Infection cycle of Togaviridae begins when the virion is taken up into cellular vesicles by receptor-mediated exocytosis

Infection cycle of Togaviridae

1. The virion is taken up into cellular vesicles by receptor-mediated endocytosis

2. A pH drop due to the merging of the carrier vesicle with a cellular lysosome digests the nucleocapsid proteins releases the genomic RNA to the cytosol where replication begins

3. (+) sense RNA is immediately translated

4. New virions spontaneously assemble following viral translation and replication

5. The virion then buds through cellular membranes

Viral Properties of Togaviridae

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Viral Properties of Togaviridae

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Viral Properties of Togaviridae

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Viral Properties of Togaviridae

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Alphavirus is an _________ and is usually restricted to a specific arthropod vector, its vertebrate host, and their ecologic niche

To be an arbovirus, the virus must be able to:

All members are antigenically related, thus may show cross-reactivity towards each species

Summarize Properties of Alphaviruses

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Summarize Properties of Alphaviruses

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Summarize Properties of Alphaviruses

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Summarize Properties of Alphaviruses

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(Alphavirus) Proteins

Nonstructural protein that is used for synthesis of (-) strand of RNA

(Alphavirus) Proteins

Nonstructural protein that is used for regulation of strand synthesis (i.e., initiation of sub-genomic RNA synthesis, processing of N5 polyprotein)

(Alphavirus) Proteins

Nonstructural protein with unknown function

(Alphavirus) Proteins

Nonstructural protein that is used for viral polymerase

(Alphavirus) Proteins

An envelope (type of structural protein) glycoprotein that's a surface glycoprotein

(Alphavirus) Proteins

An envelope (type of structural protein) glycoprotein that's another surface glycoprotein and interacts with host cell receptors for attachment

(Alphavirus) Proteins

An envelope (type of structural protein) glycoprotein that contains signal sequence for protein translocation but the ultimate function is unknown and is not present in mature alphaviruses

(Alphavirus) Proteins

A membrane-associated protein (type of structural protein) that acts as a signal sequence and is important in virus assembly and budding

(Alphavirus) Pathogenesis

Main hosts are domesticated and wild animals

(Alphavirus) Pathogenesis

These viruses can cause _______ infections of both vertebrate and invertebrate hosts

(Alphavirus) Pathogenesis

The death of an infected cell results from a combination of virus-induced insults. Which of the ff. are the results of infected cell death?

(Alphavirus) Pathogenesis

Steps:

1. On biting, the female mosquito regurgitates the virus from the salivary glands, to the bloodstream of the vertebrate host

2. Virus spreads to other target tissues including muscles, joints, skin, and brain

3. The virus then circulates freely in the host’s plasma and comes into contact with susceptible target cells

4. Initial viremia follows resulting in systemic infection

5. Virus travels to the skin and reticuloendothelial system where the primary infection occurs

6. Systemic symptoms during the initial viremia includes fever, chills, headaches, backaches, and other flulike symptoms, within 3 to 7 days of infection

7. A secondary viremia can produce sufficient virus to infect target organs and tissues

(Alphavirus) Pathogenesis

Virus is eliminated by the immune system, but arthritis or central nervous system impairment may persist for weeks

(Alphavirus) Clinical manifestations

Viremia coincident with abrupt onset of fever, chills, malaise, and joint aches where viremia subsides in ____, and antiviral antibodies appear in the blood within 1 to 4 days of the onset of symptoms

(Alphavirus) Clinical manifestations

This manifestation typically develops around the 3rd to 5th day of illness and happens when the patient is already defervescing.

(Alphavirus) Clinical manifestations

This manifestation is a characteristic feature of alphaviruses diseases, & involves mainly the small joints

→ Occurs more prominently in adults than in children

→ In severe cases, joints maybe swollen and tender

(Alphavirus) Clinical manifestations

• The prototype for those causing an acute febrile illness (3-7 days) with malaise, rash, severe arthralgias, and sometimes arthritis

• The etiology of the word means “walk bent over” since this is usually seen in patients infected with the virus due to severe, painful arthritis

• Same vector and almost the same clinical presentation as dengue

(Alphavirus) Clinical manifestations

These viruses are closely related antigenically to chikungunya virus and they causes similar or identical clinical manifestations with that of Chikungunya virus

(Alphavirus) Clinical manifestations

This virus causes similar but milder diseases known as Ockelbo (in Sweden), Pogosta (Finland), or Karelian fever (Russia)

(Alphavirus) Immune response

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(Alphavirus) Diagnosis

Suggested by clinical evidence and known risk of exposure to the virus so it is important to know the epidemiology (pero di ko na nilagay maliban dun sa chikungunya virus)

There are confirmatory tests like:

1. Viral isolation and identification

2. Specific rise in IgG antibody, presence of IgM by viral isolation from the blood during the viremic phase

3. Detection of Viral RNA (e.g. PCR) or proteins (e.g.

Immunohistochemistry) in frozen or fixed tissues

Question: Is it essential to perform the confirmatory tests given?