Mosquito-Borne Diseases: Dengue, Chikungunya, and West Nile Virus

Mosquito-Borne Diseases: Dengue, Chikungunya, and West Nile Virus is a topic covered in the 5-Minute Emergency Consult.

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Basics

Description

  • Vector-borne diseases account 17% of infectious diseases. Mosquitos are best known vector
  • Severity of illness: Asymptomatic to fatal
  • Despite control efforts, mosquito-borne illnesses are increasing. Climate change, animal migration patterns, travel and international trade contribute
  • Several diseases are of particular importance in addition to malaria
    • Dengue: 390 million dengue infections/yr; ¼ result in clinical illness. Endemic in more than 100 countries. 2nd most common cause of fever in returning travelers. 3.2 million cases in 2015 (WHO); substantial underreporting. Continuum of disease ranges from mild illness (Dengue fever [DF]) to severe findings (Dengue hemorrhagic fever [DHF] and Dengue shock syndrome [DSS]).
    • Chikungunya: First reported in Americas (Caribbean) in 2013
    • Zika: Significant concern in pregnant women (severe neurologic defects in developing fetus, esp. microcephaly). Between 2015–2018, 5,635 symptomatic cases reported in the U.S. (95% of cases were in travelers)
    • West Nile Virus (WNV): Wild birds are main reservoir. Introduced in the U.S. in 1999. An outbreak in 2011 had a mortality rate of 4–5%. Cases were reported in 48 states

Etiology

  • Mosquito-borne viruses are spread by 1 of 3 species of mosquitos: Anopheles (Malaria), Aedes (Dengue, Chikungunya, Zika), and Culex (WNV)
  • Anopheles sp.
    • Night biter
    • Only transmits Malaria
  • Aedes sp:
    • Day biter
    • Ae aegypti is the main vector; Ae albopictus is also able to spread disease. Breed in standing water (tires, garbage containers, buckets, vases)
    • Transmits:
      • Dengue: Tropical, subtropical regions: Asia, Africa, Central and South America, Caribbean. 4 serotypes of the virus: DEN-1, DEN-2, DEN-3, DEN-4. Subsequent infection by other serotypes increases risk of severe disease
      • Chikungunya: Located in same regions as Dengue
      • Zika: Pacific Islands and South America have the heaviest burden of infection. In North America, Mexico has the highest numbers of cases; however, Florida (2014) and Texas (2015) have reported cases
  • Culex sp.:
    • Night biter
    • Transmits
      • WNV: First discovered in 1937 in Uganda. Secondary to bird migratory patterns, Endemic in Europe, India, Africa, Asia, Middle East, Australia, and North America. Horse and bird (crows) illness predictive of human risk
      • Japanese encephalitis and lymphatic filariasis
  • Other possible modes of transmission: Maternal fetal transmission, sexual contract, laboratory exposure, blood transfusion, breastfeeding
    • WNV: Solid-organ transplant
    • Breastfeeding is still recommended despite transmission risk due to benefits

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Basics

Description

  • Vector-borne diseases account 17% of infectious diseases. Mosquitos are best known vector
  • Severity of illness: Asymptomatic to fatal
  • Despite control efforts, mosquito-borne illnesses are increasing. Climate change, animal migration patterns, travel and international trade contribute
  • Several diseases are of particular importance in addition to malaria
    • Dengue: 390 million dengue infections/yr; ¼ result in clinical illness. Endemic in more than 100 countries. 2nd most common cause of fever in returning travelers. 3.2 million cases in 2015 (WHO); substantial underreporting. Continuum of disease ranges from mild illness (Dengue fever [DF]) to severe findings (Dengue hemorrhagic fever [DHF] and Dengue shock syndrome [DSS]).
    • Chikungunya: First reported in Americas (Caribbean) in 2013
    • Zika: Significant concern in pregnant women (severe neurologic defects in developing fetus, esp. microcephaly). Between 2015–2018, 5,635 symptomatic cases reported in the U.S. (95% of cases were in travelers)
    • West Nile Virus (WNV): Wild birds are main reservoir. Introduced in the U.S. in 1999. An outbreak in 2011 had a mortality rate of 4–5%. Cases were reported in 48 states

Etiology

  • Mosquito-borne viruses are spread by 1 of 3 species of mosquitos: Anopheles (Malaria), Aedes (Dengue, Chikungunya, Zika), and Culex (WNV)
  • Anopheles sp.
    • Night biter
    • Only transmits Malaria
  • Aedes sp:
    • Day biter
    • Ae aegypti is the main vector; Ae albopictus is also able to spread disease. Breed in standing water (tires, garbage containers, buckets, vases)
    • Transmits:
      • Dengue: Tropical, subtropical regions: Asia, Africa, Central and South America, Caribbean. 4 serotypes of the virus: DEN-1, DEN-2, DEN-3, DEN-4. Subsequent infection by other serotypes increases risk of severe disease
      • Chikungunya: Located in same regions as Dengue
      • Zika: Pacific Islands and South America have the heaviest burden of infection. In North America, Mexico has the highest numbers of cases; however, Florida (2014) and Texas (2015) have reported cases
  • Culex sp.:
    • Night biter
    • Transmits
      • WNV: First discovered in 1937 in Uganda. Secondary to bird migratory patterns, Endemic in Europe, India, Africa, Asia, Middle East, Australia, and North America. Horse and bird (crows) illness predictive of human risk
      • Japanese encephalitis and lymphatic filariasis
  • Other possible modes of transmission: Maternal fetal transmission, sexual contract, laboratory exposure, blood transfusion, breastfeeding
    • WNV: Solid-organ transplant
    • Breastfeeding is still recommended despite transmission risk due to benefits

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