The hotter the summer here and the closer to drought conditions, the higher potential for mosquito populations to grow, along with heightened concern for mosquito-borne infections, particularly West Nile Virus (WNV). WNV was introduced to the United States in 1999, and has become the prevailing mosquito-borne disease in the nation. Colorado was particularly hard hit by the untreatable disease in 2022 and 2023; in the latter year one Custer County was hospitalized and in long recovery, the first case since 2007. Â
 And the Colorado Department of Public Health announced on July 25 that a man died in Boulder County from the Virus.
Nationally, since its introduction WNV infection has caused over 30,000 cases of the severe, neuroinvasive form of the diseaseâWest Nile Virus Neuroinvasive Disease, or WNNDâand nearly 3,000 deaths. That significant impact has recently led to the development of a new forecast model, one which takes into account a variety of climate and weather conditions. Previously, forecasting relied only on historical data. The new model for more effective WNV forecasting is intended to enhance and aid proactive public health responses and WNV awareness campaigns.
As of this writing, the forecast for our immediate area is not yet available, yet there are ordinary measures we can take in the outdoors to mitigate the likelihood of bites and mosquito-borne disease. Just as in avoiding tics and tic bite, use insect repellent, and wear long sleeved shirts and long pants when on outings where one would expect mosquitos to be. To mitigate mosquito population growth, do away with standing water where they might hatch.
Last seasonâs 76 Colorado WNV cases accounted for six deaths, and included 39 WNND infections. According to the Center for Disease Control and the Colorado Department of Health and Environment, there are no preventive vaccines for, nor medications to treat, WNV in people. Most WNV-infected people do not feel sick or develop symptoms, but about one in five experience fever and other symptoms such as head and body aches, joint pains, vomiting, diarrhea, or rash. In recovery, fatigue and weakness can continue for weeks or months. About one out of 150 infected people develop WNND that affects the central nervous system. Symptoms of severe illness include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis.
People over 60 years of age are at greater risk for severe illness if they are infected, as are people with certain medical conditions, such as cancer, diabetes, hypertension, kidney disease, and people who have received organ transplants. Recovery from severe illness can take from several weeks or months, and some effects to the central nervous system might be permanent. About one out of ten people who develop WNND die.
Although, as noted, WNV is most commonly spread to humans by mosquito bite, in a very few cases people have been infected through laboratory exposure, blood transfusion and transplant, or mother to infant during pregnancy, delivery or breast feeding. Data Availability
Data sources for both U.S. West Nile virus case counts and climate data are publicly available at the corresponding links: West Nile virus neuroinvasive disease counts (https://www.cdc.gov/west-nile-virus/data-maps/historic-data.html), PRISM (https://prism.oregonstate.edu/), gridMET (https://www.climatologylab.org/gridmet.html), NLDAS (https://ldas.gsfc.nasa.gov/nldas). Finally, code developed by the authors for the data analysis and visualization is openly available at https://github.com/ryandharp/regionally_determined_clima
West Nile virus is NOT spread through coughing, sneezing, or touching, by touching live animals, from handling live or dead infected birds (although the CDC advises avoiding bare-handed contact when handling any dead animal; if disposing of a dead bird, use gloves or double plastic bags to place the carcass in a garbage can), or through eating infected animals, including birds.
The CDC also notes that if you think you or a family member might have WNV, talk immediately with your health care provider who can diagnose the infection based on signs and symptoms, a history of possible exposure to mosquitos that can carry the virus, and laboratory testing of blood or spinal fluid.
Arapahoe County Public Health manager in communicable disease epidemiology Melissa Adair noted last year that, âWhile we know West Nile Virus is endemic to Coloradoâmeaning we expect cases each yearâwe never quite know how many to expect or just how bad a season will be.â So, follow the news; when a first case is confirmed in Colorado e will know that WNV is present in our mosquito population, and as mosquito numbers increase, the risk of WNV will as well.
In the meantime, should one care to follow current data, sources for both U.S. WNV case counts and climate data are available at www.cdc.gov/west-nile-virus/data-maps/historic-data.html, www.prism. oregonstate, www.climatologylab.org/gridmet.html, and ldas.gsfc.nasa.gov/nldas.
W.A. Ewing
