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.
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| 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.
