Interpretation of total and differential worm counts is not absolute, but depends on clinical history and several interacting factors such as age, sex and nutritional status of the host.

Further information

Sheep

Rumen and Reticulum

Paramphistomes. The immature forms occur in the small intestine. Heavy infections of adults, e.g. 5,000 paramphistomes may be associated with ill health.

Abomasum

Haemonchus contortus. In young sheep 500 worms (light), 3,000 (heavy) and in adults 1,000 (light), 9,000 (heavy).

Ostertagia spp. 3,000-5,000 worms is a heavy infection in young sheep; 5,000-10,000 worms in adult animals may cause mortality. Usually there is a concurrent infection with Trichostrongylus spp. and other intestinal worms.

Trichostrongylus axei. Heavy infections may cause unthriftiness and gastritis.

Small intestine

Trichostrongylus spp. In young poorly grown weaners, 5,000 worms may cause mortality, while in older weaners, 20,000 worms can be considered a heavy infection. A similar number of worms in adult crossbred sheep can be responsible for illthrift and scouring but probably 30,000-40,000 worms are needed to cause mortalities.

Nematodirus spp. In young sheep 1,000-2,000 worms is considered a light burden, but heavier infections of 5,000-10,000 worms may be an important cause of diarrhoea, ill thrift and sometimes mortality. Usually observed as a concurrent infection with Trichostrongylus spp. The importance of immature stages of Nematodirus spp. should be considered in the diagnosis of clinical parasitism.

Strongyloides spp. Not considered of pathogenic importance under field conditions except in young lambs when infection is heavy (10,000-15,000). May be a problem under penned conditions.

Cooperia spp. Heavy infections in young lambs may be of importance.

Paramphistomes. Infections with >5,000 immature stomach fluke cause clinical disease. (80% of immatures are in duodenum).

Moniezia spp. Questionable importance.

Large intestine

Oesophagostomum spp. There may be a heavy infection with larval forms, or very marked nodule formation in previously exposed older sheep due to Oesophagostomum columbianum, when adults may be rare and egg count consequently low. Oesophagostomum columbianum is usually restricted to northern and western district pastoral areas of NSW. Serious chronic effects are caused by severe nodule formation. In young sheep 100 worms is a serious infection and in adult animals 100-200 worms may be significant.

Chabertia ovina. Both immature and adult worms can cause ill effects. In both young and adult sheep, 100-200 worms is a heavy infection.

Trichuris ovis. Heavy infections have been observed in sheep during prolonged drought periods. Inflammatory lesions in the caecum resulting from large numbers of parasites probably cause scouring and illthrift.

Liver

Fasciola hepatica. Mortalities from the acute disease may be associated with 700 or more immature liver fluke and from the chronic disease with 50 or more adult fluke.

Lungs

Lung worms (Dictyocaulus filaria, Muellerius capillaris) are relatively rare in sheep. greater than 50-100 worms may be considered a serious burden.

Cattle

Rumen and Reticulum

Paramphistomes. The immature forms occur in the small intestine. Heavy infections of adults, e.g. 5,000 paramphistomes, may be associated with ill health.

Abomasum

Haemonchus placei. In 6 month-old calves, 5,000 adult worms may be pathogenic causing anaemia, sub-mandibular oedema, and sometimes diarrhoea. Less important in cattle than in sheep.

Ostertagia spp. An important pathogenic parasite of both young and adult cattle as 30,000-50,000 adult worms may cause diarrhoea, weight loss, anaemia and harsh coat. The number of immature stages in the histotrophic form in the abomasal wall should be considered when planning anthelmintic treatments against outbreaks of ostertagiosis. Following a single anthelmintic treatment which removes adult worms, the ensuing development of up to 50,000- 90,000 immature worms could easily cause a second serious wave of adult infection (Type II ostertagiosis). Ostertagiosis should be considered in the differential diagnosis of illthrift and loss of condition in adult cattle, including bulls.

Trichostrongylus axei. Usually found in association with Ostertagia spp., but in lower numbers.

Small intestine

Cooperia spp. The most common small intestinal worm. Always occurs in mixed infections with Ostertagia spp. Heavy burdens of more than 200,000 worms may occur in dairy calves, but clinical signs are due primarily to ostertagiosis.

Trichostrongylus spp. Rarely found in large numbers.

Bunostomum phlebotomum. In young calves 500 worms may be significant. This hookworm causes anaemia, haemorrhagic enteritis and dark, foetid scour.

Moniezia spp. Common in calves but relatively unimportant.

Nematodirus spp. Rarely found in large numbers. Heavy infections may be seen in dairy calves (10,000 worms). Low numbers (2,000-3,000) may be found in young cattle in concurrent infections with other intestinal trichostrongyles.

Paramphistomes. Infections with > 10,000 immature stomach fluke cause clinical disease. (80% of immature worms are in duodenum).

Large intestine

Oesophagostomum radiatum. Found in calves 4-12 months old. A burden of 500-800 worms is a light to medium one, while 1,000 worms may produce clinical signs of parasitism - anaemia, haemorrhagic enteritis, and a watery, mucoid scour. The prepatent stages of this worm in the intestinal wall may also cause ill-effects.

Trichuris spp. Usually found only low numbers and is of little pathogenic importance.

Liver

Fasciola hepatica. An important cause of liver condemnations at abattoirs. Light infestation up to 50; medium infestation 50-100 and heavy infestation, over 100.

Lungs

Dictyocaulus viviparus. Common in dairy calves in cooler areas, but seldom seen in beef cattle. Often seen in conjunction with gastrointestinal parasite burdens.

Pigs

Small intestine

Ascaris suum. Very pathogenic. Any number is significant in young pigs.

Macracanthorhynchus spp. Not common. Heavy infection is 200 worms.

Strongyloides spp. Heavy infections may affect young suckers.

Large intestine

Oesophagostomum spp. Widespread and common cause of scouring in pigs.

Trichuris spp. Heavy infections can cause typhlitis in young pigs.

Lungs, liver and kidneys

Metastrongylus spp. Prevalent lungworm. Immature forms of Ascaris, Stephanurus and Strongyloides may be found wandering in the lung.

Stephanurus denatatus (kidney worm). Very rare parasite in modern pig husbandry, but still found in feral pigs in some locations. May be re-introduced if trend to free-range pigs continues. Heavy and pathogenic burden is 50-100 larvae

References

Cole VG (1986). Animal Health in Australia Volume 8, Helminth Parasites of Sheep and Cattle. Australian Agricultural Health and Quarantine Service, Department of Primary Industries, AGPS, Canberra.
Love SCJ, Hutchinson GW (2003). Pathology and diagnosis of internal parasites in ruminants. In Gross Pathology of Ruminants, Proceedings 350, Post Graduate Foundation in Veterinary Science, University of Sydney, Sydney;Chapter 16:309-338.
Skerman KD, Hillard JJ (1966). A Handbook for Studies of Helminth Parasites of Ruminants. Near East Animal Health Institute, Iran Unit, UNDP, FAO, Rome.
Smeal MG (1995). Parasites of Cattle, Veterinary Review No. 32, Post Graduate Foundation in Veterinary Science, University of Sydney, Sydney.