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Title: WORM AND GERMS: HOW HELMINTHIC PARASITISM SUPPRESSES BOVINE IMMUNITY, AND THE IMPLICATIONS FOR DEWORMING AND VACCINATION

Author
item Gasbarre, Louis
item STROMBERG BERT E

Submitted to: Topics in Veterinary Medicine
Publication Type: Other
Publication Acceptance Date: 7/2/1994
Publication Date: N/A
Citation: N/A

Interpretive Summary: Gastrointestinal roundworms of cattle can cause severe economic losses because of their effects upon animal growth and performance. These losses are due to the direct effects of the parasites on nutrient utilization in infected animals, and also the result of the parasites ability to interfere with the animal's immune system. A number of researchers have shown that roundworm infections strongly interfere with the animal's ability generate immune responses after exposure to other infectious agents or to vaccines. Although there are a number of new approaches to parasite control being developed, until these procedures are refined, the most effective means of reducing losses is through the use of anthelmintics. The most efficient use of these drugs is to reduce pasture contamination and thus interfere with parasite transmission. Total eradication of the parasites from pastures is not only unfeasible, it is virtually impossible. Drug treatments should be scheduled at times to 1) reduce production losses, 2) ensure adequate parasite exposure for the development of immunity in the cattle, and 3) enhance the ability of the treated cattle to respond to vaccination with unrelated infectious agents.

Technical Abstract: Gastrointestinal nematodes, most notably Ostertagia ostertagi, cause significant production losses in cattle. The most easily recognized losses are due to reduced growth resulting from the direct effects of the parasite on feed utilization. In addition, these parasites exert profound effects upon the host immune system. O. ostertagia infections have been shown to suppress both cell- mediated and humoral immune responses to the parasite itself, and to unrelated antigens. These results imply that gastrointestinal nematode infections may reduce the ability of cattle to respond to heterologous infections, and they may also reduce the host's ability to mount effective immunity after vaccination. Current parasite control practices are completely dependant upon the repeated administration of anthelmintic drugs. In the future alternative control procedures including manipulation of the host genome, biologically based control, and host immunity to the parasites will likely play a larger role in control procedures. Until these developing technologies are perfected, control will remain drug- dependent. Proper chemotherapeutic control procedures should rely upon strategic administration of anthelmintics. The dosing schedules should be devised to reduce pasture contamination and hence parasite transmission to levels where the parasites exert no negative effects upon either host growth, or host immunity. In addition, the timing of treatment should also be arranged to enhance the animal's ability to respond to vaccination. Complete eradication of the parasites from pastures is not only impractical, but also may interfere with the generation of immunity against the parasites.