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Protecting parasites prevents gastro-damage.

Protecting Parasites Prevents Gastro-damage

Some folks might find Phillip Klesius' philosophy on internal parasite infection in livestock a little shocking. In a nutshell, it's "live and let live."

In fact, Klesius, who is an Agricultural Research Service microbiologist, goes a step farther. At the animal Parasite Research Laboratory at Auburn, Alabama, he's developing a vaccine that would actually run interference between the parasite and the animal's own immune system.

That's because, in the natural chemical warfare between immune system and parasite, the immune system plays so rough that it causes more damage to the animal than the parasites do, Klesius contends.

Gastrointestinal parasites such as Ostertagia ostertagi typically get into a grazing animal's body by being gobbled up along with forage. The invaders then tuck themselves away in fingerlike gastric glands in the abomasum, the true stomach of ruminants such as cattle.

"The parasites cause a minimum of damage inside the animal as they mature or develop," Klesius notes. "And there's no evidence they produce any toxins that would result in the physical damage we normally associate with parasite infection."

However, the parasites do produce chemical materials called excretory-secretory substances. Within these substances is a chemical attractant. This attractant, discovered by Klesius in 1986, causes infection-fighting white blood cells called eosinophils to migrate to the site of parasite infection.

The arrival of the eosinophils is hardly good news for the infected animal. Eosinophils carry tiny bags of toxic enzymes to unleash on the parasites. But those same enzymes also wreak havoc on cells in the gastric glands where the parasites are snuggled, destroying the glands.

"The gastric glands are vital to digestion because they produce pepsinogen, which converts to the enzyme pepsin," explains Klesius.

The internal struggle between enzymes and parasites, with its accompanying devastation, leaves farmers with an animal that doesn't gain much weight, no matter how much it eats.

However, there is a bright spot in this generally grim situation, according to Klesius. The peculiar bond between the parasites and the animals own immune system could offer researchers a new route for circumventing the damage usually associated with parasite infection in livestock.

"We want to neutralize the chemical attractant produced by the parasite, and any other substances from the parasite that cause a reaction in the host animal's immune system," Klesius says.

"If, for example, the cow's body doesn't recognize that Ostertagia is present, it won't wind up with gastric glands damaged by eosinophils. The parasitic relationship would result in no disease."

Once they've identified the materials, they plan to use them as the basis for a vaccine to stimulate the animal's immune system to produce antibodies against the parasite's secretions.

"These antibodies will naturally neutralize substances such as the chemical attractant as soon as the parasites produce it," Klesius says. "This way the eosinophils never get the signal to migrate.

"We'll set up trials where we vaccinate the animals with material to neutralize the attractant from the parasites," he adds. "Then we'll infect them with gastrointestinal parasites and see if they show any of the typical signs of infection, such as poor feed conversion."

If this chemical interference works, Klesius and his co-workers may be opening the door to a new world of preventive medicine for livestock.

In the past, concepts for developing antigens in vaccines to control animal parasites have depended on finding substances from the parasites that stimulate the host's immune system to produce antibodies that eliminate the parasites.

"That approach works in developing vaccines against viruses and bacteria, but it's been largely unsuccessful with parasites - probably primarily because of the extremely complex relationship between the parasite and the host," he notes.

"We think our approach will work with any internal parasite that produces excretory-secretory substances; the concept of neutralizing a possible chemical attractant would apply."

PHOTO : A cross section of a stomach parasite Ostertagia ostertagi magnified about 250 times. Rust-colored area is source of a chemical attractant that causes the host's infection-fighting white blood cells to attack.
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Title Annotation:vaccine research to stimulate antibodies instead of the immune system to fight livestock parasites
Author:Hays, Sandy Miller
Publication:Agricultural Research
Date:Jan 1, 1991
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