Common Gastrointestinal Parasites of Small Ruminants

Haemonchusis prevalent in tropical or subtropical regions and in regions with summer rainfall, andH contortusis the most common pathogenic GI parasite in small ruminants。For descriptions and life cycles, seeCommon Parasites of the Abomasum in CattleCommon Parasites of the Abomasum in CattleAdult flukes of the speciesParamphistomumare occasionally found in ruminal fluid or on necropsy in cattle, and eggs may be found on fecal sedimentation. Adults attached to the rumen...read more。

Haemonchosis in sheep may be classified as hyperacute, acute, or chronic. In hyperacute disease, death may occur within 1 week of heavy infection without notable clinical signs. Acute disease is characterized by severe anemia accompanied by generalized edema. Anemia is also characteristic of chronic infection with low worm burdens, and is accompanied by progressive weight loss.

Diarrhea is not a characteristic clinical sign of pureHaemonchusinfection; when diarrhea is present, a mixed infection with other worm genera should be suspected. The abomasum is edematous, and in the chronic phase, gastric pH increases, leading to abomasal dysfunction. Periparturient rise occurs commonly withHaemonchusinfections, and mature sheep and goats may develop fatal infections in late pregnancy and early lactation.

FAMACHA scoring (seeMonitoring诊断接头nosis, Treatment, and Control of Gastrointestinal Parasites in Small RuminantsNematodes of the abomasum in small ruminants cause erosion and ulceration of the gastric mucosa leading to gastritis. Damage to the gastric mucosa decreases the amount of pepsin and hydrochloric...read more) is an important tool in the diagnosis, monitoring, and control of haemonchosis in herds of goat and sheep.

The brown stomach wormsTeladorsagia(formerlyOstertagia)circumcinctaandOstertagia trifurcataare more common in cooler areas with wet winters and temperate zones than areHaemonchusspecies. The lesions, pathogenesis, and clinical signs of infection by these parasites are similar to those of ostertagiasis in cattle (seeCommon Parasites of the Abomasum in CattleCommon Parasites of the Abomasum in CattleAdult flukes of the speciesParamphistomumare occasionally found in ruminal fluid or on necropsy in cattle, and eggs may be found on fecal sedimentation. Adults attached to the rumen...read more).Teladorsagiaadults are 14 mm long and brown, and the female’s tail is annulated.

Even subclinical infection depresses appetite, impairs gastric digestion, and decreases nutrient utilization。Teladorsagiais also involved in the periparturient rise in fecal egg counts in sheep and goats, and heavy infections may lead to diarrhea and depress milk production in dams. The output of eggs is the main source of contamination in lambs and kids. The same type of inhibited larval development that occurs in cattle has been observed with bothOstertagiaandHaemonchusin small ruminants.

Trichostrongylus axeiis also more common in temperate zones than areHaemonchusspecies.T axeiinfections in small ruminants show the same lesions, pathogenesis, and clinical signs as infections in cattle (seeCommon Parasites of the Abomasum in CattleCommon Parasites of the Abomasum in CattleAdult flukes of the speciesParamphistomumare occasionally found in ruminal fluid or on necropsy in cattle, and eggs may be found on fecal sedimentation. Adults attached to the rumen...read more).

Mecistocirrus digitatusis ahematophagoustrichostrongyle with a pathology similar to that ofHaemonchus; however,M digitatusadults are much larger, ~40 mm. This parasite is typically present only in tropical climates.

Trichostrongylus colubriformis,Trichostrongylus vitrinus, andTrichostrongylus rugatusare found in the small intestine of small ruminants. The life cycle and appearance of eggs on fecal flotation are typical of a trichostrongyle, and the prepatent period is 18–21 days.

Anorexia, persistent diarrhea, and weight lossare the main clinical signs ofTrichostrongylusinfection. Villous atrophy (or stunting of villi) impairs digestion and malabsorption; protein loss occurs across the damaged mucosa.

Strongyloides papillosusis not a trichostrongyle, and it has a complex life cycle (seeCommon Gastrointestinal Parasites of CattleAdult flukes of the speciesParamphistomumare occasionally found in ruminal fluid or on necropsy in cattle, and eggs may be found on fecal sedimentation. Adults attached to the rumen...read moreCommon Parasites of the Small Intestine in CattleCommon Parasites of the Small Intestine in cattleAdult flukes of the speciesParamphistomumare occasionally found in ruminal fluid or on necropsy in cattle, and eggs may be found on fecal sedimentation. Adults attached to the rumen...read more). Heavy infections by adult worms cause a disease resembling trichostrongylosis. The means of infection is usually skin penetration; however,S papillosuscan also infect the animal via milk.

Damage to the skin between the claws, produced by skin-penetrating larvae, resembles the early stages offootrotFootrot and Foot Scald in GoatsFootrot and foot scald are serious problems of sheep and can also have a major adverse impact on goats under certain management conditions.read moreand may aid penetration by the causative agents of foot rot. Most infections are transitory and inconsequential.

Bunostomum trigonocephalum(hookworm) adults are found in the jejunum. The life cycle and clinical findings are essentially the same as for thecattle hookwormCommon Parasites of the Small Intestine in cattleAdult flukes of the speciesParamphistomumare occasionally found in ruminal fluid or on necropsy in cattle, and eggs may be found on fecal sedimentation. Adults attached to the rumen...read more, withas few as 100 worms causing clinical signs。

Gaigeria pachyscelisis found in Africa and Asia and resemblesBunostomumin size (2–3 cm) and form. Larvae ofG pachyscelisinfect the host only by skin penetration。It is avoracious bloodsucker and highly pathogenic。

The species ofNematodirusfound in the small intestine of sheep and goats are similar in morphology and life cycle to theNematodirusspp found in cattle (seeCommon Parasites of the Small Intestine in CattleCommon Parasites of the Small Intestine in cattleAdult flukes of the speciesParamphistomumare occasionally found in ruminal fluid or on necropsy in cattle, and eggs may be found on fecal sedimentation. Adults attached to the rumen...read more).Clinical infections ofNematodirusare of considerable importance in the UK, New Zealand, and Australia, where lamb mortality may reach 20% in affected flocks if animals are untreated。The parasites are also endemic in some parts of the US, where they occasionally cause disease in young animals. The life cycle can be broken if lambing or kidding takes place in different areas each year. Most clinical infections occur in animals 6–12 weeks old.

Nematodirus battusis an important parasite of lambs in the UK and other parts of Europe and North America. Eggs hatch after a period of chill and then a rise in ambient temperature to a day/night mean of 10°C (50°F), which in temperate areas occurs in late spring. These hatching requirements mean that there is generally one generation ofN battusper year; in the UK, however, occasional outbreaks in the fall have been reported.

因为larg可以高致病性寄生虫e numbers of larvae hatch over a short period at a time when young lambs are beginning to consume sizable quantities of grass. Disease may be associated with developing larval stages and may occur within 2 weeks of challenge (the prepatent period is 15 days). OtherNematodirusspp often are found in low-rainfall regions (eg, the Karoo in South Africa and inland Australia) where other parasites are rare.

Nematodirosis is characterized bysudden-onset unthriftiness, profuse diarrhea, and marked dehydration, with death as early as 2–3 days after an outbreak begins. Nematodirosis is commonly confined to lambs or weaner sheep, but in low-rainfall country where outbreaks are sporadic, older sheep may have heavy infections.

Nematodirosis lesions usually consist of dehydration and a mild catarrhal enteritis; however, acute inflammation of the entire small intestine may develop. Counts of ≥ 10,000 worms, together with characteristic clinical signs and history, are indicative of clinical infections. Affected lambs may pass large numbers of eggs, which can be identified easily. If the onset of disease precedes maturation of the female worms, eggs will not be identified on fecal examination.

Aonchotheca(formerlyCapillaria)longipesis closely related toTrichuris, but its eggs are slightly smaller and lighter brown, and the bipolar plugs are less prominent.A longipeshas been detected on routine fecal examination; however,no specific pathogenicity has been reported in small ruminants。For more information regarding egg identification, seeCommon Gastrointestinal Parasites of CattleAdult flukes of the speciesParamphistomumare occasionally found in ruminal fluid or on necropsy in cattle, and eggs may be found on fecal sedimentation. Adults attached to the rumen...read moreCommon Parasites of the Small Intestine in CattleCommon Parasites of the Small Intestine in cattleAdult flukes of the speciesParamphistomumare occasionally found in ruminal fluid or on necropsy in cattle, and eggs may be found on fecal sedimentation. Adults attached to the rumen...read more。

Moniezia expansa,Moniezia benedeni, andMoniezia capraecan all be found in small ruminants; however, the pathogenicity ofMonieziahas long been debated. Many earlier observations, which associatedMonieziainfection with diarrhea, emaciation, and weight loss, did not accurately differentiate between tapeworm infections and infection with certain small nematodes (eg,Trichostrongylus colubriformis).

绦虫是相对不致病的,但重infections can result in mild unthriftiness and GI disturbances。诊断接头nosis may be made if individual segments (which are much wider than they are long) are found in the feces, if lengths of adult tapeworms are observed protruding from the anus, or if the characteristic square to rectangular eggs are evident on fecal examination.

The life cycle ofMonieziaspp is indirect and involves an oribatid mite that lives on the pasture. The prepatent period is 6–7 weeks. Infections are seasonal, aligned with mite activity, and unusual in animals older than 5–6 months.

Thysanosoma actinioidesinhabits the duodenum, the bile ducts, and the pancreatic ducts of small ruminants. It is commonly found in sheep from the southern and western parts of the US and South America. The adult tapeworm can be up to 50 cm long, the head (scolex) is 1.5 mm, and the segments (proglottids) are much wider than they are long and have fringed posterior borders.

Although it has not been associated with disease,T actinioidesis of economic importance because livers are condemned when tapeworms are found in the bile duct.