Efficacy of ivermectin against inhibited larvae of Ostertagia ostertagi

The efficacy of ivermectin against inhibited early 4th-stage larvae of ostertagia ostertagi and other nematodes of the abomasum and intestinal tract was determined in naturally infected yearling beef cattle. The time when large numbers of inhibited larvae were acquired was determined by monthly slaughter of monitor cattle, beginning in January. In April, 12 animals were removed from pasture and maintained free of further helminth exposure until slaughter (21 days). At 9 days after the cattle were removed from pasture, ivermectin was administered to the principals by subcutaneous injection (200 micrograms/kg); the other 6 animals were given subcutaneous injections of the ivermectin vehicle. both groups were klled and necropsied at 12 days after treatment. Mean numbers of O ostertagi in the 6 controls were: adults, 41,906; developing 4th stage, 73,813; and early 4th stage, 334,965. The mean proportion of early 4th-stage larvae was 73.7%. In the 6 principals (treated with ivermectin), the following reductions were observed: O ostertagi adults, 100%; developing 4th stage, 99.8%; and early 4th stage, 99,9%. Small numbers of dead and degenerated O ostertagi of all developmental stages were recovered from abomasal washings before fixation; few viable worms were recovered.     

Studies on Ostertagia spp. from Greenlandic sheep: arrested development and worm length

Studies were conducted to investigate earlier observations that lambs slaughtered in Greenland in late September/early October have relatively few arrested larvae in the abomasal mucosa and that the adult Ostertagia from such lambs are abnormally large. Post mortem examination of naturally infected ewes in mid-winter demonstrated that a significant proportion of their Ostertagia population was hypobiotic at this time of year, while an experimental study showed that considerable numbers of larvae of Greenlandic origin became arrested following cold conditioning for 10 weeks. A comparison of adult Ostertagia of Greenlandic and Britain origins from lambs experimentally infected with larvae cultured under identical conditions demonstrated that the "giant" size of the arctic worms was attributed mainly to environmental rather than genetic influences.     

Effect of Ostertagia ostertagi on lamb performance and cross resistance to O circumcincta

Fifteen worm-free lambs (two-and-a-half to three months or four to four-and-a-half months old) were infected with 3500 or 4000 Ostertagia ostertagi larvae on five days each week for six weeks, and their performance compared to that of controls. Eleven lambs were killed after eight weeks and four were challenged with O circumcincta to determine whether any cross resistance had developed. A feature of the O ostertagi infection was the considerable variation in response. Overall liveweight gain was lowered by 24 per cent in the two-and-a-half to three-month-old infected lambs, mainly due to reductions of 27 to 40 per cent in four of the seven lambs. There was no consistent effect in the older lambs. The worm populations consisted mainly of early fourth stage larvae and developing worms, but a small percentage reached sexual maturity and these produced a low faecal egg count (1 to 63 eggs per gram). Numerous intraluminal refractive crystals were present in the gut of both adult worms and developing stages, possibly reflecting degenerative changes. Hypertrophy of the abomasal mucosa with patchy loss of differentiation was a feature of the infection, and in four lambs serum pepsinogen concentrations were elevated. Exposure to O ostertagi did confer some protection against challenge with O circumcincta in that worm counts were reduced to about 60 per cent of those in controls, although no increase was observed in the numbers of arrested larvae. The successful passage of O ostertagi through young lambs could be important in mixed or alternate grazing systems by providing a reservoir of infection for the alternate host.     

Efficacy of albendazole, levamisole and fenbendazole against gastrointestinal nematodes of cattle, with emphasis on inhibited early fourth stage Ostertagia ostertagi larvae.

An experiment was conducted to compare the anthelmintic efficacy of albendazole (ABZ), levamisole (LEV) and fenbendazole (FBZ) against inhibited early fourth stage larvae (EL4) of Ostertagia ostertagi during April in Louisiana. Forty cross-bred beef heifers (average weight 165 kg) were acquired during winter and grazed on pastures contaminated with O. ostertagi and other nematodes until early April. The cattle were weighed and randomly allotted into four groups of ten animals on 6 April and treatments were administered on 7 April. Experimental groupings were: Group 1, non-treated controls; Group 2, ABZ by oral drench at 10 mg kg-1; Group 3, LEV by topical, pour-on administration to back midline at 10 mg kg-1; Group 4, FBZ by oral drench at 10 mg kg-1. Equal numbers of cattle from each group were slaughtered daily between 10 and 13 days after treatment. Mean numbers of O. ostertagi developmental stages present in untreated controls were: adults, 13,714; developing L4 (DL4), 6487; inhibited EL4, 21,719. The mean percentage of inhibited EL4 was 51.8. Smaller numbers of Haemonchus placei, Trichostrongylus axei and Cooperia spp. were recovered uniformly in control cattle. Percentage reduction values for the three compounds against O. ostertagi adults, DL4 and EL4, respectively, were: ABZ, 99.0, 95.3, 84.9; LEV, 1.0, 21.8, 32.1; FBZ, 99.2, 97.2, 97.5. Differences between ABZ and LEV EL4 counts were not significant, but in all other cases worm counts in ABZ and FBZ-treated cattle were significantly lower (P less than or equal to 0.05) than in LEV-treated and control cattle. Both ABZ and FBZ were 98-100% effective against Haemonchus adults and L4, T. axei adults, and Cooperia spp. adults and L4. LEV was 100% effective against Haemonchus adults and L4, 85.6% against T. axei, and 94.6% and 89.59% effective against Cooperia spp. adults and L4, respectively.     

Seasonal changes of gastrointestinal nematode burden in sheep under an intensive grazing system

A study was conducted of the monthly fluctuations of worm burdens and arrested development of gastrointestinal (GI) nematodes in sheep from a commercial farm of the Ebro valley (Spain). Twenty-four previously helminth-free female lambs (permanent lambs) grazed together with a flock of 500 resident ewes for 12 months following a three lambing/2-year reproductive management system. Two helminth-free lambs (tracer lambs) were added to the flock each month and allowed to graze for 4 weeks. Measurements were made of the population of infective larvae on the pasture, and of levels of serum pepsinogen and faecal worm eggs in ewes and lambs. Additionally, post-mortem worm counts from two tracer and two permanent lambs were used to establish the level of infection at monthly intervals. Three generations of parasites were identified in the experiment. The generation derived from eggs deposited the previous autumn gave rise to the first infection of the animals in January and May. This infection had low consequences for the animals, but it signified the initiation of infection and the resumption of the annual cycle of pasture contamination. The second generation, appearing between June and July, was the year's most important source of infection and gave rise to an outbreak of parasitism in permanent lambs. This was indicated by an increase in levels of serum pepsinogen, the appearance of diarrhoea, and an important decrease in lamb growth rates. The third wave of infection, occurring in October and November, there was less impact than the previous one with respect to the level of infection, but it was the origin of the future over-wintering population. Teladorsagia circumcincta was the predominant species, followed by Haemonchus contortus and Trichostrongylus colubriformis. The highest numbers of worm recovered from both the tracer and permanent lambs were observed in July, with average numbers of 7900 and 19,200, respectively.The inhibition phenomenon was more evident in permanent than in tracer lambs, and mainly affected H. contortus as evidenced by populations exhibiting arrested larvae values of over 70% in January and February.Results obtained in this study confirm the epidemiological importance of the over-wintering L(3) generation as the initial source of the animal's infection and the origin of the annual resumption of pasture contamination cycles.     

Seasonal Fluctuation an Inhited Development of Populations of Dictyocaulus filaria in Ewes and Lambs

The fluctuation of populations of Dictyocaulus filaria in sheep was studied under field conditions in which animals are housed during the winter and grazed from late spring to autumn. A comparison was made between residual pasture contamination with overwintered larvae, the fecal larval deposition by ewes from June and both of these factors combined as sources of infection for spring born lambs. Ewes and lambs were killed serially over a year and worms were recovered from the lungs and counted. It was found that during the stabling period most of the ewes were carrying moderate numbers of D. filaria. However, while the vast majority of lungworm populations in the winter was inhibited in development at the early fifth larval stage, virtually all worms in the spring were adults. Any one source of infection studied contributed to the acquisition of important burdens of D. filaria by lambs as well as ewes. Worm counts reached peak in all lambs by November and this pointed to only one important Dictyocaulus generation per grazing season. It would also appear that larvae picked up by ewes and lambs as the grazing season advanced had become inhibited in development with the inhibition rate being most marked in autumn.     

Inhibition of the development of Trichostrongylus spp. as third stage larvae in sheep

In non-lactating Frisian ewes slaughtered in September and November 1975 and in ewes slaughtered in March/April 1976 at lambing, the majority of Trichostrongylus axei, T. vitrinus and T. colubriformis found were inhibited third stage larvae (L₃). However, some larvae at various stages of development were found in the animals slaughtered at lambing. In contrast, in lactating ewes slaughtered 6 weeks after lambing in April 1976, almost all Trichostrongylus spp. appeared to be adults. All ewes grazed a pasture heavily contaminated with gastro-intestinal nematodes from June 1975 until at least 2 weeks before necropsy.In lambs on the pasture from April or June 1975, and slaughtered in September and November 1975 and March 1976 after at least 2 weeks of isolation, only small proportions of the Trichostrongylus spp. populations appeared to be L₃. Similar results were obtained from tracer lambs kept at pasture from August 1975 to March 1976. The implications of these findings are discussed.     

Pasture infectivity with trichostrongylid larvae in the northern Guinea Savanna of Nigeria

For the study of pasture infectivity in the northern Guinea Savanna of Nigeria, variable numbers of helminth-free tracer lambs grazing an unimproved pasture were slaughtered monthly throughout a period of 12 months. The numbers of worms recovered showed that large numbers of infective trichostrongyle larvae were ingested with the pasture from June till October. Infectivity started to decline from November until the end of January after which the pasture became completely free of parasitic nematode larvae and remained so until the end of May.     

Efficacy of febantel against abomasal nematodes and lungworms in cattle

The efficacy of febantel at a dosage of 5 mg/kg (45.5% paste formulation) against inhibited early 4th-stage larvae (EL4) of Ostertagia ostertagi, other nematodes of the abomasum, and Dictyocaulus viviparus was investigated in 4- to 6-month-old Holstein calves that grazed on pasture heavily contaminated with parasites from February 24 to April 1, 1986 (36 days). In Louisiana, this is the first month of a 3-month period in which increasing numbers of inhibition-prone O ostertagi larvae are acquired, and infection risk with D viviparus may remain high. Three of 4 calves that died of lungworm infection during the pasture-exposure period were necropsied. Large numbers of abomasal nematodes, including inhibited O ostertagi larvae, and large numbers of D viviparus were recovered. Twenty-five calves were randomly allotted by equal distribution of body weight to 2 groups and treated on April 4: placebo-treated calves (n = 13) and febantel-treated calves (n = 12). Equal numbers of treated and control calves were killed at 6 and 7 days, respectively, after treatment. Mean numbers of O ostertagi in control cattle were: adults, 4,931; developing 4th-stage larvae (DL4), 1,119; and inhibited EL4, 3,410. Ostertagia lyrata, Trichostrongylus axei, Haemonchus sp, and D viviparus were well distributed in nearly all control calves. Percentage reduction of O ostertagi in treated calves, when compared with controls, was: adults, 83.6%; DL4, 57.8%; and inhibited EL4, 34.8%. Percentage reductions of other species were: O lyrata, 92.6%; T axei adults, 99.3% and 4th-stage larvae (L4), 100%; Haemonchus sp adults, 66.7%, and L4, 64%; D viviparus adults 90.6%, and immature forms, 97.1%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Recovery of different stages of Dictyocaulus viviparus from cattle lungs by a combination of a perfusion and a Baermann technique

The lungs of 71 calves used in two grazing studies were examined for lungworms with a perfusion method combined with a modified Baermann method. The numbers of worms recovered from the lungs were 11,630 in total, 7495 adults, 872 juvenile fifth stage larvae (L5) and 3263 inhibited L5. The percentages found after perfusion were 78.9 per cent in total, 91.8 per cent adults, 78.6 per cent juvenile L5 and 49.6 per cent inhibited L5. The perfusion method seemed adequate and rapid for recovering the adult and juvenile stages but not the inhibited stage. For estimating the numbers of inhibited larvae a combination of perfusion with the Baermann technique is necessary.     

Interactions between Teladorsagia circumcincta and Trichostrongylus vitrinus infections in young lambs

Groups containing six lambs that previously had been infected five times each week for four, eight or 12 weeks, either with 1000 Trichostrongylus vitrinus third stage larvae (L3) or 1000 T vitrinus L3 and 2500 L3 Teladorsagia (previously Ostertagia) circumcincta were challenged, along with six worm-free control lambs, with 3000 75Se-labelled T vitrinus L3. The lambs were killed 10 days after challenge. Those given a dual infection for four and eight weeks had significantly lower total T vitrinus numbers than monospecifically infected lambs. Significantly fewer radiolabelled larvae were recovered from the dual infected group killed after four weeks exposure to infection than from lambs infected monospecifically. The negative interaction between these two nematode species appears to be physiologically mediated and may be an important factor in accounting for differences in their seasonal prevalence.     

Comparison of two techniques used for the recovery of nematode infective larvae from pasture

The recovery of gastrointestinal nematode infective larvae from herbage collected manually was compared with the recovery from herbage ingested by sheep with oesophageal fistulae, on five occasions during the grazing season. At least three times more larvae were recovered from the oesophageal fistulates than by manual collection. There was no significant variation between the numbers of larvae collected at 09.00, 12.00 and 15.00, nor was there any difference in the distribution of genera recovered by the two methods. The worm burdens of tracer lambs and the larval counts from the fistulated sheep were used to estimate the rate of larval establishment.     

Hosts, seasonality and geographic distribution of the South African tortoise tick, Amblyomma marmoreum

The tortoise tick Amblyomma marmoreum was collected from large numbers of reptiles and other animals during the course of numerous surveys conducted in South Africa. A total of 1229 ticks, of which 550 were adults, were recovered from 309 reptiles belonging to 13 species, with leopard tortoises, Geochelone pardalis being the most heavily infested. The 269 birds sampled harboured 4901 larvae, 217 nymphs and no adult ticks, and the prevalence of infestation was greatest on helmeted guineafowls, Numida meleagris. Only two larvae were recovered from 610 rodents, including 31 spring hares, Pedetes capensis, whereas 1144 other small mammals yielded 1835 immature ticks, of which 1655 were collected from 623 scrub hares, Lepus saxatilis. The 213 carnivores examined harboured 2459 ticks of which none were adult. A single adult tick and 6684 larvae and 62 nymphs were recovered from 656 large herbivores, and a total of 4081 immature ticks and three adults were collected from 1543 domestic animals and 194 humans. Adult male and female A. marmoreum were most numerous on reptiles during January and February, and larvae during March. The largest numbers of larvae were present on domestic cattle and helmeted guineafowls in the Eastern Cape Province during March or April respectively, whereas larvae were most numerous on helmeted guineafowls, scrub hares and the vegetation in north-eastern Mpumalanga Province during May. In both provinces nymphs were most numerous between October and December. Amblyomma marmoreum appears to be most prevalent in the western regions of the Western and Eastern Cape and Free State provinces, and the north-eastern regions of the Northern Cape, KwaZulu-Natal, Mpumulanga and Limpopo provinces.     

Pilot project to investigate over-wintering of free-living gastrointestinal nematode larvae of sheep in Ontario,Canada

This study investigated the overwintering survival and infectivity of free-living gastrointestinal nematode (GIN) stages on pasture. The presence of GIN larvae was assessed on 3 sheep farms in Ontario with a reported history of clinical haemonchosis, by collecting monthly pasture samples over the winter months of 2009/2010. The infectivity of GIN larvae on spring pastures was evaluated using 16 tracer lambs. Air and soil temperature and moisture were recorded hourly. Free-living stages of Trichostrongylus spp. and Nematodirus spp. were isolated from herbage samples. Gastrointestinal nematodes were recovered from all tracer lambs on all farms; Teladorsagia sp. was the predominant species. Very low levels of Haemonchus contortus were recovered from 1 animal on 1 farm. The results suggest that Haemonchus larvae do not survive well on pasture, while Teladorsagia sp., Trichostrongylus spp. and Nematodirus spp. are able to overwinter on pasture in Ontario and are still infective for sheep in the spring.     

Influence of two levels of concurrent infection with Ostertagia circumcincta and Trichostrongylus vitrinus on the growth performance of lambs

Groups of seven lambs were infected on five days each week for 11 weeks with either 1000 or 2000 Trichostrongylus vitrinus larvae alone or concurrently with 1500 or 2500 Ostertagia circumcincta larvae and their growth performance compared to that of worm-free controls. The cumulative liveweight gain of the infected groups was significantly lower than that of the controls but the gain of the concurrently infected lambs did not differ significantly from the respective T vitrinus group. There were no significant differences in the numbers of T vitrinus or O circumcincta recovered from the single and concurrently infected groups, although there was a tendency for lower mean T vitrinus burdens at the higher level of ostertagia/trichostrongylus infection. The distribution of T vitrinus along the small intestine was similar in single and concurrently infected lambs. The reason for the lack of a marked additive effect on growth rate with concurrent infection is discussed in relation to changes in the concentration of two plasma constituents and lesions in the gastrointestinal tract.     

The effect of phenothiazine treatment on arrested Haemonchus contortus larvae in sheep

An experimental infection of freshly cultured Haemonchus contortus larvae was given to housed, non-pregnant sheep in October. Phenothiazine was administered to all animals shortly after patency, but the egg output remained negative until mid-April indicating that removal of adult worms from the abomasum did not stimulate the resumption of development of arrested larvae. Worm burdens at post mortem suggest that adults were not being expelled to any great degree during the winter from the host, but this information is clouded by the difference in numbers of both adult worms and arrested larvae in sheep of different haemoglobin type. The results suggest that haemoglobin type may also be a factor in arrest of larvae as it is in the resistance of sheep to adult H. contortus.     

Elephant shrews as hosts of immature ixodid ticks

Two hundred and seventy-three elephant shrews, consisting of 193 Elephantulus myurus, 67 Elephantulus edwardii and 13 animals belonging to other species, were examined for ixodid ticks at 18 localities in South Africa and Namibia. The immature stages of Ixodes rubicundus, Rhipicentor nuttalli, Rhipicephalus warburtoni and a Rhipicephalus pravus-like tick were the most numerous of the 18 tick species recovered. Substantial numbers of immature Rhipicephalus arnoldi, Rhipicephalus distinctus and Rhipicephalus exophthalmos were also collected from elephant shrews at particular localities. Larvae of I. rubicundus were most numerous on E. myurus in Free State Province from April to July and nymphs from June to October. Larvae of R. nuttalli were most numerous on these animals during April, May, August and September, and nymphs in February and from April to August. The immature stages of R. warburtoni were collected from E. myurus only in Free State Province, and larvae were generally most numerous from December to August and nymphs from April to October.     

Parasitism by Oestrus ovis: influence of sheep breed and nematode infections

Previous studies showed that Santa Ines (SI) hair sheep were more resistant to gastrointestinal nematode infections (GIN) than Ile de France (IF) sheep. The present experiment aimed to evaluate if that reported resistance difference against GIN also occurred against Oestrus ovis infestation and also to evaluate the influence of O. ovis infestation on the gastrointestinal nematodes (GIN) infections. SI (n=12) and IF (n=12) young male lambs were weaned at 2 months of age and moved to a paddock (0.3 ha) with Brachiaria decumbens grass, where they also received concentrate ration. The animals were kept together during the experimental period (September to early December 2009). Fecal and blood samples were taken from all animals every 2 weeks and body weight and nasal discharge score (oestrosis clinic signs) were recorded on the same occasion. In early December 2009, all lambs were sacrificed and O. ovis larvae and GIN were recovered, counted and identified according to the larval stage. All animals were infested by different larval instars of O. ovis without any statistical difference between breeds (P>0.05). The SI lambs had an average of 24.8 larvae, and the intensity of infection ranged between 14 and 39 larvae, while the IF lambs showed an average of 23.5 larvae with the minimum and maximum from 11 to 36 larvae, respectively. SI lambs presented the lowest nematode fecal egg counts (FECs) and the lowest mean numbers of Haemonchus contortus, Trichostrongylus colubriformis and Strongyloides papillosus, however, there was no significant differences between group means (P>0.05). Inverse relationship between numbers of O. ovis larvae and gastrointestinal nematodes was observed in both breeds. SI sheep showed a significant increase in blood eosinophils and total IgE serum levels and these variables were negatively correlated with nematode FEC. A negative correlation was observed between total IgE serum level and H. contortus burden in both breeds. In conclusion, there was no breed difference regarding O. ovis infestation and in each breed, animals with more nasal bot fly larvae tended to display smaller worm burden.     

Parasites of domestic and wild animals in South Africa. IV. Helminths in sheep on irrigated pasture on the Transvall Highveld.

The seasonal incidence of helminth infestation in sheep on newly established irrigated pastures was determined by the slaughter of pairs of tracer lambs exposed for periods of approximately 33 days from October 1968--July 1970 and of sets of 3 lambs from March 1971--May 1973. It took several months for the infestation to become established on the pasture, but thereafter, of the various species present; Haemonchus contortus was most prevalent. In general, peak burdens of this species were recovered from January--May or June, while marked inhibition of larval development was evident from April--August. Ostertagia circumcinta usually occurred in increased numbers from April--October, and larval development was inhibited during July and August. Although the sizes of the burdens varied considerably from year to year, Trichostrongylus spp. were present mainly from April--August. Oesophagostomum columbianum, although present in the lambs slaughtered during the first 5 months of the survey, virtually disappeared until May 1971. After this it reappeared in small numbers in nearly all the sheep, reaching peak burdens during April and May 1972, and May 1973. Moniezia expansa were generally recovered from the lambs slaughtered from November--May.     

The population dynamics of nematode parasites of sheep in northern England.

An investigation into the population dynamics of sheep nematodes was carried out between April 1970 and September 1971. Faecal egg counts were made from both ewes and lambs at weeks intervals while grass samples were taken fortnightly throughout the summer and monthly during the winter. From these results absolute numbers of nematode eggs and infective larvae were estimated and these figures used as a basis for determining the level of mortality occurring during development from egg to infective larva. The figures were also used to assess the relative importance of the ewe 'spring rise' and the egg output of the lambs in June while grazing contaminated pasture. These calculations suggest that larval mortality was very high and that it may vary considerably from year to year depending upon the climatic conditions prevailing. There was also an indication that the ewe 'spring rise' was the major source of the wave of infection which occurs in the lambs in late August and September.