Stephanurus dentatus

Epidemiology

Free living larvae cannot survive the cold temperatures encountered during winters in the northern U.S. As a result, kidney worm infections are more common in the southern United States.

Infected older sows and boars are the usual source of infection for younger animals and the longevity of adult worms in their host (2-3 years) means that adult infected pigs may be constant sources of infections for young animals.

Batte and his colleagues demonstrated transplacental transmission in pregnant gilts but it is uncertain how important this is as a factor in transmission.

The dependency of the life cycle on free living preparasitic larvae and earthworms as transport hosts means that this is a parasite primarily seen in pigs raised outdoors. Raising pigs indoors will significantly reduce the prevalence of kidney worms.

The "gilts only" system of breeding and rearing pigs was devised as an effective method to control swine kidney worms. In this system, breeding is confined to gilts which are then marketed immediately after weaning their first litters. The long prepatent period of 9-16 months means that pigs are raised , bred and marketed before infections become patent and this system was shown to be an effective method of controlling transmission of Stephanurus dentatus. The problem is that the system fails economically since gilts have smaller litters than older sows and the economic return from these smaller litters is not enough for the system to be viable.

Clinical signs

Overt clinical signs are unusual in Stephanurus infections. Aberrant migrations of larvae to the spinal cord may cause a posterior paralysis but these cases are not common.

The usual picture is one of failure to thrive with the primary effects on weight gains. Heavy infections in pigs raised outdoors may cause enough liver damage to result in emaciation and death. The image to the right is of a  pig showing   chronic effects of Stephanurus dentatus infections. Strongyle-type eggs were present in the urine and at necropsy there were extensive liver lesions and adult worms in the perirenal areas.


Sw022.jpg (19090 bytes)
Image courtesy of Merial Inc.

 

Diagnosis

The long prepatent period of Stephanurus means that patent infections are unusual in pigs less than two years old. Infections in adult sows and boars are easily diagnosed by finding the distinctive strongyle-type egg in urine of infected animals - as shown in the accompanying image. Infections often go undiagnosed in live animals, especially in 

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Image courtesy of Dr. Edward Batte

pigs less than a year old. Therefore infections are more often diagnosed at necropsies or at meat inspections when the characteristic liver lesions are found.

 

    

 

Parasites and Parasitic Diseases of Domestic Animals
Dr. Colin Johnstone (principal author)
Copyright 1998 University of Pennsylvania
This page was last modified on January 24, 2000