Zoonotic Viruses Flashcards
Zoonotic Viruses
- Arthropod Borne (Arbovirus)
- Non Arthropod Borne (Hemorrhagic Fever and Encephalitis Viruses)
Zoonotic Viruses Reservoirs
Reservoir in lower vertebrates or insects.
Arthropod Borne (Arboviruses)
- Togaviruses
- Bunyaviruses
- Flaviviruses
- Reoviruses
Non Arthropd Borne
- Rhabdoviruses
- Arenaviruses
- Filoviruses
- Hantavirus (Bunyavirus)
Arbovirus Transmission
3 Major Manifestations of Arbovirus Disease
•Viral tropisms for human organs play important roles.
- CNS is primarily affected leading to aseptic meningitis or encephalitis.
- The second syndrome involves many major organs with particular damage to liver as in yellow fever.
- The third is manifested by hemorrhagic fever with damage to small blood vessels and intestinal and other hemorrhages.
Arbovirus Immunity
Togavirus and Flavivirus
- ( + ) ss RNA icosohedral enveloped
- Envelope contains hemagglutinin and lipoproteins
- Alphavirus of the family Togaviridae and flavivirus of the family Flaviviridae include most of the arthropod borne viruses
Togavirus and Flavivirus Structure
- Single stranded, positive sense RNA viruses
- Enveloped virions, 40 to 70nm in external diameter
- Envelope contains hemagglutinin and lipoproteins
- Alphavirus of the family Togaviridae and flavivirus of the family Flaviviridae include most of the arthropod borne viruses
- Each genus possesses its own unique structure of RNA genome
- Replication can occur in cells of infected arthropods and vertebrate hosts
- Viruses within these genera are frequently serologically related to one another
Western Equine Encephalitis
- caused by Alphavirus
- Western U.S.
- Horses and Humans = blind hosts
- more severe in children
- Mild nonspecific febrile illness to aseptic meningitis, severe and overwhelming encephalitis.
- Mortality estimated at 5% for cases of encephalitis.
- Serious disease in infants below 1 yr of age;60% of survivors have permanent neurologic impairment
Eastern Equine Encephalitis
- caused by Alphavirus
- New England to South AMerica
- usually animals, sometimes human outbreak
- virus can cause severe encephalitis
- highest attack rate –> infants and children
St. Louis Encephalitis
- caused by Flavivirus
- Major cause of arbovirus encephalitis in the United States
- Mosquito vector: Culex tarsalis
- Disease spectrum similar to western equine encephalitis virus; mild nonspecific febrile illness to aseptic meningitis, severe and overwhelming encephalitis
- Major morbidity and mortality as well as highest attack rates among adults more than 40 years of age
Yellow Fever
- caused by Flavivirus
- Caribbean, Central America and South America.
- Potential threat to the southeastern and southwestern United States because of presence of mosquito vector (Aedes aegypti)
- abrupt onset of fever, chills, headache and hemorrhage
- May progress to severe vomiting (sometimes with gastric hemorrhage), bradycardia (slowness of heart beat), jaundice and shock
- Live attenuated yellow fever virus vaccine (17-D strain) recommended for endemic areas
Dengue
- caused by Flavivirus
- Distributed throughout the world, particularly in the Middle East, Africa, India, the Far East, and the Caribbean Islands.
- Domestic vector: Aedes aegypti (mosquito).
- Transmission cycle: human-mosquito-human, a sylvatic cycle involving monkeys may exist.
- Clinical illness usually results in fever, an erythematous rash, severe pain in the back, hand, muscles and joints.
- A severe form is characterized by shock, pleural effusion (liquid in lungs lining), and hemorrhage often followed by death.
- Risk in Southeast/west U.S. because of the vector
Dengue Immunity
Japanese B. Encephalitis
- caused by Flavivirus
- Prevalent on Eastern coast of Asia, on its offshore islands (Japan, Taiwan and Indonesia) and in India.
- Transmission cycle: mosquito, similar to St. Louis encephalitis and Western equine encephalitis viruses
- High proportion of human infections are subclinical: especially in children
- Development of encephalitis is severe and often fatal
- Inactivated Japanese encephalitis (JE) vaccine (IXIARO) is licensed in the U.S. for use in 2 months and older
West Nile Virus
- caused by Flavivirus
- Epidemiology: Distributed throughout Africa, the Middle East, parts of Europe, the USSR, India and Indonesia
-West Nile infection has been appearing in the United States since 1999 and in Arizona from 2003
•Vector: mosquito
- Principal vertebrate host: Bird
- Transmission may be via transplanted organs or blood transfusion
- During pregnancy, breast feeding
WNV Incubation
•2-14 days (average 2-6)
WNV Infection
- Asymptomatic
- West Nile Fever
- Severe West Nile Disease
WNV Asymptomatic
•About 80% of WNV-infected people do not get any symptoms.
WNV West Nile Fever
- 20% infected people develop West Nile Fever
- Typical case is mild characterized by fever, headache, backache, generalized myalgia
- Rash appears in half of the cases, involving the chest, back and upper extremities
- Generalized lymphadenopathy is a common finding
- Pharyngitis and gastrointestinal symptoms (nausea, vomiting, abdominal pain) may occur
- The disease runs its course 3 to 6 days, followed by recovery for several weeks
- Children experience milder illness than adults
WNV Severe
- 1 in 150 infected persons develop severe disease
- WNV invades the nervous system causing aseptic meningitis, meningo-encephalitis, encephalitis, or West Nile poliomyelitis, especially in the elderly, and some cases result in death
- Symptoms of severe disease include headache, fever, stiff neck, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis. Severe disease may last for weeks and cause permanent injury or, in some cases, death.
- Serious illness can occur in people of over age 50 and immunocompromised
WNV Lab Findings
•leukopenia CNS infection: CSF pleocytosis and elevated protein
[] chemokine receptor provides resistance to West Nile Virus infection.
CCR5 chemokine receptor provides resistance to West Nile Virus infection.
[] homozygosity is significantly associated with severe outcome.
Δ32CCR5 homozygosity is significantly associated with severe outcome.
WNV Diagnosis
•Serology, Confirmed by PCR
WNV Treatment
•supportive
WNV Prevention
•Antiviral and vaccine research underway
Zika Virus
•caused by Flavivirus