Fleas are small wingless insects, 2-3 mm long, with highly sclerotised, laterally compressed bodies and reddish-brown colour. Antennae short, stout, pectinate or clubbed and concealed in a groove. Mouth parts are modified for piercing and sucking. Legs adapted for clinging with curved claws. Hind leg longer, modified for jumping.
Body bears backwardly directed spines that help them to move through the hairs of the hosts. Male abdomen is directed upwards at the apex and flat. Apical part of abdomen possesses a coiled cirrus organ which is the copulatory organ of the male. Female abdomen is directed straight backwards and carries a small pouch-like structure called spermatheca which stores sperms after copulating with the male.
LIFE CYCLE: Fleas breed in dark and secluded places with high moisture contents, such as dusty floors, under carpets, rat burrows, granaries, chicken houses and godowns. Female lays 300-400 eggs in lifetime and the incubation period is 2-3 days (maximum 12 days). Larvae yellowish-brown, caterpillar-like, 13-segmented, hairy and move about actively, feeding on decaying organic matter and on faeces of the adult fleas. Larva is about 4 mm long and does not have eyes, antennae and legs but has long bristles on the body, which also help it in locomotion. There are 3 instars and larval period ranges between 7 and 10 days.
Pupation takes place in a very tough, dull whitish cocoon that is concealed in dust particles. Pupal period is 7 days. Pupa may hibernate for up to one year. Total life cycle is completed in about 20 days under favourable conditions. After emergence adults hop on to the passing rats or other hosts and start sucking blood. They suck more blood than necessary and a lot of undigested blood passes along with faeces that form food for the larvae. An adult can jump up to 8 inches high and 13 inches in length. Longevity of the adult is about 2 years and it can resist starvation up to 6 months.
SPECIES OF FLEAS
There are about 200 species of fleas in India but few common species are given below.
Fleas transmit plague that is caused by the safety pin bacillus called Yersinia pestis or Pasturella pestis. The disease is caused in man as well as in rats and produces three types of symptoms in man.
1. Bubonic plague. The bacillus infects lymphatic system, causing swelling and pain in the lymph glands but no fever occurs. Rats also suffer from similar symptoms.
2. Septicemic plague. Infection spreads to the blood vascular system causing fever. There is headache and pain in the back. Sudden chilliness, blood-shot eyes, rapid pulse, thick speech and high fever are other symptoms. In the case of prolonged illness spleen enlarges and becomes brick-red in colour and liver is also enlarged. Comma and death can occur due to heart failure in about a week.
3. Pneumonic plague. In this case bacillus multiplies in the lungs and pleural cavity, causing pneumonia-like symptoms. Yellowish fluid fills the lungs and pleural cavity, causing excessive coughing and heavy breathing. Infection can spread directly from man to man through droplets release during coughing. This is the most dangerous type of plague as it spreads very fast by droplet infection, particularly in high population density areas and brings about quick deaths.
Mode of infection
When a flea sucks blood from a plague-infected rat, it gets bacillus into the crop along with the blood meal. The bacilli get attached to the spines of proventriculus and form mucilaginous colonies there, multiplying very fast, blocking the passage of blood into the intestine. Such fleas are called blocked fleas that always remain hungry as the blood does not pass into the intestine. Hence they keep biting and sucking blood repeatedly but regurgitating it in the same wound as the stomach is already full of blood and bacilli. In doing so, they keep transmitting bacilli from their stomach to the new hosts. Blocked fleas can survive up to 40 days and transmit disease continuously.
This is another disease transmitted by Xenopsylla cheopis. It is a mild typhoid fever caused by the PPLO, Rickettsia mooseri. The causative organism multiplies in the gut of flea and is excreted through faeces. Man gets infected either by contamination of wounds by the flea faeces or by inhalation of dust containing faeces.
Some fleas act as intermediate hosts for the tape worms like, Dipylidium caninum and Hymenolepis diminuta.
Control of fleas
Control of rats is an effective method of controlling fleas. Trapping, baiting and fumigation can eradicate rats. Cyanogas fumigation kills not only rats but also all stages of fleas in the rat burrows. Fumigation should be done every 2-3 months. Construction of rat proof godown having metalled doors and meshed windows is also an effective method to keep the rats away from human dwellings.
Dusting the houses, floors, godowns and other places frequented by rats should be done frequently using residual insecticides such as BHC, endosulfan, dieldrin, aldrin etc. This will kill all stages of fleas as they breed in dust and abandoned corners.
Patients suffering from plague can be treated with streptomycin injections or oral doses of antibiotics such as tetracycline, sulphadiazene, chloramphenicol, doxycycline, azithromycin etc. given two or three times in a day.