Virology

 1. Biology:

Virus are too small to be seen with a light microscope. Viruses like other microorganism (MOs) e.g. bacteria, fungi, and parasite are the infectious agents that are associated with disease in humans. They are obligate intracellular parasite and they require living host in order to multiply. The virion of the virus particle consists of a nucleic acid (single type of nucleic acid i.e. either DNA or RNA); genome which is packed into a protein coat (capsid) and capsid is enclosed by an envelope of lipid, protein, and carbohydrate. And the scientific discipline concerned with the study of the biology of viruses and viral diseases called virology.

 

2. Pathogenesis

 

3. Epidemiology:

Epidemiology is the study of the distribution, the dynamics and the determinants of diseases in populations. Viral infection show seasonal differences. Some are prevalent in summer season e.g. enteric fever due to poor hygiene and use of contaminated water. And some are prevalent during winter e.g. Respiratory viruses.

 

3.1 Reservoir & source of infection:

Human as well as animals acts as reservoir for many viral disease.

Viral disease transmitted from animal reservoir to human are called zoonotic viral disease. E.g. Rabies, Coronaviruses (SARS-CoV, MERS-CoV, SARS-CoV-2), Brucellosis etc.

Arthropods e.g. mosquitoes, fleas, ticks, lice, and flies that usually act as vectors for transmission of diseases called as viral vector borne disease. E.g. Dengue fever, Leishmaniasis, Malaria etc.

Note: Asymptotic patients are most important source of infection. When virus change antigenic structure of their genome which infect a large number of immunologically naive population e.g. Influenza

 

3.2 Transmission

Virus transmission is affected by behavioral, environmental and ecological factors. The mode of transmission basically depends on, the site of the viral replication & secretion and presence or absence of envelope in the virus.

 

4. Symptoms

The viral disease results in a wide variety of symptoms and its character and severity depends on type of viral infection and factors like person’s age & health status. Some symptoms of viral disease are as follows;

•           Flu-like symptoms (fatigue, fever, sore throat, headache, cough etc.)
•          Gastrointestinal disorder ( diarrhea, nausea, vomiting)
•          Unexpected weight loss
•          Difficulty with feeding
•          Rashes, malaise, stuffy nose etc.

In some cases, viral disease can results in serious complication, possibly life threating complications like dehydration, chest pain, shortness of breath etc.

 

5. Laboratory diagnosis of viral disease

Tests to support a specific diagnosis of viral infection are;

•          Demonstration of virus induced cytopathic effect (CPEs) in the cells.
•          Direct detection of viruses.
•          Virus isolation and viral assay.
•          Detection of viral protein & other enzyme.
•      Detection of viral genome.
•          Viral serology.

 

6. Prevention and control

The spread of many viral diseases can be prevented by;

•            Adoption of good hygiene.
•        Control of the vectors.
•          Immunization of the population.

(Immunization of the population by vaccine is the best means for the control of many disease.)

 

Thank you!