Oesophagostomosis is one of important parasitic diseases of all farm animals except horses caused by the nematode, Oesophagostomum spp. which lodge in the posterior small intestine and large intestine of cattle, sheep, goat, pigs, etc. The disease is popularly known as ‘nodule worm disease’ or ‘pimply gut’.
Aetiology
Important species of Oesophagostomum are generally host specific. Cross infection occurs very rarely.
Sheep and Goat: O. columbianum, O. venulosum, O. asperum.
Cattle: O. radiatum.
Pig: O. dentitatum, O. quadrispinulatum.
Incidence: Oesophagostomosis is prevalent in warmer temperate region and subtropical caiuntries of the world. In pigs, Oesophagostomum infections are cosmopolitan in distribution.
Life Cycle
The life cycle is direct. Eggs are passed in the faeces and hatch and after undergoing 2 moults 3rd stage larvae come out which are infective. After ingestion of these infective larvae, infestation generally occurs. The ingested larvae penetrate the intestinal wall and provoke a nodular host reaction after undergoing another moult. Then they return to the intestinal lumen and another moulting occurs there and they become matures. Egg laying is started within 40-50 days.
Epidemiology
O. columnianamum eggs and larvae are particularly susceptible to cold and dryness. In sheep, the disease is mostly confined to warmer summer rainfall regions. In sufficient larvae are ingested, acute disease may set up during summer months.
Disease in cattle is similarly most common in warmer summer rainfall areas.
In pigs, the infective larvae thrive best when sheltered by thick vegetation in outdoors. During dry summer or winter season, the larvae numbers decrease on bare soil. A periparturient egg rise has been described in case of sows which is an important source of contamination in the farrowing pen. Malnutrition is a primary cause of parasitism. In group fed animals, the sows which can not satisfy their hunger, eat the bedding materials through which the infective larvae enter their bodies.
Pathogenesis
In lambs or in older sheep having no resistence against the parasite, the larvae practically incite no reaction by their migration into the mucosa, so that a large number of adult worms can be found in the colon. But, in other cases, probably due to previous sensitization, the larvae pass into the submucosa and a marked reaction takes place in the form of a localized inflammation around each larva and subsequently there is fibrous encapsulation. There is infiltration of leucocytes specially eosinophils, caesation and metastatic calcification. The larvae may remain alive in these nodules for a period of upto 1 year but many are destroyed by host response. When the resistance of the animal is lowered, larvae leave the nodules, enter the intestinal lumen and pass down to the colon to become adult.
O. columbianum is a serious pathogen of sheep in which 200-300 adult worms may constitute a severe infection. Extensive nodular formation of both small and large intestine seriously interfere with absorption, bowel movement and digestion. The nodules are frequently suppurative and may rupture to the peritoneal surface causing peritonitis and multiple adhesions.
Young susceptible ruminants generally suffer as a result of emergence of larvae from the mucosa provoking a catarrhal colitis and feeding activities of the adults produce small ulcers and mucosal bleeding.
The hypoproteinaemia follows oedema of the caecum and colon and is caused by loss of albumin into the lumen. Anaemia results from blood loss when mucosal larvae re-enter the lumen. In sheep, the nudules can cause considerable pain and result in an arched back and a stilted gait.
Oesophagostomosis is sometime implicated as a primary cause of intussesception in young sheep.
The nodules are much smaller in pigs but heavy infestation may cause oedema and thickening of the colon and caecum. Outbreaks of necrotic enteritis may be activated in pigs carrying Salmonella spp. populations.
Clinical Findings
In lambs, the first sign is a marked and persistent diarrhoea which results in exhaustion and death unless the animals are removed from the infected pasture. The faeces usually have a dark green colour and contain much mucous and sometimes blood. The debilitated animal shows a humped back, the action of the hind legs is stiff and elevation of the tail. In more chronic cases there may be an initial diarrhoea, later followed by constipation and occasional spells of diarrhoea. The animal shows progressive emaciation and weakness. The skin becomes dry and the wool is unthrifty. Nodules may be palpated on rectal examination. Anaemia is not characteristic.
Young calves may show anorexia, diarrhoea, emaciation and anaemia. Initially the diarrhoea may alternate with constipation, but later it is continuous and is dark and foetid.
In pigs, clinical signs are less severe. There are loss of condition and diarrhoea in weaners and growers. In thin sow syndrome-lactating sows become thin in spite of good appetite they become emaciated in severe infestation.
Diagnosis
Examination of the faeces may show the 4th stage larvae in acute cases with diarrhoea or the presence of eggs in other cases. Chronic cases without adult parasites can be diagnosed only tentatively by consideration of the clinical signs together with the history. Because the eggs of Oesophagostomum spp. can not be differentiated easily from those of many G.I nematodes, faecal cultures have to be made and examined when the larvae have reached the infective stage.
Necropsy Findings
There is marked emaciation of the carcass and an almost complete absence of fat. In heavy initial infections a large number of adult worms are seen, the mucous membrane is thickened, reddish and covered with mucous in which the worms are embedded. After repeated infections, the ileum and colon may be studded with nodule of various sizes, some having been converted to abscesses and containing a green to yellowish pus or caseous material.
Differential Diagnosis
- Phenothiazine is highly effective. Dose = 600-700 mg/kg
- Piperazine is highly effective @ 125 mg per kg.
- Thiabendazole is highly effective @ 50 mg/kg
- Benzimidazole compounds are also highly effective against adult Oesophagostomum.
- Moxidectin provides upto 4 weeks protection from reinfection with Oesophagostomum columbianum in sheep.
- Oesophagostomum spp. strains resistant to pyrantel have been detected on some pig farms in Denmark.
Control
In sheep flock at pasture, the infestation may be kept under control by the following three anthelminitic dosing such as in early spring, mid summer and late autumn. The flock should be moved to a clean pasture after each drenching.
In pig, the thin sow syndrome can be prevented by anthelmintic treatment along with providing proper nutritional support to the animal at risk.
The sows should be dewormed before their entry into the furrowing house and the boars should be treated at least once ayear. Over depedence on anthelmintics should be avoided as resistance can develop in Oesophagostomum spp. The ability of the eggs and larvae to survive on the pasture must be considered in case of grazing pigs.
