New Virus That Could Wipe Out Pigs

Some pigs in the United States have been hit with AIDS-like symptoms.
(ArtToday) Porcine Problem
Pigs Hit With AIDS-Like Symptoms; Farmers' Herds Suffering

Commentary
By Nicholas Regush

March 30 - 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.

STORY HIGHLIGHTS
Pigs are Dying No Virus Trace in People or Meat Some Similarities
to AIDS More Research Necessary

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.

Nicholas Regush produces medical features for ABCNEWS. In his
regularly featured column, he investigates medical trouble spots,
heralds innovative achievements and analyzes health trends that may
greatly influence our lives. His latest book is The Virus Within.