BIOL 6576 Exam 3 Study Guide Lectures 9 11 Lecture 9 Polio Poliomyelitis caused by the polio virus is characterized by aseptic meningitis and a lytic infection of the anterior horn cells of the spinal cord In the late 19th century polio made a shift from being endemic to an epidemic disease in the US and Europe Why This is possibly due to a large mutation It is more likely due to the development of closed sewer systems Children were no longer naturally immunized by playing in the streets with feces and there was a loss of herd immunity Poliovirus Family picornaviridae genus enterovirus Small linear ssRNA icosahedral capsid naked polyprotein cleaved into many proteins replicate in cytoplasm in vesicles transmitted via fecal oral route and infects the intestines 3 serotypes each one causes different antibodies each one causes paralytic polioreceptor PVR poliovirus receptor is part of the immunoglobulin family It is normally expressed in muscle end plates and motor neurons However in people with acute poliomyelitis muscle fibers express PVR Pathogenesis of polio 1 Polio is ingested and infects tonsils oropharynx and intestines In the intestines it infects the M cells of a tissue called Peyer s patches Very efficient replication occurs 2 Virus spreads to the lymphnodes and produces a minor viremia which infects organs and the bone marrow 90 of people clear the virus at this point 3 The other 10 this replication leads to a major viremia Minor symptoms occur here 37 days These symptoms include fever headache and sore throat 4 8 of people clear the virus at this point in 1 2 days 4 1 this major viremia goes into the CNS Replication in the skeletal muscle allows viruses to move up the peripheral nerves to the spinal cord Symptoms of the major illness include headache vomiting myalgia and muscle weakness which occurs 9 12 days after infection CSF pleocytosis occurs at the early stages of this major illness 1 3 of this 1 yields nonparalytic polio with aseptic meningitis This usually resolves itself in about 10 days 5 2 3 of 1 virus in the CNS causes necrotic lesions of the gray matter of the anterior horn of the spinal cord and the motor nuclei of the pons and medulla as well as inflammatory infiltrates This leads to paralysis The severity of the paralysis depends on the intensity of the lesions a 2 types of paralytic polio i spinal weakness of skeletal muscles innervated by motor nerves ii Bulbar weakness of face also problems with swallowing and respiration These are innervated by cranial nerves iii Both types can happen at the same time in the same person Prognosis Most patients who experience paralysis can recover some mobility 2 3 of patients retain some motor deficits from minor weakness to major paralysis Bulbar paralytic poliomyelitis causes significantly more deaths than spinal This is because it prevents breathing due to paralysis of diaphragm muscles Polio and guillian barre GB has ascending paralysis and occurs symmetrically on both sides of the body Polio is usually only on one side and not ascending GB has sensory abnormalities in 80 of cases Polio doesn t have them GB doesn t exhibit CSF pleocytosis Polio does Vaccines 2 early vaccines Brodie killed homogenized monkey spinal cord Killed with formalin Kolmer live attenuated passed through mokey brain These vaccines yielded little to no protection in monkeys or children Monkeys that received the kolmer vaccine developed paralysis Some children that had this vaccine developed poliomyelitis Live vs killed Live o o Killed o o Adv provides excellent immunity and no booster is needed Disadv difficult to prepare and less safe can revert Adv quick to prepare and very safe Disadv the immunity doesn t last a long time and boosters are needed Current vaccines Salk IPV killed inactivated with formaldehyde Uses the most virulent strains of all 3 Sabin OPV live attenuated passed through monkey brain trivalent oral gives gut immunity IgA no reversion observed and no booster needed o Mutations in 5 noncoding regions and or capsid proteins We currently use the salk vaccine Polio has been eradicated in both Americas Post poliomyelitis 20 30 of patients who recover from paralytic polio get this This is a new onset of muscle weakness atrophy pain and fatigue 2 possible causes Nerve fatigue motor neurons are exhausted because of overworking during acute phase and recovery Direct infection or immunopathology virus is still around in the body and it begins to replicate and infect again o IgG and IgM bands in CSF IgM is for primary infection o polio like RNA in CSF Lecture 10 Arboviruses Arboviruses ARthropod BOrne viruses are viruses transmitted by arthropods like mosquitos and ticks and can cause encephalitis The 4 viral families containing arboviruses are togaviridae flaviviridae bunyaviridae and reoviridae Family Togaviridae genus alphavirus western equine encephalitis eastern equine encephalitis and Venezuelan equine encephalitis Family Flaviviridae genus flavivirus west nile virus St Louis encephalitis virus Japanese encephalitis virus tick borne encephalitis virus murray valley encephalitis virus Family Bunyaviridae genus Bunyavirus LaCrosse virus and other California viruses Family Reoviridae genus Coltivirus Colorado tick fever virus These viruses have 3 different patterns of disease 1 Fever arthritis and rash 2 Hemorrhagic fever 3 Neurologic diseases encephalitis Ecology of Arboviruses The virus is transmitted within an enzootic cycle involving birds and rodents and mosquitos Humans get infected when we encroach on this natural cycle The species of mosquito that brings the virus to us is called the bridging vector Sometimes a mosquito can bring the virus to an animal to which we are closer to usually a horse This horse is called an intermediate invertebrate This transmission is called an epizootic event We are dead end hosts meaning the virus doesn t get passed on from us to another animal or mosquito and it dies This is somewhat because we usually have a low viremia in comparison to the vector which has a high and prolonged viremia Most human infection in asymptomatic or causes a minor illness Only a few are major These viruses replicate both in the vector and the host in an extrinsic cycle The host usually clears it The vector is usually infected for life o The virus is ingested by the vector when it takes an infected blood meal o It replicates in the mesenteron midgut o It leaves the midgut and goes to the salivary glands and