Here in the northeastern U.S., mosquito-borne illnesses are making headlines. At the time of this writing, there are reports of West Nile virus circulating earlier than usual this year and an uptick in the number of cases of Dengue fever which is raising concerns. Let’s take a closer look at these and other diseases spread by mosquitos. Learn the signs and symptoms of each, as well as important patient education about prevention.

West Nile Virus (CDC, 2024a)

West Nile virus can cause acute febrile or neurologic illness. The incubation period is typically 2 to 6 days but can be up to 14 days and even longer in patients who are immunocompromised.

Signs and Symptoms of West Nile Virus

About 70-80% of cases are subclinical or asymptomatic. Patients who develop symptoms often experience the following:

• Headache
• Weakness
• Myalgia or arthralgia
• Gastrointestinal symptoms
• Transient maculopapular rash

Progression to meningitis, encephalitis, and acute flaccid myelitis may occur.

Dengue Fever (CDC, 2024b)

Dengue fever has an incubation period of 5 to 7 days; symptoms then begin abruptly, and the course follows 3 phases: febrile, critical, and convalescent. Laboratory findings commonly include leukopenia, thrombocytopenia, hyponatremia, elevated aspartate aminotransferase (AST) and alanine aminotransferase (ALT), and a normal erythrocyte sedimentation rate (ESR).

Signs and Symptoms of Dengue Fever

Febrile Phase

• Fever for 2 to 7 days; can be biphasic
• Severe headache
• Retro-orbital pain
• Myalgia and arthralgia
• Macular or maculopapular rash
• Minor hemorrhagic manifestations including petechia, ecchymosis, purpura, epistaxis, gingival bleeding, hematuria, or a positive tourniquet test result 

Watch for the following warning signs of progression to severe dengue:

• Persistent vomiting
• Severe abdominal pain
• Fluid accumulation
• Mucosal bleeding
• Lethargy/restlessness
• Postural hypotension
• Liver enlargement
• Progressive increase in hematocrit

Critical Phase

• Begins when fever resolves; lasts 24 to 48 hours
• Many patients clinically improve, but those with substantial plasma leakage can progress to severe dengue:
  • Initially, narrowed pulse pressure occurs due to compensatory mechanisms.
  • Severe plasma leakage may lead to pleural effusions, ascites, hypoproteinemia, or hemoconcentration.
  • Irreversible shock, hemorrhagic manifestations, and death can occur.

Convalescent phase

• Extravasated fluids, pleural and abdominal effusions are reabsorbed.
• Hemodynamics stabilize and diuresis occurs.
• Hematocrit stabilizes or decreases, white blood cell count rises, and platelet count recovers.
• Rash may desquamate and itch.

Zika Virus (LaBeaud, 2023)

Zika virus has an incubation period that typically lasts 2 to 14 days. Illness is usually mild, and symptoms resolve within 2 to 7 days. Infection during pregnancy can cause serious birth defects and other problems.

Signs and Symptoms of Zika Virus

Clinical illness is consistent with Zika virus disease if two or more of these symptoms are present:

• acute onset of low-grade fever
• pruritic rash (erythematous macules and papules may be present on the face, trunk, extremities, palms, and soles)
• arthralgia (notably in the small joints of the hands and feet)
• nonpurulent conjunctivitis

Other commonly reported clinical manifestations include myalgia, headache, dysesthesia, retro-orbital pain, and asthenia. Signs and symptoms that are less common include abdominal pain, nausea, diarrhea, and mucous membrane ulcerations.

Chikungunya Virus (CDC, 2024c)

While caused by the bite of infected mosquitos, people infected with Chikungunya virus can also spread the virus to mosquitoes (and rarely to other people). There is a vaccine available to travelers at higher risk of exposure or increased risk of severe disease.

Signs and Symptoms of Chikungunya Virus

• Fever
• Joint pain
• Headache
• Muscle pain
• Joint swelling
• Rash

Malaria (CDC, 2024d)

Malaria can be deadly if it’s not diagnosis and treated quickly. Most cases in the U.S. are related to travel to countries where malaria spreads.

Signs and Symptoms of Malaria

Early symptoms

• Fever and flu-like illness
• Chills
• Headache, muscle aches, and tiredness
• Nausea, vomiting, and diarrhea

Severe symptoms (if not treated quickly)

• Kidney failure
• Seizures
• Mental confusion
• Coma

Less Common Diseases Caused by The Bite of An Infected Mosquito

• Eastern Equine Encephalitis
• Japanese Encephalitis
• La Crosse virus
• St. Louis Encephalitis
• Yellow Fever

References:

Centers for Disease Control and Prevention (CDC). (2024a, May 15). Clinical Signs and Symptoms of West Nile Virus Disease. CDC. https://www.cdc.gov/west-nile-virus/hcp/clinical-signs/index.html

Centers for Disease Control and Prevention (CDC). (2024b, June 5). Clinical Features of Dengue. CDC. https://www.cdc.gov/dengue/hcp/clinical-signs/index.html

Centers for Disease Control and Prevention (CDC). (2024c, May 15). About Chikungunya. CDC. https://www.cdc.gov/chikungunya/about/index.html

Centers for Disease Control and Prevention (CDC). (2024c, March 12). About Malaria. CDC. https://www.cdc.gov/malaria/about/index.html#cdc_disease_basics_risk-causes-and-risk

LaBeaud, A.D. (2023, December 8). Zika virus infection: An overview. UpToDate. https://www.uptodate.com/contents/zika-virus-infection-an-overview

 

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