"I think we have to ask ourselves: Is it a coincidence that we are seeing such an increase in West Nile virus, or is that something that is being tested as a biological weapon against us?" Sen. Patrick Leahy, D-Vt., said in a radio interview earlier this month.
The public health community has generally dismissed the idea that West Nile virus could be used a bio-terror weapon. "There is no scientific evidence that West Nile virus is a result of bioterror," said Bernadette Burden, a spokesperson for the Centers for Disease Control and Prevention in Atlanta.
Scientists say Americans should get used to the disease — and certainly expect plenty more like it in the future. "We're going to live with West Nile for the rest of our lives," said Tulane University's Clements.
West Nile virus has been long known outside the United States, and probably appeared as a result of increased interconnectedness of the world, and fostered by the climate changes here, scientists say.
"It's a wonder it was never here before," said Michael Donnenberg, head of the Division of Infectious Diseases at the University of Maryland in Baltimore.
However, West Nile is not a very effective disease to use as a bioweapon, scientists say, because it is vector-borne — that is, it needs a host to move to another host, instead of simply being spread through the air.
With West Nile, mosquitoes become carriers when they feed on infected birds, and then transmit the infection to humans or other animals when they feed on them.
Like West Nile virus, dengue fever is a disease that was previously thought to be limited to the tropics, and whose symptoms include fevers, headaches, body aches and a rash. But dengue can be more devastating. One of its four distinct types is the severe and fatal hemorrhagic form, which causes breathing difficulties and bleeding from the nose, mouth, and gums.
Its route is much more direct, too. With dengue, the disease simply moves from human to mosquito to human.
"There's been a lot of debate on how dengue might be used as a bio-weapon," Cattani said. The CDC says between 100 and 200 suspected cases are introduced into the United States every year by way of travelers, and it was detected in South Texas as early as 1980.
Added Clements: "I think it's going to be more serious than West Nile."
Nature Still Trumps Man
Another disease that could be used as a bio-terror agent is hantavirus, also a vector-borne disease spread by the urine, droppings and saliva of rodents.
Early symptoms include fatigue, fever and muscle ache. Sufferers who go untreated experience coughing and shortness of breath, and eventually die of respiratory failure after their lungs fill with fluid.
And after hantavirus, scientists told ABCNEWS infectious diseases like plague, cholera and typhoid are potential threats.
These diseases are for the most part easily kept at bay by cleanliness, but they could also be genetically altered to make them more potent, in the way that multi-drug-resistant TB is, said Samuel Watson, a director at University of Pittsburgh's Graduate School of Public Health.
Hantavirus, in fact, is classified by the CDC as a Category C biological agent and threat because it could be "engineered for mass dissemination because of availability, ease of production, and potential for high morbidity."
Today's most common diseases of course were discovered independent of terrorists. "It's said scientists discover [at least] one new disease a year," said Weedn.
Increased contact with nature brought us Lyme disease in 1975. Indoor living and poor ventilation brought us Legionnaires' disease in 1976. Better testing methods found Campylobacter in 1977. And modern methods of meat processing have introduced new forms of E. coli over recent years.
"They say in Africa, there are viruses we don't even have tests for. It's inevitable that we'll find surprises in the future," Cattani said.