Cyathostomes (the small strongyles or small red worms) are an important cause of intestinal disease in horses. They spend a significant part of their life cycle as inhibited larvae within the mucosal wall of the intestine. Mass emergence of the larvae causes acute colitis and diarrhoea. Cyathostomes may be associated with colic, and are known to cause chronic weight loss and malaise.
The diagnosis of cyathostomiasis presents problems. The disease is caused by larval stages of the worms, before they start to produce eggs. Faecal worm egg counts give no indication of the extent of mucosal infection levels. It is also difficult to assess the efficacy of possible treatments because there is currently no way of measuring the severity of the disease.
A study carried out by researchers in Liverpool , Glasgow and Kent raises the possibility of a blood test to detect cyathostome larvae in the gut wall. A report of the work was published recently in Veterinary Parasitology.
Firstly they investigated the relationship between cyathostome infection and antibody production. They used samples from two groups of three ponies. One group had been infected with Cyathostomes, the other had not.
They measured the number of Cyathostomes in the mucosa and lumen of the intestine and collected blood samples to assess the antibody response. Preliminary investigations, using pooled sera from the two groups of ponies, demonstrated that IgG(T) was the only type of antibody to consistently produce a difference between infected and control sera.
They then measured the IgG(T) levels in the experimentally infected and control ponies at weekly intervals. They found that they could detect an increase in IgG(T) as early as five weeks after infection. This was before any worm eggs were present in the faeces. The uninfected group of ponies had IgG(T) levels which were either always low or declining.
Looking more closely at the blood from infected ponies, they found that the antibodies recognised two bands of protein from the body of the cyathostome larvae, which they called antigen complexes A and B. None of the uninfected ponies produced antibodies to complexes A or B. Anti-bodies to complexes A and B were detectable by seven weeks after infection. "Interestingly, the onset of production of antigen specific IgG(T) to these complexes coincided with a notable reduction in weight gain between the infected and control ponies" they point out.
In the second part of the study they used samples from twenty three horses at an abattoir. They then compared the IgG(T) reaction to complexes A and B with the total number of Cyathostomes present in both in the gut wall and in the lumen. They found IgG(T) antibodies to complexes A and B in eighteen horses which had positive mucosal worm burdens, although the antibody level and number of Cyathostomes were not correlated. Five horses which had no mucosal worms had no detected antibodies. There was no correlation between the total mucosal burden of Cyathostomes and the faecal worm egg count - confirming that faecal egg counts are not helpful in assessing the extent of cyathostome infection.
Finally they looked at blood samples from five clinical cases of larval cyathostomiasis. All cases showed IgG(T) responses to either complex A or B or both. Samantha Dowdall, speaking on behalf of the researchers, said "As far as we are ; aware, this is the first report of an antigen specific IgG(T) response in experimental and natural cyathostome infection. The two antigenic complexes we have identified have potential for use in a non-invasive diagnostic test for pre-patent cyathostominae infection in horses."
"We are still a long way off the production of a commercially available test" she added." The production of the antigens used for the test is a long process and is not commercially viable. We are hoping to continue the research to characterise the antigen complexes. When a commercially available diagnostic assay is developed veterinarians will be able to send blood samples to Diagnosteq (www.diagnosteq.com) for testing."
For more details see: Antigen specific IgG(T) responses in natural and experimental cyathostominae infection in horses. SMJ Dowdall, JB Matthews, T Mair, D Murphy, S Love, CJ Proudman. Veterinary Parasitology. 106 (2002) 225 - 242.