We asked Dr. Craig Reinemeyer, an esteemed expert in internal parasites, if he would help us determine how strong a threat tapeworms are to our horses and if there are any special measures we should take in controlling them.
We seem to be hearing more about tapeworms. Are they more of a threat now or just being recognized more?
The increased interest in equine tapeworms is mostly due to the combined influence of two factors. The first was formal approval by the FDA in the last few years of equine dewormers with label claims for efficacy against tapeworms, otherwise known as Anoplocephala perfoliata. The pharmaceutical sponsors escorted the launch of these new animal health products with marketing campaigns, so the drug manufacturers have created some buzz to educate horse owners and to help sell more products. The second factor is publication of research findings that described improved diagnostic methods for detecting tapeworm infection, and documented tapeworms as serious pathogens of the horse.
Are tapeworms any more, or less, dangerous to the horse than other types of intestinal parasites?
Parasites differ from viruses and bacteria in that they can't amplify their numbers within the host. Rather, they must cycle through the environment with each new generation. So, parasitic disease is consequently a numbers game. More worms cause greater damage.
What types of problems do tapeworms cause for horses?
Epidemiologic research has demonstrated that tapeworm infection is associated with an increased incidence of three syndromes: spasmodic colic, ileocecal intussusception, and ileal impaction. These are potentially serious problems that may have to be managed surgically.
A recently published study from the Netherlands found evidence of tapeworm infestation was associated with a risk of colic in general, of all types. How can tapeworms influence the health or function of the digestive tract even in areas where they aren't attached?
Most A. perfoliata are attached around the ileocecal valve, the point where the small intestine empties into the large intestine, and they cause intense inflammation and scarring of local tissues. This may interfere mechanically with the passage of ingesta from the ileum into the cecum. A less obvious explanation is that tapeworms in the cecum are somehow able to modulate motility in distant portions of the alimentary tract through altered nerve conduction, production of active chemicals, etc.
