Disease causing organisms

Some Insects are injurious to man as vectors of human diseases.Through the ages millions of people have died of diseases transmitted by insects.There are a number of insect borne diseases,and they may be transmitted in different ways.


House flies are cosmopolitan in distribution.They are closely associated with humans and thrive best where people are careless in the disposal of wastes.Adult flies are non parasitic.They feed on all kinds of decaying and decomposing matter.It is an important mechanical vector in the transmission of diseases like typhoid, dysentery and cholera.The housefly cause diseases through food contaminations.

House fly control is normally done in three different ways, namely sanitary, mechanical and chemical methods.Populations of house flies can be controlled by proper disposal of manure, garbage,sewage,food waste,human excreta and other organic materials.Mechanical practices such as screening, using of traps or sticky paper or baits can be valuable in excluding houseflies.Insecticides may be used against larvae.Spraying with 2% malathion,1% chlordane or lindane,0.5% tremephos are effective.

Sand flies

These flies are 4 mm long.Only the female possess piercing sucking mouth parts and are haematophagous.The males are non parasitic, feeding on moisture.They are small slender insects with hairy bodies.Through biting this fly transmits the disease called kala-azar.During the day time the flies remain hiding.At night they come out to feed.The sand fly attacks during night times.The insect sucks the parasite from an infected person,along with blood.Inside the body of the fly,the parasite undergoes changes.When an affected fly bites man,the parasites pass into the blood and fresh infection is effected.The parasites mostly concentrate in the capillaries of spleen,liver and bone marrow.The disease is characterized by the symptoms like anaemia and emaciation.

Spraying of 5% DDT/BHC easily kills the flies.The pyrethrum ointment used on exposed part of the body works as a repellent.

⭐Rat fleas

Both male and female fleas take in the bacillus pasteurella pestis from infected rats during feeding.This rat flea is responsible for the transmission of plague from man to man,or from rat to man.When this bacterium is introduced into the skin,the lymph glands become inflamed.This is known as bubonic plague.When the rat flea sucks the blood of man or a rat infected with plague,the bacilli enter into its stomach and grow there into larger numbers.The flea thus heavily laden with the bacilli,may bite a healthy man and introduce the bacilli into the wound and cause infection.The bacilli are deposited by the flea on the skin along with the faeces.The bite of the flea causes scratchings and the bacilli are introduced into the blood when the skin is scratched.

Destruction of rats and other rodents is an effective method.Dusting of 1 to 2% chlordane,or 2% Y-BHC is very much effective in the elimination of fleas on the body of pet animals.Application of 5% DDT is recommended for spraying at the time of the spread of plague in all areas.

⭐The human louse

Louse is a blood sucking ectoparasite of man.It is cosmopolitan in distribution.The human louse is a major vector for three important human diseases,relapsing fever,typhus and trench fever.Wearing clean clothes,and having regular bath avoids infestation.

⭐ Mosquitoes

Mosquitoes are cosmopolitan in distribution.They are nocturnal in habit and are found in abundance in damp,marshy lands near stagnant water.Only female mosquitoes are adapted to suck the blood of human beings and function as carrier of viral,protozoan and nematode diseases.

When the infected mosquito bites another person,the larvae penetrate the superficial skin to find their way into the lymphatic vessels,and attain sexual maturity.In severe infection the adults cause blocking of lymphatic system which results in the enlargement of legs,arms,scrotum,and mammary glands.Another type of mosquito transmits yellow fever through a virus.

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