STEPTRACKERMICROBIOLOGY + TROPICAL MEDICINE | ARBO- & HEMORRHAGIC VIRUSES | HIGH-YIELD REVIEW

Arboviruses & Hemorrhagic Fever Viruses

Viruses carried by mosquitoes and ticks, plus the rodent- and bat-linked hemorrhagic fevers — geography, vector and one hallmark sign make the diagnosis.

FOCUS ON
Flaviviruses: dengue (Aedes; fever, retro-orbital pain, "breakbone" myalgia, ⁺ tourniquet test, thrombocytopenia; second infection with a different serotype → dengue hemorrhagic fever/shock via antibody-dependent enhancement), yellow fever (Aedes; fever, jaundice, black vomit, Councilman bodies; live vaccine), Zika (Aedes, sexual, vertical → microcephaly), West Nile (Culex, birds → encephalitis, flaccid paralysis in elderly). Chikungunya (togavirus) → severe polyarthralgia. Ebola (filovirus; bats; body fluids) and hantavirus (bunyavirus; deer-mouse droppings → pulmonary syndrome).
VIRUS
VECTOR · RESERVOIR
CLINICAL PICTURE
CLUE · PREVENTION
Dengue
Flavivirus · Aedes aegypti (day-biting); tropics
High fever, severe headache, retro-orbital pain, myalgia/arthralgia, rash, leukopenia, thrombocytopenia
⁺ tourniquet test · avoid NSAIDs · supportive fluids
Severe dengue (DHF/DSS)
Second infection, different serotype → non-neutralizing antibodies enhance uptake
Plasma leak (↑ hematocrit, effusions), bleeding, shock as fever falls
Vaccine only for seropositive patients
Yellow fever
Flavivirus · Aedes; Africa, South America; monkeys
Fever, bradycardia → jaundice, hepatitis, hemorrhage ("black vomit")
Councilman bodies (apoptotic hepatocytes) · live vaccine
Zika
Flavivirus · Aedes; also sexual and transplacental
Mild fever, rash, conjunctivitis, arthralgia; fetus: microcephaly, brain calcifications
Guillain-Barré · test pregnant travelers
West Nile
Flavivirus · Culex; birds are reservoir (dead crows); US summer
Most mild fever; elderly: encephalitis, acute flaccid paralysis
Most common US arboviral encephalitis · CSF IgM
Japanese encephalitis
Flavivirus · Culex; pigs, birds; Asia
Encephalitis, movement disorders
Travel vaccine
Chikungunya
Togavirus (alphavirus) · Aedes
High fever + severe symmetric polyarthralgia lasting months
Less bleeding than dengue
Eastern / Western equine encephalitis
Alphaviruses · mosquitoes; birds, horses
Encephalitis (EEE high mortality)
Eastern US coastal
Ebola · Marburg
Filoviruses; fruit bats; spread by body fluids, burial practices
Fever, myalgia → vomiting, diarrhea → hemorrhage, DIC, multiorgan failure
Strict isolation · anti-Ebola mAbs, rVSV vaccine
Hantavirus pulmonary syndrome
Bunyavirus (Sin Nombre) · aerosolized deer-mouse urine/droppings; US Southwest
Prodrome then rapid noncardiogenic pulmonary edema, shock, thrombocytopenia
Cleaning a cabin or shed
Hemorrhagic fever with renal syndrome
Old-World hantaviruses (Asia, Europe)
Fever, hemorrhage, AKI
—
Lassa · LCMV
Arenaviruses · rodent excreta (Mastomys in West Africa; house mice)
Lassa: hemorrhagic fever, deafness · LCMV: aseptic meningitis, congenital chorioretinitis
Ribavirin for Lassa

Mechanism — antibody-dependent enhancement

First dengue serotypeAntibodies made
→
Different serotype laterAntibodies bind, don't neutralize
→
Fc receptor uptake by macrophagesMore infected cells
→
Cytokine storm, capillary leakShock

Vector → virus

VECTOR
VIRUSES
REGION
Aedes mosquito
Dengue, yellow fever, Zika, chikungunya
Tropics
Culex mosquito
West Nile, Japanese encephalitis
US, Asia
Rodent excreta
Hantavirus, Lassa, LCMV
Southwest US, West Africa
Bats
Ebola, Marburg, rabies, Nipah
Africa, worldwide
Ticks
Powassan, Crimean-Congo, Colorado tick fever
Varies

How it's tested

COMMON CONFUSIONDengue (marked thrombocytopenia, retro-orbital pain, bleeding) vs chikungunya (disabling joint pain, milder labs) — same Aedes vector.
THE TRAPDengue shock occurs as the fever breaks (critical phase), not at its peak.
YOUR APPROACHTravel/exposure + vector → family → hallmark (thrombocytopenia, jaundice, microcephaly, encephalitis, arthralgia, pulmonary edema) → isolation and vaccine questions.

If you see… think…

Traveler with fever, retro-orbital pain, ⁺ tourniquet test, platelets 40k → dengue
Second dengue infection with shock → antibody-dependent enhancement
Jaundice, bleeding, Councilman bodies in liver → yellow fever
Microcephaly after maternal travel to Brazil → Zika
Elderly with encephalitis and flaccid weakness, dead crows nearby → West Nile
Fever then months of crippling joint pain after Caribbean trip → chikungunya
Fever, vomiting, hemorrhage after contact with a patient's fluids in West Africa → Ebola
Rapid pulmonary edema after cleaning a rodent-infested cabin → hantavirus
Hemorrhagic fever treated with ribavirin, rodent source → Lassa
Mosquito genus behind dengue, Zika, yellow fever → Aedes