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5 Bunyaviruses

Arenaviruses

Prion

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There are at least 200 viruses in 5 genera. Most are arboviruses and few are rodent born viruses (hantaviruses). They cause encephalitis, hemorrhage fever, and pulmonary syndrome (Table 1).

Table 64-1. Notable Bunyaviridae Genera

Genus MembersInsect Vector Pathologic Conditions Vertebrate Hosts

Bunyavirus Bunyamwera virus, California encephalitis virus, La Crosse virus, Oropouche virus; 150 members

Mosquito Febrile illness, encephalitis, febrile rash

Rodents, small mammals, primates, marsupials, birds

Phlebovirus Rift Valley fever virus, sandfly fever virus; 36 members

Fly Sandfly fever, hemorrhagic fever, encephalitis, conjunctivitis, myositis

Sheep, cattle, domestic animals

Nairovirus Crimean-Congo hemorrhagic fever virus; 6 members

Tick Hemorrhagic fever Hares, cattle, goats, seabirds

Uukuvirus Uukuniemi virus; 7 members Tick - Birds

Hantavirus Hantaan virus None Hemorrhagic fever with renal syndrome, adult respiratory distress syndrome

Rodents

  Sin Nombre None Hantavirus pulmonary syndrome, shock, pulmonary edema

Deer mouse

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1. Structure  segmented –ssRNA (S, M, L) (Table 2)  capsid  envelope

Genome* Proteins

L RNA polymerase, 170 kDa

M Spike glycoprotein, 75 kDa

  Spike glycoprotein, 65 kDa

  Nonstructural protein, 15-17 kDa

S Nucleocapsid protein, 25 kDa

  Nucleocapsid protein, 10 kDa

Table 64-2. Genome and Proteins of California Encephalitis Virus

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2. Replication virus enters cells via G1 glycoprotein and receptor-mediated endocytosis.Virus are assembled by budding into the Golgi apparatus and are released by cell lysis and exocytosis.

3. Most viruses in bunyavirus genus are not in Taiwan. Most members of bunyavirus genus are arboviruses (transmitted by arthropod) and cause encephalitis and hemorrhagic fever in a way very similar to togaviruses and flaviviruses.  

BOX 64-2. Disease Mechanisms for Bunyaviruses

•Virus is acquired from an arthropod bite (e.g., mosquito) •Initial viremia may cause flulike symptoms. •Establishment of secondary viremia may allow virus access to specific target tissues, including the central nervous system, organs, and vascular endothelium. •Antibody is important in controlling viremia; interferon and cell-mediated immunity may prevent the outgrowth of infection.

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4. Hantavirus   Hantaan virus was first isolated from mice around Hantaan River of Korea in 1976. It causes Hantaan hemorrhagic disease (fever, hemorrhage, kidney failure, shock, and death)

  Sin Nombre virus is isolated from grand canon of US in 1993. It causes hantavirus pulmonary syndrome. (fever, muscle ache, interstitial pulmonary edema, respiratory failure, and death).

Virus is transmitted by secretion of rodent like deer mice.

5. Lab. diagnosis: It can be confirmed by serological tests and RT- PCR.

6. Treatment: There is no specific therapy or vaccine (except for Rift Valley fever). Arthropod or rodent controls for prevention.

Arenaviruses associated with human disease (c64, p654)

Virus Disease Distribution

Lassa Lassa fever West Africa

Junin Argentine hemorrhagic fever South America

Sabia Brazilian hemorrhagic fever South America

LCMV meningitis Worldwide

LCMV: lymphocytic choriomeningitis virus

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Virions appear sandy because of ribosome.

Enveloped virion with 2 single strand RNA circles (L and S).

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Transmission (zoonoses)

Rodent-to-human:

1. Inhalation of aerosolized virus

2. Ingestion of food or materials contaminated by infected rodent excretion.

3. Catching and preparing mice as a food source

Human-to-human:

1. Direct contact with blood, tissues, secretions or excretions of infected humans

2. Needle stick or cut

3. Inhalation of aerosolized virus

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Epidemiology and clinical syndromes

1. LCM

• There are 5 to 20% mice have LCMV in US.

• LCM is characterized by fever and meningeal illness. About 10% patients have CNS syndromes.

• LCM is usually not fatal. In general, mortality is less than 1%.

• Avoid contact with mice and pet hamsters.

2. Lassa and other hemorrhagic fever Clinical illness is characterized by fever, coagulopathy, petechia, hemorrhage, and shock. Death occurs in about 50% of Lassa fev

er cases. 5-11

Laboratory diagnosis

--Infection can be detected by serology and RT-PCR.

--If the case is suspected, laboratory personnel should be warned.

Specimens should processed in BSL 3 (LCM) or 4 (Lassa and others)

facilities.

Treatment --Ribavirin is used to treat Lassa fever. --Supportive measures

Prevention and control of outbreak by limiting contact with rodents.

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Unconventional slow viruses: Prions (C67, p691)

Prion :Proteinaceous infectious particle

1.causes spongiform encephaolpathies observed in hosts

2. Characteristics of diseases--long incubation periods (30 years) before developing clinical illness

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BOX 67-1. Slow Virus Diseases

Human •Kuru •Creutzfeldt-Jakob disease (CJD) •Gerstmann-Sträussler-Scheinker (GSS syndrome) •Fatal familial insomnia (FFI) Animal •Scrapie (sheep and goats) •Transmissible mink encephalopathy •Bovine spongiform encephalopathy (BSE; mad cow disease) •Chronic wasting disease (mule, deer, and elk)

3. Comparison of Classic Viruses and Prions

Filterable, infectious agents Yes Yes

Presence of nucleic acid Yes No

Defined morphology (electron microscopy) Yes No

Presence of protein Yes Yes

Disinfection by:

  Formaldehyde Yes No

  Proteases Some No

  Heat (80°C) Most No

  Ionizing and ultraviolet radiation Yes No

Disease

Cytopathologic effect Yes No

Incubation period Depends on virus Long

Immune response Yes No

Interferon production Yes No

Inflammatory response Yes No

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  PrPSc PrPC

Structure Globular Extended

Protease resistance Yes No

Presence in scrapie fibrils

Yes No

Location in or on cells

Cytoplasmic vesicles and extracellular milieu

Plasma membrane

Turnover Days Hours

Table 67-2. Comparison of Scrapie Prion Protein (PrPSc) and (Normal) Cellular Prion Protein (PrPC)

4. Scrapie :

b. model for proliferation of prion

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Death (vacuolation) of neurons

5. Pathogenesis and immunity

BOX 67-2. Pathogenic Characteristics of Slow Viruses

No cytopathologic effect in vitro

Long doubling time of at least 5.2 days

Long incubation period

Cause vacuolation of neurons (spongiform), amyloid-like plaques, gliosis

Symptoms that include loss of muscle control, shivering, tremors, dementia

Lack of antigenicity

Lack of inflammation

Lack of immune response

Lack of interferon production

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6. Epidemiology

-- CJD is transmitted by injection, transplantation of contaminated tissues (corneas), contact with contaminated medical device (brain electrode), and food.

-- CJD, GSS, and FFI are also inheritable.

-- Kuru is due to the eating of dead body.

-- variant form CJD (vCJD) in younger people (<45 years old) in UK after mad cow disease in 1980.

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Kuru: shivering or trembling in Fore tribe of New Guinea , who used to eat dead human body.

Women and children are high risk.

7. Clinical syndromes:

--Spongiform encephalopathies are characterized by a loss of muscle

control, shivering, myoclonic jerks, tremors, loss of coordination,

dementia, and death.

8. Lab. diagnosis: Western blot for tonsil biopsy and histology for autopsy.

9. Treatment, prevention, and control

-- Rigorous disinfection by autoclaving at 15 psi for 1 hour instead of

20 minutes and treatment with 5% HCl, and 1 M NaOH 5-20

BOX 67-4. Clinical Summaries

CJD: A 63-year-old man complained of poor memory and difficulty with vision and muscle coordination. Over the course of the next year, he developed senile dementia and irregular jerking movements, progressively lost muscle function, and then died.

VCJD: A 25-year-old is seen by a psychiatrist for anxiety and depression. After 2 months, he has problems with balance and muscle control and has difficulty remembering. He develops myoclonus and dies within 12 months of onset.

Case study and questions: A 70-year-old woman complained of severe headaches and appeared dull and apathetic with a constant tremor in the right hand. One month later, she suffered memory loss and moments of confusion. The patient’s condition continued to deteriorate, and an abnormal electroencephalograph tracing showing periodic biphasic and triphasic slow-wave complexes was obtained 2 months later onset of symptoms. By 3 months, the patient was in a comalike state. She also had occasional spontaneous clonic twitching of the arms and legs and a startle myoclonic jerking response to a loud noise. The patient died of pneumonia 4 months after the onset of symptoms. No gross abnormalities were noted at autopsy. Astrocytic gliosis of the cerebral cortex with fibrils and intracellular vacuolation throughout the cerebral cortex were seen on microscopic examination. There was no swelling and no inflammation.

1. What viral neurological diseases would have been considered in the differential diagnosis formulated on the basis of the symptoms described? What other diseases? 2. What key features of the postmortem findings were characteristic of the disease caused by unconventional slow virus agents (spongiform encephalopathies, prions)?3. What key features distinguish the unconventional slow virus diseases from more conventional neurological viral diseases? 4. What precautions should the pathologist have taken for protection against infection during the postmortem examination?

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