Amphistomiasis is aparasiticdisease oflivestockanimals, more commonly ofcattle andsheep, andhumans caused byimmaturehelminthic flatworms belonging to the orderEchinostomida. The term amphistomiasis is used for broader connotation implying the disease inflicted by members of Echinostomida including thefamily Paramphistomidae/Gastrodiscidae (to be precise, the speciesGastrodiscoides hominis); whereas paramphistomiasis is restricted to that of the members of the familyParamphistomidae only.G. discoides andWatsonius watsoni are responsible for the disease in humans, while mostparamphistomes are responsible in livestock animals, and some wildmammals.^{[1][2][3][4][5]} In livestock industry the disease causes heavy economic backlashes due to poor production ofmilk,meat andwool.^[6][7]

Symptoms include:

• Physical weakness,emaciation or lethargy^[8][9]
• Foul smell of faeces, greasy consistency and scour or diarrhoea^[8]
• Anorexia, refusal to eat food^[10][11]
• Dehydration and frequent drinking of water^[8][9]
• Submaxillaryoedema (bottle jaw)^[10] and pale mucous membrane^[8][9]
• Intestinal bleeding (haemorrhagic enteritis) with anaemia and low blood protein (hypoproteinaemia)^[8][11]
• Damage to the bile duct, andliver cirrhosis^[11]
• In humans (specifically gastrodiscoidiasis) symptoms includediarrhoea,fever, abdominal pain,colic, and an increasedmucus production. Large amounts of eggs can cause tissue reactions in theheart ormesenteric lymphatics, which may lead to death. Mortality among native Assamese children is attributed to this infection.^[9][12]

Amphistomiasis in farm and wild mammals is due to infection of paramphistomes, such as the species ofParamphistomum,Calicophoron,Cotylophoron,Pseudophisthodiscus, etc. These are essentially rumenflukes, of whichParamphistomum cervi is the most notorious in terms of prevalence andpathogenicity. Infection occurs throughingestion of contaminated vegetables and raw meat, in which the viable infectivemetacercaria are deposited fromsnails, which are theintermediate hosts.^[13][14] Theimmature flukes are responsible for destroying themucosal walls of thealimentary tract on their way to growing into adults. It is by this fervent tissue obliteration that the clinical symptoms are manifested. The adult flukes, on the other hand, are quite harmless, as they merely prepare for reproduction.^[15]

Thezoonotic infection in human is caused byG. discoides andW. watsoni which are essentially intestinal flukes. The disease due toG. discoides is more specifically termed gastrodiscoidiasis.^[16] In their natural hosts such aspigs andmonkeys, their infection inasymptomatic, but human infection is prevalent, by which they cause serious health problems, characterised bydiarrhoea,fever, abdominal pain,colic, and an increasedmucous production. In extreme situations such as inAssam,India, a number of mortality among children is attributed to this disease.^[17]

Adult flukes are known to be quite harmless, as they do not attack on thehost tissue. It is the immature flukes which are most damaging as they get attached to the intestinal wall, literally and actively sloughing off of the tissue. Thisnecrosis is indicated byhaemorrhage infaeces, which in turn is a sign of severe enteritis. Under such condition the animals becomeanorexic and lethargic. It is often accompanied by pronounced diarrhoea,dehydration,oedema,polydipsia,anaemia, listlessness and weight loss. In sheep profuse diarrhoea usually develops two to four weeks after initial infection. If infection is not properly attended death can ensue within 20 days, and in a farm mortality can be very high. In fact there are intermittent reports of mortality as high as 80% among sheep and cattle.^{[3][4][18][19]} Sometimes chronic form is also seen with severeemaciation, anaemia, rough coat, mucosal oedema, thickenedduodenum and oedema in the sub maxillary space.^[5][20][21] The terminally sick animals lie prostrate on the ground, completely emaciated until they die. Inbuffalos, severe haemorrhage was found to be associated withliver cirrhosis and nodularhepatitis.^[22]

Under most situations, infection is hard to recognize because the symptoms are mild or even absent. In humans and wild animals, infection is not easily identified. Especially the adult flukes, even if in large number, generally do not cause complications. There is not yet a standard diagnostic test. Therefore, manual diagnosis is done at many levels. Diagnosis basically relies on a combination ofpostmortem analyses, clinical signs displayed by the animals, and response todrenching. In heavy infection, symptoms are easily observed in sheep and cattle as they become severelyanorexic or inefficiently digest food, and become unthrifty. Copious fetid diarrhea is an obvious indication, as the soiling of hind legs and tails with fluid feces are readily noticeable.^[3][16]

Even though it not always the case, immature flukes can be identified from the fluid excrement. On rare occasions, eggs can be identified from stools of suspected animals.^[1] In developing countries diagnosis andprognosis is often hindered by multiple infections with other trematodes, such asFasciola hepatica andschistosomes, because these flukes are given primary importance due to their pervasive nature.^[5]

Amphistomiasis is considered a neglectedtropical disease, with no prescription drug for treatment and control. Therefore, management of infestation is based mainly on control of the snail population, which transmit the infective larvae of the flukes. However, there are now drugs shown to be effective including resorantel,oxyclozanide, clorsulon,ivermectin,niclosamide, bithional andlevamisole.^{[13][23][24][25]} An in vitro demonstration shows thatplumbagin exhibits high efficacy on adult flukes.^[26][27]

Since the juvenile flukes are the causative individuals of the disease, effective treatment means control of the immature fluke population.Prophylaxis is therefore based on disruption of the environment (such as proper drainage) where the carrier snails inhabit, or more drastic action of usingmolluscicides to eradicate the entire population. For treatment of the infection, drugs effective against the immature flukes are recommended for drenching. For this reason oxyclozanide is advocated as the drug of choice. It effectivelykills the flukes within a few hours and it effective against the flukesresistant to other drugs. The commercially prescribed dosage is 5 mg/kg body weight or 18.7 mg/kg body weight in two divided dose within 72 hours.^[2][28] Niclosamide is also extensively used in mass drenching of sheep. Successfully treated sheep regain appetite within a week, diarrhoea stops in about three days, and physiological indicators (such as plasma protein and albumin levels) return to normal in a month.^[3]

• Veterinary Technical Information
• Drug information at Poulvet
• Drug information at Medivet Pharmaceuticals Lab Pvt Ltd
• Drug information at PVS Animal Health
• Disease information at Merial Sanofi

• Parasitic diseases
• Helminthiases
• Tropical diseases

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