Viral infections of the CNS 1 Acute infections

1. Viral infections of the CNS 1Acute infections Ikuo Tsunoda, MD, PhD MPID 3 (Micro #289 Pathogenesis of Infectious Diseases II) March 15, 2016 itsunoda@hotmail.com

4. neural cells • Neurotropism: the ability to infect neural cells (neuronotropism means infections specifically of neurons) • Neuroinvasiveness: the ability to gain access to the nervous system • Neurovirulence: the ability to cause disease

5. Four CNS cell types • Neuron • Cell body, dendrites, axons • Oligodendrocyte • Myelin forming cell • In the periphery, Schwann cells • Astrocyte • Gliosis (scar), blood-brain barrier (astro = star) • Microglia • Monocyte / macrophage lineage cell Glial cells = oligodendrocyte + astrocyte + microglia Color Atlas of Neuroscience http://ebooklibrary.thieme.com/SID0000000000000/ebooklibrary/flexibook/pubid-169111625/show_pdf.html?/pdf/pubid-169111625_1039.pdf

6. CNS cell types and viruses • Neuron • Poliovirus (motor neuron), Rabies (limbic system), West Nile, Herpes, Theiler’s virus • Oligodendrocyte • JC virus, Theiler’s virus • Astrocyte • Canine distemper virus • Microglia • HIV, Theiler’s virus

7. Myelination and demyelination Myelin Oligodendrocyte Axon Neuron Demyelination Cell death Tsunoda, Virology, 228: 388-393, 1997

8. Principles and Practice of Neuropathology - 2nd Ed. (2003) http://online.statref.com/Document/Document.aspx?FxId=120&SessionId=122CF6EUTITBOLWU “Although viruses come in a wide variety of sizes and shapes and chemical composition, it is not essential for the pathologist to commit to memory all the nuances of viral taxonomy. “

9. Neurotropism: the ability to infect neural cells (neuronotropism means infections specifically of neurons) • Neuroinvasiveness: the ability to gain access to the nervous system • Neurovirulence: the ability to cause disease

10. Portals of entry for viruses causing CNS disease • Barriers • Skin • Mucous membranes – respiratory, gastrointestinal, genitourinary • IgA, mucous film, cilia, macrophages, acidity, enzyme, thermal inactivation

11. Pathways of neuroinvasion • Hematogenous route • Most viral infections are acquired from blood • Neural route • Virus spread to the CNS along peripheral nerves • Olfactory route • Experimental intranasal virus inoculation results in olfactory bulb infection

12. Hematogenouse route • Viral particles in the blood • 90% clearance in less than 1 hour by the reticuloendothlial system (macrophages) • Viruses 1) grow at some extraneural site, 2) establish viremia, and 3) cross to brain • 1) Extraneural growth • Initial replication of virus may give prodromal symptoms: poliovirus→gastrointestinal; lymphocytic choriomeningitis virus → respiratory; arbovirus → myalgia (muscle infection) , • 2) Maintenance of viremia • Absorb to red blood cells, infect white blood cells • 3) Invasion of the CNS • Blood-brain barrier is impervious to viruses • Infect the vascular endothelial cells of the CNS • Carried in infected leukocytes, Trojan horse

13. Blood-brain barrier (BBB) • Endothelial cells of the BBB lack fenestration, have a very low pinocytotic activity and are connected by tight junctions • Specific transport systems mediate the transport of nutrients into the CNS or of toxic metabolites out of the CNS • Endothelial cell barrier, endothelial basal membrane, glia limitans (astorycte endfoot)

14. α4β1 integrins =VLA-4

15. How viruses travel from blood to tissues • In several well-defined parts of the brain, the capillary epithelium is fenestrated (with “windows” between cells’ loosely joined together), and basement membrane is sparse; the choroid plexus (produces the cerebrospinal fluid) • Infect directly, or be transported across the endothelium • Cross the endothelium within infected leukocytes (Trojan horse: HIV, measles) How viruses gain access to the CNS

16. Steps in the hematogenous spread of virus into the CNS • Invasion of the CNS from blood requires sequence of events • This explains why CNS infections are rare, even though infections that have the potential to cause CNS disease are common Johnson p52

17. Neural pathway for CNS infection • Virus is taken up at sensory or motor endings and moved within axons • Axonal transport of virus • Herpes virus latency and exacerbations

18. Which direction, anterograde or retrograde? • Spread from the primary neuron to the second-order neuron in the direction of the nerve impulse is said to be anterograde spread • Anterograde spread • Virus invades at dendrites or cell bodies and spread to axon terminals

19. Tracing neuronal connections in the nervous system with viruses • Some alphaherpes viruses and rhabdoviruses have promise as self-amplifying tracers of synaptically connected neurons

20. Olfactory route • Olfactory neurons are the only neural cells whose processes synapse within the CNS and whose distal axons are in direct contact with the environment • Experimentally, many viruses can invade the CNS directory from the olfactory mucosa

21. Pathways of neuroinvasion • Hematogenous route • Poliovirus, mumps, measles, filovirus, HIV, arbovirus • Neural route • Rabies, herpes simplex, varicella-zoster • Olfactory route • Experimental herpes simplex, aerosol infections (rabies in bat-infested caves)

22. Neurotropism: the ability to infect neural cells (neuronotropism means infections specifically of neurons) • Neuroinvasiveness: the ability to gain access to the nervous system • Neurovirulence: the ability to cause disease

23. Neurovirulence • Ability to cause CNS disease • Experimentally, defined by effects following intracerebral inoculation • In humans, difficult to assess • Neuroinvasiveness and neurotropism are difficult to sort out • Poliovirus neurovirulence, using transgenic mice containing the human poliovirus receptor • Mumps is highly neuroinvasive, but its neurotropism appears limited to ependymal cells, which may account for low neurovirulence • Human T-cell lymphotoropic virus I (HTLV-I) infects inflammatory cells, not infect neural cells, but it is neurovirulent (HAM, HTLV-I-associated myelopathy)

24. Neuroinvasiveness, tropism and virulence

25. Neurotropism: the ability to infect neural cells (neuronotropism means infections specifically of neurons) • Neuroinvasiveness: the ability to gain access to the nervous system • Neurovirulence: the ability to cause disease

26. Which of the following statements is true? • A neurotropic virus can enter the central nervous system after infection of a peripheral site. • A neuroinvasive virus can infect neural cells. • Herpes simplex virus has high neuroinvasiveness of the central nervous system, and high neurovirulence. • Rabies virus has low neuroinvasiveness but high neurovirulence. • Mumps virus has high neuroinvasiveness but low neurovirulence. Answer (E)

27. Classification by the areas of the CNS • Encephalitis: Encephalon + itis = inflammation of brain • Encephalopathy: Any disorder of the brain • Myelitis:Myel+ itis = inflammation of spinal cord • Meningitis:Meninges + itis = inflammation of the meninges • Lack of cerebral & spinal cord parenchymal involvement • “Aseptic” implies non-bacterial etiology of syndrome • Arboviruses often cause combinations called; • Meningoencephalitis (meninges & brain) • Encephalomyelitis (brain & spinal cord) • Poliomyelitis;inflammation in the gray matter of the spinal cord. [polio- [G. polios] gray matter + G. myelos, marrow, + -itis, inflammation]

28. Viral infections of the CNS • Meningitis • Inflammation restricted to the meninges • Echoviruses, Coxsackeiviruses, other enteroviruses, HSV-2, Mumps, HIV, Lymphocytic choriomeningitis virus (LCMV) • Polioencephalitis / poliomyelits • Disease restricted to the gray matter • Poliovirus, Coxackieviruses, Echoviruses, Enteroviruses, Rabies, Arboviruses (West Nile, Japanese encephalitis) • Leukoencephalitis / leukoencephalopathy • Disease restricted to the white matter • Papovavirus (JC virus: PML), HIV • Panencephalitis / panmyelitis • Disease of both gray and white matter • HSV-1, HSV-2, CMV, VZV, HIV, Measles (SSPE), Arboviruses

29. Which of the following statements is true? • Four major cell types in the central nervous system (CNS) are neurons, Schwann cells, astrocytes, and microglia. • Astrocytes are monocyte/macrophage lineage cells. • The blood-brain barrier is composed of the endothelial cell barrier, endothelial basal membrane, and microglia foot processes. • Olfactory neurons are the only neural cells whose processes synapse within the CNS and whose distal axons are in direct contact with the environment • Leukoencephalitis / leukoencephalopathy is a disease restricted to the gray matter.   Answer (D)

30. Viral Meningitis (Enteroviruses, HIV, HSV type 2, Arboviruses) Headache Stiff neck Photophobia Little alteration in consciousness No focal signs Viral Encephalitis (HSV, Arboviruses, Rabies, Nipah virus) Altered consciousness Focal neurological signs Seizures Meningeal signs Viral Meningitis vs. Encephalitis Dr. John E. Greenlee, MD, University of Utah https://www.youtube.com/watch?v=bj2CNkjvY4o

31. Aseptic meningitis • “Aseptic meningitis” meningitis is not due to bacterial cause • Non-polio enteroviruses are responsible for > 80% of cases • Herpes simplex virus type 2, HIV, lymphocytic choriomeningitis virus, arbovirses, measles • Mumps, >50% have a CSF lymphocytosis, but only 1-10% develop clinical features of meningitis (CSF, cerebrospinal fluid) • 26,000 – 42,000 hospitalizations / year in the US • Benign self-limited illness • Headache, fever, nausea, vomiting, nuchal rigidity (detected with flexion)

32. Theiler’s virus-induced meningitis Coxsackievirus meningitis. Scanty perivascular and meningeal infiltration of lymphocytes in a patient with aseptic meningitis. The patient died from myocarditis

33. Poliomyelits and polioencephalitis • Most often caused by the genus Enterovirus • Poliovirus, coxackievirus, echovirus, enterovirus • Until the development of poliovirus vaccine, poliovirus was responsible for most cases • Intestinal infection, viremia, hematogenous spread (experimentally, retrograde axonal transport from muscle to the CNS) • Headache, vomiting, neck stiffness, flaccid paralysis (lower limbs > upper limbs) • Motor neurons of the spinal cord • Neuronophagia; microglia aggregation around infected dying neurons Fig. 16.5. Children crippled by poliomyelitis. Hopefully, this will soon become a disease of the past. L. Collier and J. Oxford, 2011

34. Neuronophagia (neuronophagy) in poliomyelitis, a dense cluster of inflammatory cells marks the site of degeneration of an infected neuron

35. White Matter anterior horn Gray Matter Normal spinal cord Old poliomyeiltis. Preserved (a) and affected (b) anterior horns of spinal cord. Note the absence of anterior horn cells

36. A group of healthcare workers from the United States staffing a clinic in Madagascar were working with children admitted with acute flaccid paralysis. The illness began with fever nausea, vomiting, and severe headache followed by neck stiffness, muscle pain and weakens and constipation. None of the workers became ill because they had been vaccinated against this disease. Which viral vaccine protected these workers? A. Hepatitis A virus • Measles virus • Rubella virus • Yellow fever virus • Poliovirus

37. Experimental poliomyelitis by Theiler’s virus infection Virus infection in neurons in the gray matter of the spinal cord Neuronophagia (n) in Theiler’s virus infection Tsunoda I and Fujinami RS. (1999). Theiler’s murine encephalomyelitis virus . In: Persistent Viral Infections.

38. Postpolio syndrome (PPS) • Development of new muscle weakness 25 to 30 years after paralytic poliomyelitis • Poliovirus belongs to the family Picornaviridae • Risk factor: severity of the acute poliomyelitis • Unknown cause: excessive stress on remaining motor neurons eventually results in the dropout of the motor neurons? • Myopathic and neuropathic features: group atrophy Dalakas, 1995

39. Pathophysiology in post-polio muscular atrophy (PPMA). Post-Polio Syndrome: Pathophysiology and Clinical Management Anne Carrington Gawne and Lauro S. Halstead Critical Reviews in Physical and Rehabilitation Medicine, 7(2):147-188 (1995)

40. Herpesviruses • Herpes encephalitis caused by HSV-1 and 2 • HSV-1; fever, headache, seizure, coma at any age, 20% patients die despite acyclovir therapy • HSV-2; neonates born by vaginal delivery to women with HSV infection, poor feeding lethargy, seizure, long-term neurologic sequelae • Hemorrhagic necrosis affecting the temporal lobe • Infection in neurons, glia, and endothelium • PCR amplification of viral DNA in the cerebrospinal fluid (CSF)

41. Hemorrhagic necrosis in the temporal lobes. Viral antigen in most neurons. Hemorrhage and inflammation

42. Case: Herpes simplex virus type 1 • In January, a 74-year-old woman is brought to the hospital emergency department by her husband, who states that she had complained of a fever and headache during the past week. During the last 2 days, she has been confused and cannot perform her daily chores. Shortly after arrival she suffers a seizure. Her physical examination indicates neck stiffness and her head MRI shows necrosis in the right temporal lobe.

43. Varicella-zoster virus (VZV) infection • VZV is the cause of chickenpox (varicella), an acute febrile exanthematous illeness • Latent infections in neurons of the cranial and dorsal root ganglia • Reactivation of virus leads to disorders of the peripheral nervous system, shingles (zoster, Greek for ‘girdle’ shingles often produces a girdle or belt of blisters or lesions around one side of the waist) • Rash and postherpetic neuralgia • Treatment; anti-viral, steroids, antidepressants, etc

44. Cytomegalovirus (CMV) encephalitis • In the US, 80% of the population is seropositive • CMV encephalitis in adults occurs in AIDS patients • Confusion, gait disturbances, cranial nerve palsy • Neonatal infections occur in the pregnant mother with a primary infection • Petechiae, hepatosplenomegaly, microcephaly • Surviving infants have mental retardation, seizures, spasticity, hearing loss and optic atrophy • Antiviral agents improve the outcome of infection • Any cell type within the CNS may be infected; the virus often identified within ependymal cells (cytomegalic cells contain viral inclusions)

45. Cytomegalic cells Inclusion bodies known as “owl eye” inclusions

46. Rabies • A fatal infection caused by rabies virus • 60,000 death per year (Asia and Africa) • Animal bite (aerosol transmission with infection in olfactory epithelium) • Replicate in muscle, taken up by axons at the neuromuscular junction • Reached the CNS via intra-axonal transport • Polioencephalomyelitis, neuronophagia • Postexposure prophylaxis prevents clinical illness • Wound cleansing, postexposure vaccination, hyperimmune globulin motor fibers

47. (a) Purkinje cells contain Negri bodies, cytoplasmic inclusions. (b) Immunohistochemical demonstration of viral antigen within infected Purkinje cells Rabies neuropathology

48. http://rabidthebook.com/

49. Arboviral Encephalitis

50. What is an “arbovirus”? Three key properties… • Transmitted between vertebrate hosts by the bite of infected arthropods • i.e., arthropod-borne • Multiply and produce viremia in vertebrate hosts • Multiply in the tissues of arthropod vectors (WHO Definition) Remember: Arbovirus is an epidemiological classification, not taxonomic!