Neurovirology

1. Neurovirology • Acute viral infections • Rabies, Enteroviridae, Mumps, Arenaviridae, Arboviruses • Herpes viral infections • HSV, VZV, CMV • Chronic viral infections • JC-virus (PML), Measles (SSPE)

2. Acute viral infections • Forms of acute neurological disease • Meningitis, Panencephalitis, Leukoencephalitis and Poliomyelitis • Uncommon complications of common systemic infections • Clinical Features: Depend on which cells are infected • Meningitis • headache, fever, stiff neck, CSF pleocytosis • Most common cause of viral meningitis: enteroviruses, HSV2, mumps, HIV LCMV

3. Acute viral infections: Clinical features • Encephalitis • Increased intracranial pressure common • Altered consciousness, focal neurological signs, accentuated tendon reflexes, seizures, tremors, • Involvement of hypothalamus can lead to hypothermia diabetes insipidus, SIADH • Spinal cord involvement - flaccid paralysis, bowel and bladder symptoms. • With the exception of HSV, the topography of lesions is of little help in diagnosis

4. Encephalitis: Histopathology / Etiology • Panencephalitis (involving both gray and white matter) • Necrotizing • HSV-1 or -2, VZV, Arbo • Non-necrotizing • HIV, CMV, HTLV-1, measles • Polioencephalitis (predominantly involving gray matter) • Polys followed by lymphs, neuronophagia and microglial nodules • Enteroviruses, rabies, arboviruses • Leukoencephalitis (predominantly involving white matter) • PML, HIV, Post-infectious

5. Rabies: Virus • One of the rhabdoviruses, a group of negative-single-strand RNA viruses with a distinct bullet shape • Receptor: NCAM (CD56), Acetylcholine receptor • Can grow in a wide variety of cell cultures • generally noncytopathic, in curious contrast to the fatal outcome of infection in vivo in virtually all warm blooded animals. • Susceptibility is variable as are periods of latency and infectivity and salivary excretion

6. Rabies: Epidemiology • Virus is sustained in wild carnivores and insectivorous bats • Sylvatic reservoirs: foxes, skunks raccoons and bats • Skunk now the commonest reservoir of wildlife rabies in US. • Airborne transmission in bat caves • Transmission from man to man has not been documented (except for corneal transplants)

7. Rabies: Epidemiology • 50% of dogs with proven rabies do not have virus in saliva. • Overall transmission through bite is 15%. • Dog excretes virus up to 5 to 7 days prior to clinical symptoms • other carnivores viral secretion not known, therefore quarantine and observation of no use except for dogs (e.g. bats frequently without clinical symptoms).

8. Rabies: Clinical • Incubation period in man 15 days to 1 year (?) • Half of patients in US with no history of bite. • Half develop hydrophobia. • Ascending paralysis with pleocytosis in 25% and elevation of protein

9. Rabies: Pathology • Bland pathologic findings - • Grossly normal • diagnosis in dogs used to be made by examining stomachs • Microscopic • Perivascular inflammation • Without tissue necrosis • Neuronophagia uncommon • Pathognomonic feature is Negri body • 1 to 7 micron inclusions mostly in neurons • Found in ammon's horn and Purkinje cells of cerebellum

10. Rabies Negri Body From: Neuropathology Illustrated 1.0

11. Rabies • H&E stained section of cerebellum showing purkinje cell with eosinophilic cytoplasmic inclusion (Negri body) • Electron micrograph of myelinated axon showing viral inclusions (between arrows) with axoplasm From C.A. Wiley From C.A. Wiley

12. Rabies: Pathogenesis • Saliva inoculation through bite • Local infection of individual muscle cells • Incubation period determined by persistent infection of muscle fibers prior to ascension of nerves • Replicates in parikaryon and dendritic processes of neuron • Localized to limbic system with relative sparing of the cortex • Later transmitted centrifugally to many organs including hair follicles

13. Enteroviruses: Virus • Nonenveloped positive single-stranded RNA viruses • 70 human enteroviruses are known • Replication is species-specific • Cell receptor for polio on chromosome #19 • Approximately 3000 copies of receptor on HeLa cells

14. Enteroviruses: Epidemiology/Clinical • Cause 30 to 50% of viral meningitis and most cases of paralytic polio • Transmission by fecal to oral contamination • "man's fecal veneer" • High infectivity 76% of household contacts for coxsackie, • Epidemic Poliomyelitis • 1916 9,000 cases in NYC, • 80% in children under 5 • But primary infection of adults and adolescents 10 times more likely to progress to paralysis.

15. Enteroviruses: Diagnosis • Coexistence of rash and meningitis may be helpful but confusion with meningococcemia • Meningitis lasts days to weeks • CSF may contain a few polys initially but progresses to lymphocytes by 24 hours.

16. Polio: Pathology • Gray matter hemorrhage • Neuronophagia • Viral binding within CNS is greater than restricted distribution of receptor. • Neuron phagocytosed by surrounding microglia Dieing neuron From: Neuropathology Illustrated 1.0

17. Mumps: Clinical / Epidemiology • Respiratory route during winter • Single most common cause of aseptic meningitis and mild encephalitis • 15% of all cases of aseptic meningitis • Half of all infections associated with CNS symptoms • 50% of cases with CNS involvement without parotitis. • Most resolve without neurological complications • CSF pleocytosis may extend for 1 year

18. Mumps: Pathogenesis • Excretion and viremia for 6 days prior to clinical symptoms • Cleared with appearance of IgA and IgM respectively. • Infection of CNS is secondary to choroid plexus infection • CSF isolation within first 4-5 days(20-50%) • Compression of facial nerve with parotitis, hearing loss due to cochlea infection. • Occasionally associated with lower motor neuron disease

19. Adenoviruses: Virus / Epidemiology/Clinical • Fecal to oral in families, respiratory in epidemics. • Can be transmitted by fomites • 50% of infections cause clinical disease. • Respiratory infections, conjunctivitis, hemorrhagic cystitis and gastroenteritis. • Encephalitis rather than aseptic meningitis occurs but rare • Very rare neurological complications • almost exclusively in children

20. Arenaviruses: Epidemiology / Clinical • Zoonotic infection in which man acquires virus from the mouse or hamster • Biphasic course- pneumonitis followed by meningitis (and encephalitis in half of these)suggests that second phase may be immunologically mediated • Multisystem disease in which primary viral attack of lymphoid and bone marrow cells leads to damage of cells, release of vascular permeability mediators, shock. • Clinical CNS disease remains unexplained

21. Arenaviruses: Pathology/Pathogenesis • Lassa fever more virulent - 10 reported autopsies • No consistent findings- no CNS lesions seen in 4 patients. • Lassa fever (Nigeria 1969) human to human spread hospital outbreaks with 30 to 60% mortality among infected personnel • Pathologist who preformed the first autopsy died of Lassa.

22. Arboviruses: Epidemiology • Include majority of Togaviruses,Flaviviruses, Bunyaviruses, Reoviruses and Bunyaviruses. • Obligatory cycle of multiplication in arthropod • In ticks and mosquitoes infection can be transovarian. • Incubation in mosquitoes for 4 days to 2 weeks • Geographic and seasonal limitations

23. Arboviruses: Clinical • 4 syndromes associated with arboviruses • Encephalitis • Yellow fever • Hemorrhagic fever • Undifferentiated tropical fevers. • Pathology • nonspecific inflammation

24. Arbovirus Encephalitis Neuron Neuron From: Charleen Chu MD/PhD Viral Capsids Viral Capsids From: Charleen Chu MD/PhD

25. Eastern Equine Encephalitis: Epidemiology • Usual transmission between marsh birds and mosquitoes • Changes in marsh condition etc. lead to spill over into mosquito hosts that feed on mammals. • Horse being important sentinel animal but dead-end host for virus. • Ratio of inapparent infections to apparent infections is low (20:1) • Pathology • meningeal and perivascular inflammation, neuronophagia.

26. Western Encephalitis • Mosquito and birds in cycle but mosquito does feed on large vertebrates • Ratio of unapparent to apparent infections is very high • 1000:1 sequelae rare but fatal

27. St. Louis Encephalitis • Commonest cause of human arbovirus encephalitis • Paradoxically urban epidemics occur in drought years • Poor drainage, rural outbreaks with high rainfall • Man can become active intermediate host

28. Other arboviruses • Venezuelan Equine Encephalitis • California Encephalitis • Japanese Encephalitis • Colorado Tick Fever virus • Tick-borne Encephalitis • Undefined virus • Recapitulate epidemiological patterns of virus dissemination

29. Differential Diagnosis of Acute Viral Infections • Infections masquerading as viral CNS infections • TB, brucellosis, fungi, Syphilis, Lyme disease, Rickettsial Diseases, Leptospirosis, Mycoplasma • Noninfectious disease • carcinomatosis meningitis, gliomatosis cerebri, glaucomatous angitis, sarcoidosis, SLE, rheumatoid meningitis, ruptured cysts in subarachnoid

30. Post-Infectious Encephalomyelitis Diffuse inflammatory infiltrate Perivascular inflammatory cuff From: Neuropathology Illustrated 1.0 From: Neuropathology Illustrated 1.0

31. General consideration of herpes viral infections • Most herpesviruses are restricted to their natural host, only herpes simiae of macaque causes significant disease in man. • Host never clears infection • To have endemic acute disease virus you need: • a population of 200,000 • or zoonotic infection • or LATENCY

32. Latency • Property of all herpes viruses • Term used in two ways: • Continuous shedding of small amounts • or more usually implies persistent without production of recoverable virus

33. HSV Latency • virus particles and antigen not present during quiescent periods • may involve integration of viral DNA into chromosomal, • but since integration usually occurs during cellular DNA synthesis for latency in neurons must postulate that integration occurs during DNA repair or that episomal form of virus is sequestered. • Latency in either neural cells or hematopoetic cells • Transport up sensory nerve fiber during primary infection leading to establishment of latency

34. 8 Human Herpesviruses • Alpha- (HSV1 & 2, VZV) • variable host range • short reproductive cycle • latency usually in ganglia • have viral encoded thymidine kinase • Beta- (CMV, HHV6 & 7) • resticted host range • long reproductive cycle • latent in secretory glands & lymphoreticular tissue • Gamma - (EBV, HHV8) • limited host range • frequently arrested replication pre-viral production

35. Herpes Replication • Very similar to adenovirus with some splicing • Cascade - Immediate early, early, late • Immediate early proteins peak at 2-4 hours • required to synthesize early proteins • Early proteins peak 5-7 hours • TK and other DNA synthesis related proteins • Late proteins require DNA synthesis • capsid proteins

36. HSV1: Epidemiology • 90% of adults have antibody, despite rare involvement of the CNS it is the commonest cause of nonepidemic fatal encephalitis in US • 1000 to 2000 cases per year with death in over half of untreated • Spread by salivary or respiratory contact, primary infection is asymptomatic or gingivostomatitis • herpes gladiatorum from inoculation with saliva • Most patients who develop CNS complications in good health with cold sore of similar incidence to rest of population

37. HSV: Clinical presentation • Initial infection (e.g. gingivostomatitis) • Half of the cases first infection does not produce clinically apparent disease • In immunosuppressed spreads rapidly and is lethal • Otherwise primary infection terminated with appearance of immune response • Significant neurological disease • Insidious or fulminant onset, fever and headache, • Local lesion in one or both fronto-temporal lobes giving personality changes • Seizures and coma late

38. MRI of HSV Encephalitis • T-2 weighted MRI showing increased signal in frontal lobe (orbital gyrus on right) and bilaterally in temporal lobe From C.A. Wiley

39. HSVE Gross Swollen Hemorrhagic Temporal lobe From Neuropathology Illustrated 1.0

40. HSV: Pathology • Adults: HSV I localization to orbital-frontotemporal lobes - often unilateral • Children: diffuse encephalitis caused by type 1 or 2 • Immunofluorescence shows virus in ipsilateral olfactory nerve, but not in all patients. • Not usually found in CNS with primary infection except in immunosuppressed, rather reactivation of trigeminal latency

41. HSV Encephalitis H&E Microscopic hemorrhages From Neuropathology Illustrated 1.0 Perivascular and parenchymal inflammation From Neuropathology Illustrated 1.0

42. HSV Immunohistochemistry Low power of needle biopsy immunostained (red) for HSV antigens From C.A. Wiley

43. HSV Encephalitis Cowdry A Inclusions From Neuropathology Illustrated 1.0 Intranuclear Viral capsids From Neuropathology Illustrated 1.0

44. HSV: Diagnosis • Earliest change EEG slowing sometimes focal, similar to SSPE. • MRI abnormalities early • CT abnormalities are late • CSF shows increased pressure early few cells or polys, but late usually mononuclear cells. • Protein up and glucose normal. • CSF PCR usually positive during encephalitis

45. HSV: Treatment • Prophylactic Acyclovir to bonemarrow transplant patients • Age and level of consciousness at time of initiation of treatment is critical in prognosis • Half of patients suspected of HSV encephalitis turn out not to have it • 20% of these have a different, treatable disease • Therefore diagnosis is critical part of care • Acyclovir - acyclic nucleotide that is selective substrate for herpesvirus thymidine kinase. • Cellular thymidine kinase in uninfected cells does not use acyclovir. • Therefore drug is phosphorylated only in infected cells.

46. HSV 2: Epidemiology • Primary infection can occur in utero or during parturition. • Majority of infections between 14 and 35 years of age (when 20 to 30% develop antibody). • 250,000 genital infections / year in US • Shedding can occur without disease • 80% recovery from second or fourth sacral ganglia of routine autopsies.

47. HSV 2: Clinical • Infected at birth develop disseminated herpetic infections. • Adults primary infection is complicated by acute benign meningitis • With exacerbations of genital lesions, meningitis or radiculitis may recur in contrast to the lack of correlation of mucocutaneous lesions with HSV I. • Immundeficiency disease can lead to fatal dissemination • Recurrences more often in type 2 (74/123) than type 1 (2/14). • Pathology • Infants hepatitis and adrenal necrosis and diffuse encephalitis.

48. Varicella-Zoster: virus • Varicella= diminutive form of variola-smallpox • Cell associated- inoculation with infected cells necessary even though virus is stabled in cell-free form in vesicular fluid. • ganglionic latency

49. VZV: Clinical / Epidemiology • Two distinct clinical diseases (chickenpox and shingles) • Shingles (herpes zoster= Greek to girdle) less common endemic disease of older or immunocomrpomised individuals • First suggestion that both diseases were manifestations of the same infection in 1888.

50. Varicella: Clinical Highly contagious generalized exanthematous disease with marked seasonality (winter and spring) Occurs at a rate of 5 per 1000 population per year Spread by respiratory route Majority of infections are clinically obvious less than 4% escape detection. Rare pulmonary infection and acute neurological complications Including encephalomyelitis, localized myelitis, acute ataxia, GBS or Reye's syndrome. CNS involvement in 1:1000 acute cerebellar ataxia - transient Neonatal varicella in utero infection with cicatricial scarring during first trimester