Zoonotic or Vector Borne Infections of the CNS Flashcards
disease of vertebrate animals that can be transmitted to man; either directly or indirectly through an insect vector
zoonoses
if an insect vector is involved the disease is also known as an
arboviral disease
are all arboviral diseases zoonosis
no
two examples of viral zoonoses
rabies, hantaviruses
Rabies and Lymphocytic Choriormeningitis are viruses that are
directly transmitted to humans from other mammals
What form of vector transmission is most common.
Animal to Human, not Human to Human
Transmitted by mosquitoes (4)
West Nile, Dengue, Yellow Fever, St. Louis Encephalitis
cause of febrile illness and encephalitis in man and horses
West Nile Virus
West Nile was first discovered in the US
in New York in 1999
most common arboviral infection that we worry about in the US now
West Nile Virus
% of cases that are neuro-invasive
50%
Why might west nile cases vary year to year?
Amount of rain, mosquito populations, perhaps other factors
West Nile is transmitted by mosquitoes from this organism to humans and horses and other mammals (cattle, dogs, and cats).
Birds
Are humans and horses a normal part of the west nile life cycle or the SLE life cycle?
No, they normally go back and forth between birds and mosquitoes.
Are humans a good host for the west nile virus or SLE virus?
No, there is no viremia-so it is hard for mosquitoes to feed on us and pick up some of the virus (dead end host)
Only cases of human to human transmission of WNV found are from these behaviors
transfusions, organ transplant, breast feeding
West Nile Fever
mild illness 1/5 infected with WNV
symptoms of west nile fever
malaise, anorexia, nausea, vomiting, headache (eye pain), myalgia, rash, lymphadenopathy
symptoms of neurological disease from WNV
encephalitis (mostly) and meningitis, fever, headache, weakness, GI disturbance, change in mental status, ataxia, seizures, disorientation, visual distrubances (progress to coma, paralysis)
WNV progression to neurological disease usually occurs in this population
the elderly
Dx: WNV
suspected in older adults who develop unexplained encephalitis or meningitis in summer or early fall, do serology of CSF fluid, usually against a panel of summertime arboviruses
Tx: WNV
treatment is supportive
Vaccine available for WNV?
vaccine for horses, but not humans
transmitted to humans by Culex mosquitoes that acquire virus from infected birds, horses can also serve as reservoirs
SLE
Found in temperate areas of the US in the late summer, early fall and year round in the southern US
SLE
SLE vaccine available?
no
Tx: SLE
supportive care (90% of severe disease requires hospitalization)
Leading cause of viral encephalitis in Asia most are seropositive due to high exposure rate
Japanese Encephalitis Virus
transmitted to humans and other animals by mosquitoes that obtain the virus by infected rodents and birds-horses are major reservoirs
Togaviruses (alphaviruses)
significant causes of vector borne viral encephalitis in the US
Eastern Equine Encephalitis, Western Equine Encephalitis
primarily occurs in South and Central America, but sporadic cases occur in the US
Venezuelan Equine Encephalitis
usually preceed EEE human infection
equine epidemics
30% fatality rate of those that develop clinical encephalitis, nay suffer permanent brain damage w/ some requiring permanent institutional care
EEE
important cause of encephalitis in horses and humans in N. America mainly in Western parts of US and Canada
WEE
WEE which populations are affected most severely
children affected more severely than adults and may be left with permanent neurological sequelae (mortality 3%)
has caused large epidemics in both horses and humans and is predominatly found in South and Central America
Venezuelan Equine Encephalitis
most infections are symptomatic-initially present with flu-like symptoms, children are more likely to have CNS involvement
Venezuelan Equine Encephalitis
spread by inhalation of dried feces and urine from infected rodents
Hantaviruses
Bunyaviruses
Hantaviruses, LaCrosse (California) Encephalitis Virus
arbovirus that is transmitted by the bite of mosquitoes and is a bunyavirus
LaCrosse Encephalitis Virus
infections primarily occur in Midwestern and Mid-Atlantic states, mostly in children
LaCrosse Encephalitis Virus
chipmunk and tree squirrel resevoirs
LaCrosse Encephalitis Virus
prior to vaccination in the US hundreds of deaths occurred each year
rabies
worldwide distribution excluding australia, great britain, and hawaii
rabies
Why has there been such a decrease in the number of rabies cases in the US?
animal control and vaccination
Often rabid in the US
skunks, fox, raccoon, mongoose (puerto rico)
transmission of rabies
saliva-bites, contamination of mucous membranes, aerosol transmission, corneal transplants, exposure to infected dogs or bats
prevention
post-exposure prophylaxis
Is Rabies fatal?
Yes, once the patient has symptoms the patient will die it is just a matter of how quickly, usually within 2 weeks. (99.9% fatal)
virus enters peripheral nerves and is transported to the CNS (sensory and motor nerves)
rabies virus
incubation period of a few days to months starting with nonspecific flu-like signs and the virus rapidly disseminates within the CNS and spreads to peripheral nerves
rabies
During cerebral infection, behavioral changes are seen-anxiety, confusion, agitation, delirium, abnormal behavior, hallucinations, insomnia, hydrophobia (50%), ending in coma and death
Rabies
Prevention
vaccination of animals and high risk individuals (animal handlers, veterinarians)
Tx:
1 dose of immune globulin and 5 doses of vaccine over a 28-day period.
Dx:
usually post-mortum, presence of Negri bodies (distinct intracytoplasmic inclusions) in infected neurons, also serology and viral identification
example of an arenavirus
lymphocytic choriomeningitis virus (LCMV)
rodent-borne virus that can cause aseptic meningitis,encephalitis, or meningoencephalitis but most infections are asymptomatic or produce mild febrile illnesses
Lymphocytic choriomeningitis virus (LCMV)
pregnancy-related infection has been associated with abortion and neurological deficits
Lymphocytic choriomeningitis virus (LCMV)
transmission of LCMV
inhalation of rodent urine/feces/saliva, or ingesting food contaminated with the virus
spread by the house mouse Mus musculus
LCMV
biphasic: first phase includes fever, malaise, anorexia, muscle aches, headache, nausea, and vomiting. remission for a few days and then followed by a second phase including symptoms of meningitis or encephalitis
LCMV
most patients recover completely and some have temporary or permanent neurological damage
LCMV
cause slowly developing neurodegenerative diseases (spongiform encephalopathies)
prions
cannabalistic tribes in New Guinea acquire this prion disease from ingesting brain and other neuronal tissue or handled it
Kuru ( a human spongiform encephalopathy)
human spongiform encephalopathies
kuru, creutzfeldt-jakob disease, gestermann-straussler-scheinker disease, fatal familial insomnia
animal spongiform encephalopathis
scrapie, transmissible mink encephalopathy, bovine spongiform encephalopathy (mad cow), chronic wasting disease (mule deer, elk)
infectious form of prion protein that has a globular conformation with beta-pleated sheets
PrPSC
normal cellular prio-related protein that has an extended conformation containing numerous alpha-helicies
PrPC
what happens to PrPc when exposed to PrPSc
Its released from the cell surface and converted to PrPSc-aggregates form and are internalized by neurons-neurons become vacuolated and amyloid plaques are deposited, also causes astrocyte and glial cell proliferation
some spongiform encephalopathies are not infectious, but
inherited or spontaneously formed (thought to be due to mutations in the PrPc
it is believed that those with vCJG became infected through their consumption of
cattle products contaminated with the agent of BSE
incubation period of prion diseases
long-years to decades, death ensues rapidly (months) after symptoms appear
symptoms include loss of muscle control, shivering, jerks, tremors, behavioral changes and dementia and is associated with an infectious protein
prion diseases
Dx: prion diseases
postmortem histological examination of brain tissue-serological tests (difficult to distinguish PrPc from PrPsc)
Tx: prion diseases
no current treatment for transmissible spongiform encephalopathies
