Alpha-, Arena- and Bunyavirus
Hemorrhagic Fevers

Austin G. Meyer


Road Map

  • Arboviruses
    • Serogroup A (Alphaviruses)
      • History
        • New World
        • Old World
      • Basics of their biology
      • Clinical disease
      • Diagnosis and treatment
    • Serogroup B (Flaviviruses - covered later)
    • Serogroup C (Bunyaviruses)
      • Brief history and categorization
      • Several Viruses
        • Geographic distribution
        • Relevant diseases
        • Diagnosis and treatment
  • Other viruses that cause VNF
    • Arenaviruses
      • History
      • Virus geography
      • Biology and current investigation
      • Ecology and epidemiology
      • Clinical disease
      • Diagnosis and treatment
      • Prevention and control


History of alphavirus infections

Alphaviruses have been around humans
far longer than other common zoonoses.

The history of New World alphaviruses

  • First certain reports of epidemic encephalitis occurred in Massachussets in 1831
    • That outbreak killed 75 horses
  • Intermittent outbreaks continued throughout the Atlantic seaboard for the next 100 years

  • First alphavirus cultured was Western equine encephalitis virus (WEEV) in 1930
    • Isolated from CNS of an affected horse in the San Joaquin Valley, CA
  • Second isolated virus was Eastern equine encephalitis virus (EEEV) in Virginia in 1933

  • Third isolated virus was Venezuelan equine encephalitis vires (VEEV) in 1936

  • Outbreaks almost always occurred during the summer

The history of Old World alphaviruses

  • It is likely these have been around forever, but it is hard to distinguish it from more prevalent viruses like Dengue
    • For example, the first Old World alphavirus, Chikungunya (CHIKV), was not identified until much later
  • First outbreaks occurred as summertime epidemics of polyarthritis in Australia and New Guinea in 1928

  • CHIKV was isolated first in Tanzania in 1953 from the blood of humans with severe athritis

  • In 1954, first classification distinguished Arthropod-borne viruses (Arboviruses) on the basis of Hemagglutinin Inhibition
    • Group A cross-reacting arboviruses included WEEV, EEEV, and VEEV
    • Group B cross-reacting arboviruses included St. Louis, Dengue, and Yellow fever
    • Group C were non-reactive
    • Eventually Group A became alphaviruses while Group B became Flaviviruses

A lot of alphaviruses have been described!!

This is only A-P
This is only A-P

Basics of alphavirus biology

Background biology of alphaviruses

  • Enveloped (+)ssRNA viruses

  • The definitive alphavirus cellular receptor is not known
    • MHC I serves as a sufficient, but not necessary receptor
    • Probably more than one exists
  • In mice, virus primarily infects muscles and fibroblasts

  • Induce substantial viremia to spread to other skeletal muscle

  • Capable of recombination with other alphaviruses
    • In particular Sindbis-like and EEEV can recombine in nature
    • That is how WEEV was made
  • In-vector incubation time requires 2-7 days for infectivity

  • Vectors include many mosquito species and even other arthropods
    • Ae. albopictus is common for CHIKV
    • Culex is common for WEEV

Evoution of alphaviruses

Epidemiology and Ecology of New World viruses

  • Occurs virtually anywhere the vector is present
    • Gulf Coast
    • Atlantic Seaboard
    • Carribean
    • Great Lakes
    • Amazon Basin
  • For children, 1 in 8 infections results in encephalitis

  • For adults, 1 in 23 infections results in encephalitis

  • CFR is high; usually between 30-50%
    • CFR is much lower for South American EEEV
  • Epizootic cycle appears every 5 to 10 years and is associated with heavy rainfall and warmer water

  • Approximately 8 human cases occur every year in the US

Epidemiology and Ecology of Old World viruses

  • These viruses are common and widespread in the Old World

  • Separate rural and ubran cycles
    • Rural: disease is endemic with small of number cases every year
    • Urban: explosive outbreaks within large populations being infected in just a few weeks
  • Most common viruses are CHIKV and Ross River virus

  • CFR is ~1 in 1000 with most deaths in neonates

  • May be maintained in mosquitoes via vertical transmission

Geography of CHIKV

Clinical disease

New World alphaviruses produce primarily encephalitis
so we’ll skip the rest

Old World alphaviruses produce polyarthralgia and rash

  • CHIKV incubation time of 3-12 days

  • Rash appears 4-8 days after initial illness

  • Two most important things
    • Where were they recently?
    • Do their muscles hurt or do their joints hurt?
  • If muscles primarily hurt, probably dengue

  • If joints hurt and there is a rash
    • Central Africa: CHIKV, O’nyong-nyong (ONNV)
      • Can distinguish the two with ONNV having cervical lymphadenopathy
      • Cervical lymphadenopathy is common for ONNV
    • Other Africa: CHIKV
    • Central Australia: Ross River (RRV), Barmah Forest (BFV)
      • Can distinguish by symptom prominence: Rash = BFV, Arthritis = RRV
    • Other Oceania: Ross River
    • Anywhere (even Europe, Russia and West Asia): Sindbis (SNV)
      • If you think parvo B19, also think Sindbis
  • Other symptoms include conjunctivitis (not as common for Dengue), headache, GI complaints

  • Rash may cause a second rise in fever and be itchy

  • Leukopenia is common

Generic Alphavirus timeline

Alphavirus diagnosis

  • There are specific rtPCR primers for all alphaviruses and IgM serologies are very specific

  • Old World viruses
    • CHIKV: PCR, IgM present for two months,
    • ONNV: PCR in early illness, IgM present for two months
    • RRV: usually made by IgM serology which is positive for 1-2 years
    • SINV: IgM serology for 3-4 years
    • BFV: Serology?

Treatment is supportive and symptomatic.

There are many vaccines under development as well as medications that are specific for the etiology of these arthralgias/myalgias.

Do your best!


History and categorization

History of Bunyaviruses

  • First discovered in mosquitoes in 1943 during a yellow fever outbreak

  • Essentially the largest class of RNA viruses
    • There are more than 350 categorized
  • All of them except for Hantaviruses (i.e. probably the only ones we care about) are spread via arthropods
    • Can also be spread by blood contamination

Categorization of Bunyaviruses

  • (-)ssRNA virus
    • Segmented genome
    • Phylogenetically more in common with Arenaviruses and Ebola than other Arboviruses
  • There are five genuses
    • Four cause human infections
  • The diseases that I think we should have heard of:
    • Phlebovirus: Rift Valley Fever
    • Nariovirus: Crimean-Congo Hemorrhagic Fever (CCHF)
    • Hantavirus: Seoul virus, Sin nombre (Nameless) virus (Hanta Pulmonary Syndrome)
    • Orthobunyavirus: Probably none

Several viruses in series

Rift Valley Fever geography

Since 2000 there have probably been around 1000 cases in humans
Since 2000 there have probably been around 1000 cases in humans

Rift Valley Fever patients are not very sick

  • Causes massive spontaneous abortion epidemics in livestock
    • Typically human outbreaks occur in the waning stage of livestock outbreaks
    • Transmitted by mosquitoes and direct blood transmission
    • Must ask about contacts!
  • No documnated cases of human-to-human transmissions

  • Incubation time of 2-6 days

  • Typically: Fever, generalized weakness, back pain, dizziness. Most recover in a few days

  • Around 10% get severe disease
    • Ocular form: Lesions anywhere on the eye within 1-3 weeks and resolved within 12
    • Encephalitis: About 1% of infections.
    • Hemorrhagic fever: Although this is around 1% of infections, death occurs in 50%.
      • Death occurs 3-6 days after hemorrhagic fever
  • Diagnose with standard PCR, ELISA-Ag, ELISA-IgM

  • No specific treatment and generally not necessary

Rift Valley Fever life cycle

CCHF Geography

CCHF patients are very sick

  • Spead by ixodes (hard) ticks
    • Also serve as reservoir
    • Transmission can also happen by direct blood contamination
  • Typically: Sudden onset with headache, high fever, back pain, joint pain, stomach pain, vomiting (influenza-life syndrome)

  • Commonly: Conjunctivitis, flushed face, palatal petechiae

  • Occasionally: Jaundice, mood changes, sensory misperception

  • Progresses to uncontrolled bleeding, bruising starting of day 4 with CFR = 10-50%

  • Diagnosis: Same as Rift Valley Fever

  • Treatment: Sensitive in vitro to Ribavirin. Supportive care in shock phase.

  • Prevention: Agricultural workers need tick precautions
    • There is an inactivated mouse-brain derived vaccine that is only used in some sketchy parts of Europe

(Hantaviruses) Hemorrhagic fever with renal syndrome geography

  • Viruses (there are several that cause this) are found worldwide, but outbreaks previously occurred mostly in Asia

  • We are in the midst of an outbreak of Seoul virus right now (it has really ended as of 03/2017)!
    • Currently 17 cases in 15 states
    • Started in rat breeders in the midwest
  • Transmission is identical HPS with aerosolized excreta

  • Incubation time is 1-2 weeks usually but can take up to 8 weeks

  • Sudden onset headaches, back and abdominal pain, fever, chills, nausea, and blurred vision

  • In less than 5% progresses to hypotension, shock, and acute renal failure

  • Diagnosis: Same as above

  • Treatment: Supportive


History of Arenaviruses

Need to know Lassa, Limited number of outbreaks for others

  • First discovered was lymphocytic choriomeningitis virus in 1933
    • Found while studying St. Louis encephalitis
  • Many subsequent case reports involved other Arenaviruses
    • Lassa Fever first infections 1969
      • Old World, mostly in the region of the 2014 Ebola outbreak
      • 300,000-500,000 cases annually, CFR Overall = 1%, CFR Severe Cases = 15%
    • Tacaribe, 1956, but doesn’t infect humans
      • New World
    • Junin, 1958: CFR = 15-30%
      • New World, Argentina
    • Machupo, 1963: CFR = 25%
      • New World, Bolivia
    • Guanarito, 1989: CFR = 25%
      • New World, Venezuela
    • Sabia, 1990: CFR = 1/3
      • New World, Brazil
    • White Water Arroyo, 1996: CFR = 3/3
      • New World, New Mexico (same as Hantavirus)
    • Chapare, 2008
    • Lujo virus, 2008: CFR = 4/5
  • Generally classified into two groups
    • Old World: LCMV-Lassa complex
    • New World: Tacaribe serocomplex

Biology of arenaviruses

Molecular biology of arenaviruses

  • Enveloped, segmented (-)ssRNA virus

  • Life cycle restricted to cellular cytoplasm

  • Similar to Ebola, it encodes RNA-dependent RNA polymerase

  • Use various cell surface receptors
    • Some use extracellular matrix proteins
    • Others including MACV and JUNV use the transferrin receptor

Epidemiology and ecology

The reservoir for arenoviruses are rodents

Distribution of viruses are limited to their rodent host
Distribution of viruses are limited to their rodent host

Easiest to separate by geography rather than clades

Most of these have not been found in humans
Most of these have not been found in humans

Lassa is probably the most important to know geographically

In 2014, easily confused with Ebola
In 2014, easily confused with Ebola

Clinical manifestations

Other than LCMV, all of these viruses are similar

  • Old World (Lassa Fever) and New World are similar except that neurologic symptoms, -penias, and bleeding are less common for Old World viruses

  • Incubation time of 5-20 days

  • Disease begins with fever, chills, malaise, anorexia, headache, and myalgias

  • After several days, GI, neurologic and cardiac symptoms
    • Nausea/Vomiting/Constipation/Diarrhea/Epigastric pain
    • Dizziness/Photophobia/Retro-orbital pain
    • Low back pain
  • During symptom onset they may experience swelling and bleeding gums, swelling and bleeding conjunctiva

  • Patients often develop petechiae from thrombocytopenia

  • Patients often experience bradycardia and orthostatic hypotension

  • Should never have cough, sore throat or congestion to distinguish from flu
    • There should be no pulmonary signs or symptoms
  • During second week patients either begin to recover or begin to die

Hemorhaggic fever signs

Ocular Manifestion of Argentine HF
Ocular Manifestion of Argentine HF
Gingival Manifestion of Argentine HF
Gingival Manifestion of Argentine HF

Diagnosis and treatment

Most important to know Lassa and Junin (AHF)

  • Isolation in Vero cells

  • ELISA for antigen
    • Availability of specific antibodies are limited
    • Lassa is best diagnosed with ELISA to IgM and antigen
      • Antigen disppears when IgM emerges so testing both is critical
      • Sensitivity is 90% at 48 hours
      • Antigen is in blood within a few days of infection
      • IgM peaks at 10-12 days
      • IgG is present after 3 weeks
  • rtPCR

  • Fatal cases can be diagnosed with immunohistochemistry with fixed tissue

  • Neutralization assay is useful if specific convalescent serum is available

Supportive treatment is helpful

  • No steroids and no IFN-\(\gamma\)
    • Except maybe steroids for cerebral edema
  • Only oral and IV therapies
    • SubQ and IM often cause hematomas
  • For ANF, secondary pneumonias are common

  • Platelets, activated factor VII, desmopressin, and transfusion have not been systemically evaluated

  • Specific treatments
    • Ribavirin
      • Effective in vitro against most arenaviruses
        • This is not the case for Ebola
      • Articles from mid-1980s indicate efficacy against Lassa in vivo
        • Important for severe infections
    • Convalescent plasma
      • AHF: Reduces CFR from 15-30% to 1%
      • Lassa: Probably does not work
    • In pregnant patients, abortion improves survival of mother

    • High-throughput screens with pseudo-typed virus indentifies several in vitro viral entry inhibitors

Prevention and control

Do not play with rodents

  • All arenaviruses are difficult to transmit between humans
    • It occassionally occurs by parenteral innoculation with Lassa
    • Lassa may have had airborne transmission in one Nigerian outbreak
  • Rodent control is sufficient for Bolivian hemorrhagic fever
    • Won’t work for Lassa because its reservoir is a common rat
  • Vaccines
    • AHF live attentuated vaccine (Candid #1) developed in 1980’s by Salk Institute
      • Licensed in late 2000s for use exclusively in Argentina
      • Very effective
      • Probably has some cross over to Bolivian hemorrhagic fever
    • Lassa
    • Lots of smoke, but no fire so far

Take home: Could control or stop Arenaviruses
There isn’t enough money there to pursue it