Are mosquito-borne viruses becoming more common and serious? A clinical virologist explains the risk

There have been several deaths from eastern equine encephalitis reported in the Northeast in recent weeks. Dr. Anthony Fauci was hospitalized in late August after being infected with West Nile virus and is now recovering. And this week there was a New Hampshire resident reported of being hospitalized after testing positive for EEE, West Nile virus and St. Louis encephalitis virus. This leaves many wondering, “Are mosquito-borne viruses on the rise and becoming more serious?”

What viruses are transmitted by mosquitoes in the US and what are the symptoms?

Although simply considered a nuisance to many, mosquitoes are in fact the most common deadliest animal on the planet. The mosquito can transmit a number of deadly infections, including malaria, dengue, yellow fever, chikungunya, Zika, West Nile and EEE. Every year, diseases resulting from a mosquito bite cause at least 1 million deaths according to estimates worldwide.

Fortunately, not all types of mosquito-borne diseases are endemic to the US, but that may change over time. Climate change, human activity (i.e. the development of natural habitats), and changes in the geographic distribution of animals have led to an increase in mosquito- and tick-borne infections over the past decade. Currently, the most common mosquito-borne infection in the US is West Nile virus, although cases of EEE, dengue, St. Louis encephalitis virus, Jamestown Canyon virus, and malaria also result from local transmission. Typically, states in the Northeast and upper Midwest experience higher rates of mosquito-borne infections, but malaria and dengue have been detected in Texas and Florida, and West Nile virus can occur nationwide.

The vast majority of individuals infected with a mosquito-borne virus do not develop symptoms. However, when symptoms do occur, they are often flu-like and nonspecific and may include fever, headache, chills, rash, and joint pain. In cases of dengue, the body aches and joint pain can be so severe that the disease is commonly known as breakbone fever. In rare cases of West Nile virus, EEE, and St. Louis encephalitis, the disease can progress to neurological conditions such as encephalitis and meningitis, or become fatal.

Are tests available for these viruses?

Although testing for mosquito-borne viruses is available, it is mainly limited to large reference laboratories and public health institutions. Unlike testing for COVID-19 and the flu, molecular tests (i.e. PCR) are not a good option for diagnosing mosquito-borne viruses. This is because the period that viruses like West Nile and EEE are present in the bloodstream is relatively short, and PCR tests can be negative by the time a person goes to the doctor.

For this reason, serological (i.e. antibody-based) tests are the most common way to diagnose infections caused by mosquito-borne viruses. During the first week or two after an infection, a type of antibody known as IgM is produced, an early immune response to a virus. IgM antibodies usually remain in a person’s bloodstream for three to six months. Serological tests that detect IgM may indicate a recent infection; However, these tests are often not specific enough, meaning false-positive and cross-reactive results can occur.

For example, a person infected with West Nile virus may also test positive via IgM testing for St. Louis encephalitis or dengue. This is because West Nile virus, St. Louis encephalitis, and dengue all belong to the same family of viruses (i.e. Flaviviruses), and therefore IgM antibodies produced in response to West Nile virus may cross-react with tests designed to diagnose other members of the virus. the flavivirus family.

Other serological tests are designed to detect IgG antibodies, which take longer for the body to produce but function to provide longer-term immunity. Tests that look for IgG antibodies are more specific (that is, they do not show the level of cross-reactivity seen with IgM tests), but it can take two to three weeks after an infection for IgG antibodies to reach detectable levels reaches. This limits the use of IgG-based serological tests in the diagnosis of acute mosquito-borne viral infection.

What are the steps you can take to prevent mosquito-borne infections?

Unfortunately, vaccines are not widely available for the prevention of mosquito-borne infections. Currently, vaccines exist against chikungunya virus, yellow fever, Japanese encephalitis virus and dengue. To prevent other viral infections (e.g., West Nile Virus, EEE, St. Louis encephalitis) transmitted by mosquitoes, the best steps you can take are to reduce mosquito breeding sites and reduce the chance that you gets bitten.

Mosquitoes lay their eggs in standing water, so dispose of the water in old tires, flower pots and bird baths. Avoid the times of day when mosquitoes are most active, including before sunrise and after sunset. And if you must be outside when mosquitoes are present, wear a long-sleeved shirt and pants and apply insect repellent. Taking these steps can help protect yourself and others from mosquito-borne diseases, which will remain a risk until temperatures cool.