Rodents

Rodents

A rodent is an animal having powerful teeth used for probing, such as a rat or a mouse. Since they frequently coexist with humans in the environment, rats and mice have an exponential population growth rate. Rodents coexist closely with humans. They not only damage buildings, consume and contaminate food and other commodities and cause economic loss, but they also serve as a source or reservoir for some contagious diseases like the plague and typhus fever. Eliminating rodents is therefore crucial for environmental health measures.

Types of Rodents

Rodents may be classified into two distinct groups:

• Domestic Rodents.
• Wild Rodents.

Domestic Rodents:

Domestic rodents are those that coexist closely with humans. Black rat (Rattus rattus), Norway rat (Rattus norvegicus), and house mouse, for example (mus musculus). The range of motion for Rattus rattus, a domestic animal, is often constrained. It is a major issue for public health. The rattus rattus is a good climber as well, and it usually infests the roofs of houses, though it will occasionally burrow. On the other hand, Rattus norvegicus is a semi-domestic animal that frequents drains, sewers, and homes.

Wild Rodents:

There are many species of wild rodents. The commonly found wild rodents are Tatera indica, Bandicota bengalensis varius (Gunomys kok), B.indica, Millardia meltada, M.gleadowi & mus booduga. Tatra indica has been found to be the natural reservoir of plaque.

Rodents & Disease

A number of diseases are associated with rodents are:

• Bacterial: Plague, tularaemia, salmonellosis
• Viral: Lassa fever, hemorrhagic fever, encephalitis
• Rickettsial: Scrub typhus, murine typhus, rickettsial pox.
• Parasitic: hymenolepsis diminuata, Leishmaniasis, amoebiasis, trichinosis
• Others: rat bite fever, leptospirosis, histoplasmosis, ring worm etc.

The mode of transmission may be directly hrough rat bite (eg. rat fever), some through ontamination of food or water (e.g. almonellosis, leptospirosis) & some through rat eas (e.g. plague & typhus).

Control of Rodents

The effective measures should be adopted to remove the rodent population from the human environment. For control of rodents some anti rodents' measures have to be done, they are as follows:

• Trapping
• Rat poisons or rodenticides
• Fumigation
• Improvement of sanitation
• Chemosterilants

Trapping:

It is a simple & ancient method of capturing rats. But it causes temporary reduction in the number of commensal rodents. The traps are usually attracted with indigenous foods of the locality. The captured rats must be destroyed which may be done by drowning them in water. Rats by nature are suspicious animals & will soon become 'trap- wise' & avoid baited traps. Trapping therefore should be considered supplementary to other methods of rodent control. To make this method effective, it must be done on community basis.

Rat Poisons or Rodenticides:

There are main two types of rodenticides as single dose (acute) & multiple doses (cumulative). The single dose is more effective & lethal over another. An expert committee of the WHO grouped the 'acute rodenticides' as follows:

• Those requiring ordinary care:
  • Red squill.
  • zinc phosphide.
  • Nor bromide.
• Those requiring maximal precaution:
  • Sodium fluorocetate.
  • Strychnine.
• Too dangerous for use:
  • Arsenic trioxide.
  • Phosphorus.
  • Thallium sulphate.
  • ANTU.
  • Gophacide.
  • Fluoroacetamide.
• The commonly used rodenticides are
  • Barium carbonate.
  • Zinc phosphide.

Barium Carbonate:

This is a white tasteless powder, & is very cheap. It is mixed with wheat or rice flour in the ratio of 1 part to 4 parts of flour. The mixed material is moistened with water & made into small round marbles. The poisoned baits are placed near the rat burrows & in dark, secluded places. On eating the pills, rats are killed in 2-24 hours. Barium carbonate is weak rodenticides of uneven performance, & probably easily detected by rats in many baits. In the opinion of many workers in view of the availability of more efficient rodenticides, barium carbonate should not be used any more.

Zinc Phosphide:

Zinc phosphide is efficient rodenticides. When moist, the O chemical slowly gives off phosphine whose garlic odour is nauseating to man & domestic animals, but seems to have no adverse effect on rats. It is used in the ratio of 1 part to 10 parts of wheat or rice flour & mixed with a few drops of edible oil in order to attractive to rats. Rats are killed in about three hours. The use of rubber gloves is recommended in handling zinc phosphide as it is highly poisonous

Fumigation:

It is an effective method of destroying both rats & rat fleas. The used fumigants are calcium cyanide (often called cynogas), calcium disulphide, methyl bromide; sulphur dioxide etc. cynogas is commonly used for the fumigation of burrows. This chemical is prepared in powder from & is pumped into rat burrows by a special foot pump called the 'cynogas pump.' About 2 ounces of the poison is pumped into each rat burrow after closing the exit openings & then the burrow is promptly sealed with wet mud. The chemical on contact with moisture gives off hydrogen cyanide gas which kills both rat & fleas. Trained personnels are required to carryout fumigation.

Improvement of Sanitation:

Sound environmental sanitation is the most effective weapon in deratization campaign. Rats require three things: food, water & shelter. If these are denied, rats will naturally decrease in density. The environmental sanitation includes following measures:

• Proper storage, collection & disposal of garbage
• Elimination of rat burrows by blocking them with concrete

Chemosterilants:

t is a chemical that can cause temporary or permanent sterility in either sex or both sexes. Rodent chemosterilants are still in the experimental stage. Sanitation is therefore essential to the permanent control of rats & mice, & all measures should be regarded as supplementary to sanitation.

• Construction of rat proof buildings
• Proper storage of food stuffs