The barber pole worm is a blood sucking internal parasite that affects sheep. They often affect younger sheep and can cause potentially fatal anaemia if left untreated. Barber pole worms infect the stomach of sheep and are one of the most commonly found internal parasites in flocks.
Sheep become infected with barber pole worms by grazing. The eggs of the parasite are deposited into the environment through the faeces of infected sheep where they develop into infective larvae. The larvae wait until they are ingested by other sheep, where they migrate down the digestive tract, mature into adults and begin reproducing, starting the process over again.
Sheep are particularly susceptible to barber pole worm infection, even more so than other grazing animals, due to the fact that they graze much closer to the surface of the soil. Because of repeated exposure to the worms, older sheep begin to develop immunity to infection. However, lambs lack this immunity and can quickly succumb to anaemia if left untreated. Ewes experience a temporary lapse in immunity directly after giving birth.
Symptoms of barber pole worm infection includes pale mucous membranes and bottle jaw. Mucous membranes include the membranes around the eyes, gums and inside the cheeks. These membranes are usually pink in colour. Adequate blood volume in an animal can be quickly measured by timing how long it takes for the capillaries to refill after placing pressure on them with your thumb to force the blood out. Anaemic animals have a capillary refill time of greater than two seconds. Severely anaemic animals do not have any blood available in these smaller vessels to measure refill time. Bottle jaw is a condition in which fluid builds up under the animal's jaw and is another possible symptom of infection.
Sheep that are infected with barber pole worms can be treated to remove the worms. An anthelmintic or medication designed to kill the adult worms is administered via a technique known as drenching. A syringe filled with medication is placed into the mouth of the infected sheep and the medication is forced down the oesophagus and into the stomach.
The rate of reinfection in sheep that remain in infected pastures is extremely high. The best method to prevent reinfection is to treat sheep that show clinical signs of infection and move them to a pasture that has been confirmed to be parasite free. The reason for only treating infected sheep versus the entire flock is that the worms can develop immunity to the drugs designed to kill them, making the drugs ineffective. Targeting treatment slows the progression of the immunity and buys time for scientists to develop new drugs.
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