The Hidden Dangers of the Small Redworm

The importance of controlling the small redworm threat is due to the ongoing and sometimes lethal damage that the small redworms can inflict on our horses. This is due to the small redworm lifecycle taking one of two potential courses, either the faster 5-6 weeks route or the slower inhibited EL3 route. In both lifecycles, the infective larvae cause damage as they burrow into the horse's gut wall, form a cyst and then cause more dramatic inflammatory damage as they emerge. In the shorter lifecycle, the larvae continue to develop in their cyst (encysted developing small redworm) into non-inhibited L4 larvae, which emerge into the gut lumen and are then become susceptible to treatment with most commonly available wormers.

The impact of encysted small redworm on the gut of an infected horse.
	Small redworm larvae encysted in the gut wall. Impairing nutrient absorption.
	Young adult small redworms emerge from the gut wall causing chronic damage.
	The small redworm larvae emerge 'en masse;(cyathostominosis) and the gut wall is severely damaged causing massive inflammation and allowing toxins to leak into the horses circulation. Many horses will die of this mass emergence in spite of expert veterinary care.

In the slower lifecycle however, the encysted inhibited EL3 can remain dormant for many months and even for as long as 2 years. Hundreds of thousands of EL3 small redworm can line the gut wall in the areas of the horse's caecum and upper colon - large intestine. These important tracts of intestine normally absorb essential nutrients but the dormant infestation of encysted inhibited EL3 impairs absorption, often leaving the horse in poor condition.

It is possible however for horses with an early EL3 infestation to appear healthy and well. Furthermore, if a Faecal Egg Count (FEC) test is carried out on an EL3-infected horse, the small redworm burden may not appear to be high because it is mainly present in the dormant EL3 form.

Once in the encysted inhibited state, the EL3 larvae are not affected by protected from treatment with the ivermectin or pyrantel-based wormers. Only EQUEST or a five-day doses course of fenbendazole in areas that are unaffected by fenbendazole resistance will beare able to control the EL3 redworms.

At the end of the dormant inhibited period, the developing larvae can emerge 'en masse' from the gut wall causing massive inflammation, colic, acute pain and diarrhoea. This potentially lethal condition is known as larval cyathostominosis. The large intestine is physically weakened and the toxins released from the EL3 cysts are highly poisonous causing toxic shock and ultimately death, despite expert veterinary support. Finally, the gut wall integrity may also be so damaged that it may be prone to twisting.

Information kindly provided by Fort Dodge For Further information visit :- www.wormingyourhorse.info