AIDS-Like Symptoms Threaten Pigs

March 30, 2001 -- Forget about the current media spotlight on Mad Cow and Foot and Mouth diseases for a moment. Our discovery today is about a disease in pigs that in many ways is like AIDS.

This horrendous disease, at one point called “swine mystery disease,” “blue abortion,” and “swine infertility,” and now referred to as “Porcine Reproductive and Respiratory Syndrome,” or PRRS, has infected some pigs in about 75 percent of American pig herds, according to experts. Vaccines have only partially been effective.

The disease also has been creating a nightmare for many other nations since at least the mid-1980s.

Pigs Are Dying

The reproductive and respiratory syndrome, which often kills baby pigs, is characterized by a variety of conditions and is causing economic hardship for pig farmers. Affected mothers lose up to 10 percent of their pregnancies. Their babies are spontaneously aborted or are stillborn. As many as 20 percent to 30 percent of survivors may suffer and die from respiratory disease, such as pneumonia.

The PRRS virus is said to primarily attack a pig’s immune system, leaving the body open to a host of other infections, particularly in the lungs. Some pigs develop a chronic infection and become carriers but show no symptoms.

Research reveals that the virus is transmitted via semen, saliva and blood. Those pigs herded closely together and transported at close quarters by trucks may be more susceptible to infection.

To date, there is no evidence that the virus can infect humans from any source, including via food. Researchers looking for signs of the virus in pig meat haven’t found any.

Scott Dee with the University of Minnesota College of Veterinary medicine, a PRRS researcher, says the disease is the “most economically devastating swine disease there is,” and that the “problem is getting bigger,” but he bristles a little when I introduce the term “AIDS” into the conversation.

I do so because the PRRS virus, while not a member of the family of viruses to which HIV belongs, is also said to strike the immune system and then cause some changes in the body that are similar to AIDS.

No Virus Trace in People or Meat

Beth Lautner, vice president of science and technology at the National Pork Producers Council, says PRRS is a complex disease, acknowledges that some of the symptoms are AIDS-like and notes that no trace of the disease has been found in people or meat. She worries that “some people will jump to the wrong conclusion, that pigs gave AIDS to humans.”

Monte McCaw, a PRRS researcher with North Carolina State University’s College of Veterinary Medicine, believes that while the differences between PRRS and AIDS are obvious to researchers, it is also important to study the similarities.

McCaw has so far been low-key about his AIDS-related findings. I had to initially research farm bulletins, obscure scientific reports and speeches he gave in order to piece some of his views together.

“I am stunned you found this,” he said, after I had almost given up trying to contact him for an interview.

Some Similarities to AIDS

McCaw has concluded that the following key conditions in PRRS-infected pigs are similar to what is found in AIDS:

Secondary infections, mainly in the lungs, are common due to the immune-suppressive abilities of the PRRS virus.

PRRS reproduces in cells called macrophages, which are front-line cells in the body’s immune system.

PRRS primarily reproduces in cells called alveolar macrophages, which are immune cells in the lung. Damaging these lung immune cells makes the animal susceptible to opportunistic infections.

Key white blood cells of the immune system (lymphocytes) go through some of the same changes that occur in AIDS.

Lymphocytes produce higher levels of a variety of biochemical substances, as in AIDS.

McCaw adds, however, that some baby pigs that manage to survive the onslaught of infections in the lungs that the PRRS virus triggers end up thriving.

“This is an obvious difference in the way [AIDS and PRRS] generally develop,” he says.

But McCaw thinks enough of the similarities between AIDS and PRRS that he indicated in a report that he would like to study novel immune therapies in pigs. He also told me: “We would hopefully learn more about PRRS in pigs and maybe AIDS in humans,” and to possibly “find ways to help treat both diseases.”

A recent finding in Dee’s camp should further encourage McCaw’s foray into the AIDS-like dimension of this disease. “We have just learned that PRRS can be transmitted from one pig to another via the repetitive use of [vaccination] needles,” Dee says.

Dee also says that PRRS hides out in the lymph nodes. The same is claimed for HIV.

More Research Necessary

McCaw, Dee and Lautner all agree that much more research will be necessary in order to get a proper handle on PRRS, in the hopes of better understanding and controlling it. They point to the manner in which the PRRS virus is capable of changing and the difficulty this creates for vaccine strategies against the virus.

Much more will need to be learned about how the pig’s immune system behaves in PRRS. Will PRRS, for example, be capable of unleashing some previously undetected microbe in pigs that could potentially be transmitted to humans?

Or, for that matter, is this pig disease being oversimplified by focusing so much of the attention on the PRRS virus? There may well be a number of factors that initially combine to trigger PRRS. The disease has often been referred to as a “mystery,” and in many ways it remains so.

While progress has been made, no one should be overconfident about any aspect of this terrible disease in pigs.