6 Viral CNS Infections Flashcards
Destruction of motor neurons in spinal cord, resulting in asymmetric flaccid paralysis
Poliomyelitis (previously “infantile paralysis”)
Describe poliovirus
Picorna virus with three antigenic types (type 2 possibly eradicated)
Much more of an enterovirus transmitted by droplets but spread by fecal contamination
What are the classifications of poliovirus infection?
- Inapparent infection - most common (90-95%), assymptomatic to minor malaise
- Abortive illness
- Nonparalytic poliomyelitis
- Paralytic poliomyelitis - the least common but most feared
- Post polio syndrome
What percentage of poliovirus infections result in paralytic poliomyelitis?
Less than 1% of infected individuals
Flaccid paralysis from lower motor neuron damage
Most fear manifestation, but rarest outcome
What’s the deal with post polio syndrome?
Muscle weakness, pain and fatigue in paralyzed polio patients - looks like the disease is coming back but it is instead a result of the consequences of their previous disease and normal aging
30 or more years after acute case of paralyzing polio
Remaining motor units of CNS now react to over use and fail
Which was developed first, Inactivated Polio Vaccine (IPV) or the live oral polio vaccine (OPV)?
IPV
But we stopped using the OPV in the US b/c it was causing ~10 cases of vaccine associated paralytic polio per year. We went back to IPV but OPV still used in other countries
Does IPV prevent poliovirus infection?
NO - it prevents the paralytic version due to invasion of nervous tissue
It prevents DISEASE, not infection
What are arboviruses?
Arthropod-borne viruses, with mosquitos and ticks the usual vectors
Wide range of animal reservoirs (primarily birds and small mammals) but disease may not be apparent in these hosts)
Humans are typically dead end hosts
What are the three groups of arboviruses discusses in lecture?
Togaviridae group
• ss(+) RNA, small (40nm), enveloped
• Eastern Equine Encephalitis (EEE), Western Equine Encephalitis (WEE), and Venezuelan Equine Encephalitis (VEE)
Flaviviridae group**
• St. Louis Encephalitis
• West Nile virus
•Dengue virus
Bunyaviridae group
• California encephalitis virus
Clinical manifestations of arboviruses
Infection is typically subclinical
Abrupt onset of fever, HA, vertigo, photophobia, nausea, vomiting
Confusion and personality changes, focal or general seizures
Recovery may be complete or patient may have long term deficits
A newly emerged virus in North America first recognized in NYC area during summer 1999
Has expanded its range and caused a large scale outbreak of encephalitis in 2002
West Nile Virus
Is a flavivirus, most closely related to yellow fever and St. Louis encephalitis
Antigenic cross reaction between WNV and YF/SLE
How do we diagnose West Nile Virus?
Time of year, location, and patient age are important
Specific tests for IgM antibody with CSF or serum (antibody capture ELISA or MAC-ELISA)
Caution: can get cross reactions with yellow fever, dengue, Japanese encephalitis, St Louis encephalitis
Vaccination against YF and/or Japanese encephalitis may induce long-lasting positive IgM titers
How do we treat West Nile Virus
Only supportive measures are available
What do we do to prevent arboviruses?
Interrupt chain of transmission
Eradication of vector (mosquito spraying, get rid of standing water)
Avoidance of exposure (window screens, repellent)
Immunization of nonhuman amplifying hosts (horses)
What is the only arbovirus known to be teratogenic?
Zika —> microcephalic, Guillain-Barré syndrome
How is Zika diagnosed?
Travel history
Nucleic acid test (PCR) and MAC ELISA
Some antigenic cross-reaction with flaviviruses (ie dengue, YF)
What’s the name of the protocol that has “saved” a patient from rabies?
Milwaukee protocol
Only known cases of recovery from rabies infection, as it is considered invariably fatal once symptoms are overt
What is the incubation period for Rabies?
Highly variable
2-16 weeks to years is documented
5-6 day fatal course once overt symptoms appear
What is the clinical presentation of rabies?
Prodrome - mild fever, pharyngitis, HA
Abnormal sensations (pain, burning), referred to site of inoculation
Increased sensory sensitivity
Excitatory phase (furious in dogs) - anxiety, apprehension hydrophobia
Paralytic phase - coma, hypotension, death
How do we diagnose rabies
History of bite by rabid animal plus symptoms of patient
Especially Hx of exposure to/bite from skunk, fox, raccoon, bat sufficient to initiate post exposure prophylaxis
What to do if you suspect rabies
Initiate post exposure prophylaxis
Kill and examine animal immediately (FA test)
Quarantine healthy dogs/cats for 10 days
Kill and examine strays immediately
Halt if animal negative for viruses
What do you do if a rabbit or rat bites you
Cry
But don’t worry about rabies. Rodents and rabbits rarely infected. No action needed.
Pathognomonic microscopy finding for rabies
Negri body
What does the rabies virus look like?
Rhabdovirus family
ssRNA
Enveloped
Unique bullet shape
How is rabies transmitted?
Usually by animal bite (injection of virus-laden saliva)
Aerosol transmission has been documented (bat caves)
Touching bats (ew gross)
Prevention of rabies is by…
Avoidance of exposure
Prophylactic vaccination of companion and herd animals
Immunization after exposure (post-exposure prophylaxis)
Vaccination of wild animals with immunogenicity bait is promising
What is used for post-exposure prophylaxis?
Rabies vaccine (HDCV) plus hyperimmune serum after contact with reservoir animal
While there are few US fatal cases, there are a substantial number of post-exposure immunizations each year
