Pests of Medical Importance :-1

Many dangerous diseases are transmitted through the agency of insects. Insect-borne diseases take a heavy toll of human life. About a million of people die and a few hundred million suffer from such diseases throughout the world within a year. About 400 million people live in areas where malaria is still highly endemic. It is estimated that at least 100 million cases occur annually resulting in death of one million. Filariasis is a common disease in tropical areas affecting more than 250 million people. The number of deaths due to plague during 1898-1957 has been estimated, up to 12,707,475. Similarly, between 1970-1980, sleeping sickness took toil of one million lives in West Africa.

A MODE OF TRANSMISSION

The insects often transmit pathogens at the time of blood sucking. The pathogens are mostly the bacteria, viruses, rickettsiae, spirochaetes, protozoans and helminths. The insects transmit these pathogens primarily in three ways (Chamberlain and Sudia (1961): mechanical transmission, biological transmission, and myiasis.

1.The Mechanical Transmission :

It is of two types - indirect and direct.

1) Indirect Mechanical Transmission :

It is the exogenous infection carried out with the help of feet or body of an insect. It is indirect transmission, in that, . the insect acts merely as a passive agent, e.g., housefly.

The common housefly, Musca domestics visits infected human faeces or dirty places and picks up pathogenic microbes on their legs and other parts of body and subsequently contaminate human food- stuff. It spreads various dangerous diseases such as; typhoid by Salmonella typhi, summer diarrhoea and dysentery by Entoamoeba and cholera by a bacterium Vibrio cholerae transmission.

il) Direct Mechanical Transmission :

It is the endogenous contamination made due to direct way in which the insect picks up the germs from an infected animal and directly inoculate them into the blood of a host animal : e.g., common eye fly, cyclorrhaphan, Siphunculina funicola is responsible for spreading conjunctivitis (viral infection) from man to man. Other eyeflies are Hippelates, Chlorichaeta tuberculoso etc..

2. The Biological Transmission :

The Insect plays a part in the life of the pathogenic organism. It may be of three types; (I) propagative, (H) cyclopropagative and (iii) cyclodevelopmental.

1) Propagative Transmission :

The pathogen undergoes no cyclic changes but simply multiplies inside the body of insect as in an artificial culture tube. Most of the bacterial and viral multiplication occurs in the same way e.g., Bubonic plague. The Bacillus pesos germs are swallowed by a flea during feeding the blood from an infected rat They multiply in a sort of filtering chamber of the gut and then they are transmitted to a man in the nod biting.