Virus Host Interactions

Virus Host Interactions: Virus Infections

At the cellular level

 Abortive

infection  Lysis or cell death  Cellular proliferation  Malignant transformation

Inclusion Bodies  Crystalline

aggregates of virions (or) degenerative changes produced by virus  Confers altered staining properties on the cell  Staining by Giemsa (or) Eosin Methylene blue  Demonstrated by light microscopy

Contd..  Distinct

size, shape, location & distinct staining properties  Generally acidophillic

Examples

Negri bodies

Bollinger Bodies

Cowdry type A

CMV inclusion bodies

Pathogenesis of viral Infection

Latent Infection – Herpes Zoster

Pathogenesis – Mouse Pox (eg..)

Routes of entry and shedding

Cycle of infection Entry

Primary site Spread

Shedding

Local Lymphatic Neuronal Blood (viremia)

Secondary sites Shedding

Local versus Disseminated Infections 

LOCAL INFECTIONS : Viral replication restricted to portal of entry. Short incubation period. Examples: rhinoviruses, influenza



DISSEMINATED INFECTIONS: Virus spreads to tissues beyond portal of entry. Usually have prolonged incubation periods. Examples: measles, rabies

Non immunological responses  Interferons

are host coded proteins produced by cells on induction by viral (or) non-viral inducers.  No direct action on viruses, but render the cells of same species ( from previous infection) – refractory to virus infection

What types of specimens are collected to diagnose?

•

Respiratory tract infections: Nasal and bronchial washings, throat and nasal swabs, sputum

• • • • •

Eye infections: throat and conjunctival swab/scraping

• • •

Gastrointestinal tract infections: stool and rectal swabs Vesicular rash: vesicle fluid, skin scrapings Maculopapular rash: throat, stool, and rectal swabs CNS (encephalitis and meningitis cases): stool, tissue, saliva, brain biopsy, cerebrospinal fluid Genital infections: vesicle fluid or swab Urinary tract infections: urine Bloodborne infections: blood

Three General Approaches for Laboratory Diagnosis of Viral Infections  Direct

detection

• Microscopy or staining

 Virus

Isolation  Molecular Techniques - PCR  Serology

• Antibodies – ELISA, Hemagglutination Test & Complement Fixation Test

Direct Detection  Electron

Microscopy

• Examine specimen for viruses

 Immuno-electron

• Labeled antibody

Microscopy

 Immunoflourescence

• Fluorescent tag bound to Fc region of Ab

Virus Isolation  Cell

Culture techniques  Animal Inoculation  Embryonated Egg Inoculation

Figure 5.17a: Tissue culture cells are grown on coverslips on the bottom of shell vials.

Reproduced from Athmanathan, S., S. R. Bandlapally, and G. N. Rao, BMC Clin. Pathol. 2 (2002): 1-5.

Figure 5.17b: Detection of Herpes Virus Simplex 1 using the shell vial technique and immunofluorescence.

Anti viral drugs

Viral Vaccines