Oesophagostomum species

Pathogenesis

The most serious problems seen in Oesophagostomum infections arise from larvae penetrating the musosa of the intestine. After initial infections, small nodules about 1mm in diameter form around larvae in the mucosa.  When larvae move back into the intestinal lumen the remaining nodules may be hemorrhagic particularly in
acute infections but often they fill with pus, in which cases they are more properly described as small abscesses.

In heavy infections, the mucosa becomes inflamed and edematous and regional lymph nodes are often much enlarged. Chronic infections will produce an intestinal mucosa that is filled with nodules particularly if these repeat infections have been heavy. In these chronic cases  tissue reactions are more severe and the nodules are much larger (up to 6mm in diameter) and creamy in color due to the development of connective tissue around them.

In chronic infections, most infecting larvae will be killed by  host reactions. Therefore older animals will usually show extensively nodular intestines but with few, if any, adult worms in the colon.

cj042.jpg (19557 bytes)

cj058.jpg (14905 bytes)

Acute infection with Oesophagostomum radiatum in cattle. Hemorrhagic nodules in the small intestine. Chronic infection with Oesophagostomum dentatum in pigs. Fibrous nodules in the small intestine.

In sheep, Oesophagostomum venulosum is much less pathogenic than Oesophagostomum columbianum, apparently because it does not stimulate nodule formation. infections with 500 L3s have been reported to produce a transient diarrhea accompanied by petechiae and small ulcers in the small intestine.

Epidemiology

All domestic animals are infected by grazing pastures contaminated with L3s. Oesophagostomum radiatum in cattle is common throughout the world especially in tropical and subtropical areas and is also common in North America. In tropical areas with seasonal rainfall (such as Queensland in Australia) heavy infections with high mortalities may be seen in calves under natural grazing conditions during the rainy season.

In sheep and goats, Oesophagostomum columbianum is seen throughout North America except for the west coast. The climatic requirements for survival of preparasitic larvae are similar to Haemonchus contortus therefore O. columbianum is more commonly seen in tropical and subropical areas. However, the requirements for survival of O. venulosum preparasitic larvae are similar to those for Ostertagia and Trichostrongylus and therfore it is more common in temperate areas.

Hypobiosis at the L4 stage is the primary method of survival of O. venulosum during winters in temperate areas of the world. O. dentatum and O. quadrispinulatum also undergo hypobiosis at the L4 stage in pigs but L3s are also known to survive winters on pasture. The resumption of development of these two species in spring can give rise to a periparturient rise in egg counts(PPR) in pregnant and lactating sows. It is speculated that hypobiois may occur in O. columbianum although definite experimental confirmation of this is still awaited.

Transmission of Oesophagostomum in housed pigs has been explained by the possibility of percutaneous infections, the easy development of infective larvae in feces and pen to pen transmission by dipteran flies carrying infective L3s on their legs.

    

 

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