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Vol. 6 No. 1 - Millennium Issue - January 2000

Viruses in relation to mankind

By: B.P. Singh

Viruses contain genetic material in the form of DNA or RNA and interact with hosts and vectors carriers under the canopy of environment. These interactions cause several lethal diseases in major crops i.e. rice, wheat, maize, sugarcane and sorghum besides horticultural, medicinal and ornamental crops.

The devastating viruses of plants are Rice Tungro Virus, Wheat Dwarf Virus, Maize Streak Virus, Coconut Cadang Cadang and Bean yellow mosaic virus of Gladiolus. Similarly human and animal viral diseases like Hepatitis, Dengue, Influenza, AIDS, Herpes, Foot and Mouth disease etc. adversely affect human and animal health.

Environmental factors influence the incidence of diseases caused by these viruses in several ways:

  • Environment may favour the multiple of a given vector of the virus leading to a rise in its population. This automatically leads to wider spread of the virus which leads to higher incidence of the disease.

  • Environment may adversely affect the population of an antagonist of a vector which once again leads to a rise in the vector population.

  • If the environment adversely affects the population of the vector itself then the disease is unable to spread widely and its incidence drops.

  • The alternate host of the virus may have a population explosion which leads to a great rise in the availability of viral inoculum for spread to human or crop hosts.

  • In agriculture, indiscriminate use of pesticides sometimes leads to the great reduction in the population of an antagonist of a vector. The vector population, being free from any antagonism now rises rapidly and the incidence of the disease transmitted by this vector rises.

Recent outbreak of plague in Surat confirms the importance of environmental factors in the incidence of viral diseases.

Efforts are on to understand and manage these diseases to eliminate or minimize their ill effects on the society. Recent developments in molecular biology have provided tools for quick and reliable diagnosis of various viral pathogens both in plants and animals. This means that most diseases can now be detected before they assume alarming proportions. It also helps us to find out the various ecological niches in which the virus survives.

Several viruses (e.g. Nuclear Polyhedrosis Virus) are responsible for keeping insect populations under check. Some fungi also kill insects. But if our pesticides eliminate these fungi then insect population will rise and so will the incidence of any disease transmitted by them.

Molecular biology is helping us to design highly effective vaccines based on detailed knowledge of the surface proteins of the virus and better vaccine delivery systems.

We have to manage our environment such that the viruses, their vectors and we (or our crops) can all coexist without any significant disadvantage or advantage to anyone of them. Only balance can bring health.

Dr. B.P Singh, former head of the Plant Pathology and Protection Division, NBRI is currently an Emeritus Scientist at the National Botanical Research Institute, Lucknow (India),

This article has been reproduced from the archives of EnviroNews - Newsletter of ISEB India.

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