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.     

Absence of hypobiosis in abomasal nematodes of sheep and goats in Egypt

A total of 96 abomasa from sheep and goats at the Zagazig abattoir, Sharkia Province, Egypt, were examined, during the four climatic seasons from April 1986 to March 1987, for the presence of adult and larval nematodes. Adults of Trichostrongylus axei were most numerous followed by adult Haemonchus contortus. Adult Ostertagia sp. and Parabronema skrjabini were less prevalent. There was no significant difference between sheep and goats in infection rates, but worm burdens of the nematodes other than Ostertagia sp. were significantly higher (P less than 0.05) in sheep than in goats. The animals were uniformly infected with these parasites throughout the year as there were no significant differences in the incidence or intensity of infections between the four seasons. The numbers of larvae recovered from the wall of the abomasa were small in relation to the total adult worm population throughout the year with a slight increase during the summer. Hypobiosis, therefore, seems not to be important in the life cycle of abomasal nematodes of sheep and goats in Sharkia Province, Egypt.     

The effect of γ-radiation on the development of infective larvae of Trichostrongylus colubriformis in guinea pigs and sheep

Infection of guinea pigs with normal Trichostrongylus colubriformis larvae was characterized by an initial logarithmic decline of total worms recovered over the first few days of infection (“loss phase”) followed by a “plateau phase” when worm numbers remained stationary and a third “expulsion phase” when worm numbers again declined logarithmically with time. Irradiation of infective larvae at 50 and 100 kilorads (krad) affected the subsequent pattern of infection by prolonging the initial “loss phase” and contracting the “plateau phase”. The rate of decline of total worms during either the “loss phase” or the “expulsion phase” was not affected by larval irradiation.Few males were recovered at any stage of infection with larvae irradiated at 50 or 100 krad. However, the irradiated larvae (females) which survived continued development at a rate which was similar to that of normal larvae and it was apparent that these parasites were not able to maintain their position in the small intestine, but continued development during migration towards the posterior.The radiosensitivity of male larvae and worm egg production (eggs in utero) over a range of radiation doses (25 to 100 krad) were remarkably similar. On the other hand, female larvae were clearly less sensitive to γ-radiation. These observations suggested that the depressed egg production in females may be due to the absence of males.     

Abomasal parasitism in dairy cows in Belgium

Over a period of one year, from March 1984 to April 1985, the abomasa of 157 dairy cows in East Flanders (Belgium) were collected and examined for the presence of nematodes. Faeces and blood were also collected from the animals. No worms were recovered from 18 cows (11.5%), 118 cows (75%) had a low to moderate worm burden (10-10,000) and 21 cows (13.5%) a high worm burden (greater than 10,000). The geometric mean total number was 2171. Ostertagia ostertagi and Trichostrongylus axei were the main species involved, with the former accounting for 90% of all trichostrongyles recovered. For both worms a seasonal pattern was evident, with the highest worm counts in December-January. Between December and February greater than 97% of the Ostertagia spp. worm burden were EL4. For all animals the average pepsinogen level was 1391 +/- 494 mU tyrosine with no statistically significant relationship between pepsinogen levels and the total number of gastric nematodes. Only 45% of the faeces samples were positive for strongylid eggs with a mean of 43 eggs per gram. The percentage generic composition of L3 larvae collected from faeces was 62% Ostertagia, 18% Trichostrongylus, 6% Cooperia, 4% Oesophagostomum and 0.2% Bunostomum.     

Observations of the sheath extension of the third stage, infective larvae of Trichostrongylus rugatus

The length of the sheath extension of third stage (L(3)), infective larvae of Trichostrongylus rugatus is reported. The total length and length of the sheath extension of L(3) recovered from the faeces of sheep originating from two localities in South Australia were measured. The total length of larvae was 615-722 microm and the length of the sheath extension was 46-56 microm (mean 51.5). The larvae of T. rugatus comprised up to 72% of the larvae recovered. Worm free sheep were infected with larvae from the two localities and L(3) were recovered following culture of faeces from these experimentally infected animals. L(3) measured 640-746 microm in total length with a sheath extension of 46-56 microm (mean 51.4). Adult nematodes recovered from gastro-intestinal tracts were identified as T. rugatus. The length of the sheath extension used in conjunction with the total length is a characteristic that enables confident differentiation of infective larvae of T. rugatus from other Trichostrongylus species infecting sheep in southern Australia and Haemonchus contortus.     

Efficacy of ivermectin against the swine kidney worm, Stephanurus dentatus

Ivermectin in solution was given subcutaneously (in the neck) at the rate of 0.5 mg/kg of body weight to 5 sows naturally infected with kidney worm (Stephanurus dentatus). Six similar sows were used as nontreated controls. A total of 114 kidney worms were recovered from daily urine samples of 4 of the 5 treated sows (the 5th sow's samples were negative) during the first 4 days after treatment. Ten kidney worms were recovered from daily urine samples of 1 control sow on the 2nd and 3rd days of the post-treatment period. Examination of urine samples from treated sows for kidney worm eggs showed a precipitous numerical decrease. Treated animals became negative between the 5th and 12th days after treatment, and remained negative until necropsy on the 61st day. Compared with control sows, hatchability of eggs and survival of larvae from treated sows was reduced by 9% and 7%, respectively. Kidney worms were not recovered at necropsy from the treated sows, and a total of 392 kidney worms were recovered from the control sows (av 65).     

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.     

Worm burdens in cows II. An analysis of the population of nematodes in the abomasa of adult dairy cows

Over a period of one year, from February 1979—February 1980, the abomasa of four dairy cows were examined each week for the presence of parasitic nematodes. Based on the identification of adult male worms, Ostertagia ostertagi (94%) and Trichostrongylus axei (75%) were the most prevalent species, and Haemonchus contortus was absent. Total worm burdens varied from zero (one cow) to 100 890. The geometric mean total number was 3011. The geometric mean number of arrested larval stages was 685. Of the adult worm burden, more than 85% consisted of O. ostertagi, about 12% of T. axei the remaining 3% was other species. No relationship could be found between worm burdens and the age of the cow, the weight of the abomasum or the milk yield.

The adult Ostertagia burden was highest in the period July–September. The numbers and the percentages of arrested larvae were highest in winter, lowest in summer. Besides those of O. ostertagi, small numbers of arrested larvae of T. axei were observed from September onwards. Cows from farms with a zero-grazing system had significantly fewer worms than cows from other farms independently of the time of the year.     

Abomasal secretion in sheep receiving adult Ostertagia circumcincta that are prevented from contact with the mucosa

AIMS: Both adult and larval Ostertagia circumcincta infections raise abomasal pH and serum gastrin and pepsinogen concentrations, either because of physical effects of the worms or from their chemical secretions. The study was designed to examine whether adult worms require contact with the gastric mucosa to effect changes in gastric secretion. METHODS: Abomasal pH and serum gastrin and pepsinogen concentrations were measured in four groups of sheep: Group A (n = 4): abomasal contents containing about 18,000 adult O. circumcincta were obtained from donor sheep, concentrated and infused into 5 microm mesh porous bags attached to surgically implanted abomasal cannulae. A second worm transplantation was carried out 1 week later to assess worm survival after 16 hours. Group B (n = 4): about 9000 adult worms, recovered after migration out of abomasal contents set in agar, were placed in small 5 microm mesh bags which were inserted through indwelling abomasal cannulae and left for 3 days. Group C (n = 2): about 3000 adult worms from the population recovered from agar were infused through abomasal cannulae which allowed. free movement in the abomasum. Group D (n = 3) was left uninfected. RESULTS: Worms transplanted directly into the abomasum (Group C) caused rapid and marked effects on abomasal secretion. Adult O. circumcincta died within 16 hours of transfer into the abomasum when they were restrained within porous bags. Nevertheless, in sheep receiving 18,000 worms, abomasal pH increased soon after new feed was presented on Days 1, 2 and 4 after worm transfer; serum gastrin was elevated in three sheep from 113 hours and serum pepsinogen increased in one animal. Sheep receiving 9000 worms showed similar trends but the results were equivocal. CONCLUSIONS: Adult O. circumcincta prevented from physical contact with the gastric mucosa by restraint in porous bags are able to raise abomasal pH. This study implicates parasite excretory-secretory products in mediating changes in gastric secretion caused by adult abomasal worms.     

Nematode parasites of adult dairy cattle in the Netherlands

Abomasa, blood samples and faecal samples for examination of nematode infections were collected from 125 dairy cows during the period November 1997-October 1998. Of these, 12 had no grazing history and were, therefore, excluded from this study. From the remaining 113, 88.5% had nematode eggs in the faeces. Larval identification of the positive cultures showed that Ostertagia spp. larvae were most frequent (97%), followed by Trichostrongylus spp. (29%), Oesophagostomum spp. (23%), Cooperia punctata (20%), Cooperia oncophora (4%), Haemonchus contortus (2%) and Bunostomum phlebotomum (1%). The geometric mean EPG was 2.4. Two cows excreted larvae of Dictyocaulus viviparus (0.1 and 0.6 LPG resp.). Worms were found in the abomasa of 108 cows (96%). In all these abomasa Ostertagia spp. was present (100%). Trichostrongylus axei was found in 47 abomasa (43.5%) and two cows (2%) were infected with Capillaria bovis. The geometric mean of the total abomasal worm counts was 1743 and of Ostertagia spp. alone 1615. Almost all male worms were Ostertagia ostertagi, only occasionally Skrjabinagia lyrata10,000) total worm burden.Ostertagia specific antibodies were highest in late summer and autumn and lowest in spring and early summer. The same pattern, although not so pronounced, was observed for the serum pepsinogen values. No clear seasonal pattern was found for the Cooperia specific antibodies. Antibodies against D. viviparus were detected in seven cows (6%).     

Effect of ivermectin on feeding by Haemonchus contortus in vivo

While several in vitro studies have shown that the anthelmintic ivermectin inhibits feeding by parasites, the relevance of this putative site of action in vivo has not been demonstrated. For this study, techniques to measure feeding by Haemonchus contortus in vivo relied on the blood feeding characteristics of the worm, and utilised tritiated inulin administered to sheep intravenously and subsequently measured in worms recovered from abomasa. Nematodes recovered from sheep treated with ivermectin 4 h prior to the [3H]inulin administration showed equivalent feeding levels (over a 1 h period) to those recovered from sheep not treated with ivermectin. In addition, there was no difference in the radioactivity in nematodes of an ivermectin-susceptible and an ivermectin-resistant isolate recovered from individual sheep with concurrent infections after a dose with ivermectin. Ivermectin, therefore, had no effect on feeding by H. contortus in vivo under these experimental conditions. The results are discussed in relation to the dynamics of the expulsion of H. contortus from sheep following ivermectin treatment.     

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.     

The establishment and development of Trichostrongylus colubriformis in goats

Twelve goats were inoculated with 20,000 infective larvae of Trichostrongylus colubriformis and two were killed on each of Days 4, 7, 11, 14, 18 and 21 after inoculation (DAI). The number of worms that established, and the site of development were recorded. Most of the worms established within the first 3 m of the small intestine. There was little relocation or loss of nematodes after establishment. The worms started to migrate from the mucosa to the lumen 11 days after infection. At 4 DAI, 63% of the worms were still at the late L3 stage; the remainder of the worm population had completed the third moult to the L4 stage. The population at 11 DAI comprised largely young adults. When 21 DAI was reached, about 57% of the female worms had eggs in their uteri.     

Are bacillary bands responsible for expulsion of Trichinella spiralis?

Newborn larvae, muscle larvae, intestinal larvae, and adults of Trichinella spiralis were examined by light, scanning and transmission electron microscopy for the presence of bacillary bands and pores of the gland cells. Vital staining of living adults disclosed that the bacillary bands, approximately 5 microm in width, begin at the cephalic end of the worms, on each side of the worm, as a row of single cells. The bands extend, gradually increasing in width, to the posterior end of the worms; and in the mid-body and posterior end of the worms they measure approximately 17 microm wide and accommodate at least two cells side by side. Each gland cell communicates with the outside of the worms through a 1.5--2 microm pore, containing dense material, in the cuticle. The pores constitute anatomic weak points of Trichinella since they can be can be targeted by the host's humoral immune responses and enzymatic attacks. The appearance of patent pores after the first intestinal molt correlates in time with the early expulsion of Trichinella from the intestine, suggesting that the bands may be the source of secreted metabolic or antigenic irritants that initiate, or contribute, to the expulsion mechanisms. Further studies to elucidate the functions of these organs would greatly increase our understanding of the biology of Trichinella and the mechanisms of expulsion.     

Resistance of cotton rats,Sigmodon hispidus,to primary infection by Nippostrongylus brasiliensis

The resistance of cotton rats, Sigmodon hispidus to Nippostrongylus brasiliensis infection was examined and compared the response to that of the susceptible Indian soft-furred rat, Millardia meltada. After a primary infection with infective third-stage N. brasiliensis larvae (L3), the number of eggs in feces and adult worm recovery rates from the small intestine of cotton rats were significantly lower than in the controls. To determine whether cotton rat resistance was observed during the migratory phase or the intestinal phase, cotton rats and control animals were challenged subcutaneously with L3 or intraduodenally with adult worms, and larval recovery from lungs and adult worm burden were evaluated. The recovery rate of larvae from the lungs of cotton rats was about five-fold lower than from controls. Adult worm recovery from the small intestine of cotton rats was also lower than that from the controls, but the difference (two-fold lower) was smaller than that observed for lung recovery. Carbon treatment at a dose of 250-500 mg/kg effectively increased larval worm recovery from the lungs of cotton rats. However, this treatment had no effect on worm recovery from the intestine after intraduodenal implantation of adult N. brasiliensis. These results suggest that macrophage function have important role in the expression of strong resistance during the migratory phase of N. brasiliensis infection in cotton rats.     

Evaluation of techniques for the recovery of live intestinal Trichinella spiralis worms from experimentally infected foxes

Previously described methods for the recovery of intestinal Trichinella worms from rodents are not feasible when applied in larger experimental animals such as foxes. In this study,worm recovery by standard technique of simple incubation of the intestine in saline was compared to embedment of the intestine in an agar gel. The small intestines of Trichinella spiralis infected foxes (4-5 days post inoculation) were slit lengthwise and the two corresponding halves were processed with one of the two incubation methods.Worms were recovered from all samples, and the total worm recovery ranged from 0.2-4.4% of the infection dose. The samples from the standard incubation were very unclear and time consuming to count compared with samples from the agar gel embedment,in which the intestinal debris were kept inside the agar. As the agar gel technique generally yielded higher numbers of worms than the corresponding standard incubation sample, it is with some optimisation, recommended for recovery of intestinal Trichinella worms from foxes.     

Monthly and seasonal fluctuations in abomasal nematode worm burden of naturally infected cattle in Austria

From October 1980 until September 1981, 191 abomasa of naturally infected cattle were obtained from the slaughter-houses of Mürzhofen and Graz in the province of Styria, and of Wiener Neustadt in the province of Lower Austria and examined to study the monthly and seasonal occurrence of hypobiosis in Ostertagia ostertagi and Trichostrongylus axei. Infections in pastured animals (cows, steers and heifers) were compared with those in stabled animals (bulls fed on green forage and silage). Except for 10 bulls fed on silage all animals were parasitized. The results indicate that in Austria inhibited early fourth stage larvae of Ostertagia accumulate during the winter. Pastured animals showed a higher intensity of infection than stabled animals. Cows less than 3 and greater than 5 years of age had higher worm counts than those between these ages. There was a simultaneous accumulation of third stage larvae and adult worms of Trichostrongylus axei in autumn in steers and heifers. In bulls fed on green forage a higher adult worm burden was seen in winter. No significant correlation existed between the number of worm nodules in the abomasal mucosa and the various developmental stages of the worms. The count of in-utero immature eggs was higher in stabled than in pastured animals. No significant correlation between the number of in-utero eggs and that of female worms was noticeable. Numbers of mature Ostertagia eggs rose in spring, while in fall and winter the immature eggs predominated. An increase in the uterine egg count was observed in Trichostrongylus in autumn. Statistical analyses of our data show that the most decisive factor influencing the numbers of inhibited and adult Ostertagia as well as in-utero eggs is the system of animal management.     

Migration of Strongyloides venezuelensis in rats after oral inoculation of free-living infective larvae

Strongyloides venezuelensis (SVZ) infection was chronologically monitored in 85 Sprague-Dawley rats (SDR), which were orally inoculated with approximately 1,000 infective larvae. In order to describe the characteristics of migrating larvae (MLS) in various visceral organs (the liver, lung, cardiac blood, and small intestine), 5 SDR were sacrificed at 20 min, 45 min, 1 hr, 2 hr, 3 hr, 4 hr, 8 hr, 12 hr, 16 hr, 48 hr, 72 hr, 96 hr, 120 hr, 144 hr, 168 hr and 192 hr post inoculation (PI). MLS were recovered from the liver and blood 20 and 45 min PI and measured 788 +/- 26 microm and 846 +/- 40 microm in length, respectively. MLS were first observed in the lung tissue 45 min PI and measured 925 +/- 38 microm on the average. In the trachea, MLS measuring 849 +/- 75 microm appeared 3 to 96 hrs PI. Adult worms (AWS) measuring 1,926 +/- 521 microm to 2,956 +/- 159 microm in length were observed in the small intestine from 120 hr PI. The worms appeared to mature more than 168 hr PI and attained the average maximum length of 2,420 +/- 532 microm. At 3 hr PI focal hyperemic and necrotic lesions were evidently observed in the liver and lung, together with eosinophilic infiltration in the stomach, liver, and lung. The parasites were histologically detectable in the lung tissues but were very difficult to find in the liver and the epithelial layer of small intestine. These data demonstrate that SVZ parasites take 20 min to reach the liver via the stomach and only three hours to reach the trachea through the same route. The development from eggs to adults takes 168 hr in the SDR model.     

Development of immunity to incoming radiolabelled larvae in lambs continuously infected with Ostertagia circumcincta

Infective larvae of Ostertagia circumcincta were radiolabelled with 75selenium by a method which did not affect their viability. Three groups of five-month-old lambs were infected daily with 1000 unlabelled infective larvae for four, eight and 12 weeks, respectively. After each period one of these groups and a group of worm-free controls were challenged with three consecutive daily doses of 1000 radiolabelled third stage larvae. The lambs were killed 13 days after the first dose of challenge larvae and their worm burdens examined. The first indication of immunity was retardation of developing worms observed at four weeks. Resistance to the establishment of incoming worms developed between four and eight weeks and a brief period of population turnover probably took place at this time. Simultaneously a greater inhibition of worm development occurred resulting in an increase in the number of parasites recovered as early fourth stage larvae. By 12 weeks the animals were almost completely immune to incoming worms. The development of resistance to incoming worms correlated with a rise in serum antibody titre and an increase in the number of intraepithelial globule leucocytes in the gastric mucosa.     

Multiple species of nematodes resistant to ivermectin and a benzimidazole-levamisole combination on a sheep farm in New Zealand

AIM: To confirm the presence of multiple anthelmintic resistance on a sheep farm in New Zealand. METHODS: Three groups of 10 weaned Romney-cross lambs were treated either with an oral dose of ivermectin (0.2 mg/kg), or a benzimidazole/levamisole (BZ/LEV) combination (4.75 albendazole and 7.5 mg/kg levamisole), or were left untreated. Ten days later, animals were necropsied, and adult worms recovered and identified from the abomasa and small intestines. Pre- and post-treatment faecal nematode egg counts (FEC) were recorded, and larval cultures were performed. RESULTS: In a faecal egg count reduction test (FECRT), adjusted to reflect pre- and post-treatment larval culture results, ivermectin resistance was detected in Teladorsagia (Ostertagia), Trichostrongylus and Haemonchus spp, while BZ/LEV combination- resistant Teladorsagia and Trichostrongylus spp were also present. Adult worm counts confirmed these results, and identified the species involved as Teladorsagia circumcincta, Trichostrongylus colubriformis and H. contortus. CONCLUSION: Multiple, multi-generic anthelmintic resistance was confirmed on a sheep property in New Zealand. This included the first confirmed case of ivermectin resistance in T. colubriformis from sheep in New Zealand.