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Miscellaneous mosquito-borne diseases

Last updated: February 16, 2021

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Mosquito-borne diseases are a group of viral infections transmitted by the bite of an infected mosquito, typically from the Culex, Anopheles, or Aedes species. Vertical and human-to-human transmission (e.g., via blood transfusions, organ, and tissue transplants) are also possible. These viral diseases belong to three main families: Togaviridae (Chikungunya virus, Eastern equine encephalitis (EEEV), Western equine encephalitis (WEEV), Flaviviridae (West Nile virus, Dengue virus, Zika virus, Yellow fever virus, Japanese encephalitis virus), and Bunyaviridae (Rift Valley fever virus, La Crosse encephalitis virus). Clinical features of these diseases vary but often include an initial systemic febrile illness (i.e., fever, headache, myalgias, gastrointestinal symptoms) that progresses to a neuroinvasive disease (e.g., meningitis, encephalitis). Diagnosis is made via antibody detection (e.g., IgM, IgG), ELISA, FIA, or PCR. Treatment is typically supportive. Prevention primarily consists of mosquito control measures (i.e., adequate clothing, insect repellents, mosquito nets, minimizing mosquito breeding).

Overview of mosquito-borne Togavirus diseases
Ross River fever (RRF) Eastern equine encephalitis (EEE) Western equine encephalitis (WEE) Venezuelan equine encephalitis (VEE)
Epidemiology
  • Found predominantly in Australia, Papua New Guinea, the Solomon Islands, and other parts of South East Asia
  • Outbreaks during summer and early autumn
  • Found primarily in the Americas
  • In the US, occurs east of the Mississippi River (e.g., New York, New Jersey, Michigan)
  • Bimodal distribution
    • ≤ 5 years of age
    • ≥ 60 years of age
  • Outbreaks occur from late spring to early fall.
  • Occurs on the west coast of the United States and Canada
  • Outbreaks during summer
  • Found predominantly in the Americas (Colombia, Venezuela, Panama, Guatemala, Mexico, the United States, Ecuador, Nicaragua, Costa Rica, Peru)
  • Sporadic outbreaks
Etiology Pathogen
  • Ross river virus (RRV)
Vectors
  • Mosquitoes (Aedes vigilax, Aedes camptorhynchus, Culex annulirostris, and Aedes aegypti)
  • Mosquitoes (Culiseta melanura, Aedes, Coquillettidia, and Culex spp.)
  • Mosquitoes (Culex tarsalis, Aedes spp.)
  • Mosquitoes (Ochlerotatus taeniorhynchus, Ae. sollicitans, and Ae. taeniorhynchus transmit epizootic strains)
Reservoirs
  • Wallabies, kangaroos, possums, horses
  • Horses, birds
  • Horses, mules, birds
  • Horses, mules, donkeys, rodents
Route of transmission
  • Mosquito bite
  • Human-mosquito-human transmission
  • Human-to-human: blood transfusions from an infected host
Incubation period
  • 3–9 days [1]
  • 4–10 days [2]
  • 2–7 days [3]
  • 2–5 days [4]
Clinical features
  • Systemic febrile illness (acute EEE)
    • Lasts up to 14 days [2]
    • Fever
    • Headache
    • Gastrointestinal symptoms (nausea, vomiting)
  • EEE
  • Most affected individuals are asymptomatic.
  • Systemic febrile illness (acute WEE)
  • WEE
    • Adults have more mild symptoms than children and elderly individuals.
    • Severe forms of encephalitis are more common in children.
    • Neurological symptoms include seizures, confusion, somnolence, spasticity, cognitive impairment, and coma.
  • Systemic febrile illness (acute VEE)
  • Venezuelan equine encephalitis
    • Manifests in ≤ 15% of patients [4]
    • Severe forms of encephalitis are more common in children.
    • Neurological symptoms include seizures, confusion, motor, and cognitive impairment, and focal disabilities.
Diagnostics Laboratory studies
Confirmatory tests
Lumbar puncture
Other
  • Viral culture
  • Brain MRI
  • Viral culture
  • EEG: diffuse slowing activity
  • Viral culture
Differential diagnosis
Treatment
  • Supportive treatment
    • Analgesics for pain and fever
    • Management of fluids and electrolyte balance
    • Maintenance of blood pressure and oxygenation
    • Anticonvulsive treatment of seizures
Complications
  • Severe neurological sequelae [6]
    • Epilepsy
    • Cognitive disabilities
    • Behavioral changes
  • Death: occurs within 5 days of diagnosis [6]
Overview of mosquito-borne Flavivirus diseases
West Nile virus Murray Valley encephalitis (MVE) St. Louis encephalitis
Epidemiology
  • One of the most widely distributed arboviruses
  • Endemic in Africa, parts of Europe, South Asia, Australia, the United States, and the Middle East
  • Outbreaks during summer and fall
  • Found in Australia, Papua New Guinea, and Indonesia
  • Sporadic outbreaks
  • Found in North, Central, and South America
  • Outbreaks during summer

Etiology

Pathogen
  • MVE virus
Vectors
  • Mosquitos (Culex, Aedes, or Anopheles spp.)
  • Mosquitos (Culex spp.)
  • Mosquitos (Culex spp.)
Reservoirs
  • Mosquitoes, birds, horses, dogs
  • Mosquitoes, birds
  • Mosquitoes, birds
Route of transmission
  • Mosquito bites
  • Human-to-human
  • Mosquito bites
  • Mosquito bites
Incubation period
  • 2–14 days [8]
  • 1–4 weeks [9]
  • 4–21 days [10]
Clinical features
  • Most affected individuals are asymptomatic.
    • Illness only manifests in ∼ 1% of affected individuals. [10]
    • Age is the most important risk factor for the development of symptomatic disease (more common in individuals > 60 years of age).
  • Prodromal illness
  • SLE/aseptic meningitis
    • Children have more mild symptoms.
    • Neurological symptoms include drowsiness, irritability, confusion, tremors, ataxia, and meningismus.
Diagnostics Laboratory studies
Confirmatory tests
Lumbar puncture
Brain MRI
  • Normal or demonstrates nonspecific changes (increased signal intensity)
  • Normal or demonstrates nonspecific changes
Other
  • Viral culture
  • EEG: shows slow delta wave activity
  • Viral culture
Differential diagnosis
Treatment
  • Supportive
    • Management of fluids and electrolyte balance
    • Anticonvulsive treatment of seizures
Complications
  • Permanent neurological deficits (∼ 50% of symptomatic individuals) [12]
  • Death (∼ 33% of patients with neurological symptoms) [12]
  • SIADH
  • Neurologic sequelae
  • Death

Overview of mosquito-borne Bunyavirus diseases
La Crosse encephalitis Rift Valley fever
Epidemiology
  • Found in the midwestern, central, and southeastern parts of the United States
  • Common in children (1–15 years of age) [13]
  • Outbreaks during the summer
  • Found in Egypt, Sub-Saharan Africa, and the Arabian Peninsula
  • Sporadic outbreaks
Etiology Pathogen
Vectors
  • Mosquito: Aedes triseriatus (tree hole mosquito)
  • Mosquito (Aedes and Culex spp.)
Reservoirs
  • Chipmunks, foxes, squirrels, woodchucks
  • Cattle, sheep, goats, camels
Route of transmission
  • Mosquito bite
  • Mosquito bite
  • Direct contact with blood or tissues of infected animals
  • Inhalation of aerosols from infected animal tissue
Incubation period
  • 5–15 days [13]
  • 2–6 days [14]
Clinical features
  • Most affected individuals are asymptomatic.
Diagnostics Laboratory studies
Confirmatory tests
Lumbar puncture
Other
  • EEG: shows slowing, epileptiform discharges
  • Viral culture
Differential diagnosis
Treatment
Complications
  • Vision loss
  • Neurological sequelae
  • Death
    • Seen in ∼ 50% of patients with hemorrhagic fever form [14]
    • Typically due to shock or hepatic insufficiency

Mosquito bite prevention

  • Clothing
    • Wear light-colored clothing.
    • Long-sleeved shirts and long pants
  • Insect repellent
    • Use insect repellants (e.g., DEET, permethrin, oil of lemon eucalyptus)
    • Apply to clothing and footwear.
  • Mosquito nets
    • Place screens at doors and windows.
    • Use mosquito nets on baby strollers, carriers, and cribs.
  • Remove open water containers, trash containers, and water-holding plants to minimize mosquito breeding.

Obligation to report

  • Mosquito-borne diseases are nationally notifiable diseases in most countries worldwide (i.e., the physician is required by law to report cases of such diseases).
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  2. Banda C, Samanta D. Eastern Equine Encephalitis. StatPearls. 2020 .
  3. Simon LV, Coffey R, Fischer MA. Western Equine Encephalitis. StatPearls. 2020 .
  4. Crosby B, Crespo ME. Venezuelan Equine Encephalitis. StatPearls. 2020 .
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  12. Saint Louis Encephalitis. https://www.cdc.gov/sle/technical/symptoms.html. Updated: December 4, 2018. Accessed: December 9, 2020.
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  14. Selvey LA, Speers DJ, Smith DW. Long-term outcomes of Murray Valley encephalitis cases in Western Australia: what have we learnt?. Intern Med J. 2016; 46 (2): p.193-201. doi: 10.1111/imj.12962 . | Open in Read by QxMD
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