Parasites of domestic and wild animals in South Africa. I. Oestrus ovis in sheep

Separate groups of 3 oestrid-free lambs were exposed to infestation on irrigated pasture for periods of approximalely 33 days each over30 months, and on dry-land pasture for approxomately 42 days over a period of 18 months. With some exceptions, the lambs slaughtered from October-June were found to be infested with Oestrus ovis while, with one exception, those slaughtered from July-September were free. A minimum of 4 sheeps' heads, obtained weekly over 24 months from the Pretoria Municipal Abattoir, was examined for infestation. Of a total of 542 heads examined, 73,4% were infested, having a mean burden of 15,2 larvae. Mean larval burdens were slightly greater in hornless than in horned sheep in Dorper-type than in Merino-type sheep, and in lambs than in sheep with 2 or more permanent incisors. The largest larval burdens were recovered from sheep slaughtered during May and June and the smallest during September and October. The greatest number of 1st instar larvae were recovered during May and June and the smallest during September, but those recovered during the latter month were the largest. With one exception, mature larvae which pupated after 21 March or before 16 August failed to hatch as viable flies. Those which pupated after 16 August hatched as flies after a pupal stage of approximately 50 days and the first flies to hatch were invariably recovered during the first 2 weeks of October. The pupal stage decreased to approximately 25 days during December and January and increased again to approximately 50 days for flies hatching during May. No flies hatched between 18 May and 1 Cctober. The following life cycle ofr Oestrus ovis is suggested: sheep are repeatedly infested from October-June; thereafter infestation survives in the sheeps' heads until August, mainly as 1st instar larvae, then as pupae and larvae until fresh infestation takes place during October.     

Parasites of domestic and wild animals in South Africa. VI. Helminths in calves on irrigated pastures on the transvaal highveld

Sets of tracer calves, which were exposed for 2 months on irrigated pasture and then slaughtered, provided evidence of the extent of seasonal helminth infestation. Haemonchus spp. were the most abundant nematodes, the largest numbers of which were generally recovered from May--August. Marked inhibition of development in the 4th larval stage was noted from May--November. Trichostrongylus spp. were recovered in modest numbers with the highest burdens generally present in May, June and October. In the first year of the survey Cooperia spp. were recovered in small numbers, but in the second year burdens increased from February--June.     

Parasites of domestic and wild animals in South Africa. XLII. Helminths of sheep on four farms in the Eastern Cape Province

At monthly intervals for periods ranging from 9 to 25 consecutive months between three and four Merino yearling-sheep and two Merino lambs on three farms in Eastern Cape Thornveld, and two Dorper yearling-sheep on a farm in Valley Bushveld were slaughtered and examined for helminths. The Merino sheep were infected with 15 nematode species, of which Haemonchus contortus, Nematodirus spathiger and Trichostrongylus spp. were the most numerous, and with four cestode species. The Dorper sheep were infected with 17 nematode species, of which Trichostrongylus rugafus and N. spathiger were the most numerous, and with two cestode species. Haemonchus contortus was most numerous in older sheep during the summer months and exhibited no tendency to over-winter as arrested fourth stage larvae. The largest numbers of N. spathiger were present in sheep on the most coastally located of the farms during autumn and winter; on a farm further inland during spring; and on an inland farm in Valley Bushveld during spring and summer. As Merino lambs progressed from birth to 9 months of age a larger proportion of their dwindling burdens of N. spathiger was present as fourth stage larvae. Dorper sheep in Valley Bushveld harboured most Teladorsagia circumcincta in May and from October to January. Trichostrongylus rugatus was most numerous in Merino sheep on one of the Thornveld farms during September, whereas all Trichostrongylus spp., including T. rugatus, were most numerous in Dorper sheep on the Valley Bushveld farm during January.     

Parasites of domestic and wild animals in South Africa. XXV. Ixodid ticks on sheep in the north-eastern Orange Free State and in the eastern Cape Province

The tick burdens of 115 Merino sheep, slaughtered over a period of 15 consecutive months on a farm in the north-eastern Orange Free State, were determined. A total of 7 ixodid and 1 argasid tick species were recovered and the seasonal abundances of Boophilus decoloratus, Hyalomma marginatum rufipes, Margaropus winthemi and Rhipicephalus evertsi evertsi were determined. One hundred and forty-nine Merino sheep were slaughtered over periods varying from 10 to 25 months on 3 farms in Eastern Province Thornveld in the eastern Cape Province and their tick burdens determined. Fourteen ixodid tick species were recovered from these animals and the seasonal abundances of Amblyomma marmoreum, B. decoloratus, Haemaphysalis silacea, R. evertsi evertsi and Rhipicephalus nitens were ascertained. On a farm in Valley Bushveld in the eastern Cape Province, 2 Dorper sheep were slaughtered each month for a period of 24 consecutive months. These 48 sheep harboured 10 ixodid tick species and the seasonal abundances of A. marmoreum, H. silacea, Rhipicephalus appendiculatus and Rhipicephalus glabroscutatum were determined. A total of 17 ixodid tick species, of which 12 had reached the adult stage, where recovered from the sheep on the 5 farms.     

Parasites of domestic and wild animals in South Africa. XXVIII. Helminth and arthropod parasites of Angora goats and kids in Valley Bushveld.

Two adult Angora goats were slaughtered each month for 24 consecutive months on a farm in Valley Bushveld in the eastern Cape Province. On the same farm 2 Angora goat kids were slaughtered each month for 2 consecutive years from the time they were 1 week old until they reached 12 months of age. All these goats were processed for the recovery of helminth and arthropod parasites. Fourteen nematode species, 2 nematode genera and 1 cestode species were recovered. Worm burdens were generally low in the adult goats. Nematode burdens increased erratically in the kids reaching the greatest numbers when they were 1 year old. The tapeworm, Moniezia expansa, was present in kids at 3 or 4 months of age and had usually disappeared by the time they reached 7 months of age.     

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.     

Overberg Research Projects. IV. The development of resistance to Nematodirus in lambs and spontaneous cure of Teladorsagia in weaners

Soon after 12-week old suckling lambs reached a peak infestation of Nematodirus resistance developed, worm burdens falling by 43.1-97.5% in 18 week and 11-month old sheep respectively. Both Teladorsagia (syn. Ostertagia) and Trichostrongylus reached a peak geometric mean (G) of 18,099 and 3,278 worms on 02 December 1987 in weaners 5-6 months old. Within 6 weeks-6 months of sheep grazing on safe pastures, spontaneous cure of Teladorsagia occurred, worm burdens falling by 77.3-98.7% but not of Trichostrongylus which was only reduced by 34-40%.     

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.     

Parasites of domestic and wild animals in South Africa. III. Oestrus spp. and Gedoelstia h?ssleri in the blesbok

Four blesbok culled in the Rietvlei Nature Reserve, Pretoria, District during May 1972 were found to harbour large burdens of 1st instar Oestrus spp. larvae and from 16-37 3rd instar larvae of Oestrus macdonaldi. They were also infested with large numbers of 1st instar Gedoelstia h?ssleri larvae but only 2 harboured 3rd stage larvae of this species. During an 18-month period 34 blesbok were culled in pairs in the Percy Fyfe Nature Reserve, Potgietersrus District. These antelope harboured peak numbers of 1st instar Oestrus spp. larvae during February, July and December but few if any during early October. Third instar Oestrus variolosus larvae were generally recovered from July-February and those of O. macdonaldi during July 1972 and from May-September 1973. Some 1st instar larvae of these flies appeared to undergo a pulmonary migration before returning to the naso-pharyngeal area to mature. The pupal period of O. variolosus varied from 67 days during the spring to 35 days during the summer. G. h?ssleri larvae reached peak numbers from October 1972-January 1973 and during May and June 1973. The lowest numbers were recovered from August-October 1973. Recovery and measurement of 1st instar larvae indicated that they either undergo an ocular-cranial or ocular-vascular-pulmonary migration before reaching the naso-pharyngeal area. Pupal periods varied from 46 days for flies hatching during October to 22 days for those hatching during December.     

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.     

Ostertagia circumcincta infection in lambs originating from larvae which survived the winter

Four worm-free lambs were grazed from May to October 1972 on a paddock carrying a low residual infection of O. circumcincta larvae whilst another group grazed a similar paddock carrying a substantial residual larval infection. On the first paddock the lambs acquired low worm burdens of mature worms passing large numbers of eggs, but in spite of this, pasture larval infection remained low. On the second paddock the lambs acquired high worm burdens, a large proportion of which were immature. On this paddock a rise in pasture larval count was observed and this reached a peak in July and August. In spite of the differences in worm burden of the two groups there was no significant difference in weight gain. The mechanism by which the differences in worm burdens may have developed as well as their implications in worm control are discussed.     

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. VIII. Helminths in pigs kept under semi-intensive conditions

The seasonal incidence of nematode infestations in pigs raised under semi-intensive conditions was determined by the monthly slaughter of 2--4 tracer pigs exposed to infestation in an earthernfloored pen for periods of 1 or 2 months. Although worm burdens were generally small, Ascarops strongylina appeared to be more prevalent from November to March than during the other months of the year. Once Ascaris suum became established in the pen nearly all the pigs became infested. The number of worms never exceeded 88, however, and no seasonal incidence pattern could be determined. Trichuris suis favoured the warmer months from November to March, the smallest numbers being recovered during September and October. One pig only harboured Trichostrongylus colubriformis and 3 had Oesophagostomum dentatum.     

Resistance of Santa Ines, Suffolk and Ile de France sheep to naturally acquired gastrointestinal nematode infections

A study was conducted to assess the breed resistance against nematode infections in Santa Ines, Ile de France and Suffolk male lambs over a 9-month period in S?o Paulo state, Brazil. Lambs were born during the winter (year 2000) and were weaned at 2 months of age. The animals were then housed and treated with anthelmintics to eliminate natural infections by gastrointestinal nematodes. In late October 2000, lambs were placed in a paddock, where they stayed until August of the following year. Fecal and blood samples were taken from each animal every 2 weeks. On the same day, a pasture sample was collected to determine the number of infective larvae on the herbage. To prevent deaths, individual treatment with anthelmintics was provided to lambs with fecal egg counts (FEC) higher than 4000 eggs per gram (EPG) or with a packed cell volume (PCV) lower than 21%. In August 2001, all animals were slaughtered and the worms present in samples of the gastrointestinal contents were identified and counted. Most of the Suffolk and Ile de France sheep received three to six anthelmintic treatments over a period of 7 months, while most of the Santa Ines were not treated. Reductions in PCV and plasma protein values associated with high FEC and worm burdens were recorded, particularly, in Suffolk and Ile de France lambs. Haemonchus contortus and Oesophagostomum columbianum burdens and number of nodular lesions caused in the large intestine by O. columbianum larvae were significantly lower in Santa Ines sheep. All three breeds showed similar Trichostrongylus colubriformis worm burdens. The relative resistance of Santa Ines young male sheep was superior to that of Suffolk and Ile de France sheep.     

The distribution of Nematodirus spp. occurring in sheep in New Zealand

Extract

Most outbreaks of parasitic gastro-enteritis in sheep in New Zealand have been ascribed to the presence of nematodes of the family Trichostrongylidae, and in particular the genera, Haemonchus, Ostertagia, and Trichostrongylus. However, during the period 1956–58, a number of outbreaks of disease occurred in lambs and the condition was associated with heavy Neniatodirus infestation. Although Neinatodirus spp. are commonly foundin sheep in this country, only moderate numbers of worms are usually present in any individual and the worm has been regarded as non-pathogenic. Similar views were held in the British Isles until about 1951, when an acute disease condition of lambs, associated with heavy Neniatodirus burdens, caused serious losses.     

Seasonal variations in the larval burden distribution of Oestrus ovis in sheep in the southwest of Spain

A chronobiological study of oestrosis was conducted for larval instars of Oestrus ovis from November 2000 to September 2002 with the examination of 477 adult sheep of the southwest region of Spain. Skulls from slaughtered sheep were examined and the different O. ovis larval stages (L1, L2, L3) were recovered from the nasal-sinus cavities. O. ovis larvae were detected in 339 sheep, reaching a prevalence of 71.1%. Only one farm was free of infested sheep indicating a prevalence of the 97.91% among studied flocks. The mean larval burden was 18.54 larvae per infested head during the coldest months in the southwest of Spain when the larval burden reached its highest levels, especially of the first larval stage (L1). However, the maximum percentage of L1 coincided with the minimum percentage of the second larval stage (L2). The third larval stage (L3) was observed in relatively low levels during the entered study period, but two peaks occurred in April-May and in September-October. During the 2 years of sampling, all the different larval stages were simultaneously recovered throughout the year, indicating the existence of a long favourable period for the evolution and development of the larval instars, which would start between February and March and finishing in November.     

Studies on the epidemiology of Dictyocaulus filaria infection in Blackface sheep on a low-ground Scottish farm.

The excretion of Dictyocaulus filaria larvae in the faeces of Blackface sheep on a heavily stocked lowland farm in south east Scotland, showed considerable individual, week to week and year to year variation. Patent infections were first observed in lambs in May or June but the heaviest and most prevalent infections occurred in the autumn. Infection levels were generally low but infections tended to be prolonged and reinfection occurred following anthelmintic treatment until the late autumn or winter. Only a few very light, short-lived, patent infections were observed in yearlings or adult ewes. Pasture sampling and the use of tracer animals showed that the numbers of infective larvae on the pasture were minimal during the summer months but reached a low peak in the autumn.     

The effect of feeding sulla (Hedysarum coronarium) or lucerne (Medicago sativa) on lamb parasite burdens and development of immunity to gastrointestinal nematodes

Two experiments investigated the efficacy of the legume Hedysarum coronarium (sulla), which contains condensed tannins (CTs), for reducing gastrointestinal nematode infections relative to lucerne. Experiment 1 was aimed to show whether the lower faecal egg count (FEC) and larval establishment previously reported in lambs grazing sulla were due to direct effects of the forage on Ostertagia circumcincta and Trichostrongylus colubriformis or were mediated through an enhanced immune response. Experiment 2 evaluated the impact of feeding sulla relative to feeding lucerne (Medicago sativa), before, at, or after larval challenge on subsequent FECs and nematode burdens. In experiment 1, 64 Romney lambs were fed either freshly cut lucerne or sulla (32 lambs per herbage) for the duration of the trial. Within each herbage there were four treatment groups (n=8 per group). Initial levels of immunity were assessed in uninfected (UN) lambs which were maintained parasite-free until challenged with 15,000 O. circumcincta and 15,000 T. colubriformis larvae on day 63, and slaughtered on day 81. The other three treatment groups were trickle-infected with each of 5000 O. circumcincta and 5000 T. colubriformis larvae three times per week from day 1 to 35. Non-steroid infected (CONTROL) and steroid-treated (STER) groups were treated with anthelmintic on day 49 and challenged with 15,000 O. circumcincta and 15,000 T. colubriformis on day 63 and slaughtered on day 81. The STER lambs were given dexamethasone trimethylacetate from day 49 to 81 to determine effects of immunity on parasite infection. From day 35 an establishment group (EST) on each herbage was fed a common pelleted lucerne diet and slaughtered on day 56 to determine nematode establishment during trickle-infection. Diet did not affect FECs but feeding lucerne increased (P<0.05) numbers of T. colubriformis in CONTROL lambs compared to those fed sulla. O. circumcincta numbers were lower (P<0.05) in UN lambs fed sulla than lucerne. The sulla diet was associated with higher (P<0.05) antibody titres against secretory-excretory antigens to adult O. circumcincta and to adult and larval T. colubriformis, so there appeared to be some immunogenic response to the sulla diet but effects upon T. colubriformis numbers were not significant. The second experiment involved 48 Romney lambs grazing conventional pasture which were infected with 10,000 each of O. circumcincta and T. colubriformis larvae either 7 days before, 7 days after, or at the time they commenced grazing either sulla or lucerne. Lambs which grazed sulla had lower (P<0.05) FEC and lower (P<0.05) O. circumcincta burdens than lambs which grazed lucerne but timing of infection had no effect on FEC or worm burdens. T. colubriformis numbers were not affected by treatment or herbage. In conclusion, the sulla diet resulted in lower O. circumcincta numbers compared to lucerne outdoors and some evidence of an immunogenic response was obtained indoors. However, neither the herbage nor the immunogenic response reduced T. colubriformis numbers in either experiment.     

Parasites of domestic and wild animals in South Africa. XXXVII. Ixodid ticks on cattle on Kikuyu grass pastures and in Valley Bushveld in the eastern Cape Province

Individual calves, exposed to infestation for 14 d on dry-land Kikuyu grass pastures on the coast near Alexandria, were slaughtered at approximately monthly intervals over a period of 2 years and examined for ticks. Although seven species were recovered total tick burdens were for the most part low. Changing the acaricide with which other cattle on the farm, but not the survey calves, were treated from an organophosphate-based compound to a synthetic pyrethroid resulted in a marked sustained reduction in the number of ticks on the calves. Successive pairs of yearling cattle exposed to infestation on a farm in Valley Bushveld were slaughtered at monthly intervals over a period of 2 years and examined for ixodid ticks. Eleven species were recovered, of which Amblyomma hebraeum, Haemaphysalis silacea, Rhipicephalus appendiculatus and Rhipicephalus glabroscutatum were the most abundant and prevalent. Adult A. hebraeum were generally most numerous from early to late summer, adult R. appendiculatus from mid to late summer, and adult R. glabroscutatum from spring to mid-summer.     

Age and seasonal variations in the prevalence of Oestrus ovis larvae among sheep in northern Jordan

During the period March 1996-July 1997, 417 heads of Awassi sheep slaughtered at the Irbid Abattoir (northern Jordan) were examined for the three larval instars (L1, L2 and L3) of Oestrus ovis. Of the 417 heads, 242 (58%) were infested with O. ovis larvae. Larval numbers were highly aggregated. The lowest number of larvae and the lower quartile were both zero, whilst the median was two and the upper quartile was 12. The highest number of larvae recovered from one head was 151. All three larval instars were observed in each month of the year. July and October had the highest proportions of L1, 75 and 78%, respectively, among infected animals (adjusted for age). The number of larvae increased with age. Infestation with live larvae was associated with inflammatory responses in the upper respiratory tract and with catarrhal or purulent discharge. The percentage of infested sheep and the mean monthly total number of larvae/sheep peaked in the warmer part of the year. Most larvae were L1 except during the spring when L2 and L3 predominated. Distribution analysis demonstrates that the numbers of larvae recovered in the sheep population followed a negative-binomial distribution. Furthermore, the negative-binomial constant k for each month correlated with the monthly prevalence.