Sand flies are of great importance as the transmitters of various kinds of leishmaniasis, of a filtrable virus disease called three-day fever or more commonly sand-fly or papatasi fever and of Oroya fever. These are blood sucking flies and they belong to the genus Phlebotomus. These are small, moth like flies, rarely over 5 mm long. Their bodies and wings are black and hairy.
The legs are long and the wings are held roof-like over the abdomen during rest. The antennae are long, consisting of 16 segments which often have a beaded appearance and they are thickly covered with hairs. They live in moist dark place and lay eggs in sandy soil so they are called sandflies.
Several species of Sandflies are recognised. These are P. papatasii, P. minutus, P. argentipes, P. orientalis, P. sergenti, P. nogouchi etc. Among these species—P. papatasii is found in North India, P. argentipes in Assam and West Bengal, and P. minutus in other states of India (Fig. 15.13).
Method of Transmission:
Sand flies act as the transmitters of various types of diseases, such as Leishmaniasis, Sand-fly fever, Oroya fever, Carrions disease etc.
Leishmaniasis:
Kala-azar, also known as Dum-dum fever, is a serious oriental disease of man. It is found in India, China, Mediterranean countries and parts of Africa and South America. Its causative agent is a pathogenic flagellate, known as Leishmania donovani which is transmitted by the bite of small blood sucking sandflies called Phlebotomus argentipes (Fig. 15.16). The transmission of this pathogen (L. donovani) from man to man is carried out by a certain species of Sand-fly.
The species concerned are as follows:
Indian vector:
P. argentipes; Chinese vectors: P. chinensis, and P. sergenti; Mediterranean vectors: P. perniciosus (Italy and Sicily); Turkestan vector: P. caucasicus; Tropical American vector: P. intermedius; Sudanese vector: P. orientalis; East African vector: P. martini, Russian vector: P. arpaklensis. The symptoms of kala-azar include swelling, high fever, and enlargement of spleen and liver. It is followed by general weakness, emaciation, anaemia and a peculiar darkening of the skin.
Sand-fly fever:
It is a mild virus disease and in many respects this Sand-fly fever resembles dengue. It comes on suddenly with fever, headache, pain in the eyes, stiffness of neck and back and rheumatic pain and is often followed by a prolonged period of malaise and depression.
It was experimentally shown by Doerr (1908) to be transmitted by P. papatasii. The insects become infective about 6 or 7 days after feeding on a patient in the first or second day of the fever. Since Sandflies are so short lived and frequently suck blood only once and since the disease appears as soon as the adults emerge in May in Mediterranean area, evidently being passed the winter in the larvae, transovarial transmission had long been suspected.
Since only man is known to be susceptible, transovarial transmission seems necessary for survival of the virus from one season to another. Thus P. papatasii is the only known transmitter throughout the definite range of the disease.
Oroya fever or Carrions disease:
It is an acute febrile disease caused by a very minute organism, Bartonella bacilliformis. P. nogouchi is a Sand-fly which is found in South America. This Sand-fly acts as a vector of this pathogen which is responsible for Carrions disease.
Both the sexes of this Sand-fly suck blood of man and domesticated animals. The acute stage of the disease is characterised by high fever, severe anaemia, aches and albuminuria and is often fatal. In chronic cases it is followed by an eruption of nodules called verruga peruviana.
Control:
The methods applied for mosquito control can be applied to control Sandflies.
