Arboviruses/Ebola Flashcards
What are Arborviruses?
From Arthropods - Arthropod Borne Virus
mostly from the genus aedes mosquitos
Virus replicates usually in mosquito salivary gland, then is available to be transmitted to new host through biting (what makes you itchy is the immune response to the saliva)
Examples of Arborviruses
Yellow Fever virus
West Nile virus
Dengue Virus
Zika
hep C falls in same family of Flaviviruses
Structure of Arborviruses
Flavivirus family
+ssRNA viruses
What do Arborviruses cause?
Encephalitis
Febrile diseases
Occasionally hemorrhagic fevers
Although most infections are asymptomatic
Prevention of Arborviruses
Prevention depends on surveillance
Physicians, veterinarians
Curbing mosquito habitats is important Remove standing water
Sylvatic (Jungle) Cycle v. Urban Cycle
Jungle cycle or Sylvatic cycle: typically the reservoir for the virus is animal (West Nile, Zika) and then it gets transmitted from the animal through the insects, cycling from animal to insect, insect to the animal. So the humans are not in that cycle. and that’s typically how these viruses exist in nature, but they can exit that cycle and in humans.
Urban Cycle: if the virus is replicating not in an animal/ doesn’t require an animal reservoir, it can go from human to insects to human, and back again. This cycle is because humans have reached the critical concentration where the insects will be finding humans frequently enough to infect. (Dengue, Yellow Fever, Zika)
What is the major vertebrate reservoir for Arborviruses?
BIRDS! Patterns correspond to the flyways for the birds’ migratory paths in US
West Nile Virus
Transmission: Culex mosquitoes
Incubation period: 2-14 days
Symptoms: Serious Symptoms only a few people (1 in 150) such as coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis;o last a few weeks but neurological symptoms may be permanent
Milder Symptoms in Some People (up to 20%) similar to flu like symptoms and skin rash; can last a few days or several weeks.
Dengue Fever
Transmission: aedes mosquitoes; humans are only vertebrate reservoirs aside from monkeys
4 serotypes - they used to be localized, but have spread
Symptoms: Fever, headache, myalgia, bone ache (breakbone fever).
Restricted mainly to tropics
Immunopathology of Dengue
reinfection with a second serotype results in antibodies from the first infection making the second infection worse - ADE: Antibody Dependent Enhancement of infectivity.
Vaccine for Dengue
If people have already been infected with one of the Dengue strains, it turns out the vaccine is useful and protective.
If people have never been infected with any of the dengue strains, it made your disease worse if you’ve got infected rather than better.
Zika Virus
Transmission: Two types of mosquitoes that can carry it are Aedes aegypti and Aedes albopictus.
Symptoms: Fever, rash, joint pain, red eyes, and muscle aches. Guillain-Barré syndrome.
Can infect skin cells, dendritic cells, placental cells, brain glial cells, neurons, neural progenitor cells and probably many more. It uses many cell receptors.
Shows up in a person’s bloodstream about one week after infection.
“Firsts” of Zika
First Arborvirus to be sexually transmitted
First insect-borne disease with proven link to serious birth defects
Zika and Pregnancy
Dependent on when the pregnant woman is exposed.
Earlier in pregnancy = more detrimental effects
Congenital Zika syndrome is the more general term for a pattern of birth defects that could result from the virus, including severe microcephaly, decreased brain tissue, damage to the eye, clubfoot, and muscle development problems that lead to restricted movement soon after a baby is born
Why did Zika disappear?
If it kills people or otherwise “selects” against them, you could have selection in the gene pool of those that are more resistant inherently.
Also have what’s probably going on now is formation/ induction of memory responses in people or in memory immunity. T cells. B cells. Antibodies. Cytotoxic T cells.
Both of these things can cause a virus or any infection agent to have a peak and then a down.
Ebola Virus
Filovirus (Filoviridae genus) - single-stranded, RNA, enveloped virus (easy to decontaminate)
5 strains; rapid accumulation genetic variation
First discovered in 1976 near the Ebola River in the Democratic Republic of Congo
Sporadic outbreaks in Africa
Bats are the most likely reservoir (zoonosis)
Ebola Virus Infection
Transmission: spread through
DIRECT CONTACT with blood or body fluids of a person sick with Ebola; Objects (needles and syringes) contaminated with virus Infected animals
Airborne transmission has never been demonstrated
Incubation period: 2-21 days – average is 8-10 days
The incubation period may be related to the infection route (e.g., 6 days for injection versus 10 days for contact).
Symptoms Fever
Severe headache Muscle pain
Weakness Fatigue Diarrhea Vomiting Abdominal pain
Hemorrhage (Bleeding or Bruising)
Death (~20% of the time)
How does Ebola infect us?
1) Virus enters the patient through mucous membranes or parenterally, e.g. breaks in the skin.
2) virus infects many cell types, including monocytes, macrophages, dendritic cells, endothelial cells, fibroblasts, hepatocytes, adrenal cortical cells and epithelial cells.
3) migrates from the initial infection site to regional lymph nodes and subsequently to the liver, spleen and adrenal gland.
4) Trigger a release of pro-inflammatory cytokines with subsequent vascular leak and impairment of water retention ultimately resulting in multi-organ failure and shock.
Pre-exposure Ebola Vaccine
Recombinant, replication-competent vaccine.
It consists of a vesicular stomatitis virus (VSV), which has been genetically engineered to express a glycoprotein from the Zaire Ebola virus so as to provoke a neutralizing immune response to the Ebola virus.
It is 70-100% effective.
Post-exposure Ebola Vaccine
Developed artificial antibodies that bind the regions that are not variable in the 5 Ebola serotype (constant among the different strains)
They give you two antibodies. It’s protected ferrets and monkeys. Now they’ve tried it in humans but it hasn’t been licensed and mass produces for humans.
