REO virus is a malady that appears and goes away, only to re-appear now and then, here and there, seemingly defying any pattern of severity or species. It is so hard to spot that often only vigilant farmers and/or veterinarians who conduct more than cursory examinations are likely to become suspicious of an REO virus presence. At a recent annual Penn-Ag sponsored Meat & Egg Meeting held at Shady Maple in Lancaster County PA, Dr. Donna Kelly, interim head of Clinical Microbiology at the University of Pennsylvania’s School of Veterinary Medicine PADLS New Bolton Center, brought an audience up to speed on the REO.
REO is an acronym for Respiratory Enteric Orphan, a disease discovered in 1954. “When it was named,” Kelly said, “there was apparently no clinical disease associated with the virus.” As with all orphan viruses there are no apparent diseases. However, they may be pathogenic. REO viruses of mice and avian species are more pathogenic in their hosts than other REO viruses. The virus is also associated as an arthritis viral agent, and also Runting and Stunting Syndrome. Eighty percent of the REO virus isolated from chickens is non-pathogenic. However, the intestinal tract is the last place for the virus to clear the body. In other words, you can have a healthy recovered bird that may still be shedding virus.
REO is found throughout the world and is relatively hardy in the environment. It is a double-stranded RNA virus. More important, it is non-enveloped, which means that many viruses have viral envelopes covering their protective protein capsids (the protein shells of viruses); this REO doesn’t have that.
“Early detection is best,” says Kelly. “Real viruses are found throughout the world in poultry and they are very hard to kill.”
Kelly also notes concurrent infections/stressors or husbandry immune-suppression as other potential troublemakers. “Over-crowding and so forth that put high demands on these birds are still others. They might not be able to have proper immune system function. You can see synergism with REO virus with other entities. Hosts are primarily meat type chickens but light egg breeds are also susceptible. Specific turkey strains qualify, as do other breeds like guineas, Muscovy ducks, chukars, pigeons, pheasants and geese. “The disease is most severe in chicks that are affected through egg transmission,” Kelly says.
“These birds may actually be very susceptible in the first seven days of life and usually that’s where I have my best recoveries — from 7 to 10 days. Birds in general, chickens and turkeys, have 9 to 14 days of disease in birds without maternal antibodies. Chicks that have maternal antibodies usually do not develop the disease.
“If the hen is infected she can transmit that virus for two to three weeks. You might see transient egg production drops but there haven’t been a lot reported for the flocks that have had infection with arthritis during the laying period. They get over it, and start passing the antibodies onto the babies.
I’m talking about mothers who did not have a previous infection or a vaccination before they developed viral arthritis, hence an adult.”
“Horizontal spread is from chick-to-chick, bird-to-bird, primarily fecal,” Kelly notes. “Fecal shedding can be aerosolized, and they can breathe it in and become infected. The virus can also be transported by mechanical means due to its high environmental resistance.
“Darkling beetles harbor this virus. Insect control is very important. It is easy to spread from flock to flock, depending upon the number of beetles on premises. And there is an age-related host resistance, normally, with previous REO viruses as opposed to the novel ones we’re getting now. It is a young bird disease.”
About 10 years ago in the south, there was a late-breaking REO where they were discovering severe proventriculitis, pericarditis, or mild carditis lesions and getting runting and stunting and profuse watery diarrhea about 28 to 32 days.