Page 931 - Veterinary Immunology, 10th Edition

born, the infected pups can re-infect their mother by the more
VetBooks.ir conventional fecal-oral route.

Genetically mediated resistance to helminths is seen in the
superior resistance of sheep with hemoglobin A (HbA) to

Haemonchus contortus and Teladorsagia circumcincta compared with
sheep with hemoglobin B. The reasons for this are unclear, but
sheep with HbA mount a more effective self-cure reaction and a
better immune response to many other antigens as well. Another

example is the enhanced resistance to Cooperia oncophora seen in
Zebu cattle compared to European cattle. In many cases, resistance
to parasites is linked to MHC polymorphisms. Thus cattle
possessing BoLA-Aw7 and A36 tend to have low fecal egg counts,

whereas animals with Aw3 tend to have high fecal egg counts.
Some BoLA haplotypes may also be associated with high antibody
levels against Ostertagia. The effects of the SLA complex on parasite
immunity in pigs have also been assessed. Thus there was a 50%

lower muscle larval burden in Trichinella spiralis–infected cc
minipigs compared with pigs with the dd or aa haplotype.
Resistance was characterized by a predominance of lymphocytes
and macrophages in the cellular reaction around each larva.

Polymorphisms in the IFN-γ gene affect the inflammatory response
in sheep and their responses to helminths.
Innate factors that influence helminth infestations include not
only host effects but also the influence of other parasites within the

same host. For example, calves infected with Cysticercus bovis show
increased resistance to further infestation by this parasite. Similarly,
lambs can acquire resistance to Echinococcus granulosus so that
multiple dosing with large numbers of ova does not result in the

development of massive worm burdens. The original dose of ova
may stimulate rejection of subsequent doses. Interspecies
competition among helminths for mutual habitats and nutrients in
the intestinal tract will also influence the numbers, location, and

composition of an animal's helminth population.

Adaptive Immunity

Helminths present the immune system with a challenge. Most
parasitic worms migrate through the tissues as larval forms and

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