The epidemiology of nematode infections in sheep in a cool tropical environment

A Review: Haemonchus contortus Infection in Pasture-Based Sheep Production Systems, with a Focus on the Pathogenesis of Anaemia and Changes in Haematological Parameters

Simple Summary

Infection with Haemonchus contortus parasites (haemonchosis) is an important cause of anaemia in sheep. Haemonchosis is a global problem, although sheep that are kept in warm, high rainfall environments are at the greatest risk of infection due to the favourable conditions for H. contortus survival. Following ingestion, the parasites develop in the abomasum of sheep. Various factors such as age, breed, health, nutritional status, and larval challenge influence the severity of clinical disease. Hyperacute, acute, and chronic haemonchosis are reviewed, focusing on the pathophysiology of haemonchosis, associated clinical signs, and haematological and biochemical findings.

Abstract

Haemonchosis is an important cause of anaemia in sheep worldwide, particularly those that are kept in pasture-based systems in warm, high rainfall environments. Potential outcomes vary based on the severity of infection and the sheep’s immune response, however, in some sheep infection can lead to death. The consequences of Haemonchus contortus infection mean that it has been well-studied in a range of different farming systems. However, to our knowledge, there has not been a recent review focused on the pathophysiology of anaemia caused by haemonchosis. Thus, this review provides an in-depth discussion of the literature related to the pathophysiology of haemonchosis and associated clinical signs for hyperacute, acute, and chronic haemonchosis. Additionally, haematological and biochemical findings are presented, and various diagnostic methods are assessed.

Morbidity Parameters Associated with Gastrointestinal Tract Nematodes in Sheep in Dabat District, Northwest Ethiopia

Gastrointestinal nematode (GIN) infections of sheep and their interaction with selected morbidity parameters were studied in smallholder farms. 120 faecal samples were collected and examined using faecal flotation to determine nematode infection in sheep. Thus, the study demonstrated overall prevalence of 57.5% GIN infections, while the mean faecal egg count (FEC) was 517.5 EPG. The severity of GIN infection was determined based on EPG as a mild infection (EPG <500), 55.1%, moderate infection (EPG = 500–1500), 30.4%, and heavy infection (EPG >1500), 14.6%. Five genera of nematodes were identified using coproculture: Haemonchus (33.3%), Trichostrongylus (26.7%), Bunostomum (20%), Oesophagostomum (13.3%), and Cooperia (6.7%). A significant difference was observed in the mean FEC among the FC (P < 0.001), FAMACHA© score (P < 0.01), and the BCS of the animals (P < 0.001). FEC was positively correlated with the FAMACHA© score (FS), while FC and BCS were negatively correlated. Thus, FAMACHA© chart can suggest well the severity of nematode infections and can serve as a suitable on-farm tool to identify nematode-infected sheep and gives a guide to identify sheep that need to be treated with an anthelmintic.

Investigations into nematode parasites of goats in pastoral and crop livestock systems of Ethiopia

We generated epidemiological information on the prevalence of nematode parasites and possible resistance/resilience of goats in three areas, Bati, Shinille, and Borana, of Ethiopia. A total of 350 breeding does were randomly selected and monitored for one year. Fecal egg counts (FEC), packed cell volume (PCV), body weight (BW), body condition score (BC), and fecal larvae identification were done. In Borana, the long rainy season had higher FEC, lower PCV, lower BC, and smaller BW compared to dry and short rainy seasons (p < 0.01). For Bati and Shinille, the differences between the seasons were significant (p < 0.01) but not clear-cut. Breed differences were also evident (p < 0.01) on FEC, PCV, and BW. The mean FEC for Borana goat was 158.5 ± 1.12, whereas for Bati it was 38.9 ± 1.12. Age differences did not have effect on FECs, PCV, and BC. No differences in parasite load, as reflected by FEC, was verified between male and female goats. In the wet season, large numbers of larvae were recovered from the study sites except for Bati. In the three sites, Haemonchus contortus followed by Trichostrongylus colubriformis were the dominant species. In the dry season, however, very little number of larvae was recovered, only of H. contortus in Bati and of H. contortus and T. colubriformis in Borana. Generally, the level of nematode infection was low. Therefore, nematode parasites are not a major problem and strategic control program using broad spectrum anthelmintic is not advisable. Rather, monitoring parasite load and selective de-worming should be sufficient to reduce productivity loses and pasture contamination.

Gastrointestinal nematode infection in small ruminants in Ethiopia: A systematic review and meta-analysis

Gastrointestinal (GI) nematode infections are a major health challenge affecting productive and reproductive performance of sheep and goats in Ethiopia. However, there is no comprehensive summary on the occurrence and distribution of the infection at national level. This systematic review provides pooled prevalence estimates and assesses potential predictors of the nematode infections in small ruminants, i.e. helpful in planning interventions or control strategies. The review used 50 animal level datasets retrieved from 24 manuscripts. The studies used data collected from 9407 sheep and 3478 goats. A meta-analytical approach was employed to analyze Effect size (ES). The reported GI nematodes represented eleven genera affecting sheep and goats including: Haemonchus, Trichostrongylus, Teladorsagia/Ostertagia, Strongyloides, Bunostomum, Nematodirus, Chabertia, Trichuris, Cooperia, Skrjabinema and Oesophagostomum. The GI nematodes pooled prevalence estimate in the random effect model was 75.8% (95% CI: 69.6, 80.8). The subgroup analysis revealed significant (p<0.05) differences in the prevalence between different regions and type of diagnostic methods used. 'Postmortem technique' and 'eastern part of the country' were associated with higher GI nematode prevalence and accounted for 68.1% of the between studies heterogeneity. In light of the high parasitic prevalence in all agro-ecologies, the need for strategic intervention is recommended. Meanwhile, data need to be generated for some of the regions where dependable survey reports are lacking.

Expression of serine proteinase P186 of Arthrobotrys oligospora and analysis of its nematode-degrading activity

The nematode-trapping fungi possess a unique capability of predating and invading nematodes. As a representative nematode-trapping fungus, Arthrobotrys oligospora has been widely used to study the interactions between nematode-trapping fungi and their hosts. Serine proteinase is one of the important virulence factors during process of invasion of the nematode-trapping fungi into nematodes. In this study, using reverse transcription polymerase chain reaction, we amplified the gene sequence of serine proteinase 186 from A. oligospora, cloned it into pPIC9K vector and expressed it in the yeast Pichia pastoris. The expressed recombinant serine proteinase186 (reP186) was purified via Ni-affinity chromatography. The in vitro nematode-degrading activity of reP186 was analyzed. Sodium dodecyl sulfate polyacrylamide gel electrophoresis and Western blot analysis revealed that reP186 with molecular weight of 33 kDa was successfully obtained. ReP186 was capable of degrading a series of protein substrates including casein, gelatin, bovine serum albumin, denatured collagen and nematode cortical layer. The reP186 exhibited the maximal activity at pH 8.0 and 55 °C and was highly sensitive to the inhibitor, phenylmethanesulfonylfluoride. Treatment of Caenorhabditis elegans and Haemonchus contortus with reP186 for 12, 24 and 36 h, respectively, resulted in 62, 88 and 100 % of killing rates for C. elegans, and 52, 65 and 84 % of killing rates for H. contortus, respectively, indicating a relatively strong nematode-degrading bioactivity of reP186.

Relevance of improved epidemiological knowledge to sustainable control of Haemonchus contortus in Nigeria

Nigeria experiences losses in small ruminant production as a result of a high prevalence of infection with Haemonchus contortus, but there have been very few investigative studies into the epidemiology of H. contortus in Nigeria, particularly in the south and western parts of the country. For successful planning and execution of control of hemonchosis in Nigeria, there is a need for insight into the epidemiology of free-living stages under the prevailing local conditions and models for climatic and environmental factors that control the risk of hemonchosis and distribution of H. contortus. In this review, we assess previous studies on the epidemiology of H. contortus in Nigeria, evaluate the present climatic and epidemiological situation, and highlight areas that require further investigative studies. The goal is to identify factors that underpin better control strategies and holistic integrated farm-management practice. Previous studies on H. contortus provided important information for formulation of control strategies and development toward integrated parasite management. However, this review has revealed the need for holistic evaluation of the current epidemiology and prevalence of H. contortus in Nigeria, particularly in relation to climate change. Accurate information is needed to build useful predictive models of the population dynamics of all free-living stages, particularly the L3.

Gastrointestinal nematodes in rotationally grazing ewes in the mountainous region of central Mexico

The aims of this study were to determine the frequency of egg shedding (percentage of egg-positive faecal samples) and faecal egg counts (FEC) over 13 months in two different breeds of ewes, both pregnant and non-pregnant, in a mountainous region of central Mexico. Additionally, the effect of ivermectin and albendazole treatments on FEC reduction was recorded. The study also aimed to relate temperature and rainfall to FEC. The gastrointestinal nematode (GIN) third-stage larvae genera recovered from both faeces and grassland pastures in a temperate region were also assessed. Faecal samples were collected from ewes at monthly intervals for 13 months to investigate the FEC population of GIN larvae, their concentration and genera in grass samples collected from grazed and rested pastures. Egg-shedding frequency ranged from 0 to 92% and FEC from 0 to 12,000 eggs per g faeces (epg), with counts in Suffolk higher than in Dorset ewes. The identified genera were Haemonchus, Trichostrongylus, Teladorsagia, Cooperia, Oesophagostomum, Bunostomum, Nematodirus and Strongyloides. Haemonchus and Trichostrongylus were the most common genera. The number of L3 was higher in grazing lands than in those at rest. The highest FEC were recorded in the dry season due to peripartum, but the highest L3 counts were recorded in the rainy season. The coexistence of species of different geographical distributions at this site may be because there is a confluence of Nearctic and Neotropical geographic regions; thus, despite the temperate climate, tropical species can be found. Additionally, this study suggests that increasing temperatures could favour the presence of different tropical GIN species together with typical temperate-zone GIN species.

Epidemiology of nematode parasites of sheep around Jimma, southwestern Ethiopia

An investigation was made into the epidemiology of nematode infections of sheep in two districts of Jimma zone, southwestern Ethiopia. We used two approaches--long-term monitoring of identified sheep for nematode infection and abattoir or market survey for analysis. In the first monitoring regime, we used 80 lambs [40 sheep (20 per sex) from each district (Dedo and Yebu)] averaging 4-5 months of age. Faecal egg counts (FEC), packed cell volume (PCV) and body weight changes were monitored over a period of 1 year. Additionally, faecal samples were collected (on a weekly basis) from sheep brought to abattoir/market for 1 year to monitor faecal egg counts. The nematode parasite burden, as judged by FEC and PCV, was generally low indicating that the climatic conditions are not conducive to the development and survival of nematode eggs and the free-living stages; hence, little transmission occurred. In the experimental flocks, the highest FEC and lower PCV were recorded during the long rainy season (June to September) with peak in August and September. Faecal samples collected from abattoir/market also followed the same trend. Results from experimental sheep indicated that location had a significant (P < 0.01) effect on FEC, PCV and average daily body weight gain. The FEC and PCV for sheep in Yebu (mid-altitude) district were 126 +/- 3.33 and 30.6 +/- 0.26, whereas the values for Dedo (highland) were 93 +/- 4.35 and 32.0 +/- 0.21, respectively. The results indicate that the highland areas are comparatively less favourable to the survival and development of nematodes. Female lambs had lower FEC and higher PCV compared to male lambs (P < 0.05). The overall nematode parasite challenge in the area, however, is low. We, therefore, recommend rotational grazing management combined with monitoring parasite load and selective treatment to reduce productivity loses and pasture contamination.

Parasitological and clinical responses of lambs experimentally infected with Haemonchus contortus (L3) with and without ivermectin treatment

Haemonchus contortus is one of the most important parasites that infects sheep and exerts its pathogenic effects by sucking blood, causing disturbances of organ-functions and thus inducing alterations in various normal physiological parameters. Changes in live body weight, faecal egg count, kinetics of circulating eosinophils and PCV value were studied at weekly interval for a period of 84 days in 18 lambs of local breed after infection with a single dose of 5000 H. contortus (L(3)). In the two groups of lambs infected with nematodes both non-treated and treated with ivermectin (HcNT and HcIT), similar egg excretion patterns was observed starting from third week after infection, with a regular increase in FEC. Examination of whole abomasum of each animal revealed no developmental stage of nematode from treated and control lambs on day 84. The total mean number of H. contortus worms recovered at necropsy from abomasa of untreated infected lambs (group HcNT) was 2576.2 (+/-221.0). The significant loss of body weight, development of heavy worm burden and severe anaemia as indicated by reduced PCV in untreated infected lambs indicated high susceptibility of the lambs to H. contortus. On the other hand, complete absence of the parasite, improved PCV value and body weight after treatment of infected animals (HcIT) proved 100% efficacy of ivermectin against H. contortus.

Evaluation of the efficacy of anthelmintics sold on Ethiopian markets against Haemonchus contortus in experimentally infected Sheep

A total of 54 lambs, aged between 6-8 months were experimentally infected with Haemonchus contortus to evaluate the efficacy of different anthelmintic brands sold on Ethiopian markets using the faecal egg count reduction test (FECRT) and controlled anthelmintic efficacy trial. Accordingly four different albendazole (Alzole, Analgon-300, Albenjung_s and Ahshialben-300), two tetramisole (Tetsole and Ashitetra 600) and two tetramisole-oxyclozanide (Tetraclozan sheep and Tetraclozash 900) brands were evaluated at the dosage rates recommended by the manufacturers. Animals were allocated into nine groups of six animals each, and balanced for faecal egg counts (FEC), based on their pre-treatment FEC and treatments were randomized among the groups. One group was kept untreated as a control. Faecal egg count was conducted on day 30 post-infection (day of treatment) and on the 10th day post-treatment. Evaluation of anthelmintics based on FECRT revealed high efficacy (99.55-100% reduction in FEC) for all anthelmintic brands tested against H. contortus. The worm count reduction test using controlled anthelmintic efficacy trial also supported the above finding with 99-100% efficacy of the tested anthelmintics. Therefore, the suspicion on the anthelmintic products as being substandard in quality is not credible, at least, for the brands investigated in this study and it might rather be attributed to under dosing. The need for a good extension system for livestock producers with regard to good anthelmintic usage practices, in light of the inevitable development of anthelminitic resistance, is emphasized. Regular surveillance and laboratory quality evaluation of the anthelmintic products in Ethiopia is indicated.

Multiple anthelmintic resistance on a goat farm in Hawassa (southern Ethiopia)

A study was conducted to determine the presence of anthelmintic resistance on Hawassa University goat farm in southern Ethiopia. The 180 goats were stratified by age and sex and randomly assigned to treatment groups (albendazole, tetramisole and ivermectin and untreated control). Each treatment group included 15 goats and treatments were administered according to weight of each goat with 7.5 mg/kg bw albendazole, 22.5 mg/kg bw tetramisole and 0.2 mg/kg bw ivermectin dose rates recommended by scientists. Faecal samples were collected on day 0 before treatment, and again on day 12 post treatment. Efficacy of all the drugs was assessed on day 12 post treatment by faecal egg count reduction test (FECRT). Multiple anthelmintic resistance in Haemonchus spp. against albendazole, tetramisole and ivermectin was recorded in all age categories of the goats. Likewise, Trichostrongylus/Teladorsagia spp. showed resistance against ivermectin. Coprocultures from all pre- and post-treatments revealed the predominance of Haemonchus spp. Resistance against anthelmintics is attributed to the high frequency of treatment and low dosage of treatment practices on the farm. Large scale studies, however, are needed to assess the current status of anthelmintic resistance against the most commonly used anthelmintics in different agroecology, species of animals and management systems in Ethiopia.

Effects of non-genetic factors on responses to gastro-intestinal nematode infections in Ethiopian sheep

The effects of non-genetic factors on responses to gastrointestinal nematode infections were examined in artificially infected indigenous Horro and Menz lambs in the central highlands of Ethiopia. The experiment involved lambs of two sexes, infection and monitoring regimens (3 levels), dam parity (4 levels) and birth types (2 levels). A total of 152 weaner lambs (103 Menz and 49 Horro) were used. Endoparasite challenge involved three infection periods (primary, secondary and tertiary) each separated by an anthelmintic treatment. Data were collected on faecal egg counts (FEC), packed cell volume (PCV), worm count, and weight gain. Female lambs were found to harbor lower numbers of T. colubriformis counts and had lower (p < 0.01) FEC in tertiary infection compared to males. Younger animals were more susceptible to the nematode infections than older animals as measured by all the parameters studied (p < 0.01). Twins had higher FEC in both secondary and tertiary infections compared to singles. Lambs born to dams of first parity had higher PCV and lower FEC values during the tertiary infection compared to other parities. These results would be used as basic information in designing a more rational control strategy and should also help to advise on better management care for less resistant sheep.

Prevalence and seasonal incidence of nematode parasites and fluke infections of sheep and goats in eastern Ethiopia

A 2-year abattoir survey was carried out to determine the prevalence, abundance and seasonal incidence of gastro-intestinal (GI) nematodes and trematodes (flukes) of sheep and goats in the semi-arid zone of eastern Ethiopia. During May 2003 to April 2005, viscera including liver, lungs and GI tracts were collected from 655 sheep and 632 goats slaughtered at 4 abattoirs located in the towns of Haramaya, Harar, Dire Dawa and Jijiga in eastern Ethiopia. All animals were raised in the farming areas located within the community boundaries for each town. Collected materials were transported within 24 h to the parasitology laboratory of Haramaya University for immediate processing. Thirteen species belonging to 9 genera of GI nematodes (Haemonchus contortus, Trichostrongylus axei, T. colubriformis, T. vitrinus, Nematodirus filicollis, N. spathiger Oesopha-gostomum columbianum, O. venulosum, Strongyloides papillosus, Bunostomum trigonocephalum, Trichuris ovis, Cooperia curticei and Chabertia ovina), and 4 species belonging to 3 genera of trematodes (Fasciola hepatica, F. gigantica, Paramphistomum {Calicohoron} microbothrium and Dicrocoelium dendriticum) were recorded in both sheep and goats. All animals in this investigation were infected with multiple species to varying degrees. The mean burdens of adult nematodes were generally moderate in both sheep and goats and showed patterns of seasonal abundance that corresponded with the bi-modal annual rainfall pattern, with highest burdens around the middle of the rainy season. In both sheep and goats there were significant differences in the mean worm burdens and abundance of the different nematode species between the four geographic locations, with worm burdens in the Haramaya and Harar areas greater than those observed in the Dire Dawa and Jijiga locations. Similar seasonal variations were also observed in the prevalence of flukes. But there were no significant differences in the prevalence of each fluke species between the four locations. Overall, the results showed that Haemonchus, Trichostrongylus, Nematodirus, Oesophagostomum, Fasciola and Paramphistomum species were the most abundant helminth parasites of sheep and goats in eastern Ethiopia.

In vitro and in vivo anthelmintic activity of crude extracts of Coriandrum sativum against Haemonchus contortus

In vitro anthelmintic activities of crude aqueous and hydro-alcoholic extracts of the seeds of Coriandrum sativum (Apiaceae) were investigated on the egg and adult nematode parasite Haemonchus contortus. The aqueous extract of Coriandrum sativum was also investigated for in vivo anthelmintic activity in sheep infected with Haemonchus contortus. Both extract types of Coriandrum sativum inhibited hatching of eggs completely at a concentration less than 0.5 mg/ml. ED(50) of aqueous extract of Coriandrum sativum was 0.12 mg/ml while that of hydro-alcoholic extract was 0.18 mg/ml. There was no statistically significant difference between aqueous and hydro-alcoholic extracts (p>0.05). The hydro-alcoholic extract showed better in vitro activity against adult parasites than the aqueous one. For the in vivo study, 24 sheep artificially infected with Haemonchus contortus were randomly divided into four groups of six animals each. The first two groups were treated with crude aqueous extract of Coriandrum sativum at 0.45 and 0.9 g/kg dose levels, the third group with albendazole at 3.8 mg/kg and the last group was left untreated. Efficacy was tested by faecal egg count reduction (FECR) and total worm count reduction (TWCR). On day 2 post treatment, significant FECR was detected in groups treated with higher dose of Coriandrum sativum (p<0.05) and albendazole (p<0.001). On days 7 and 14 post treatment, significant FECR was not detected for both doses of Coriandrum sativum (p>0.05). Significant (p<0.05) TWCR was detected only for higher dose of Coriandrum sativum compared to the untreated group. Reduction in male worms was higher than female worms. Treatment with both doses of Coriandrum sativum did not help the animals improve or maintain their PCV while those treated with albendazole showed significant increase in PCV (p<0.05).

Assessment of anthelmintic resistance in nematode parasites of sheep and goats owned by smallholder farmers in eastern Ethiopia

The anthelmintic resistance status was investigated of nematode parasites of sheep and goats owned by smallholder farmers in communities that received breeding stock from a source where a high level of anthelmintic resistance has been reported. The investigation used the faecal egg count reduction technique, whereby suitable animals within each of eight separate communities were pooled to achieve the numbers required to conduct separate tests for both sheep and goats. Anthelmintics tested were albendazole (ABZ), tetramisole (TET), a combination (ABZ + TET) and ivermectin (IVM), at the manufacturers' recommended dose rates. Results showed that there was no evidence of anthelmintic resistance in nematode parasites of either sheep an goats in any community. This indicates that dilution of resistant parasites imported with introduced breeding stock, and the low selection pressure imposed by the smallholder farmers themselves, has prevented anthelmintic resistance from emerging in nematode parasites of small ruminants in these communities.

Epidemiology and seasonal dynamics of gastrointestinal nematode infections of sheep in a semi-arid region of eastern Ethiopia

A study on the epidemiology and seasonal dynamics of gastrointestinal nematode infections of sheep was carried out in a semi-arid region of eastern Ethiopia for 2.5 years (May 2003 to September 2005). The experimental flock comprised a total of 60 Black Head Ogaden sheep, consisting of four equal groups of young male and female and old male and female sheep. These grazed on communal pastures together with a larger university flock, as well as with animals owned by neighbouring small-holder farmers. A new experimental flock was established each year of the study. Parasitological data (EPG, faecal culture L3, PCV and FAMACHA estimates) and animal performance (weight change) were recorded each month on all experimental animals. In addition, four tracer lambs were assigned each month to the flock to determine the seasonal patterns of infective larvae acquired from pasture. Results showed distinct seasonal patterns associated with the bi-modal annual rainfall. High levels of infection occurred during the short and long rain seasons with peaks occurring in May and September of each year. Haemonchus contortus was the most prevalent parasite, followed by Trichostrongylus spp., with a number of other nematode species being occasionally recorded. H. contortus showed and increased propensity to undergo arrested development during the dry seasons. Correlations between EPG and PCV, EPG and FAMACHA eye scores, and PCV and FAMACHA eye scores were all highly significant (P<0.001). However, there was no significant association between the EPG and LW of the study animals during each study year. This information will provide a basis for developing epidemiologically based control strategies for gastrointestinal nematode parasites that are appropriate for flocks owned by small-holder farmers of semi-arid areas of eastern Ethiopia.

Haemonchus contortus (Nematoda: Trichostrongylidae) infection in lambs elicits an unequivocal Th2 immune response

Selection of resistant animals and host immunization have been proposed as alternative methods for the control of gastrointestinal nematode parasites. However, a better knowledge of the mechanisms involved in protective immunity against these parasites is required for the development of optimal strategies. In this study, 3 month old INRA 401 lambs (n = 81) were allocated into three groups: uninfected control, challenged either once (primary-infected animals) or twice (previously-infected animals) with 10,000 Haemonchus contortus L3. Uninfected control and challenged animals were sequentially sacrificed at 3, 7, 15 and 28 days post challenge. In both challenged groups, a clear Th2-oriented immune response was observed in the abomasal lymph node and mucosa. IL-4 and IL-13 mRNA over-expression, recruitment of eosinophils, mast cells and globule leukocytes and production of specific systemic IgG and mucosal IgA were observed earlier in previously-infected animals than in primary-infected ones. At 28 days post infection, no differences between intensities of these responses were observed between the challenged groups. Worm establishment rates were similar in previously-infected and primary-infected lambs. However, reductions of worm development, female fecundity and fecal egg output were observed in previously-infected sheep. We conclude that H. contortus infection in young INRA 401 lambs induced an unequivocal Th2 immune response resulting in the regulation of worm egg production without affecting their establishment.

Anthelmintic resistance of nematode parasites of small ruminants in eastern Ethiopia: Exploitation of refugia to restore anthelmintic efficacy

Faecal egg count reduction tests (FECRT) were conducted in May 2003 to determine the efficacy of anthelmintics used for treatment against nematode parasites in separately managed sheep and goat flocks at Alemaya University in eastern Ethiopia. These tests revealed high levels of anthelmintic resistance to albendazole, tetramisole, the combination of these two drugs, and to ivermectin in the goat flock (predominantly infected by Haemonchus contortus and Trichostrongylus spp.), whereas all drugs were highly efficacious in the sheep flock. A second FECRT confirmed these observations. Following this, a new management system was implemented on the goat flock for a period of 9 months (January-September 2004) in an attempt to restore the anthelmintic efficacy. This involved a combination of measures: eliminating the existing parasite infections in the goats, exclusion from the traditional goat pastures, and introducing communal grazing of the goats with the university sheep flock and livestock owned by neighbouring small-holder farmers. A second series of FECRTs (Tests 3 and 4) conducted 7 months after this change in management, showed high levels of efficacy to all three drugs (albendazole, tetramisole and ivermectin) in the goat flock. This is the first field study to demonstrate that anthelmintic efficacy in the control of nematode parasites of small ruminants can be restored by exploiting refugia.

Haemonchus contortus egg excretion and female length reduction in sheep previously infected with Oestrus ovis (Diptera: Oestridae) larvae

Mixed parasitic infection of animals is a common phenomenon in nature. The existence of one species often positively or negatively influences the survival of the other. Our experimental study was started with the objectives to demonstrate the interaction of Haemonchus contortus and Oestrus ovis in relation to cellular and humoral immune responses in sheep. Twenty-two sheep of Tarasconnais breed (France) were divided into four groups (O, OH, H and C) of five or six animals. Group O and OH received 5 weekly consecutive inoculations with O. ovis L1 larvae (total = 82 L1) in the first phase of the experiment between days 0 and 28. On the second phase, groups OH and H received 5000 L3 of H. contortus on day 48 while group C served as our control throughout the experimental period. Parasitological, haematological, serological and histopathological examinations were made according to standard procedures and all animals were slaughtered at day 95. There was no significant variation in the number and degree of development of O. ovis larvae between the two infected groups. Furthermore, in tissues examined in the upper respiratory tract (nasal septum, turbinate, ethmoide and sinus), group O and OH has responded similarly on the basis of cellular inflammatory responses (blood and tissue eosinophils, mast cells and globule leucocytes (GL)) and serum antibody responses against the nasal bots. This may indicate that the presence of H. contortus in the abomasa of group OH had no marked influence over the development of O. ovis larvae in the upper respiratory tract. On the other hand, we have observed a significantly lower H. contortus female worm length, fecal egg count (FEC) and in utero egg count in animals harbouring the nasal bot (OH) than in the mono-infected group (H). This was significantly associated with higher blood eosinophilia, higher packed cell volume (PCV) and increased number of tissue eosinophils and globule leucocytes. We conclude that, the establishment of O. ovis larvae in the upper respiratory tract has initiated higher inflammatory cellular activity in group OH there by influencing the development and fecundity of H. contortus in the abomasum.

In vitro effects of four tropical plants on three life-cycle stages of the parasitic nematode, Haemonchus contortus

Alcoholic extracts of four tropical plants (Zanthoxylum zanthoxyloides, Newbouldia laevis, Morinda lucida and Carica papaya) were screened in vitro for potential anti-parasitic effects against eggs, infective larvae and adult Haemonchus contortus. Significant effects were obtained with all four plants but differences were observed depending on the parasitic stage. The effects of the four plant extracts were similar on egg hatching and were dose dependent. In contrast, no dose-response relationship was found for infective larvae and adult worms, although more potent effects were usually observed with the highest concentrations. Using a larval inhibition migration test, extracts of fagara (Z. zanthoxyloides) were found to be less active against Haemonchus infective larvae than were the other plants. N. laevis was found to be highly and rapidly effective against adult worms. Overall, these in vitro results suggest that these four plants, traditionally used by small farmers in Western Africa, do possess anti-parasitic properties. These effects remain to be confirmed through in vivo studies.

Development and survival of infective larvae of nematode parasites of sheep on pasture in a cool tropical environment

The development and survival of nematode parasites of sheep were studied in a cool tropical environment of the highlands of Ethiopia on 24 plots serially contaminated with Haemonchus contortus, Longistrongylus elongata and Trichostrongylus colubriformis eggs over a period of 2 consecutive years from June 1993 to May 1995. The availability of infective larvae was monitored by monthly pasture sampling and larvae recovery. Infective larvae were recovered from the herbage collected from the plots contaminated in June, July, August, September and October of both years. The longevity of infective larvae varied between two and six weeks when eggs were deposited on pasture in June and October, respectively. During the dry and short rainy season (November through May), eggs failed to develop into L3 stage. It is suggested that the long period (7 to 8 months) of lack of development of trichostrongylid infective larvae on the pasture can be efficiently used in a strategic treatment programme to interrupt transmission of H. contortus, L. elongata and T. colubriformis in sheep in this environment.

Breed and season effects on the peri-parturient rise in nematode egg output in indigenous ewes in a cool tropical environment

A study was carried out at the International Livestock Research Institute (ILRI) Debre Berhan Research Station in Ethiopia from 1992 to 1995 to compare the peri-parturient rise (PPR) in faecal nematode egg counts (FEC) in ewes of two indigenous sheep breeds. A total of 1439 Menz and 1347 Horro ewes were single sire mated following oestrus synchronization to lamb in the wet and dry season. Three ewe treatment groups were constituted as mated/lactating/undrenched; mated/lactating/drenched; unmated/undrenched for three wet and three dry lambing seasons. All ewes grazed naturally contaminated pasture. Levels of faecal egg output were monitored at mating, 3 months after mating, 2 weeks before lambing, 4, 8 and 12 weeks post-lambing. A significant PPR in FEC occurred 2 weeks before lambing and peaked at 4 weeks post-parturition in ewes lambing just before the beginning of the dry season (October/November). There was no significant increase in FEC when lambing occurred before the onset of the long rainy season (May/June). The PPR in this study was associated with both lactation and seasonal availability of third-stage infective larvae on pasture. There was no consistent breed difference in FEC during the six sampling periods from mating to weaning. Faecal cultures and worm counts from both breeds confirmed the presence of Longistrongylus (Pseudomarshallagia) elongata, Trichostrongylus spp.and Haemonchus contortus. The role of the peri-parturient rise of FEC in ewes in gastrointestinal nematode transmission is discussed.