Understanding significant mosquito-borne diseases

West Nile

The CDC reveals that West Nile virus is the most common mosquito-borne disease in the continental U.S. As of September 3, 2024, there have been 377 total cases of West Nile Virus across 38 states in the U.S. Among those cases, 255 were West Nile virus neuroinvasive disease cases.

West Nile virus is a type of flavivirus that infects mosquitoes when they feed on infected birds. Mosquitoes then bite humans, spreading the disease to them, but the spread generally stops at the human level since the viral levels transmit to other species.

There is a small possibility that human-to-human transmission can occur through blood or organ transplantation. However, the CDC maintains that transmission via transplantation, pregnancy, delivery, and breastfeeding is rare.

Although most people infected with West Nile do not have symptoms, roughly 20% of infected individuals will develop a fever or other common symptoms, including headache, body aches, joint pains, vomiting, diarrhea or rash. A smaller subset of individuals, 1 out of 150, will develop a severe and potentially fatal version of the disease, which causes encephalitis or meningitis.

Without any available vaccines, the only way to reduce the risk of contracting West Nile virus and developing severe illness is to prevent mosquito bites.

Zika

Zika virus is a mosquito-borne virus caused by infected Aedes mosquitoes. It is typically contracted from mosquitoes in tropical or subtropical areas of Africa, the Americas, Southern Asia and the Western Pacific.

This disease is transmitted from mosquitos to humans through bites. When the virus is circulating, a mosquito can contract the virus by biting an infected human.

In addition to mosquito bites, humans can contract Zika virus from other humans through sexual contact, including vaginal, anal, and oral sex or the sharing of sex toys. However, the CDC notes that the transmission timeframes vary between males and females, as the virus can stay in semen longer.

Zika can also be transmitted from a pregnant individual to a fetus during pregnancy. While the virus has been identified in breast milk, researchers have not yet confirmed any viral transmission through breastfeeding.

Although many individuals infected with Zika will be asymptomatic or exhibit mild symptoms, including fever, rash, headache, joint pain, conjunctivitis, and muscle pain, some patients are at greater risk of complications from Zika. For example, Zika infections during pregnancy have been linked to birth defects and other pregnancy complications, such as miscarriage, stillbirth, and preterm birth.

In rare cases, the Zika virus can be more severe, causing Guillain-Barré syndrome, encephalitis, meningitis, myelitis or a blood disorder.

In addition to mosquito bite prevention, Zika can also be prevented by using safe sex practices and barriers such as condoms to prevent sexually transmitted Zika.

Chikungunya

Chikungunya virus is an alphavirus caused by mosquito bites, commonly occurring in Africa, the Americas, Asia, Europe and Indian or Pacific Oceans islands. Common symptoms of this virus include fever and joint pain; however, patients may also present with headache, muscle pain, joint swelling, or rash.

While death from Chikungunya is rare, some vulnerable populations, including newborns, elderly adults and those with underlying medical conditions might be at a greater risk for severe disease.

Although the virus does not spread from person to person through coughing, sneezing, or touching, an infected individual can infect mosquitos, which can then infect other people. Additionally, high viral loads in the blood mean that the virus can spread via blood transfusion, laboratory handling of infected blood, or drawing blood from an infected individual. Additionally, pregnant individuals can transmit the virus to their unborn fetus, with the greatest risk around the second trimester.

Unlike many other mosquito-borne illnesses, there is a vaccine available for Chikungunya. The IXCHIQ vaccine is approved as a single dose for individuals 18 and older. The CDC recommends vaccination for the following groups:

• Individuals traveling to areas with an outbreak.
• Individuals over 65 going to regions with evidence of transmission in the past five years.
• Individuals spending six months or longer in areas with evidence of transmission in the past five years.
• Laboratory workers who might be exposed to the virus.

Dengue

Dengue virus includes four closely related subtypes: dengue-1, dengue-2, dengue-3, and dengue-4. This virus is transmitted through mosquito bites but can also be transmitted from an infected pregnant individual to their fetus. Dengue virus during pregnancy has been linked to fetal death, low birth weight, and premature birth.

Approximately 25% of people infected with the dengue virus will experience symptoms, the most common of which include fever, aches, pains, nausea, vomiting, and rash. Generally, symptoms are mild, and most patients recover within a week.

However, approximately 5% of people infected with the virus will develop severe dengue, which can cause shock, internal bleeding and death. Warning symptoms of severe dengue include belly pain or tenderness, vomiting three or more times within 24 hours, bleeding from the nose or gums, blood in the stool or vomit, and extreme fatigue or extreme restlessness.

Malaria

Malaria is actually caused by a parasite that infects mosquitos; however, most people who get malaria contract it through a bite from infected mosquitos. While the condition is not endemic to the U.S., there are roughly 2,000 cases of malaria reported domestically each year.

Although malaria is not contagious like a cold or flu, in rare cases, the disease can be spread via blood transfusion, organ transplant, sharing needles or syringes, or from a pregnant individual to a fetus.

Disease symptoms can vary dramatically; however, early symptoms include fever, flu-like illness, chills, headache, muscle aches, tiredness, nausea, vomiting, and diarrhea. Severe infection can cause kidney failure, seizures, mental confusion, and even trigger a coma.

Unlike many other mosquito-related illnesses, prescription drugs are available for treating malaria; however, the type of drug and treatment regimen vary depending on the type of malaria, where a patient was infected, disease progression, age and pregnancy status.

In addition to standard mosquito bite prevention, some medications are available to prevent malaria for those traveling to high-risk areas.

Understanding mosquito-borne diseases and their prevention is crucial for public health.

Veronica Salib has covered news related to the pharmaceutical and life sciences industry since 2022.