Over time, climate change has caused several disease-carrying species to become more widespread in the United States, significantly increasing the risk of certain diseases, such as West Nile virus and Lyme disease. However, experts say the United States isn't prepared for future outbreaks, Sara Van Note writes for STAT.

Climate change has accelerated vector-borne diseases

In recent years, climate change has accelerated. In turn, the ranges of many disease-carrying species, including mosquitoes, fleas, and ticks, have greatly expanded. With these species becoming more widespread, people are at a greater risk of infection from diseases like West Nile virus, Lyme disease, Dengue fever, and more.

According to CDC, cases of 17 different vector-borne diseases have been reported in the United States, and nine pathogens that were not previously found in the country have been identified since 2004. Between 2004 and 2019, reported cases of vector-borne diseases more than doubled, reaching 800,000 cases.

However, CDC notes that this number is likely a significant underestimate of the true number of cases. Only 2% to 3% of all West Nile cases and roughly 10% of Lyme disease cases are reported. Benjamin Beard, deputy director of CDC's Division of Vector-Borne Diseases, said that there is likely a 10- to 80-fold underestimate of cases of vector-borne diseases.

In 2021, several parts of Arizona experienced an outbreak of West Nile virus. Overall, more than 1,700 cases and 127 deaths occurred — making it the largest outbreak of the disease in the United States since it first emerged in 1999.

Nelson Nicolasora, medical director of the infectious disease program at Banner University Medical Center, said that while the West Nile outbreak in Arizona was "nothing like" the COVID-19 pandemic, the illness was "life-changing" for patients who suffered debilitating neurological symptoms.

Although West Nile typically causes mild, flu-like symptoms, around 1 in 150 patients will develop severe neuroinvasive disease. "It can be devastating," Nicolasora said, noting that two of his patients died during the outbreak and others needed a ventilator to breathe or rehabilitation to relearn how to walk.

Why the US may be vulnerable to outbreaks of vector-borne diseases

Despite the growing risk of vector-borne diseases, the public health response to these cases, including research and disease surveillance, has largely been limited due to a lack of funding from both federal and local governments.

"Without sustained funding in local vector control and surveillance, it ends up stymieing that response of looking for the threats before they become really huge causes for concern for local public health," said Chelsea Gridley-Smith, director of environmental health for the National Association of County and City Health Officials (NACCHO).

According to Erin Cadwalader, director of strategic initiatives for the Entomological Society of America, federal funding for vector-borne diseases, aside from malaria, has largely been flat or in some cases "trending down" since targeted funding was provided to address the Zika virus several years ago.

In a 2022 paper published in the Journal of Medical Entomology, a team of researchers led by scientists from the University of South Carolina argued that the "cyclical and reactive" nature of federal funding for disease surveillance would leave the United States vulnerable to outbreaks of vector-borne diseases.

In particular, the researchers said the lack of widespread tick surveillance in the country is a "critical issue," given the high incidence of tick-borne diseases and the discovery of the invasive Asian longhorned tick. Insecticide resistance is also of "significant concern," they wrote.

Last year, CDC proposed a national strategy to address vector-borne diseases in the United States. The strategy outlined five goals with several underlying priorities, including modernizing surveillance systems and better understanding vectors, their associated pathogens, and the potential impact of climate change.

According to Beard, the strategy will provide a "roadmap" to help 17 federal agencies develop plans to combat vector borne issues. However, he added that since these measures are implemented by states, counties, and cities, "at the end of the day, it's out of our control." (Van Note, STAT, 3/15)