ICL 1.1: Zoonotic Viruses I Flashcards
what is an emerging virus?
it’s a causative agent of a new or previously unrecognized infection
this is NOT just a virus that we haven’t heard about that shows up somewhere, it could also be a virus that is showing up in a geographically new area
they are infections that have recently appeared within a population or those whose incidence or geographic range is rapidly increasing or threatens to increase in the near future
what could cause an emerging virus to come into existence?
- expanded host range
- transmission from wild/domesticated animals to humans (zoonosis)
- cross-species infection may establish new virus in the population
in what facilities are viruses studied?
special high containment laboratories are required to study viruses or test patient samples
this is what makes research so slow because you have to work in special containment labs so that the researchers are safe and the bug doesn’t escape which takes lots of time and money
which viruses are BSL-3?
BLS = biosafety level
- West Nile virus
- Chikungunya virus
which viruses are BSL-4?
Ebola
what are zoonoses?
infections that can be transmitted to humans from animals
what are the two main ways through which zooneses are transmitted?
- arthropods –> often through blood meals like with mosquitos
- vertebrates –> bites, body fluids, inhalation, etc.
zooneses = infections that can be transmitted to humans from animals
what is a host?
any species capable of sustained viral replication
so lots of things can be hosts!
what is a natural host/reservoir?
the host in the absence of human intervention
this is the host that you’d see in nature
often times, a virus has multiple reservoir hosts which makes getting rid of the virus tricky
what is a dead end host?
an accidental host that is not important in virus life cycle
the dead end host usually doesn’t further transmit the virus
humans are usually the dead end host! we aren’t part of the cycle; if we all died the virus would still exist and be able to replicate
however, we do usually get the most severe form of the disease
which viruses are arthropod transmitted viruses?
- Yellow fever virus (Flaviviridae)
- Dengue virus (Flaviviridae)
- West Nile virus (Flaviviridae)
- Powassan virus (Flaviviridae)
- St. Louis encephalitis virus (Flaviviridae)
- Eastern equine encephalitis virus (Togaviridae)
- Chikungunya virus (Togaviridae)
- La Crosse virus (Bunyaviridae)
which viruses are rodent transmitted viruses?
- Hantaviruses (Bunyaviridae)
2. Lassa virus and LCMV (Arenaviridae)
which viruses are bat associated viruses?
- Rabies virus (Rhabdoviridae)
- Ebola virus and Marburg virus (Filoviridae)
- Nipah and Hendra viruses (Paramyxoviridae)
- SARS (Coronaviridae)
which viruses have a severe association with hemorrhagic fever?
- Yellow fever virus (Flaviviridae)
- Dengue virus (Flaviviridae)
- Hanataviruses (Bunyaviridae)*
- Lassa virus and LCMV (Arenaviridae)
- Ebola virus and Marburg virus (Filoviridae)
which viruses have a severe association with encephalitis?
- West Nile virus (Flaviviridae)
- Powassan virus (Flaviviridae)*
- St. Louis encephalitis virus (Flaviviridae)
- Eastern equine encephalitis virus (Togaviridae)
- La Crosse virus (Bunyaviridae)
- Rabies virus (Rhabdoviridae)
which viruses have a severe association with respiratory problems?
- Nipah and Hendra viruses (Paramyxoviridae)
2. SARS (Coronaviridae)
which virus has a severe association with arthralgia?
Chikungunya virus (Togaviridae)
what are the severe disease associations of Dengue virus?
- hemorrhagic fever
2. arthralgia
what are the severe disease associations of Powassan virus?
- encephalitis
2. hemorrhagic fever
what are the severe disease associations of Hantaviruses?
- hemorrhagic fever
2. respiratory problems
what are the severe disease associations of the Nipah and Hendra viruses?
- respiratory problems
2. encephalitis
what is a vector?
an animal that delivers a virus
what are arboviruses?
arboviruses = arthropod-born viruses (blood sucking)
arbovirus is a collective term that groups together all the arthropod-borne viruses - it is NOT a virus family!!
there are hundreds of arboviruses
they all infect vertebrates
what is the sequence of transmission with arboviruses?
they are spread by ticks or mosquitos that have the virus
the tick/mosquito then transfers the virus to a vertebra such as humans, monkeys, pigs etc.
how do you control the spread of arboviruses?
best strategy for control is vector control
it’s hard to make a vaccine against the hundreds of different arboviruses so instead you have to do vector control and get rid of the mosquito or tick that’s transmitting all the viruses!
if you cut down on the vectors, you cut down on the risk of transmission!
which 4 virus families are arboviruses?
- togaviridae
- flaviviridae
- bunyaviridae
- reoviridae
what is the structure of the togaviridae virus family?
enveloped, icasahedral (+) sense ssRNA
what is the structure of the flaviviridae virus family?
enveloped, icasahedral (+) sense ssRNA
what is the structure of the bunyaviridae virus family?
enveloped, helical (-) sense, segmented ssRNA
what is the structure of the reoviridae virus family?
naked, icosahedral, segmented dsRNA
what are the common features of arboviral diseases?
- often subclinical
- initial replication in endothelial cells and macrophages/monocyte lineage
- viremia = virus in the blood
- low % infections lead to clinical cases
- not all clinical cases lead to major disease
- probably underdiagnosed
why are arboviral diseases probably underdiagnosed?
they’re usually subclinical so you won’t really develop symptoms and even if you do, it’ll just be a headache or muscle pain
so most people don’t go the hospital because they don’t have severe symptoms which means most viruses are probably under-diagnosed
this makes it really hard to assess how many people have actually been infected/exposed to the virus
what is viremia?
virus in the blood
you don’t always have high levels of viremia which makes it hard for the mosquito to pick up the virus from the blood and then transmit it to another animal
which cells are involved initially in arbovirus replication?
initial replication is in endothelial cells and macrophage/monocyte lineage
this is because these are the cells right at the bite site and the cells that are recruited to the site so they’re the first to get infected!
how do you diagnose arboviruses?
- ELISA
- antigen detection
- serum neutralization
- RT-PCR (because arboviruses are all RNA viruses)
- virus isolation by cell culture
how do you treat West Nile virus?
supportive care
you just want to make sure they can breath so you keep them on a ventilator since we don’t have any antivirals to treat them with….
how can you tell which geographical regions are at a higher risk for certain viruses?
pathogens are associated with some kind of vector so it’s easy to tell who’s at risk for these diseases based on where the vectors are commonly found
so if something is being transmitted by a tick, the areas more prone to get the disease being carried by this tick are the places that the tick lives!
so just keep this in mind when someone travels which viruses are common in those areas that they went to
how do we prevent arboviruses?
- surveillance = screen animals for infection!
- vector control
- personal protection = repellent, clothing, activity avoidance
- vaccination (rarely)
when would we vaccinate against arboviruses?
it’s very rare that we can vaccinate against arboviruses
usually when we can, they’re travel vaccines!
we don’t need these vaccines here in the US, but when people go other places they do need them
which specific viruses are arboviruses associated with encephalitis in the USA?
FLAVIVIRIDAE
1. Powassan virus
- St. Louis encephalitis
- West Nile virus
BUNYAVIRIDAE
1. California serogroup: La Crosse virus & Jamestown Canyon
TOGAVIRIDAE
1. Eastern equine encephalitis virus (triple E!)
**they all have mosquito vectors except Powassan virus which is a tick vector
what is the occurence, vector, reservoir and disease associated with Powassan virus?
disease = encephalitis
occurence = North America
vector = tick
reservoir = rodents
flaviviridae family = enveloped, icasahedral (+) sense ssRNA
what is the occurence, vector, reservoir and disease associated with St. Louis encephalitis virus?
disease = encephalitis
occurence = North America, Eastern US
vector = mosquito
reservoir = birds
flaviviridae family = enveloped, icasahedral (+) sense ssRNA
what is the occurence, vector, reservoir and disease associated with West Nile virus?
disease = encephalitis
occurrence = North America, Europe, Africa
vector = mosquito
reservoir = birds
flaviviridae family = enveloped, icasahedral (+) sense ssRNA
what is the occurence, vector, reservoir and disease associated with La Cross and Jamestown Canyon viruses?
disease = encephalitis
occurence = North America
vector = mosquiot
reservoir = small mammales like chipmunks, squirrels, etc.
bunyaviridae family = enveloped, helical (-) sense, segmented ssRNA
what is the occurence, vector, reservoir and disease associated with eastern equine encephalitis virus?
disease = encephalitis
occurence = eastern US, Canada
vector = mosquito
reservoir = birds
togaviridae family = enveloped, icasahedral (+) sense ssRNA
what are serogroups?
when you have antibodies against a certain virus, sometimes the virus is close enough in structure that your antibodies against the first virus will partially recognize it if the surface glycoproteins of both viruses are similar enough
this would mean that the two viruses are in the same serogroup because on the outside they look very similar!
which arbovirus has the most cases in the US?
West Nile virus
what is the most common mosquito borne virus in North America?
WNV
reservoir = birds
vector = mosquitos
disease = encephalitis
flaviviridae family
how can WNV be transmitted accidentally to someone?
blood transfusions!
so we have to make sure we’re really screening blood to make sure there’s nothing in blood transfusions we’re giving to people
what are sentinels? what are the sentinels for WNV?
sentinel species are organisms, often animals, used to detect risks to humans by providing advance warning of a danger
WNV sentinels = horse, quail, turkey
which population is at risk for WNV?
people over 50 years old
what is the life cycle of the WNV?
- in the summer, the warm, wet weather produces large mosquito populations that then infect birds (some of which die)
mosquitos also infect dead-end hosts like horses and humans
- then in the fall, mosquito populations decline and birds migrate
- in the spring, the virus is amplified among birds and mosquitoes
this cycle just goes on and on
which major disease is associated with WNV?
encephalitis!
WNV can effect the brain and cause direct cell killing of the neurons which causes serious mental status changes like bouts of confusion and disorientation
what are the symptoms associated with WNV encephalitis?
- Subclinical
- Fever and headache
- Rash
- Meningitis
- Acute flaccid paralysis/poliomyelitis (rare)
eventually, symptoms can lead to seizures and comas
20% have mild symptoms
0.5% have severe symptoms
what are some presenting symptoms of WNV?
A 54-year-old woman presented to our emergency department with a 4-day history of fevers, body aches, nausea and headache and a recently resolved rash. The patient’s mental status had progressively deteriorated with bouts of confusion and disorientation
- > 50 years old
- recently resolved rash (not always present though with WNV and it’s not diagnostic either)
- mental status deterioration = infection in the brain
how do you treat WNV?
supportive care
there’s literally nothing we can do except hope that they will eventually restore their brain function as the virus clears
the problem is that sometimes by the time the virus has cleared, it’s already done severe brain damage to the patient
which population is at a risk for Triple E?
bilateral distribution:
under 15 years old & over 50 years old
what are the other viruses linked to Triple E?
- Triple E = Eastern Equine Encephalitis Virus
- there’s also Western equine encephalitis virus which has less cases and a lower CFR
- Venezuelan equine encephalitis virus where horses are the reservoir and it’s more mild
is Triple E or WNV worse?
Triple E
this is because it can effect healthy, young individuals!
WNV is mostly in people over 50
what are the characteristics of Triple E?
reservoir = birds
vector = mosquitos
disease = encephalitis
CFR = 35%
togaviridae family = Eastern Equine Encephalitis Virus
what are the characteristics of the La Crosse Virus/California serogroup?
reservoir = small mammals ( chipmunks, squirrels, etc.)
vector = mosquito
disease = encephalitis
low CFR = <1%
bunyaviridae family = enveloped, helical (-) sense, segmented ssRNA
which population is at risk for the La Crosse serogroup?
children
what are the characteristics of the Powassan virus?
reservoir = small mammals
vector = ticks (Ixodes)
disease = encephalitis
flaviviridae family = enveloped, icasahedral (+) sense ssRNA
why is Powassan virus underreported?
because it has the same tick/mammal host as lyme disease and there’s alot of overlapping symptoms
the Ixodes scapularis tick could be coinfected with lots of stuff and we don’t know how this effects the disease or its transmission
which specific viruses are arboviruses associated with fever/hemorrhagic fever in the USA?
FLAVIVIRIDAE
1. Dengue virus
- Yellow fever virus
- Zika virus
TOGAVIRIDAE
1. Chikungunya virus
**all have mosquito vectors and primate reservoirs except Chikungunya which has small mammals, rodents, primates and birds as reservoirs
what is the occurence, vector, reservoir and disease associated with Dengue virus?
disease = fever, HF, arthralgia
occurence = worldwide in tropical regions
vector = mosquito
reservoir = primates, humans
flaviviridae family = enveloped, icasahedral (+) sense ssRNA
what is the occurence, vector, reservoir and disease associated with yellow fever virus?
disease = HF
occurence = south and central america
vector = Aedes mosquito
reservoir = primates, humans
flaviviridae family = enveloped, icasahedral (+) sense ssRNA
what is the occurence, vector, reservoir and disease associated with zika virus?
disease = fever, rash, microcephaly
vector = mosquito
reservoir = primates, humans
flaviviridae family = enveloped, icasahedral (+) sense ssRNA
what is the occurence, vector, reservoir and disease associated with Chikungunya virus?
disease = fever, arthralgia
occurence = worldwide in tropical regions
vector = mosquito
reservoir = small mammals and rodents, primates, birds
togaviridae family = enveloped, icasahedral (+) sense ssRNA
what is the Sylvatic/Jungle Cycle?
arthropod —> vertebrate –> arthropod –> vertebrate –> etc.
or arthropod –> human
but the human isn’t part of the cycle because there isn’t enough virus in the blood for the mosquito to pick up and transmit to another host
ex. WNV: if there isn’t enough virus in the blood it won’t be picked up by mosquitos and transmitted
what is the Urban cycle?
arthropod –> human –> arthropod –> human –> etc.
for some cycles, humans can be part of the cycle because there’s enough virus in the blood for the mosquito to pick up and transmit to another human
this is the urban cycle!
ex. Dengue virus
what are the characteristics of the Dengue virus?
it’s an emerging disease
vector = mosquito (Aedes egyptei)
host = non-human primates
is the Degnue virus a jungle or urban cycle?
both!
but for it to be an urban virus, it has to be under perfect conditions like 1000 people living in close quarters together with no screens like in underdeveloped areas
what are the symptoms of the Dengue fever?
- fever
- headache
- retro-orbital pain
- myalgia/arthralgia
- bone-ache (breakbone fever) because it infectd the BM = dengue 2
- rash
- flu-like illness
- altered taste
- RARELY: encephalitis
what are the symptoms of the Dengue hemorrhagic fever/shock syndrome?
under certain conditions, Dengue can cause hemorrhagic fever/shock which includes symptoms such as:
- thrombocytopenia since dengue infects the BM
- hemorrhages
- plasma leakage
- hypotension
- fluid accumulation in lungs
- circulatory failure
- renal failure!
- shock
what does ADE stand for?
antibody-dependent enhancement
what is ADE and which virus is it associated with??
Dengue virus
viruses can be shutdown when antibodies bind to the virus and neutralize the virus
with Dengue, there are 4 circulating serotypes
so if you get infected with Dengue 1, you’ll generate antibodies against dengue 1 for your whole life
so if you are later exposed to Dengue 4, you aren’t protected because your neutralizing antibodies aren’t against dengue 4
the problem is that dengue 1 and 4 are similar enough that the original antibodies will still bind to dengue 4 without neutralizing and this actually makes it easier for the viruses to be taken up by certain cells which is super bad for us because it’s inhancing the infection!
the virus is getting into cells it wouldn’t normally infect and it’s doing better which can lead to a more severe secondary infection because non-neutralizing antibodies enhance the uptake of the virus into cells and accelerates the disease = ADE
this isn’t specific to dengue but it’s a big thing with dengue
this is also why we can’t really vaccinate against seperate dengue strains because people will get hemorrhagic fever when exposed to a different serotype of dengue!
what do you have to avoid with ADE dengue patients?
aspirin and other anticoagulants
ADE dengue patients are probably in hemorrhagic shock and are already bleeding out so you shouldn’t be giving aspirin
how do you treat Dengue fever?
there’s no treatment, just supportive treatment
Dengvaxia is the Dengue vaccine
it’s a live recombinant tetravalent vaccine
how did yellow fever get its name?
the virus replicates specifically in the liver and destroys liver tissue so you get jaundice!!
is yellow fever a jungle or urban cycle?
both!
what are the symptoms of yellow fever?
- hemorrhagic fever with jaundice
- degeneration of liver, kidney and heart
- thrombocytopenia
- bleeding gums/stool
- petechia
- backpain
- black blood vomit
CFR = 50%!!!!
is there a vaccine against yellow fever?
yes!!
it’s a live attenuated travel vaccine
but if you already are having symptoms of HF and jaundice then it’s too late for you and you can’t get the vaccine; the vaccine is NOT a treatment!!
we have nothing to treat yellow fever once you get it…
is the zika virus a jungle or urban cycle?
both!
what are the symptoms of the zika virus?
- mild fever
- rash
what are some of the complications of zika virus?
- birth defects (microcephaly)
- Guillain-Barre syndrome = a rare disorder in which your body’s immune system attacks your nerves
what are the symptoms of the Chikungunya virus?
- fever
- headache
- rash
- joint pain = arthralgia
