The mosquito is a tiny and bothersome insect that weighs an infinitesimal 2.5 milligrams. But it poses a very real threat to humans by transmitting West Nile Virus (WNV).
Last year, the national Centers for Disease Control & Prevention (CDC) recorded 96 Colorado cases of the virus and three deaths. One of the victims was Chuck Clark-Martin, a sergeant with the Denver Sheriff's Office. The other was long-time Paonia resident and journalist, Ed Marston. The CDC reports a total of three deaths but research has been unable to confirm the name of the third victim.
Of the known victims, both 63-year-old Clark-Martin and 78-year-old Marston were in good health and at first showed no severe symptoms. The lack of definitive symptoms is a characteristic of the early stages of the virus. Early symptoms are similar to common influenza including headaches and fever and fatigue. A physician can order tests which are sometimes, but not always, decisive in diagnosing WNV. The majority of those infected show no symptoms.
So far this year (as of June 25, 2019), the CDC website has recorded zero cases of WNV in Colorado, however nearby states have reported cases of human and non-human infections including Arizona, Nevada, Idaho, Wyoming, Oklahoma and Texas. Non-human infections are detected in trapped mosquitoes and in so-called 'sentinel animals,' such as research chickens which are caged and exposed to mosquitoes in order to monitor the presence of WNV. Wild birds and sometimes domestic horses are also considered sentinel animals.
In 2018, a county-by-county count by the CDC showed that the neighboring counties of Delta, Mesa, Garfield, Montrose and San Miguel each reported from 1-10 human cases of WNV. Other nearby western slope counties reported zero human cases in 2018 whereas the counties of Larimer, Weld and Boulder in northeastern Colorado reported higher numbers of between 11-20 cases.
As the name suggests, West Nile Virus appears to have originated in Africa. By 1999, it had been detected in New York State and it was first recorded in Colorado in 2002. By 2003, when a national high of 9,862 cases were recorded by the CDC, WNV was being detected in all 48 contiguous states. Of the nearly 10,000 cases reported nationwide in 2003, 264 people died. That same year 2,947 Coloradoans were sickened with 63 deaths reported. Last year, national cases of WNV had fallen to 2,544 with 137 deaths.
WNV cases fall into two categories: neuroinvasive and non-neuroinvasive. Of the over two-thousand cases reported nationally in 2018, 63% were neuroinvasive infections which include meningitis and encephalitis -- serious diseases which impact the brain or spinal cord. Only a small percentage of human fatalities occur in either category but either type of infection can lead to long-term complications.