Acute Fasciolosis in Sheep: A Neglected Disease
K.H. Bulbul1, Z.A. Wani2, I.M. Allaie2 and Shahanur Rahman3
1Associate Professor, Division of Veterinary Parasitology, F.V.Sc. & A.H, SKUAST-K, Shuhama, Srinagar, J&K, 190006.
2Assistant Professor, Division of Veterinary Parasitology, F.V.Sc. & A.H, SKUAST-K, Shuhama, Srinagar, J&K, 190006.
3M.V.Sc. Student, Division of Livestock Production and Management, F.V.Sc. & A.H, SKUAST-K, Shuhama, Srinagar, J&K, 190006.
Abstract
Fasciolosis is an economically important and potentially fatal disease of sheep which can be associated with particular regions throughout the world directly linked to the habitat of an aquatic mud snail. Out of three forms of fasciolosis, acute fasciolosis caused by Fasciola hepatica and/or F. gigantica is perpetually noticed in sheep. Acute fasciolosis occurs 2-6 weeks after the ingestion of large numbers of metacercariae (usually more than 2,000) over a short period. Acute infection is often seen in younger animals and seasonally and is dominated by the effect of simultaneous migration of immature flukes in the liver causing bleeding and severe liver damage. The acute syndrome can be complicated by concurrent infections with Clostridium novyi, resulting in clostridial necrotic hepatitis. Acute fasciolosis can be treated with triclabendazole and diamphenetide, which is considered as drug of choice for adult as well as immature Fasciola.
Keywords: Acute fasciolosis, Fasciola hepatica, Fasciola gigantica, triclabendazole, sheep
Introduction:
Fasciolosis, a neglected snail borne trematodal disease is caused by Fasciola spp. The economic losses associated with acute fasciolosis are costs associated with diagnosis and treatment, drug resistance against fasciolosis and condemnation of affected livers at slaughter houses (Gajewska et al., 2005). Death can occur in sheep with severe infections leading to economic losses in sheep industry (Soulsby, 1982; Fiss et al., 2012). There are three types of fasciolosis in sheep viz. acute fasciolosis, sub-acute fasciolosis and chronic faciolosis. Acute fasciolosis mostly occurs in sheep which refers to the initial, hepatic phase of the parasitic disease. It is characterized by tissue destruction caused by the migration of the immature parasites from the small intestine to the biliary system. In general, fasiolosis in sheep tend to be more severe than in cattle due to their apparent lack of resistance to the parasite. In this communication transmission, pathogenesis, clinical signs, diagnosis and treatments of acute fasciolosis are discussed below.
Transmission:
Infection is acquired when sheep ingest infective encysted metacercariae that have emerged from the intermediate host, the mud/ aquatic snail Lymnaea auricularia and L. truncatula particularly in India, Bangladesh, Pakistan Nepal etc., and settled on grass.
Pathogenesis:
After excystment in the intestine in presence of bile, pepsin and trypsin, the juvenile flukes penetrate the intestinal wall and migrate to the liver, after which the disease progresses in two clinical phases. Acute fasciolosis begins within approximately two weeks of infection and results from tissue damage and haemorrhage caused by the parasites’ tunnelling and feeding activity in the liver tissue, and as a result of the immunopathology associated with the host’s immune responses. The severity of fasciolosis depends on the number of metacercariae ingested, the phase of development in the liver, and the species of host involved. A traumatic hepatitis produced by the simultaneous migration of large number of immature flukes of 6 to 8 weeks of age and causing extensive destruction of liver parenchyma and marked haemorrhages. Rupture of the liver capsules may occur with haemorrhage into the peritoneal cavity due to excessive number of immature flukes present in the liver (Soulsby, 1982; Bhatia et a., 2010). More than 10000 cysts may be required to cause the syndrome of acute fasciolosis in sheep (Soulsby, 1982). Sheep may die within a few days of the onset of the clinical signs and during this time liver is enlarged, pale, and friable and shows numerous haemorrhagic tracts on the surface and fibrinous clots on the liver surface and throughout the peritoneal cavity. A complication of acute condition occurs due to black disease caused by Clostridium novyi.
The degree of clinical pathology depends on the host, specifically their breed, condition, nutritional status and, most importantly, the burden of infection (Chauvin et al., 2001). While acute infections with large numbers of parasites that penetrate the liver within a short period of time can cause extensive damage to the liver and sudden death in sheep, trickle infections over weeks or months are considered more typical and, therefore, acute and chronic infection can occur simultaneously.
Clinical signs:
Sheep suddenly die without any previous clinical signs. Moreover, in some cases distended and painful abdomen and anaemia may also be noticed. Blood-stained froth appears at the nostril and blood is discharged from the anus, as in case of anthrax.
Epidemiology:
Pathogenic effects mostly occur in younger animals however adult animals may also suffer from this form of fasciolosis. The two major requirements for the establishment of liver fluke in sheep are a susceptible snail intermediate hosts and an environment that suits the fluke eggs, the snails and the larval fluke – such as springs, slow-moving streams with marshy banks, low laying marshy land, irrigation channels and seepages. The aquatic mud snail requires water and warm conditions for reproduction and survival. There are two types infection in snails (“summer” and “winter” infection) which play the pivotal role in availability of metacercariae on the grass/ pasture for the susceptible animals. The ‘summer’ infection of snail results from the hatching of overwintering eggs passed from the sheep in the spring. The metacercariae then appear on pasture from August to October. A less pronounced ‘winter’ infection of snails is from eggs shed by the sheep in the autumn. It is assumed that larval development in the snails ceases during the winter months and begins again in spring resulting in pasture contamination with metacercariae in May and June. Winter infection is significant prolonged survival of the parasite as the infected snail hibernates carrying infection through the winter. Geographical distribution, snail intermediate host, age, sex, breed and species of animals, management systems are considered as epidemiological factors of fasciolosis.
Diagnosis:
Accurate detection of the early onset of fasciolosis is imperative so that a targeted treatment programme can be employed. Conventionally, diagnosis relies on the identification of liver fluke eggs in faecal samples (sedimentation technique; faecal egg count), but this method is not only time-consuming and laborious, it is also insensitive, especially in the case of low fluke burdens. In addition, the method detects infection only after the flukes have matured and produced eggs within the bile ducts, well after liver damage has ensued. Accordingly, recent approaches have employed immunological techniques to improve the sensitivity and accuracy of fluke detection in sheep, for example, the use of capture enzyme linked immunosorbenr (ELISA) for the detection of liver fluke coproantigens in faeces and serological ELISA for the detection of anti-fluke antibodies in blood samples (Alvarez Rojas et al., 2014). PCR and loop-mediated isothermal amplification may also be employed to diagnose this disease.
Treatment:
Management of fasciolosis on sheep farms depends on predicting the extent of infection early so that the appropriate anthelminthic interventions can be applied to prevent losses without the risk of over-treatment and the possibility of abetting the development of drug resistance in parasites (Kelley et al.2016; Kamaludeen et al., 2019). Triclabendazole, a benzimidazole compound active against immature and adult Fasciola spp. is the drug of choice for treatment of fasciolosis. Hence, acute form of fasciolosis may usually be treated with triclabendazole. It’s given orally @10 mg/kg body weight, usually in one or two doses. The triclabendazole may be used as chemoprophylactic anthelmintic in sheep (Shahardar, 2021). A short course of corticosteroids is sometimes prescribed for acute phases with severe symptoms. Diamfenetide may also be given orally @ 120 mg/ kg body weight as chemoprophylactic as well as therapeutic treatment purpose (Shahardar, 2021). Other broad spectrum anthelmintics may be used to treat this condition.
Conclusion:
Acute fasciolosis invariably occurs in sheep throughout the world. Diagnosis of this form of disease is very difficult on faecal examination procedure as the disease caused by immature stages of Fasciola. Various serological and molecular tests are employed to detect this disease nowadays. Triclabendazole is the drug of choice for treatment of the disease.
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https://www.pashudhanpraharee.com/liver-fluke-in-cattle/
https://en.wikivet.net/Fasciolosis
