There are no commercial vaccines for any roundworm parasites which infect the gut of any host. However, recent trials at Moredun have shown that it is possible to successfully immunise sheep against Haemonchus contortus, a blood sucking roundworm which is the most important species to infest sheep and goats in the world.
Haemonchus, commonly known as the Barbers Pole worm, prefers warm, humid climates and so is particularly prevalent in the tropics and sub-tropics. However, thanks possibly to climate change, it has also recently been described as an emerging UK disease. Drug resistant strains of Haemonchus are commonplace in countries like Australia where the parasite is the bane of many sheep graziers.
Crucially, the most recent Moredun experiments showed that the dose of vaccine needed was very low, so low that it should be possible to make the vaccine commercially simply by extracting it from adult worms. Large numbers of parasites are required to make the millions of doses needed for the Australian market alone, but these can be readily obtained by deliberately infecting donor sheep which are subsequently processed by an abattoir in the usual way. The infected stomachs (which are normally discarded) are collected and processed by a Moredun machine designed to rapidly harvest clean worms at the pace of the abattoir. The parasites can then be frozen until enough have accumulated to make a large batch of vaccine; a million doses is about 10 days work for one scientist.
The vaccine is currently being tested in 100 grazing lambs in Australia. If the trial is successful, plans are well advanced to start making a commercial vaccine in Australia in collaboration with local scientists.
We are also exploring the development of a vaccine to control the sheep stomach worm Teladorsagia circumcincta which is endemic in temperate regions of the world and is currently the major cause of parasitic gastroenteritis (PGE) in sheep in the UK.
As animals can acquire an effective immune response over time, vaccination against this parasitic nematode is a possible alternative for control. We are focusing our efforts on understanding this development of immunity and identifying what factors the worms produce which both stimulate and suppress the immune response to target these molecules for vaccine development.
Brown Mang Onwuka