Watch out for worms during rains season
During Christmas holidays after writing about Rift Valley Fever, I received an email from a farmer requesting that I shed light on liver flukes. Earlier the reader had been informed by a vet at a local slaughter house that the worms had been found in his animal which was seemingly healthy before the slaughter.
Liver fluke infestation — fasciolosis — is common in animals in seasons of heavy rains. This is predisposed by pooling of water in pastures which form good habitats for snails. Mad snails are hosts for the free living stage of liver flukes. The infective stages (larvae) are shed by the snails onto grass blades from where cattle ingest them. Liver flukes are common in cows on free range pastures that have soggy (water logged patches) and these are common following season of heavy rains. Liver flukes affect cattle, sheep and horses. The leaf-shaped parasites lives in the liver and its ducts and all its effects are related to malfunction of the liver and anaemia which affects production, reproduction and growth rate.
Early warning signs
It takes about 10 to 12 weeks after ingestion for ingested larvae to mature and start shedding eggs into the environment. By the time this happens, that animal will be showing clinical signs that include; poor fertility in females shown by lack of heat, slow growth rate for the young ones and reduced milk production for those in lactation. Anaemia indicated by pale mucus membranes will be observed due to liver damage and blood feeding activity of mature worms. At slaughter, you may observe the flukes in the liver.
Is my herd safe?
Sometimes, the post-mortem may indicate presence of the worms but you may not have seen the clinical signs. This is an indicator your herd is infected and you may need to institute a treatment plan guided by your veterinary doctor. Liver fluke eggs can also be isolated from faeces. Although this method may give a negative result when the flukes are still young as only adult liver flukes shed eggs. Antibody detection from blood samples can also be used but this is mostly in research institutions and big farms.
Three factors should be considered in the control and management of liver flukes on farms. The herd fluke history is important as this will most likely show you the level of contamination and probably the extent of infection. Second, it is important to know any past treatments – the drugs type of flukicides used and treatment regime. Finally, presence of stagnant pools of water that are good habitats for snails and the prevailing of past weather conditions characterized by rainfall is also critical.
With these three factors, you should come up with a workable plan assisted by your vet that uses the flukicides to kill the liver flukes while at the same time preventing contamination of the pastures with liver fluke larvae.
Treatment must be repeated after 8 weeks to ensure all stages are killed. Most flukicides do not persist for long in the animal’s body and recently treated animals should not be allowed into contaminated pastures as they will be re-infected immediately.
Wet areas on the farm like around dams or pools of water should be fenced off to avoid contact between animals and contaminated pastures. Water can also be drained to create unfavourable habitat for the intermediate hosts – the mad snail. Alternatively, snails can be killed with molluscicides. Several chemicals can be used including chlorine, potassium permanganate among others. Quarantine new stock whose history or infection status is unknown. This helps to prevent introduction of liver flukes onto your farm. If their status is unknown, call in your vet to do a diagnosis before re-introducing the animal into the rest of the herd.
[The writer was the vet of the year in 2016 and works with the Kenya Tsetse and Trypanosomiasis Eradication Council (KENTTEC) – firstname.lastname@example.org