Allied Academies


Session: 8 Virology

Epidemiologic studies show that viral infections in developed countries are the most common cause of acute disease that does not require hospitalization. In developing countries, viral diseases also exact a heavy toll in mortality and permanent disability, especially among infants and children. Emerging viral diseases such as those due to HIVEbola virus and hantavirus, appear regularly. Now that antibiotics effectively control most bacterial infections, viral infections pose a relatively greater and less controlled threat to human health. Some data suggest that the already broad gamut of established viral diseases soon may be expanded to include other serious human ailments such as juvenile diabetesrheumatoid arthritis, various neurologic and immunologic disorders, and some tumours.

Viruses can infect all forms of life (bacteria, plants, protozoa, fungi, insects, fish, reptiles, birds, and mammals); however, this section covers only viruses capable of causing human infections. Like other microorganisms, viruses may have played a role in the natural selection of animal species. A documented example is the natural selection of rabbit’s resistant to virulent myxoma virus during several epidemics deliberately induced to control the rabbit population in Australia. Indirect evidence suggests that the same selective role was played by smallpox virus in humans. Another possible, though unproved, mechanism by which viruses may affect evolution is by introducing viral genetic material into animal cells by mechanisms similar to those that govern gene transfer by bacteriophages. For example, genes from avirulent retrovirus integrated into genomes of chickens or mice produce resistance to reinfection by related, virulent retroviruses. The same relationship may exist for human retroviruses, since human leukaemia-causing retroviruses have been reported.

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