Maria Arozamena, Illustrations Editor

In the last five years, there has been a 42 percent increase in Connecticut in the number of reported vector-borne diseases, according to the New Haven Health Department. 

Vector-borne diseases are caused by infections transmitted through blood-feeding arthropods such as mosquitoes and fleas. Eastern equine encephalitis, dengue fever, West Nile virus and malaria are all vector-borne diseases. 

In the 19th century, malaria was a leading cause of death in the United States, until the rate of infection was curbed with cooling technology and window screens, according to Joseph Vinetz, professor of infectious diseases, anthropology and microbial diseases. 

The health experts the News talked to credited the increase in vector-borne cases largely to climate change and discussed the potential dangers of mosquitoes making a comeback. 

“We used to have malaria transmitted in the United States,” Vinetz told the News. “The CDC was formed to eliminate malaria in the United States, but they didn’t do it. Good electricity, screens and air conditioning is how we got rid of malaria in the United States.” 

In the 19th century, malaria was a leading cause of death in the United States, taking responsibility for 45.7 out of every 1,000 deaths. 

Malaria cannot be transmitted from person to person — a bite from a parasite-infected mosquito must occur. Anopheles species mosquitoes, which are carriers of the parasite that causes malaria, are most active at night and in the early evening. They would have to bite people who are outdoors, and continue to survive to infect more people and reproduce to infect a community or area. This is why, Vinetz explained, air conditioning and flyscreens Melbourne have curbed malaria infections in the past.

Nathan Grubaugh, an associate professor of epidemiology, said that the main factors that create an ideal living environment for mosquitoes and infections are heat, humidity and rainfall. This means that with longer periods of warmth in America, we would see mosquitoes linger longer during such seasons, with the ability to travel and survive in higher latitudes. 

“The longer the season goes, the higher buildup of mosquitoes you can get, and the infection rate of the virus you get in mosquitoes increases,” Grubaugh explained. “It takes a while for that to really ramp up, because in the winter, those infection rates go way down again, and it has to restart. So the longer window that you give it means that there’s a higher likelihood that there is a high infection rate in mosquitoes.”

Scott Roberts, an infectious diseases specialist at Yale New Haven Health, added that climate change has pushed back and extended the typical mosquito die-off season in the winter. Now, mosquitoes have more time to circulate diseases amongst themselves, leading to increased transmission risks.

Grubaugh also stated that a good example of this is dengue fever, “this 80s mosquito which transmits dengue are able to live and even spread more northward.” 

Grubaugh explained that there is evidence of local malaria and dengue transmission in Florida, since the mosquitoes carrying these illnesses are now living in Florida in sufficient quantities when they weren’t before.

Grubaugh added, “If it becomes endemic, and you have a huge population [of mosquitoes] that is susceptible to it, then it could lead to tens of thousands if not hundreds of thousands of cases and that would put a huge, huge strain on the health system there.”

Scott added that not only are countries with lower gross domestic products connected with higher infection rates from these diseases, a great challenge is also that the patients who are most affected are vulnerable patients who are immunocompromised or very elderly. 

“Dengue is like a disease of poverty,” according to Grubaugh. Poorer communities are more susceptible to outbreaks because they have less access to preventative measures, including air conditioning and screened windows. These are also the communities that have less access to good healthcare.

Grubaugh also noted that dengue outbreaks are linked to travelers in addition to localized transmission, which isn’t actually unique to dengue. 

“In general, I think that the more globalized this world is, and people traveling between places, the more that we mix things around. And it’s more likely that we will have local outbreaks of exotic things. West Nile was once exotic in the US,” Grubaugh said. 

According to the New Haven Health Department, the West Nile Virus has been detected in 33 Connecticut towns, including New Haven. This year, there have been two cases reported in Connecticut.

The Department emphasized that “many vector-borne viral diseases, including West Nile virus, have no specific treatment options, so prevention is key.” 

Scott said that both West Nile and Eastern equine encephalitis, or EEE, are vastly underreported in terms of incidence and infection because both diseases often appear asymptomatically. In the cases where symptoms do appear, they are mild. Only in the rarest circumstances, such as when Anthony Fauci, the former chief medical advisor to the President of the United States, contracted the neuroinvasive strain of the disease, would the symptoms be very devastating. 

The New Haven Health Department told the News that EEE has been detected in six Connecticut towns this year. The Department said that although uncommon, it “has a 33% mortality rate and can cause significant brain damage in survivors.” 

Grubaugh explained that EEE is affected by climate change in a different way. It goes through cycles where every four to seven years, there is an increase in infected mosquitoes that lead to cases. He said that 2019 was the last big EEE outbreak in the US with around 30 human cases in the Northeast that led to 12 deaths. Of the four cases in Connecticut that occurred, three people died that year, according to Grubaugh.

“That was the last time we had an outbreak, and now we’re kind of back on this cycle,” Grubaugh told the News. “The reason why it cycles through is that the virus isn’t maintained in the Northeast. After it causes an outbreak, it goes locally extinct.”

Grubaugh said that this makes it difficult to predict when the next peak may be. 

Both EEE and West Nile do not have existing vaccines. Grubaugh noted that it isn’t impossible, but there simply isn’t enough interest and funding. 

Eastern equine encephalitis, dengue fever and West Nile virus are all caused by viruses, while malaria is caused by a parasite.