Managing Haemonchus worm, the nasty blood thief of sheep and goats
A boy looking after their goats at a dry Enziu river in Kitui County on December 1, 2022.
As I promised, this week I explain how to manage the ‘nasty blood thief of sheep and goats”. For those who may have missed my article last week, this is the term I use for the notorious sheep and goats killer round worm called Haemonchus contortus. The parasite also affects cattle, especially calves, and has also been found in the stomach of humans in Brazil and Australia.
In the article, I narrated my encounter with the Haemonchus worm on David’s farm in Nairobi where sheep and goats, dewormed about a month earlier, were dying even after treatment with antibiotics and dewormers.
My clinical and postmortem examination of one seriously sick sheep confirmed my suspicion of infestation with the Haemonchus contortus worms. I found large numbers of the parasites in the sheep’s stomach.
The good news is that the sheep have since recovered after treating them with a dewormer combination that had not been used on the farm before.
I call the Haemonchus worm a blood thief because it simply settles in the sheep’s stomach and literally sucks out all the blood without the owner of the animals knowing. Depending on the number of worms in the sheep, an infested animal may drop dead suddenly, waste over time or waste and also have a swelling on the lower jaw called bottle-neck jaw. Sometimes the swelling may appear and later disappear before recurring.
The swelling is caused by a collection of fluid at the lowest point of the jaw. It is occasioned by extreme loss of proteins from the blood. The blood becomes very thin and the body attempts to thicken the blood by removing some of the water from the blood stream.
Farmers should therefore always consult their animal health service provider even if the swelling appears to go because the worms would still be in the stomach. The apparent healing of the swelling may be due to some proteins getting into the blood and temporarily rectifying its density. In time, the worms suck out the proteins and the swelling recurs.
The adult Haemonchus worm is about 1-3cm long. Death in an adult sheep would normally occur when there are over 500 worms in the stomach. Lambs and young sheep may die with lower levels of infestation due to their smaller size and lower blood volume.
Each worm sucks about 30 microlitres of blood per day. Though this may appear a small amount of blood, the total amount drawn out by all the worms in the sheep may run into litres within a few weeks. This is the cause of the rapid onset of anaemia and sudden death in some sheep.
Understanding the biology of the Haemonchus worm is good for farmers to help them know when, where and how to intervene in order to effectively control the worm and minimise flock losses.
The worm has a short life cycle of about 17 to 21 days and a very high fertility for egg production. A single adult worm can lay between 5,000 and 10,000 eggs in a day. It takes between three and 10 days for the eggs to hatch and the lavae to become infective. This explains why the worms are able to contaminate large areas of pasture with eggs and infective stages of the worm. It also explains why treated sheep and goats can be rapidly re-infested with the worms.
The eggs are passed out in faeces and hatch into the first larval stage called L1. The L1 grows in the environment if the weather is warm and moist before molting into the L2 stage. If the weather is too dry or too cold, the eggs or the larval stages suspend their growth and remain alive until the situation is conducive to resume development. The L2 continues growing in the environment and molts into the L3 stage. This is the infective stage of the worm.
The L3 worms climb onto the pasture leaves and position themselves to be eaten by the sheep and goats. Once swallowed, they work their way to the abomasum or true stomach of the sheep where they attach onto the areas well-supplied with blood.
The L3 larvae suck large volumes of blood and molt into L4. By the 17th to 21st day from the time of hatching, the L4 molt into the adult Haemonchus worm. The adult continues to suck out blood and lays eggs.
For sheep and goats in a zero-grazing unit, it is easier to control the worms if feed is given in troughs that do not get into contact with animal droppings and are kept dry. Feeding animals on the floor is highly discouraged as it facilitates worm infestation.
The Haemonchus worm has been extensively studied due to its importance in sheep and goat farming. It is known to be highly adaptive to various environmental conditions and even drugs. It easily develops resistance to deworming drugs.
In many places, the worm has developed resistance against levermisole and albendazole, some of the most commonly used dewormers. Closantel, which I used on David’s farm, is recommended for treatment of Haemonchus contortus. Animals should be dewormed every three months or more frequently if the worm load in the environment is high.
The worm can also be controlled through strategic deworming to minimise the development of resistance to drugs. In this regime, animals are dewormed when most vulnerable to infestation such as 30 days before or after giving birth. The colour of mucous membranes could also be monitored and only animals showing paleness are dewormed. Farmers who would like to use strategic dosing should first seek training on the same to be able to monitor the health of their sheep and goats to make decisions on deworming.
