Getting a grip on HE requires vaccination, good management

Vaccination can go a long way toward the prevention and control of hemorrhagic enteritis in turkeys, but it’s no substitute for good management practices, cautions Dr. John Radu, senior technical service manager with Intervet/Schering-Plough Animal Health.

Subclinical hemorrhagic enteritis (HE) has become more of a concern in the turkey industry than classical HE. The subclinical version, which tends to strike birds 6 to 12 weeks of age, leads to immunosuppression and mild enteritis. Damage to the gut wall allows Escherichia coli to penetrate the bloodstream, and immunosuppression reduces the bird's ability to fight off the infection.

“Financially, sickness and mortality due to subclinical HE and the secondary E. coli infection can be devastating,” he says.

Subclinical HE is caused by the same type II avian adenovirus that causes classical HE, “but that’s where the two versions of the disease part ways,” Radu says.

Birds with classical HE have obvious clinical signs such as depression, bloody droppings and sometimes high mortality; they also have characteristic postmortem signs such as a mottled, enlarged spleen and gross intestinal lesions that are dark in color and full of red or brownish blood. The subclinical form of HE is much more difficult to diagnose because there are no obvious clinical signs, he says.

There are no good treatments for HE, so the best approach is to prevent the disease through good management and proper vaccination, Radu advises.“I emphasize proper vaccination,” Radu says, “because it’s been theorized that if HE vaccines are given improperly or administered at the wrong time, the result is suboptimal immunity, which allows subclinical HE to occur.”

VACCINATION ADVICE

Turkeys should be vaccinated against HE by 6 weeks of age, before they are moved to the grower/finisher barn, Radu says. The exact age to vaccinate depends on the maternal antibody levels passed on to poults and the timing of field challenge by the HE virus, he continues.

Poults from breeders with moderate levels of HE antibodies should not be vaccinated before 4 weeks of age because levels of maternal antibodies may interfere with the vaccination response, he says.

“In a situation of early field challenge, these poults should be vaccinated at 4 weeks of age and again at 5 weeks of age, but poults from breeders with moderate levels of HE antibodies that are challenged at a later age may only need one vaccination around 5 weeks of age,” Radu says.

Oralvax-HE, marketed by Intervet/Schering-Plough Animal Health, is a federally approved, freeze-dried live vaccine that helps prevent HE in turkeys. It is easily administered in water and has proved to be safe for turkeys. The titer of the vaccine is known, which makes it more predictable than splenic vaccines, he says.

With splenic vaccines, which are made by harvesting spleens from donor poults, the titer is often unknown, and there is a risk of spreading infectious organisms to vaccinated flocks, the veterinarian says.

The effectiveness of vaccination with Oralvax-HE can be easily determined, Radu says. “About 3 to 4 weeks after birds are vaccinated, get blood samples from 10 to 20 birds in a flock and have a lab determine how many seroconverted. If it’s less than 80% to 90%, reevaluate the timing of vaccination, vaccine mixing and administration procedures.

“However, good management practices must be employed along with the HE vaccination program,” Radu says.

Those practices are the same ones that should be used to control any infectious disease. Houses on farms where HE has been diagnosed need to be thoroughly cleaned and disinfected between flocks. Good litter conditions need to be maintained. Dead birds should be picked up and properly disposed of frequently. Workers should disinfect boots before entering houses, and there should be strict biosecurity and rodent control at all times, he says.