Fascioliosis in Ruminants
Diksha Sharma1, Harshita Sood2
1 P.hD Scholar, Department of Veterinary Parasitology, LUVAS, Hisar
2 Subject Matter Specialist (Vety & AHS), KVK Sirmour, CSKHPKV, Palampur, Himachal Pradesh
Ruminants play an important role in the development of sustainable agricultural systems and the production of food for humans. They are critical in transforming huge renewable resources such as rangeland, pasture, crop leftovers, and other by-products into food. Parasitic infections such as Fascioliosis have a negative impact on animal health and productivity. In India, Fascioliosis is commonly caused by a trematode parasite called Fasciola gigantica. Another species i.e. F. hepatica is also responsible for causing disease but is only present in himalayan region of the country. These fluke affect bile duct and liver of ruminants causing signs such as anorexia, anaemia, ascites, stiff gait, loss of appetite and bottle jaw. F. gigantica is responsible for considerable disease and production losses in terms of decreased milk yield, carcass composition and increased time to reach slaughter weight in ruminants. Human can also be infected with Fasciola spp. due to ingestion of metacercariae containing freshwater plants, especially watercress.
Etiology : Fasciola gigantica, F. hepatica
Life cycle : Life cycle is indirect, requiring snails as intermediate host (fig 1.) Adult parasites are present in bile ducts and liver of definitive host. Immature eggs are excreted in faeces of definitive host. Eggs embryonate and hatch in water to release miracidia which penetrate snail intermediate host of genus Lymnea. Miracidia further develop into different stages i.e. sporocysts, rediae, and cercariae in the snail. The cercariae are released from the snail which encyst on aquatic vegetation or other surfaces as metacercariae. Definitive hosts acquire infection due to ingestion of vegetation containing metacercariae. After ingestion, the metacercariae excyst in the duodenum and migrate through the intestinal wall, the peritoneal cavity, and the liver parenchyma into the biliary ducts, where they develop into adults.
Fig 1. Lifecycle of the liver fluke
Pathogenesis :
After ingestion, metacercariae penetrate the intestine, enter the peritoneal cavity, and penetrate the liver capsule. They burrow through the liver parenchyma for 1 to 3 months, while maturing, and finally enter the bile ducts to complete the life cycle.
The pathogenicity of liver flukes varies depending on the number of metacercariae consumed, the stage of parasite development in the liver, and the host species. The pathogenesis is essentially two-fold. The first phase is related with liver injury and haemorrhage due to migration of immature flukes in the liver parenchyma. The second phase is due to adult flukes in bile duct which feed on liver tissue and cause damage to biliary mucosa by their cuticular spines.
In sheep, the condition can be acute or chronic, while in cattle, it is usually chronic. Hepatitis and inflammation of the bile ducts are seen in light and frequent infections, which ultimately lead to fibrosis. In chronic infections, fibrosis and inflammation spread throughout the entire liver and biliary tract, causing liver enlargement. In cattle, there is calcification of bile duct wall which resemble clay pipe giving rise to the term pipey liver.
Clinical Signs
Fascioliasis ranges in severity from acute, subacute to chronic infection
Acute disease is usually seen in sheep showing signs such as anemia, painful and distended abdomen and sudden death. In acute syndrome, concurrent infections with Clostridium novyi is facilitated due to migration of liver flukes resulting in black disease (clostridial necrotic hepatitis).
In subacute disease, there is reduction in body weight. Animals are lethargic and may die after long period of survival due to hemorrhage and anemia.
In chronic cases, anemia, unthriftiness, and submandibular edema is seen in infected animals.
Diagnosis : Diagnosis is based on clinical signs along with prevailing weather patterns, seasonal incidence, previous history of fasciolosis on the farm, or the identification of snail habitats. Examination of faeces should be done for the presence of fluke eggs.
Treatment : Triclabendazole is the drug of choice for the treatment of fascioliosis as it is effective against both immature and mature flukes. Fascioliosis can also be treated with a number of anthelmintics including closantel, rafoxanide, clorsulon, nitroxinil, albendazole and oxyclozanide.
Prevention and Control : Fascioliosis in ruminants can be prevented by adopting following measures:
- All infected animals should be treated with flukicides that are effective against both juvenile and adult flukes before rainy season, so as to reduce the risk of contamination of pasture/farm with fluke eggs.
- Animals should not be allowed to drink water from snail infested water sources.
- Fodder should be converted into hay or silage which will kill metacercariae.
- Control of snail population by removal of vegetations, draining snail-infested areas, using molluscicides such as copper sulphate, Frescon, Bayluscide etc.
- Satellite surveillance and Geographic information systems (GIS): Snail born diseases can be predicted two months ahead of time using GIS using satellite monitoring and geographic information systems which further helps in their better management.
