World Association for the Advancement of Veterinary Parasitology (W.A.A.V.P.) second edition of guidelines for evaluating the efficacy of anthelmintics in ruminants (bovine, ovine, caprine)

The first edition of the W.A.A.V.P. anthelmintic guidelines for ruminants was published in 1982. Since then improved parasitological procedures have been developed, new therapeutic and prophylactic products have appeared requiring different test methods, and registration authorities are requesting more detailed record keeping and data validation. This second edition addresses these developments and fulfills the original goal of publishing guidelines for high quality, scientifically valid testing standards for trials that would be accepted as proof of efficacy by registration authorities regardless of country of origin. This second edition includes updated guidance on standard parasitological procedures, dose titration, dose confirmation and clinical trials, and provides guidelines for evaluating products for efficacy against anthelmintic resistant parasites, persistence of activity and prophylactic activity. Tests for efficacy against nematodes, trematodes and cestodes are included.

Overberg research projects. XVI. First-stage larval reduction test versus the controlled anthelmintic test to assess the efficacy of anthelmintics against nematode parasites of sheep.

Results of a first-stage larval reduction test (L1RT) were compared with those of a controlled anthelmintic test (CAT) done on naturally infected sheep which grazed on spray-irrigated grass/legume pastures at Tygerhoek Experimental Farm near Riviersonderend in the southern Cape Province. The 3 anthelmintics used were morantel, ivermectin and levamisole. According to the L1RT, treatments reduced the geometric means of Strongyloides by 74.2 to 95.2% and those of the adults of all the other genera (Haemonchus, Nematodirus, Oesophagostomum, Teladorsagia, Trichostrongylus and Trichuris) by 99.4 to 99.75%. By contrast the results of the CAT were more variable, placing the reliability of the L1RT in doubt. In addition, the CAT could also evaluate the effect against fourth larval stage Teladorsagia.

Parasitic control in intensive vs. non-intensive systems--ruminants.

The acquisition and intensity of infection with gastrointestinal nematodes and with Oestrus ovis are compared over 2 years in sheep grazed intensively (26-36 sheep ha-1) or non-intensively (12 sheep ha-1) in the winter rainfall Overberg region of South Africa. Sheep grazing intensively on grass/legume pastures, spray irrigated in summer, acquired massive mixed infections of Trichostrongylus, Haemonchus and Teladorsagia. Infections were fatal for sucking lambs. Lambs from ewes grazed non-intensively on dry land lucerne in winter became infected with Nematodirus and then with Teladorsagia and Trichostrongylus spp.; resistance to Nematodirus was apparent after 12 weeks; spontaneous cure of Teladorsagia began in hoggets grazing on safe wheat stubble pasture; but Trichostrongylus survived in the sheep. Helminth-induced host mortality was not observed on the non-intensive farm. The efficacy of various methods of control was examined in the intensively managed sheep. Removal from pasture, mixed grazing (cattle before sheep) and an albendazole slow release bolus all significantly (P < 0.05) reduced levels of infection in animals so treated, compared with control sheep which were treated periodically with anthelmintics as standard farm management practice. Removal of sheep from the pasture for 30 days in the summer seemed to have beneficial effects. Treatment of sheep weekly with albendazole increased levels of infection in the sheep over controls. The status of vaccination is described and the potential of intergenic competition in grazing management and perhaps vaccination is discussed. Resistance of nematodes to anthelmintics was relatively wide-spread. In both intensive and non-intensive systems. Oestrus ovis larvae were present in flock sheep for 10-12 months per year. Imagines failed to develop from 27 April-9 August and it was concluded that larvae had to overwinter in sheep to survive. Recommendations for integrated control are made for both intensive and non-intensive systems.

Helminth parasites of Cape mountain zebras from Cape Providence, South Africa.

Parasites were collected from 13 Cape mountain zebras (Equus zebra zebra) in the Mountain Zebra National Park, South Africa, during four seasons of 1983 and 1984. Eighteen nematode species belonging to the families Atractidae, Habronematidae, and Strongylidae, and one species of cestode were recovered. The most abundant nematodes were Cyathostomum tetracanthum, Cylicostephanus longiconus and Probstmayria vivipara. Only one of the 10 cyathostome nematodes recovered, C. longiconus was present in every zebra.

Overberg research projects. XV. The efficacy of different anthelmintics against field strains of nematode parasites of sheep in the southern Cape Province.

Controlled anthelmintic tests and faecal egg count reduction tests were carried out on natural infections of nematode parasites in sheep on 4 farms in the southern Cape Province. Albendazole, fenbendazole, ivermectin, levamisole, morantel citrate and a combination of albendazole and closantel sodium were tested. Every farm harboured anthelmintic resistant nematode parasites. Adult as well as immature Teladorsagia spp. were resistant to albendazole and fenbendazole, immature Teladorsagia spp. to albendazole/closantel, adult and immature Nematodirus spp. to albendazole/closantel and adult Nematodirus spp. to fenbendazole.

Overberg research projects. XII. The efficacy of an albendazole slow-release capsule in the control of nematode parasites of sheep.

Albendazole intra-ruminal slow-release capsules (SRC) administered to sheep grazing on irrigated pastures in the southern Cape Province, controlled Trichostrongylus for 91 d and Haemonchus and Teladorsagia for 61 d. Treating sheep with the SRC at 47 to 61 d intervals over a period of 10 months, significantly (P less than 0.05) reduced the infective potential of the pasture. Compared with sheep which received 2 disophenol and 3 broad spectrum anthelmintic treatments during the same period, the SRC reduced the infective potential of the pasture by 71.6%, while weekly drenching with albendazole over the same period, resulted in a significant (P less than 0.05) increase (73.4%) in the infective potential of the pasture.

Overberg research projects. XIII. A comparison of the efficacy of albendazole drench and an albendazole slow-release capsule against nematode parasites in sheep.

The anthelmintic efficacy of albendazole intra-ruminal slow-release capsules (SRC) and albendazole drench against field strains of 5 genera of nematode parasites of sheep, where compared. The SRC reduced the number of L4 and adult Nematodirus by 64.1% and 58.3% and the albendazole drench by 98.1% and 99.1%, respectively. Neither formulation was more than 89.5% effective against either the L4 or adult stage of Teladorsagia. The efficacy of both formulations against the adult stages of Haemonchus, Trichostrongylus and Oesophagostomum ranged from 95.9 to 99.9%.

Overberg Research Projects. XI. First stage larval reduction test to assess anthelmintic efficacy ante mortem in sheep.

Two field trials, one with suckling Merino ewe lambs and the other with yearling Dohne Merino rams, are described. In these the anthelmintic efficacy of febantel (a benzimidazole), ivermectin, levamisole and morantel are compared, using the 1st stage larval reduction test. The mean natural log (+1 for zero values) of the post treatment larval counts of the treated groups was compared with that of the untreated controls and the percentage reduction used to assess anthelmintic efficacy. Febantel was only 87.4% effective against Teladorsagia in suckling lambs but the other anthelmintics were more than 99% effective against this genus. Efficacy against Haemonchus and Trichostrongylus ranged from 93.2%-100% for all 4 compounds. In the rams all compounds were 100% effective against Trichostrongylus, with the exception of morantel which was only 87.5% effective. None of the compounds were effective against Teladorsagia, particularly morantel, animals treated with which having more larvae than the controls. The interpretation of anthelmintic efficacy; the advantages of the first stage larval reduction test, compared with the faecal egg count reduction test; and the importance of incubating cultures at 30 degrees C for 24 h, in order to harvest first stage larvae, are discussed.

Overberg research projects. X. Faecal egg counts in the interpretation of nematode worm burdens in sheep.

Worm egg counts were compared with nematode worm burdens from data collected from greater than 400 sheep killed in experiments on the epidemiology of nematode parasites in the Overberg, in the winter rainfall area of the southern Cape Province. Data were analysed in several ways but no method could be found to accurately estimate the number of nematodes present from the faecal egg count in respect of individual sheep. However, the mean natural log egg count (epg) can roughly predict the mean natural log nematode count in groups of sheep.

Overberg research projects. X. The epidemiology of helminths in ewes and lambs in the southern Cape Province during autumn.

Nematode parasite burdens of ewes grazing on grass/lucerne pasture, increased 58-fold after the first autumn rains in the southern Cape Province. Lambs were infected before the age of 8 weeks and harboured large burdens of nematode parasites before the age of 14 weeks. Oestrus ovis infections were present in 96% of the ewes, while 92% of the lambs above the age of 3 weeks were infected. Anthelmintic treatments in autumn, winter and spring are recommended for controlling parasites of sheep in this region.

Overberg Research Project. IX. First stage larvae per gram [L1p.g.] of faeces; an efficient method of diagnosing nematode parasites of sheep ante mortem.

Nematode eggs were collected by mixing the faeces with a sugar solution, filling a flat-sided medicine bottle (100 ml), and allowing eggs to float and adhere to the upper surface for 30 min. After discarding the faeces, eggs hatched within 24 h at 20-30 degrees C. Each genus was counted in a counting chamber and the L1p.g. estimated. The morphology of L1 of Haemonchus, Teladorsagia, Trichostrongylus, Oesophagostomum and Strongyloides is briefly described.

Overberg Research Projects. VIII. The productivity of Merino ewes subjected to different internal parasite control programmes in the winter rainfall region of South Africa.

Suckling Merino lambs on lucerne pasture, demonstrated no appreciable mass gain when compared with untreated controls, despite regular treatment with anthelmintics. This was ascribed to severe parasitic challenge. After weaning and transfer to wheat stubble fields with no parasitic challenge, however, the live mass of the untreated lambs, still harbouring a residual burden of nematodes, was depressed. Control sheep produced 1.2 kg less wool than regularly-treated sheep, but produced finer wool which had a higher market value. Regularly-treated ewes (F1) produced 12.1% more lambs, but their mean live mass was 2.6 kg lower than that of ewes treated less frequently. The overall financial benefit was in favour of the group which received fewer anthelmintic treatments and was due mainly to the higher market value of the finer wool produced by these apparently stressed animals.

Overberg Research Projects. I. The epidemiology of parasitic nematodes in ewes, suckling lambs and weaners.

Total differential warm counts were done on sheep slaughtered from 7 May 1987 to 19 May 1988 at Boontjieskraal Estate in the Overberg, Republic of South Africa. It was found that winter lambs became infested with Nematodirus spathiger at 5 to 7 weeks of age. At weaning in October 1987 this species was superseded by Teladorsagia circumcincta and Trichostrongylus rugatus. Small numbers of Trichuris skrjabini and Oesophagostomum venulosum were also present. From July to October, 3rd and 4th stage larvae exceeded adult Teladorsagia in ewes, and from July to December 1987 and in May 1988 in lambs and weaners. Juveniles exceeded adult Nematodirus in ewes from July to October 1987 and in suckling lambs in July 1987 and May 1988. Infective larvae aestivate in the faeces or in the soil of the lucerne pastures in the dry, hot summer months and migrate on to the herbage during the cool, wet autumn. Grazing in summer on wheat stubble and even newly sprouted lucerne is safe, in paddocks ranging from 40 to 60 ha in extent, despite massive daily contamination by weaners with more than 60 million worm eggs. Previously infected weaners underwent spontaneous cure within 6 weeks to 6 months of starting to graze safe pastures, Teladorsagia being reduced by 77 to 98%, Nematodirus by 9 to 94% and Trichostrongylus by 34 to 40%.

Availability of infective larvae of parasitic nematodes of sheep grazing on Kikuyu (Pennisetum clandestinum) pastures in the winter rainfall area.

Thirteen groups of 4 South African mutton Merinos grazed for 4 weeks with the flock on Kikuyu pastures and were slaughtered for total and differential worm counts at necropsy. Subsequently 12 groups of 8 week tracers grazed on the pastures and were killed for worm counts post mortem. The following were present in most sheep: Teladorsagia (syn. Ostertagia) circumcincta, Trichostrongylus axei, Trichostrongylus colubriformis, Dictyocaulus filaria and Oesophagostomum venulosum. Haemonchus contortus, Nematodirus spathiger and Trichuris skrjabini were less frequently recovered. Optimal conditions for infestation of grazing sheep occurred from June (late autumn)--October (spring) when mean temperatures in any 4 week period were less than 20 degrees C and a total of greater than 40 mm of rain fell on 8 or more separate days. When the mean temperatures exceeded 20 degrees C pastures were safe, sheep acquiring less than 1,000 worms in 4 weeks.

Internal parasites of horses on mixed grassveld and bushveld in Transvaal, Republic of South Africa.

Between 1980 and 1982, the gastrointestinal tracts of 17 horses which had been grazing on mixed grassveld at Potchefstroom and bushveld at Onderstepoort in the province of Transvaal, Republic of South Africa, were examined at necropsy and processed for parasite recovery. The large strongyles and their prevalences were as follows: Strongylus vulgaris and associated lesions (88-94%), Strongylus edentatus (24%), Strongylus equinus (30%), Triodontophorus nipponicus (35%) and Craterostomum acuticaudatum (18%). The seven most prevalent and abundant cyathostomes collected were Cylicostephanus longibursatus, Cylicostephanus goldi, Cylicostephanus calicatus, Cylicocyclus nassatus, Cyathostomum catinatum, Cylicostephanus minutus and Cyathostomum coronatum. Gasterophilus intestinalis was the most prevalent and abundant botfly larva recovered. Most of the cyathostome larvae and adults were present during all seasons except winter. The distribution of cyathostome species in the large intestine of the host is discussed.

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%.

Nematode parasites from Burchell's zebras in South Africa.

Twenty-five Burchell's zebras (Equus burchelli antiquorum) which were culled at monthly intervals in the Kruger National Park were examined for helminths. Twenty-nine species of nematodes belonging to the families Atractidae, Habronematidae, Onchocercidae, Oxyuridae, Strongylidae, Strongyloididae and Trichostrongylidae were recovered. The cyathostomes (small strongyles) most abundant were Cyathostomum tetracanthum, Cylicostephanus calicatus, Cylindropharynx sp. (? C. intermedia Theiler, 1923) and Cylicocyclus auriculatus. Cyathostomum alveatum, Cyathostomum montgomeryi, Cylicostephanus calicatus and Cylindropharynx sp. (? C. intermedia Theiler, 1923) were the most prevalent cyathostomes (small strongyles) while Craterostomum acuticaudatum was the most prevalent of the large strongyles. Of all the species recovered those most abundant were Crossocephalus viviparus and Probstmayria vivipara with intensities of 100 to 3,857,772 and 18,400 to 104,120,467, respectively. Four new species, two Triodontophorus spp. (Strongylidae) and two Habronema spp. (Habronematidae) were identified. Furthermore, this study furnishes a first report of Triodontophorus minor in zebras. The fourth stage cyathostomes as well as the adults of 11 of the 14 species were present in significantly greater intensities in autumn and winter.

Parasites in sheep grazing on Kikuyu (Pennisetum clandestinum) pastures in the winter rainfall region.

Regular worm counts were done post-mortem on sheep that had grazed on Kikuyu pastures at the Elsenburg Research Station near Stellenbosch, a winter rainfall region. Major species were Trichostrongylus colubriformis, Trichostrongylus axei, while Ostertagia circumcincta was usually present in large numbers. Minor species were Haemonchus contortus, Nematodirus spathiger, Dictyocaulus filaria, Oesophagostomum venulosum, Trichuris spp., Chabertia ovina and larvae of the arthropod Oestrus ovis. Muellerius capillaris caused the formation of nodules in the lungs but were not counted. The trial started in April 1982 and was concluded in March 1984. One hundred and four sheep died or were slaughtered and 99 were examined post-mortem during this period. Total worm burdens rose to a peak of 88,763 (range 67,281-124,735) worms in March 1983, i.e. sheep mortality was such that the flock had to be treated with an anthelmintic in April 1983 to prevent further losses. Kikuyu pastures provide shade, form an excellent mat, the humus layer under the grass retains moisture and is an excellent incubator for preinfective larvae and a protector for infective larvae. If these qualities are combined with more than 100 mm of rain in spring and summer, Kikuyu pastures are a paradise for the free-living stages.