West Nile Puts the Sting on Colorado

By Zahra Stavis

Nik Walker’s backyard feels barren. The large expanse of land, littered with old tires and chew toys, is the ideal environment for a dog. But no pets are playing in the backyard because, two days after Nik’s birthday in September, his dog Nikita died from the West Nile Virus (WNV), a flue-like sickness that can kill.

“She slept in my bed the night before,” Walker said. “I woke up to let her out the next morning and she was dead. One day she was fine, and by the next day she was dead.”

“She was sweating blood,” his roommate Nate Hammond said.

Nikita is one of just 21 confirmed cases of the virus infecting dogs in the entire country. Nonetheless, it is no surprise that one of these rare cases would be in El Paso County, Colorado. The county has the highest number of reported deaths from West Nile in birds, and the second highest number in other types of animals, according to data from the Center for Disease Control (CDC). The virus has decimated bird populations and killed dogs, cats, and horses in the state.

Nik’s dog was one of two in the neighborhood that were infected. After she died, Nik tried to bury her. Because he was crying too hard, he called Animal Control Services, which took the dog’s body away. They tested Nikita for WNV IgM-antibodies, the presence of which later confirmed that the animal had indeed died of the virus.

Why WNV hit Colorado’s human and animal populations so hard is difficult to say. People usually think of mosquitoes as thriving in swampy environments; however, a high number of the infected insects concentrate in arid Colorado. Meanwhile, notably wet states like Oregon and Washington have not had a single case of the virus.

Nonetheless, Colorado has the highest rates of infection from WNV. CDC, which oversees testing for the antibodies, has reported over 2,477 cases of infection in humans, 91 in El Paso County alone. The county also has the second highest number of mammal fatalities, and the highest reported number of avian fatalities at 154 deaths.

“The most documented cases are in mammals,” said Dr. Trephina Benn, a veterinarian at Airway Veterinary Hospital in Colorado Springs. “Potentially any animal that can be bit by a mosquito can get it.”

There are many reasons for the high death rates in various Colorado species, said Daniel Bowldes of the Division of Environmental Health for the El Paso County Health Department.

The virus had the ability to hit El Paso County hard in 2003 in part because it is home to two types of mosquitoes that transmit WNV, the Culex tarsalis and the Culex pipiens. The two types of mosquitoes like stagnant water.

“One theory is that we had a real wet June,” Bowldes said. “The second is [the wet weather] in combination with the Culex tarsalis and pipiens mosquitoes. Those two theories, working in combination with a healthy bird population along with a human population who admitted they did not use repellant, set the whole thing off.”

The problem is there is still too much stagnant water in El Paso County, according to Susan Hilton, a spokeperson for the Health Department. “Tarsalis mosquitoes are known to be able to breed in small containers,” she said. “We went to sites and found their larvae.”

Therefore, despite the absence of large swampy areas, mosquitoes are still able to exist. “This is bad because Culex tarsalis mosquitoes are the main vectors for WNV in mammals,” Bowldes said, adding that Culex pipiens prefer to drink avian blood. “We’ve got both in the state of Colorado,” he said.

Mosquitoes acquire the virus by feeding on carcasses of dead birds, and then carry the virus in their saliva. Although El Paso County has confirmed the highest number of dead birds, this does not indicate that El Paso County was the hardest hit in the country; in fact it means the opposite, according to Hilton.

“We used birds for surveillance of West Nile. Some counties chose only to have one bird tested to confirm the presence of the virus. El Paso continued to test dead birds, so we would have a high number.”

Humans, and animals like Nikita cannot transmit the disease to anyone else. Thus, they are called, “dead end hosts,” a rather morbid term when one considers that WNV often results in death.

The virus, which originated in Uganda and first appeared in the U.S. in 1999, amplifies when communicated back and forth between birds and mosquitoes. Birds are the virus’ reservoir or hosts and mosquitoes are the vectors that carry the disease between the birds.

“We used birds, especially early on, as an indicator of what’s going on in the county,” Hilton said. “We focus a little bit on birds because they are the amplifiers.”

Last year, WNV mainly hit the East Coast; there were only a few cases in Colorado. “What usually happens … is that the first year the virus comes into the state, there are a few cases but not many,” said Benn.

This year, Benn added, cases were high in the Southwest. “The following year, there are the greatest number of cases, and then the numbers start to decline as natural immunity increases,” Benn said, adding that she hopes that by next year, the height of the epidemic for Colorado will have passed.

To counteract the threat, El Paso County took action. “We really focused on education info through the media. We developed a coalition for governmental agencies in El Paso County,” Hilton said.

Awareness and prevention are the keys to avoiding death from WNV. The virus has infected a higher number of horses nationwide than humans; many of the horses lived in El Paso County. Horses are the luckiest of all mammals when it comes to West Nile, because there is a vaccine to protect them from the virus.

“It does not fully protect them against it, but they have a 60-percent better chance of surviving with the vaccine,” Benn said. “Thirty percent will die if not vaccinated.”

For unvaccinated horses, one out of three horses infected with WNV dies. Many horses do not exhibit any signs of illness at all when they get WNV. Others lose their ability to move. “Horses that we’ve seen had symptoms that ranged from being depressed to severe muscle tremors,” said Benn. “Half the horses that we’ve seen lie down and just can’t get up.”

When WNV reaches the state of encephalitis, or extreme inflammation of the brain, many will die. Because there is no cure for WNV once it has reached this stage,, vets try to affect a recovery by treating the symptoms. Sometimes, an advanced state of illness can call for drastic measures, according to Benn. “For some horses, if their condition has progressed to the point where they can’t get up, their owners ask us to euthanize them,” he said.

"They become a danger to people and become violent to themselves. They become very afraid when they can't get up. It's in their best interests."

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