Liver fluke (Fasciola hepatica) is a flat worm parasite that causes fascioliasis (Shrestha et al., 2020). Cattle, sheep, horses, goats, and pigs are some of the livestock affected by liver flukes (Love, 2008; Tolulope & Lawal, 2020). This worm is a massive concern for the livestock industry because it has a worldwide distribution as a consequence of climate change which causes an increase in liver fluke outbreaks (Boray & Love, 2017; Pritt et al., 2012; Shrestha et al., 2020; Tolulope & Lawal, 2020).
Lifecycle/ Distribution/ Transmission
Liver fluke infections are prominent in areas with a high rainfall but can also be found in areas with a lower rainfall supplemented with irrigation (Boray & Love, 2017; Shrestha et al., 2020). The lifecycle starts with the adult female laying eggs inside the bile duct of the host, the eggs are then passed through the faeces, as illustrated in Figure 1 (Boray & Love, 2007; Delano et al., 2002). The first stage is when miracidium develops inside each egg, when the egg hatches a mature ciliated miracidium is released (Boray & Love, 2007; Tolulope & Lawal, 2020). The miracidia penetrates the soft tissue of the intermediate host (lymnaeid snail), losing its cilia and develop into sporocysts, radiae and cercariae (Boray & Love, 2007; Delano et al., 2002; Tolulope & Lawal, 2020). During this stage, the tadpole-like cercariae leave the snail, and encyst as metacercaria (infective stage) waiting for a mammalian host to ingest the vegetation thereby ingesting the liver fluke encyst (Boray & Love, 2007; Lindquist & Cross, 2017). The liver fluke encysts in the small intestine where they migrate through the gut wall to penetrate the liver (Boray & Love, 2007). The parasites burrow and tunnel through the liver for a period of 6 to 8 weeks, thereafter, entering the bile duct and migrating to the gall bladder where adult liver flukes lay eggs that travel to the bile duct to the gastrointestinal tract of the host (Lindquist & Cross, 2017; Tolulope & Lawal, 2020; Tumwesigye, 2012).
Pathology/ Clinical signs and symptoms/ Diagnosis
Fasciolosis can occur as acute, subacute, or chronic (Boray & Love, 2017; Delano et al., 2002). Animals with acute fasciolosis normally do not show any signs and symptoms of infection, but some animals may have abdominal pian and exhibit jaundice (Boray & Love, 2017). Death of livestock is due to blood loss (hepatic haemorrhage) because of immature liver flukes that burrow through the liver of the host (Boray & Love, 2017). Jaundice, slow growth rate as well as anaemia is symptoms of subacute fasciolosis (Boray & Love, 2017). The most common liver fluke infections in livestock are chronic fasciolosis and occur when the worm enters the bile duct of the host (Boray & Love, 2017).
Black disease is a serious liver condition that can kill sheep and cattle (Boray & Love, 2007, 2017). It is commonly linked to the liver damage brought on by the immature fluke’s migration. The liver’s damage creates a favourable environment for the growth of Clostridium novyi type B bacteria spores (Boray & Love, 2007).
Diagnosis of fasciolosis is based on the clinical signs and symptoms mentioned above together with, fluke eggs present in faecal samples which can be confirmed via a faecal egg count (FEC) performed by Agri FARMACY Laboratory (Boray & Love, 2017; Delano et al., 2002). The Agri FARMACY team can help producers with our in-house laboratory that aids producers in promptly identifying relevant diseases, thereby treating animals faster.
Why is a FEC important? To answer this question, we need to know what a FEC involves. FEC is a quantitative method used for assessing the number of eggs per gram (EPG) of eggs present in a faecal sample. These eggs include Liver fluke (Fasciola hepatica). FEC can be a great tool for you and/or your veterinarian to plan a dewormer control program because it allows a means to quantify changes overtime or in response to a treatment.
Fasciolosis can alternatively be diagnosed using a serological test (blood test; antibody ELISA) (Boray & Love, 2007). It can identify infection with both immature an adult flukes and is more sensitive than a fluke egg count (Boray & Love, 2007).
Socioeconomic importance
Liver fluke cost farmers a lot of money due to production lost, death of livestock as well as the cost of treatment and prevention (Love, 2008). Death of sheep for instance attribute only a portion of the loss as wool quality is reduced, there is a lower number of lambs per lambing season, lamb growth rate decrease, whereas cattle have a decrease in milk production/quality, cattle also experience lowered growth rates which results in a decreased conversion rate (Boray & Love, 2007)
Control methods/ Treatment
The most common way of treating and controlling liver flukes is using flukicides paired with grazing management (Delano et al., 2002; Love, 2008). Two to three treatments should be done in a year, with the April to May treatments being the most important (Love, 2008). It is important to remember that some anthelmintics that work on the adult stage of the liver fluke do not necessarily work on the immature stage of the liver fluke (Boray & Love, 2007). Even if it’s too late to avert financial losses, treatments are essential as soon as clinical signs are evident, in order to prevent the disease from spreading and to reduce the infection rate to a management level (Boray & Love, 2007).
Boray, J.C. & Love, S. 2007. Liver fluke disease in sheep and cattle. (March):10.
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Delano, M.L., Mischler, S.A. & Underwood, W.J. 2002. Chapter 14 – Biology and Diseases of Ruminants: Sheep, Goats, and Cattle. In: J.G. Fox, L.C. Anderson, F.M. Loew, & F.W. Quimby, eds. (American College of Laboratory Animal Medicine). Laboratory Animal Medicine (Second Edition). Burlington: Academic Press. pp. 519–614.
Lindquist, H.D.A. & Cross, J.H. 2017. 195 – Helminths. In: J. Cohen, W.G. Powderly, & S.M. Opal, eds. Infectious Diseases (Fourth Edition). Elsevier. pp. 1763-1779.e1.
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Pritt, S., Cohen, K. & Sedlacek, H. 2012. Chapter 15 – Parasitic Diseases. In: M.A. Suckow, K.A. Stevens, & R.P. Wilson, eds. (American College of Laboratory Animal Medicine). The Laboratory Rabbit, Guinea Pig, Hamster, and Other Rodents. Boston: Academic Press. pp. 415–446.Shrestha, S., Barratt, A., Fox, N.J., Vosough Ahmadi, B. & Hutchings, M.R. 2020. Financial Impacts of Liver Fluke on Livestock Farms Under Climate Change–A Farm Level Assessment. Frontiers in Veterinary Science. 7. https://www.frontiersin.org/articles/10.3389/fvets.2020.564795 Date of access: 03 Aug. 2022