Amphistomiasis is an important pathological condition, particularly of ruminants, caused by migrating paramphistome flukes.
Incidence
The paramphistomes are cosmopolitan but the disease is most common in warmer regions, particularly Australia, Africa and India. The disease is endemic in all the states of the country.
Aetiology
Commonly recorded paramphistome species include Paramphistomum cervi, P. gotoi, P. liorchis, P. microbothrium, Cotylophoron catylophorum, Calicophoron calicophorum, Caylonocotyle streptocoelium, Gygantocotyle explanatum, Gasrothylax cruminifer, Fischoenderius elongatus.
Epidemiology
Outbreak occurs more commonly in drier months, immediately after heavy rains or flood when pastures are heavily contaminated with encysted cercariae. Planorbid snails are the intermediate hosts which multiply very rapidly in warm and watery environments. The animals are attracted by lush, green grasses around the ponds, streams and other water sources full of snails and get themselves infected.
All ages of cattle, sheep, goats and wild ruminants grazing near or land liable to flooding may be affected but younger animals are more susceptible than the older ones. Older animals, instead of suffering much act as carrier because of age or may be development of certain immunity. However, they become important by spreading eggs all over the area and are very important from epidemiological point of view.
Pathogenesis
Adult flukes are more or less harmless and reside in the rumen. They may cause focal loss of rumen at the point of heir attachment. Maximum and severe pathogenesis is caused by the immune flukes particularly in duodenum and upper ilium. They cause severe haemorrhage from the point of their attachment and they may penetrate as far as to the muscularis mucosa. In severe cases frank haemorrhagic duodenitis may occur which is caused by deep embedding of the parasites.
In case of Gygantocotyle explanatum which affects the bile duct, gall bladder and sometimes duodenum, there may be superficial haemorrhagic spots indicating the points of attachment of the fluke. In heavy infection the liver may also be affected showing paleness of liver and even fibrosis.
Clinical Findings
A characteristic and persistent foetid diarrhoea, depression, dehydration and anorexia followed by sudden and frequent death are the important clinical signs. Animals become very thirsty and drink frequently. There may be submaxillary oedema and pale mucous membrane. In India, South Africa and Australia, the death rate due to amphistomiasis is about 80-90%. In case of horse it may cause hyper acute colitis followed by acute colic.
Diagnosis
- By clinical signs and symptoms including severe enteritis unaccompanied by fever along with history of particular area because it has been observed that outbreak of amphistomiasis in a particular area almost occurs every year or alternate years.
- In acute cases diagnosis can be done by finding immature flukes in the faeces instead of eggs which may cause confusion.
- Presence of large number of amphistome eggs is also indication of future outbreak and proper precaution should be taken against it.
- Immature flukes may also be found along with eggs particularly in older animals and in endemic areas where these are very common.
- Post mortem examination shows marked enteritis along with large number of immature flukes in the small intestine.
Differential Diagnosis
- Roundworm infestation – faecal examination can differentiate it.
- Infectious enteritides – these are usually accompanied by fever.
- Johne’s disease in older animals but this is a much more chronic disease.
- Poisoning including many weeds, inorganic arsenic and lead.
Treatment
Few drugs are highly effective:
- Two doses of Oxyclozanide 18.7 mg/kg two days apart give consistent result against immature paramphistome in cattle.
- Hexachlororophene @ 7.5 mg/kg in cattle and other large animals for 3 days mixed with vegetable oil gives good result.
- Niclosomide @ 160 mg/kg as a single dose or as two doses three days apart is effective but somewhat variable. In sheep @ 100 mg/kg has goof activity against immature paramphistomes.
- Bithionol sulfoxide @ 25-40 mg/kg daily for 3 consecutive days.
- Lintex @ 50 mg/kg 3 doses at weekly interval.
These new drugs are very expensive and are difficult to use as mass control programme and can be used by individual farmer for his expensive animals.
Control
1. Control of molluscan hosts (snails) – It can be done by 3 ways
(a) Biological
- Propagation of plant like soap berry, shikakai, dividivi which inhibit the growth and reproduction of snails. Some bacteria, fungi, algae can reduce the growth of snails. Larvae of Seiomyzides fly can kill planorbid snails. Giant water bug can control snail population.
- Duck rearing. Fucks may consume large number of snails of the pond.
(b) Mechanical: Removal of vegetation; drainage of swamp and other breeding places of snails; removal of snails through fishing net.
(c) Chemical: Use of copper sulphate.
2. Therapeutic control by drugs: In areas where paramphistomes are a regular problem, a treatment between the seasonal peaks in the availability of metacercaria will reduce the number of eggs falling on the pasture and hence minimise the opportunity for snails to become infected.
3. Management: During an outbreak it is essential to remove animals from the infected pasture. They should not be allowed to graze on flood inundated pasture. Discourage grazing on green pasture surrounding tanks, ponds and bank of river and the animal should be restricted on high lands particularly in amphistome prone areas.
4. Immunization: In South Africa, immunizing agent has been developed against paramphistomiasis. But, in India this has not yet developed.
