The seasonal epidemiology of gastrointestinal nematodes in N'Dama cattle in The Gambia

From June 1987 to June 1988, a total of 180 N'Dama cattle were necropsied to identify and enumerate parasites present, including 39 sick calves and 25 dead calves from local village herds, and 116 adult cattle from a local abattoir. Of 175 animals infected with one or more helminths (97%), Haemonchus contortus was found in 67% of all necropsied animals, Cooperia punctata in 75%, Cooperia pectinata in 55%, Oesophagostomum radiatum in 71% and Bunostomum phlebotomum in 21%. There was a wide range of worm burdens (0-22 925) and a pronounced seasonal pattern occurred. Eighty-two percent of the total adult Haemonchus burden occurred during the rainy season (June-October). By the end of the rainy season, almost 100% of the Haemonchus burden was present as inhibited larvae. By contrast, a different survival strategy appeared to occur in Cooperia spp.; Oesophagostomum spp. and Bunostomum spp., which were found as adults throughout the year. Results indicated that, apart from malnutrition during the dry season, gastrointestinal nematode infections, especially haemonchosis, represent a major constraint on the health and productivity of N'Dama cattle under West African savanna conditions.     

Haemonchus contortus with low inhibited development in sheep from the highveld of Zimbabwe

The abomasa of sheep grazing on natural pastures in the highveld of Zimbabwe were examined for Haemonchus contortus. Of 304 abomasa, 213 (70%) harboured H. contortus. The worm burden increased during the rains to reach the peak in February-March. This was followed by a decline with low worm loads throughout the dry season. The fourth stage larvae (L4) accounted for 1-7% of the total H. contortus population, except during July and August when they comprised 22 and 54% of the worm burden, respectively. It appears that the inhibition of H. contortus is not common in the commercial farming sector where sheep are treated very frequently.     

The seasonal prevalence of inhibited development of Haemonchus contortus in sheep in Senegal

Throughout a period of 13 months, the abomasa of 1024 sheep, living in a sahelian region, were examined for adult Haemonchus contortus and their inhibited L4 larvae. Of these 796 (78%) were found harbouring H. contortus, but with low worm burdens (geometric mean 37). Significant numbers of inhibited larvae appeared early in the dry season (November) and they represented 49% of the total in December. A similar proportion of inhibited larvae were present until April and after that their number declined abruptly. It was concluded that Haemonchus sp. survives the dry season as hypobiotic larvae as well as adults.     

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.     

Gastrointestinal Nematodes in Indigenous Zebu Cattle under Pastoral and Nomadic Management Systems in the Lower Plain of the Southern Highlands of Tanzania

This study aimed to determine the prevalence and intensity of gastrointestinal nematode infections in indigenous Zebu cattle in the lower plain (lowland zone) of the southern highlands of Tanzania. Gastrointestinal tracts were randomly purchased at the Iringa regional abattoir and at Kihesa and Ipogolo slaughter slabs in different seasons of the year. The contents of the abomasum, small intestine and large intestine were processed separately to recover the worms. The results indicated that 140 out of 144 (97.2%) of the examined animals were infected. The mean (±SE) total worm burden was 1284±183 (range 10–12 600) worms per animal and most infected animals contained more than one nematode species. The nematode species present, their prevalence and mean burden were as follows: Haemonchus placei, 84.7%, 316; H. similis, 5.6%, 1; Oesophagostomum radiatum, 79.2%, 66; Cooperia pectinata, 55.6%, 713; C. punctata, 44.4%, 157; Bunostomum phlebotomum, 5.6%, 5; Trichuris globulosa, 5.6%, 2; and Trichostrongylus colubriformis, 1.4%, 24. The burdens were mainly composed of Cooperia pectinata (55.5%), Haemonchus placei (24.6%), Cooperia punctata (12.3%) and Oesophagostomum radiatum (5.1%). The highest burdens occurred at the end of the rainy/early dry season, while the lowest burdens were found at the end of the dry/early rainy season. There was no difference in the burdens between male and female animals. Immature cattle (<3 years) had significantly higher worm burdens than mature cattle (p<0.01). A poor grade for a live animal was associated with higher worm burdens only in immature cattle and then especially during the dry season (r = 0.456, p<0.001). Anthelmintic treatments in the late rainy/early dry season and early rainy season are recommended in order to prevent outbreaks of helminthosis during the dry season and to reduce carryover of infection into the next rainy season. An additional wet season treatment is advisable in immature cattle, but may not be needed for mature cattle owing to the availability of plenty of mature, good quality pasture.     

Gastrointestinal nematode infections of goats in a sub-tropical and humid zone of India

Twelve hundred and twenty-eight goats (Capra hircus L.) from a sub-tropical and humid zone of India were examined for gastrointestinal nematodes. The species encountered in the region were: Haemonchus contortus, Bunostomum trigonocephalum, Oesophagostomum columbianum, Trichuris globulosa, O. aspersum, and T. ovis. The overall infection rate was 86.8%. Among various species found, H. contortus emerged as the most prevalent, although B. trigonocephalum and O. columbianum were also significantly in evidence. The seasonal fluctuation in infection was assessed by monitoring the faecal egg count of 1638 goats slaughtered during the 1-year period. The maximum values for the prevalence and overall mean eggs g-1 of faeces (EPG) were observed after the heavy rainfall season and remained at a relatively high level from July to December. H. contortus and O. columbianum appear to be of major importance as parasites in the goats of this climatic zone; the role of climatic factors in their prevalence is discussed.     

Arrested development of gastrointestinal trichostrongylids in goats in Nigeria

Arrested development of Haemonchus, Cooperia and Trichostrongylus spp. was studied in (1) 14 naturally infected and eight experimentally infected West African Dwarf (WAD) goats reared in the derived savanna zone of eastern Nigeria and (2) 55 naturally infected slaughter goats obtained from the savanna and sahel regions of northern Nigeria. Six of the WAD goats carried natural infections of H. contortus and T. colubriformis and eight other (tracer) goats acquired their infections from a grass paddock artificially contaminated with H. placei, C. pectinata and C. punctata, during May to October. Another three WAD goats were artificially infected with mixed cultures of L3 of the latter three nematodes, while five goats were inoculated with 1500-2000 L3 of H. contortus harvested from cultures incubated at 25-30 degrees C for 8 days either in the dark or under normal laboratory conditions. Approximately 41% (9/22) of the infected WAD goats harboured arrested larvae of Haemonchus and/or Cooperia. No arrested larvae of Trichostrongylus were found in the six animals that were infected with this nematode. The level of inhibition varied from 0.4 to 20% and only three animals showed greater than 10% inhibition. This very low level of inhibition occurred in naturally and experimentally acquired infections, irrespective of the time of year. In the case of Haemonchus, the species and strain of the parasite and infection with L3 cultured in the dark also appeared not to influence the level of inhibition. By contrast, 65.5% (36/55) and 5.5% (3/55) of the northern savanna and sahel goats harboured arrested larvae of H. contortus and T. colubriformis, respectively. The mean percentage inhibition of the former was low (2-25%) during most of the rainy season (June-August) and high (75-90%) during the late rains and the dry season (October-April). The lowest and highest mean percentage inhibitions occurred during July and November, respectively.     

Benefit of the control of gastrointestinal nematode infection in goats in the dry zone of Sri Lanka

The benefit of gastrointestinal nematode control in cross-bred goats in the dry area of Sri Lanka was studied throughout 1 year by comparing the performances of three groups: group 1 animals (n = 11) were left untreated against gastrointestinal nematodes; group 2 animals (n = 11) were given monthly anthelmintic treatment. doramectin, at the dose rate of 300 microg/kg bodyweight during the entire study period; group 3 animals (n = 11) were also given monthly doramectin treatment at the dose rate of 300 microg/kg bodyweight but only during the rainy months, October to January and again once in April. All three groups were turned out together on to communal pasture. Tracers were used for the monthly estimation of gastrointestinal nematode burdens. Four untreated animals and a group 3 animal suffered from parasitic gastroenteritis during the study period. When compared with the controls, the treated groups had significantly lower gastrointestinal nematode infection as indicated by faecal egg counts (P<0.01). Faecal egg counts in group 3 were significantly higher than those in group 2 (P < 0.01). When compared with the controls, the treated groups had significantly greater weight gains (P< 0.05). Haemonchus contortus and Trichostrongylus colubriformis were the predominant gastrointestinal nematodes identified from tracers. The worm burden varied according to the rainfall pattern, with very minimal transmission during the dry period which extends from May to August. Under the conditions of this study, the monthly anthelmintic treatments increased weight gains and prevented parasitic gastroenteritis of goats in the dry zone of Sri Lanka.     

A stochastic model accommodating the FAMACHA© system for estimating worm burdens and associated risk factors in sheep naturally infected with Haemonchus contortus

A previously developed multiple regression algorithm was used as the basis of a stochastic model to simulate worm burdens in sheep naturally infected with Haemonchus contortus over five consecutive Haemonchus seasons (November to January/February) on a farm in the summer rainfall region in South Africa, although only one season is discussed. The algorithm associates haemoglobin levels with worm counts in individual animals. Variables were represented by distributions based on FAMACHA(?) scores and body weights of sheep, and Monte Carlo sampling was used to simulate worm burdens. Under conditions of high disease risk, defined as the sampling event during the worm season with the lowest relative mean haemoglobin level for a class of sheep, the model provided a distribution function for mean class H. contortus burdens and the probability of these occurring. A mean H. contortus burden for ewes (n=130 per sample) of approximately 1000 (range 51-28,768) and 2933 (range 78-44,175) for rams (n=120 per sample) was predicted under these conditions. At the beginning of the worm season when the risk of disease was lowest (i.e. when both classes had their highest estimated mean haemoglobin levels), a mean worm burden of 525 (range 39-4910) for ewes and 651 (range 37-17,260) for rams was predicted. Model indications were that despite being selectively drenched according to FAMACHA(?) evaluation, 72% of the ewes would maintain their mean worm burden below an arbitrarily selected threshold of 1000 even when risk of disease was at its highest. In contrast, far fewer rams (27%) remained below this threshold, especially towards the end of the worm season. The model was most sensitive to changes in haemoglobin value, and thus by extrapolation, the haematocrit, which is used as the gold standard for validating the FAMACHA(?) system. The mean class haemoglobin level at which there was a 50% probability of worm burdens being ≤ 1000 worms was 7.05 g/dl in ewes and 7.92 g/dl in rams.     

A strain of Haemonchus contortus resistant to thiophanate

The occurrence of a field strain of Haemonchus contortus resistant to thiophanate is reported for the first time in New Zealand. In a controlled anthelmintic trial with experimentally infected animals, thiophanate at 50-100 mg/kg had no appreciable effect on the Haemonchus burden. Albendazole reduced faecal strongylate egg counts by 95% in animals with naturally acquired 59 infections.     

Rumen function and digestion of Merino sheep divergently selected for genetic difference in resistance to Haemonchus contortus

The aim of this experiment was to investigate the effect of Haemonchus contortus infection on rumen function and digestion of Merino sheep from lines divergently selected for genetic resistance to H. contortus. Rumen function and whole-tract digestibility were determined in 29 Merino weaner wethers from the CSIRO Haemonchus selection flock, increased resistance to Haemonchus (IRH), decreased resistance to Haemonchus (DRH) and random bred control (C) selection lines. Wethers were fed a restricted low quality roughage diet (5.9 MJ ME/kg DM, 29 g MP/kg DM) to maintain weight and were either uninfected (NIL) or infected with H. contortus (INF). Measurements were taken at week 7 of infection, while animals were housed in metabolic crates. Animals were then euthanased to determine abomasal worm counts. IRH had significantly lower worm egg count than DRH and C lines however, adult worm and larval counts, though lower in IRH animals, did not differ significantly. DM and OM digestibility and in sacco degradability of IRH and DRH selection lines were greater than C animals. Rumen function of animals from the IRH line was altered in response to H. contortus infection with an increase in fluid outflow and turnover rate and a decrease in propionic acid concentration. These changes may be a component of a greater host resistance and begin to explain the failure of IRH animals to translate lower worm egg count into greater bodyweight gain.     

Voluntary feed intake and diet selection of Merino sheep divergently selected for genetic difference in resistance to Haemonchus contortus

This research was designed to determine if divergent selection for resistance to Haemonchus contortus had produced correlated changes in voluntary feed intake and diet selection. Voluntary feed intake, diet selection and production were determined in 54 Merino weaner rams from the CSIRO Haemonchus selection flock, increased resistance to Haemonchus (IRH), decreased resistance to Haemonchus (DRH) and random bred control (C) selection lines. Weaner rams were fed ad libitum either a high (9.2 MJ ME/kg DM, 90 g MP/kg DM) or moderate (6.3 MJ ME/kg DM, 30 g MP/kg DM) quality diet and given the choice between the two diets, when uninfected (NIL) or infected with H. contortus (INF). Symmetrical response to divergent selection for worm egg count (WEC) was not matched by a symmetrical change in feed intake and there was no difference in diet selection between selection lines. Feed intake, growth and wool production of DRH animals remained the same as that of IRH, yet DRH animals had five times greater WEC than IRH. This study begins to explain the mechanisms that allow resistant animals to effectively prevent establishment and/or development of H. contortus, by maintaining a greater immune response to infection through higher circulating eosinophils, plasma globulin and IgG(1) antibody titres. Susceptible animals have displayed resilience by improving feed conversion efficiency and increasing protein synthesis.     

Development and survival of Haemonchus contortus isolated from sheep on a pasture at Bunia (Itiri, Zaire)]

Development and survival of Haemonchus contortus larvae were studied from December 1987 to November 1988 during three different periods (dry season, first and second rainy seasons) on an experimentally infected pasture at Bunia (Ituri, Za?re). Whatever the season, eggs developed into infective larvae within six days and the largest number of larvae on the herbage occurred between the 12th and the 18th day post deposition. However, the two rainy seasons were the most favourable for transmission because of the high number of larvae on the pasture and the increased survival of these larvae after 4 weeks.     

Influence of gastrointestinal trichostrongylidosis on ram fertility

A study on the influence of gastrointestinal trichostrongyles on ram fertility was performed. Two groups of semen donor rams (Sarda breed) were utilized; one was experimentally infected with Haemonchus contortus, Trichostrongylus colubriformis and Teladorsagia circumcincta and the other was used as a control group. In all animals, coprological, haematological and reproductive parameters were studied. The results suggest that the parasites had a limited effect with some changes in phosphorus, cholesterol and chlorine levels. In our experience the parasitic burden produced no significant change on ram fertility.     

Effectiveness of clean grazing strategies in controlling Haemonchus contortus infections in sheep in the United Kingdom

The effectiveness of clean grazing systems for controlling the sheep abomasal parasite Haemonchus contortus under experimental conditions was monitored for a grazing season in ewes and lambs carrying either benzimidazole-susceptible or resistant populations of the parasite. Both preventive and evasive strategies failed to give effective control of H contortus. Lambs grazing with ewes that had received no anthelmintic showed clinical signs of haemonchosis by early July. Lambs from ewes dosed with a benzimidazole (mebendazole) before turn out, developed clinical signs of haemonchosis later in the season. The presence of anthelmintic resistant genotypes had a significant effect on the appearance of clinical signs, and on the epidemiology and control of disease. It was concluded that alternative worm control strategies will be required for the effective control of H contortus in the United Kingdom.     

Nematode parasitism in adult dairy cows in Belgium

Over a period of 1 year, from November 1997 to October 1998, the abomasa, blood and faecal samples of 121 dairy cows in Belgium were collected and examined for nematode infections. Nematodes were present in the abomasa of 110 animals. Ostertagia was found in all 110, Trichostrongylus was seen in 65 and Haemonchus in 14 abomasa. Overall, 91% of all trichostrongyles recovered were Ostertagia. The geometric mean total number of Ostertagia was 2750, with an average of 74% inhibited early fourth stage larvae (EL4). Between November and February >90% of the Ostertagia worm burden were EL4 stages. The majority of the animals (56%) harboured a low Ostertagia burden (100-5000) and 15% had a high burden (>10,000). Sixty-four percent of the coprocultures were positive and the genera recovered were Ostertagia sp. (100%), Trichostrongylus sp. (42%), Oesophagostomum (32%), Haemonchus sp. (29%) and Cooperia sp. (16%). A seasonal pattern was evident for serum Ostertagia-specific antibodies and for serum pepsinogen concentration, with the highest levels during the summer, and low values during the winter. Dictyocaulus viviparus specific antibodies were detected in the serum of eight (7%) animals.     

Performance and nematode infection of ewe lambs on intensive rotational grazing with two different cultivars of <Emphasis Type="Italic">Panicum maximum</Emphasis>

The daily live weight gain (DLWG), faecal nematode egg counts (FEC), and packed cell volume (PCV) of Suffolk, Ile de France and Santa Inês ewe lambs were evaluated fortnightly for 56 days in the dry season (winter) and 64 days in the rainy season (summer) of 2001-2002. The animals were distributed in two similar groups, one located on Aruana and the other on Tanzania grass (Panicum maximum), in rotational grazing system at the Instituto de Zootecnia, in Nova Odessa city (SP), Brazil. In the dry season, 24 one-year-old ewe lambs were used, eight of each breed, and there was no difference (p > 0.05) between grasses for DLWG (100 g/day), although the Suffolk had higher values (p < 0.05) than the other breeds. In the rainy season, with 33 six-month-old ewe lambs, nine Suffolk, eight Ile de France and 16 Santa Inês, the DLWG was not affected by breed, but it was twice as great (71 g/day, p < 0.05) on Aruana as on Tanzania grass (30 g/day). The Santa Inês ewe lambs had the lowest FEC (p < 0.05) and the highest PCV (p < 0.05), confirming their higher resistance to Haemonchus contortus, the prevalent nematode in the rainy season. It was concluded that the best performance of ewe lambs on Aruana pastures in the rainy season is probably explained by their lower nematode infection owing to the better protein content of this grass (mean contents 11.2% crude protein in Aruana grass and 8.7% in Tanzania grass, p < 0.05) which may have improved the immunological system with the consequence that the highest PCV (p < 0.05) observed in those animals.     

An abattoir survey of gastrointestinal nematode infections in cattle in the central highlands of Kenya

The gastrointestinal tracts of 672 crossbred cattle were obtained from various abattoirs in Kiambu District, Kenya from August 1992 to July 1993, and examined for the presence of gastrointestinal nematodes. Eight nematode species were found in 583 (86.8%) of the animals. The nematodes were, in order of prevalence: Haemonchus placei (67.0%), Cooperia pectinata (53.0%), Cooperia punctata (41.7%), Oesophagostomum radiatum (38.4%), Trichostrongylus axei (24.3%), Nematodirus helvetianus (19.6%), Trichuris globulosa (9.7%) and Strongyloides papillosus (3.6%). The intensity of the nematode infection was moderate; the mean burden being less than 7000 worms. H. placei accounted, on average, for 52.3% of the total burden. The total burden was least during the dry seasons and increased gradually during the rainy seasons. Adult H. placei persisted in the host throughout the year and there was no indication of hypobiosis. The heaviest gastrointestinal worm burdens were detected in 1.5- to 3-year-old animals. These findings are discussed with regard to their relevance for strategic control of gastrointestinal nematodes in cattle.     

Epidemiology of gastrointestinal parasites of Awassi sheep in Iraq

Studies on the epidemiology of gastrointestinal nematodes of sheep, conducted at two different farms in the Baghdad area, in 1979, revealed two peaks in worm egg counts in ewes, one in spring and the other in autumn; the latter coincided with the lambing season. Similarly in lambs, two peaks of infection were apparent, but the spring peak was not so well defined. During the hot and dry summer months of Iraq, helminthic infection was at a low level. Faecal culture for larvae and their identification indicated the predominance of Haemonchus contortus infection in the ewes and that of Ostertagia and Trichostrongylus spp. in the lambs examined, Trichostrongylus infection predominating during the hot, dry period of the year. The self-cure phenomenon as well as preparturient rise in egg counts, as reported in other countries, was also observed during this study.     

Epidemiological studies of parasitic gastrointestinal nematodes, cestodes and coccidia infections in cattle in the highveld and lowveld communal grazing areas of Zimbabwe

Between January 1999 and December 2000 faecal samples from 16264 cattle at 12 dipping sites in the highveld and nine in the lowveld communal grazing areas of Zimbabwe were examined for gastrointestinal (GI) nematode and cestodes eggs, and coccidia oocysts. Strongyle larvae were identified following culture of pooled faecal samples collected at monthly intervals. The effects of region, age, sex and season on the prevalence of GI nematodes, cestodes and coccidia were determined. Faecal egg and oocyst counts showed an overall prevalence of GI nematodes of 43%, coccidia 19.8% and cestodes 4.8%. A significantly higher prevalence of infection with GI nematodes, cestodes and coccidia was recorded in calves (P < 0.01) than in adults. Pregnant and lactating cows had significantly higher prevalences than bulls, oxen and non-lactating (dry cows) (P < 0.01). The general trend of eggs per gram (epg) of faeces and oocysts per gram (opg) of faeces was associated with the rainfall pattern in the two regions, with high epg and opg being recorded during the wet months. The most prevalent genera of GI nematodes were Cooperia, Haemonchus and Trichostrongylus in that order. Strongyloides papillosus was found exclusively in calves. Haemonchus was significantly more prevalent during the wet season than the dry season (P < 0.01). In contrast, Trichostrongylus was present in significantly (P < 0.01) higher numbers during the dry months than the wet months, while Cooperia and Oesophagostomum revealed no significant differences between the wet and dry season. These findings are discussed with reference to their relevance for strategic control of GI parasites in cattle in communal grazing areas of Zimbabwe.