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Is Rift Valley fever next big emerging infection?
Global conditions favor new emerging pathogens
Rift Valley fever (RVF) — which can wipe out whole herds of livestock and blind humans — may emerge as a new mosquito-borne infection in the United States in the next year or two, a leading government advisor on emerging infections warns.
"I have absolutely no doubt in my mind — whether it is next year or the year after — we are going to see the introduction of Rift Valley fever in this county," said Michael Osterholm, PhD, a key federal health advisor and director of the Center of Infectious Disease Research & Policy at the University of Minnesota in Minneapolis.
Osterholm delivered the warning recently in Chicago at an infection control conference held by the Joint Commission on Accreditation of Healthcare Organizations.
"[RVF] is a mosquito-borne agent that had its genesis in Africa and now has caused a series of outbreaks in the Middle East," he said. "Unlike West Nile virus — where the case fatality rate is probably less than one in 5,000 — with [RVF], up to 10% of people who develop it get rash and fever and 1% die."
RVF virus can cause several different disease syndromes, according to the Centers for Disease Control and Prevention (CDC). People with RVF typically have either no symptoms or a mild illness associated with fever and liver abnormalities. However, in some patients, the illness can progress to hemorrhagic fever, encephalitis, or ocular disease.
Indeed, the most common complication associated with RVF is inflammation of the retina. As a result, approximately 1% to 10% of affected patients may have some permanent vision loss. Patients who become ill usually experience fever, generalized weakness, back pain, dizziness, and extreme weight loss at the onset of the illness. Typically, patients recover within two days to one week after onset of illness.
As bad as the human impact sounds, the economic impact on the animal farm industry could be devastating. Case fatality rates are significantly higher for infected animals, approaching 100% for unborn fetuses of infected pregnant animals. "[RVF] will rip the hell out of our bovine cattle industry in this country," Osterholm said. "Seventy percent of [infected] calves die, and 20% of adult cows die; and it absolutely decimates the sheep population."
RVF is most commonly associated with mosquito-borne epidemics during years of unusually heavy rainfall. The RVF virus, a member of the genus Phlebovirus in the family Bunyaviridae, causes the disease. Veterinary officers in Kenya first reported the disease among livestock in the early 1900s.
"You know what we have done about [RVF] prevention and control in this country?" Osterholm asked conference attendees. "Nothing — no vaccines, no blood test, no attempt to stop mosquitoes coming in the cargo holds of planes. We are really good at responding after [something] happens. Blood banks will rush to get a new test for [RVF] because it, too, can be transmitted in the blood supply. They will rush to find a new vaccine for animals and, hopefully, for humans, but it will be only after the fact.
"Our system is not capable of anticipating some of these big problems and beginning to incorporate some concept of preparation beforehand," he said.
The thin line
An advisor to U.S. Secretary of Health Tommy Thompson, Osterholm also is an expert on bioterrorism. The thin line between man-made and natural afflictions may at least offer the hope that preparing for bioterrorism will arm us as well for emerging infections. It better, because according to Osterholm, they are coming.
"Expect yourself to be on the front lines more and more," he told the ICPs and epidemiologists at the meeting. "Even if you are today seen as the infection control professional at your institution, you and I both know that you are the front lines for anything that goes bad. If a crisis happens, you’re [involved]. SARS was the opening salvo."
Severe acute respiratory syndrome (SARS) likely will return due to the animal reservoir of the infecting virus in China, he added. The massive problems SARS wreaked on Toronto were an arbitrary blow by nature that could have been struck anywhere, he emphasized.
"With all due respect to Toronto, it was just bad luck," he said. "It could have been Minneapolis. It could have been Chicago. It could have been Atlanta. It could have been New York. It could have been any city that that same thing happened. And frankly, I will suggest today that we are not much better prepared to deal with SARS now than we were one year ago."
With health care budget and staffing woes self-evident, today’s clinicians face a daunting assembly of current, projected, and seemingly far-fetched crises. But the combination of the multiple threats involved in bioterrorism and emerging infections creates an ominous total picture.
"The risk of deaths and serious harm from a Mother Nature-made or man-made hit is very low for any one of us in this room," Osterholm said.
"Therefore, we must live our lives with some normalcy. On the other hand, the collective risk of any one of these events occurring on our shores in the very near future is very, very high," he added. "The subsequent social and economic disruption is absolutely inevitable. We must be prepared, because whether you are at ground zero or not, you are in the middle of it."
Emerging infections and pandemic flu
Over the last 20 years, 23 different diseases have emerged around the world, he said. The pathogens probably were there already, but a number of social, political, and economic factors made them flare to a point of emergence.
"I believe over the next few years, we are going to see that accelerate," he said.
One factor that favors the continued emergence of infections is continued population growth worldwide and particularly in the Third World.
"Think about the fact that today there are 6.2 billion people on the face of the earth," he said. "In 1900, 100 years ago — there were 700 million. Today, one of every nine people who ever lived is on the face of the earth. And, unfortunately, many of those people live in destitute poverty in the developing world."
For example, five of the 20 largest cities globally are in the developing world, with people living in crowded conditions that favor the emergence and spread of new diseases.
"We can pass more measles viruses to more people in one year today than we used to be able to pass in an entire century," he said. "Imagine, the implications of that kind of phenomenon."
In addition, constant global travel effectively has eliminated the oceans as evolutionary barriers, he said. Thus, like West Nile virus in 1999, mosquitoes and the exotic pathogens they carry easily can arrive on our shores in the holds of ships and airplanes.
By the same token, the longstanding threat of pandemic flu’s return is a foregone conclusion. Osterholm described conditions in China involving close contact with pigs and aquatic birds. Birds may live in cages in many instances above the hog pen, so their droppings can serve as an additional protein food source.
With hogs as the mixing vessel, flu viruses typically mix and blend from human and animal sources.
"If Darwin could have invented the ideal pandemic influenza laboratory, he would have created China today," he said.