. and Entamoeba spp.) may infect Galago spp. with high infection rates. The results show that: a very similar parasite spectrum is found in both host species; all the taxa identified were previously observed in other Primate species and/or Man. They also show that age, gender and forest type may influence infection rates and/or parasite diversity found in a particular host and/or geographic area.

Leaf-swallowing in Nigerian chimpanzees: evidence for assumed self-medication.

A field study in Gashaka, Nigeria, adds the fourth subspecies of chimpanzee, Pan troglodytes vellerosus, to the list of African ape populations in which leaf-swallowing occurs. Unchewed herbaceous leaves of Desmodium gangeticum (Leguminosae-Papilionoideae) were recovered in 4% of 299 faecal samples of wild chimpanzees and clumps of sharp-edged grass leaves in 2%. The ingestion is believed to serve self-medicatory purposes because the leaves had a rough surface or were sharp-edged (which could be related to parasite control through a self-induced increase of gut motility), were not chewed, were excreted whole (indicating that they were not ingested for nutritional purposes), leaf-swallowing was restricted to the rainy season (during which time parasite re-infections are more common), and parasitic worms (Oesophagostomum stephanostomum) were found together with the leaves.

Mass treatment with albendazole reduces the prevalence and severity of Oesophagostomum-induced nodular pathology in northern Ghana.

Previous surveys conducted in northern Ghana where Oesophagostomum bifurcum is endemic showed that O. bifurcum-induced nodular pathology could be detected in up to 50% of the inhabitants. The impact of albendazole-based mass treatment to control both infection and morbidity is assessed and compared with the situation in a control area where no mass treatment has taken place. A significant reduction in the prevalence of infection based on stool cultures was achieved following two rounds of mass treatment in one year: from 52.6% (361/686) pre treatment to 5.2% (22/421) 1 year later (chi(1)(2)=210.1; P<0.001). At the same time, the morbidity marker of ultrasound-detectable nodules declined from 38.2% to 6.2% (chi(1)(2)=138.1; P<0.001). There was a shift from multinodular pathology, often seen in heavy infections, to uninodular lesions. In the control villages where no treatment took place, O. bifurcum infection increased from 17.8% (43/242) to 32.2% (39/121) (chi(1)(2)=9.6; P<0.001). Nodular pathology decreased slightly from 21.5% to 19.0%, but a higher proportion of these subjects developed multinodular pathology compared with baseline (chi(1)(2)=5.5; P=0.019). It is concluded that repeated albendazole treatment significantly reduces O. bifurcum-induced morbidity.

Distribution of human Oesophagostomum bifurcum, hookworm and Strongyloides stercoralis infections in northern Ghana.

A cross-sectional study was carried out in 216 randomly selected, representative rural villages in the northeastern part of Ghana from March 1995 to May 1998. Inhabitants of randomly selected households, stratified by age and gender, were included. The geographical position of villages was recorded with a global positioning system (GPS). The prevalence of Oesophagostomum, hookworm and Strongyloides stercoralis infections in a study population of 20250 people was determined by microscopic examination of larvae in stool cultures. The overall prevalence was 10.2, 50.6 and 11.6% for the three nematodes, respectively. Hookworm infections were seen in all but one (99.5%) and S. stercoralis in 88.4% of the 216 villages, while Oesophagostomum infections were found to be common in a limited area with prevalences varying from 0 to 75%. An association was found between Oesophagostomum and hookworm infection, both at the individual and at the village level. Spatial analysis of the prevalence data indicated that the endemic area is relatively clearly demarcated to the south of the study area.

Nodular Worm Infections in Wild Non-human Primates and Humans Living in the Sebitoli Area (Kibale National Park, Uganda): Do High Spatial Proximity Favor Zoonotic Transmission?

BACKGROUND: Nodular Oesophagostomum genus nematodes are a major public health concern in some African regions because they can be lethal to humans. Their relatively high prevalence in people has been described in Uganda recently. While non-human primates also harbor Oesophagostomum spp., the epidemiology of this oesophagostomosis and the role of these animals as reservoirs of the infection in Eastern Africa are not yet well documented. METHODOLOGY/PRINCIPAL FINDINGS: The present study aimed to investigate Oesophagostomum infection in terms of parasite species diversity, prevalence and load in three non-human primates (Pan troglodytes, Papio anubis, Colobus guereza) and humans living in close proximity in a forested area of Sebitoli, Kibale National Park (KNP), Uganda. The molecular phylogenetic analyses provided the first evidence that humans living in the Sebitoli area harbored O. stephanostomum, a common species in free-ranging chimpanzees. Chimpanzees were also infected by O. bifurcum, a common species described in human populations throughout Africa. The recently described Oesophagostomum sp. found in colobine monkeys and humans and which was absent from baboons in the neighboring site of Kanyawara in KNP (10 km from Sebitoli), was only found in baboons. Microscopic analyses revealed that the infection prevalence and parasite load in chimpanzees were significantly lower in Kanyawara than in Sebitoli, an area more impacted by human activities at its borders. CONCLUSIONS/SIGNIFICANCE: Three different Oesophagostomum species circulate in humans and non-human primates in the Sebitoli area and our results confirm the presence of a new genotype of Oesophagostomum recently described in Uganda. The high spatiotemporal overlap between humans and chimpanzees in the studied area coupled with the high infection prevalence among chimpanzees represent factors that could increase the risk of transmission for O. stephanostomum between the two primate species. Finally, the importance of local-scale research for zoonosis risk management is important because environmental disturbance and species contact can differ, leading to different parasitological profiles between sites that are close together within the same forest patches.

Experimental Oesophagostomum dentatum infections in the pig: worm populations resulting from trickle infections with three dose levels of larvae.

This paper describes the worm populations in pigs experimentally infected by trickle infections with different dose levels of the nodular worm, Oesophagostomum dentatum. Four groups each of 20 helminth naïve pigs, 10-12 weeks old, were inoculated with 0 (group 1), 100 (group 2), 1000 (group 3), or 10,000 (group 4) infective larvae twice weekly, and the pigs were killed after 10-13 weeks. No overt clinical signs were observed, and only group 4 had slightly lower food conversion rate (P < 0.05) than the controls. Faecal egg counts revealed that the nodular worms in pigs of groups 2 and 3 had a short prepatent period (3-4 1/2 weeks) and a fairly stable egg output, while the worms in the pigs of group 4 had prepatent periods of 3-10 weeks and low, unstable egg excretion. The mean worm burdens increased with the dose rate (group 2: 929 worms; group 3: 7467 worms; group 4: 19,847 worms), but detailed analyses of the worm populations from 10 pigs from each of the infected groups revealed a clear dose-dependency in worm recovery, percentage adult worms, worm lengths and female fecundity, as all these measures declined significantly with increasing dose level. The adult worms seemed to be shorter and less fertile when they were located posteriorly to their predilection site, and especially in group 4 many stunted infertile adults measuring only 2-5 mm were found in the posterior half of the colon, but there were no indications of worm expulsion. Superimposed on the main experiment was a cohort study in which 4 pigs of group 3 were given a single dose of 1000 pyrantel resistant larvae at day 56 (all other larvae were pyrantel sensitive), treated with 28 mg pyrantel per kg body weight at day 85 and killed at day 90. Appropriate control groups were included. The mean establishment of the cohort was similar to previously uninfected controls, but between-animal variation was much higher in the trickle infected group.

Experimental Oesophagostomum dentatum infection in the pig: worm populations resulting from single infections with three doses of larvae.

This report describes the effect of different dose levels of infection upon worm burdens and development and fecundity of the parasites. Three groups each of 40, 9-week-old, helminth naive pigs were inoculated once with either 2000 (group A), 20,000 (group B), or 200,000 (group C) infective third stage larvae of Oesophagostomum dentatum. Subgroups of 5 pigs from each major group were killed 3, 6, 11, 14, 18, 25, 34 and 47 days post inoculation (p.i.) and the large intestinal worm burdens were determined. Faecal egg counts were determined at frequent intervals after day 13 p.i. There were no overt clinical signs of gastrointestinal helminthosis during the experiment. Faecal egg counts became positive in groups A and B at around day 19 p.i., whereas most pigs in the high dose group C did not have positive egg counts until day 27-33 p.i. and some pigs remained with zero egg counts until the end of the study. Throughout the experiment the worm populations in group C consisted mainly of immature larval stages, while those in groups A and B were predominantly adult stages after days 14-18. Adult worms from the low dose group A were significantly longer than those from group C. At high population densities, stunted development of worms and reduced fecundity among female worms were found. Furthermore, there was a tendency for the distribution of the worms within the intestine to be altered with increasing population size.

The kinetic disposition of pyrantel citrate and pamoate and their efficacy against pyrantel-resistant Oesophagostomum dentatum in pigs.

The pharmacokinetic disposition of pyrantel after intravenous (i.v.) and oral (p.o.) administration as the citrate and p.o. administration as the pamoate salt was determined in pigs. Following i.v. administration pyrantel was quickly cleared from the bloodstream, exhibiting a terminal half-life of 1.75 +/- 0.19 h and a residence time (MRT) of 2.54 +/- 0.27 h. After p.o. administration as the citrate salt, the absorption time (MAT) of pyrantel was 2.38 +/- 0.25 h and although significant quantities of pyrantel were absorbed (mean bioavailability of 41%) the rapid clearance resulted in a MRT of only 4.92 +/- 0.36 h. By comparison, the significantly extended MAT of the less soluble pamoate salt resulted in reduced circulating concentrations and a significantly lower mean bioavailability of 16%. The poor efficacy of pyrantel citrate against nematodes inhabiting the large intestine of pigs is therefore suggested to result from insufficient quantities of drug passaging to the site of infection. When tested against pyrantel-resistant adult Oesophagostomum dentatum the mean efficacy of pyrantel citrate was only 23%, whereas the efficacy of the lesser absorbed pyrantel pamoate was 75%. These results indicate that for maximum activity pyrantel should be administered to pigs as the pamoate salt.

The efficacy of ivermectin against nodular worms of pigs: the response to treatment using three different dose levels against Oesophagostomum dentatum and Oesophagostomum quadrispinulatum.

Anthelmintic efficacies of 3 different doses of ivermectin (IVM) were evaluated in 3 isolates of nodular worms in pigs. An isolate of Oesophagostomum quadrispinulatum (OQ) was recently obtained from a commercial farm where poor efficacy of IVM at the recommended dose (300 micrograms.kg-1 body weight) was detected. On this farm, IVM had been used for treatment of sows twice yearly for 6 years. Two other isolates, an O. dentatum (OD) and a mixed Oesophagostomum dentatum and Oesophagostomum quadrispinulatum isolate (ODQ) were obtained from a farm where anthelmintics had never been used. Efficacies of IVM against adult worms of the OQ-isolate at dose rates of 150, 300 and 600 micrograms.kg-1 body weight ranged from 40.5-78.6%. Efficacies against larval stages (L3 and L4) were superior. Efficacies against the OD-isolate were 88.7, 96.1 and 99.6%, respectively. In the ODQ-isolate the efficacies of IVM against adult stages furnished similar results. In conclusion, the efficacy of IVM against O. dentatum was high but against both isolates of O. quadrispinulatum poorer. This suggests that IVM is intrinsically less effective against O. quadrispinulatum and therefore not indicative of acquisition of anthelmintic resistance in the OQ-isolate.

Transmission dynamics of helminth parasites of pigs on continuous pasture: Oesophagostomum dentatum and Hyostrongylus rubidus.

An increase in alternative outdoor pig production systems is occurring in Denmark, and this study was designed to elucidate the transmission patterns of Oesophagostomum dentatum and Hyostrongylus rubidus in pigs allowed to graze continuously on a pasture. A group of pigs was turned out in May 1993 (Year 1 of the study) and subsequently inoculated with low numbers of both helminths. These pigs were followed parasitologically until October by serial necropsy and sampling of faeces, grass and soil. A non-inoculated group of pigs was similarly followed on the same pasture in Year 2 (1994). Pasture infectivity was measured using helminth-naïve tracer pigs during all seasons. The pasture vegetation was rapidly destroyed by the pigs, resulting in a dirt lot by the autumn of Year 2. The area was soon contaminated with eggs, resulting in heavy pasture infectivity and increasing worm burdens in late summer; then the numbers of larvae declined markedly. In May of Year 2, newly exposed pigs became only lightly infected (mostly O. dentatum), and no transmission was observed in July-August of Year 2, probably due to an unusually dry summer and a lack of protecting vegetation. The results indicate that both O. dentatum and H. rubidus are very sensitive to environmental factors, because significant transmission occurred only under the most favourable conditions (summer combined with protecting vegetation as in Year 1). Transmission was severely reduced during the low temperatures experienced in the winter between Years 1 and 2 and during the dry summer of Year 2, when vegetation was lacking. Continuous grazing actually reduced transmission of O. dentatum and H. rubidus because of the reduction in vegetation. This, however, is not a desirable alternative farming system, because of its adverse environmental effects. This environmental impact may be mitigated by employment of a pasture rotation system in place of continuous grazing.