The rains bring in a host of problems every year, including water-borne and pest-borne diseases. Here it is important to make a distinction between the two terms because most people confuse the two and use either loosely when talking about monsoon illnesses.
This article will focus on pests which cause pest-borne diseases, with a particular significance for public health during the monsoons.
Why the monsoons?
The summer months are usually marked by hot and dry conditions, which are not ideal for the survival of most disease-causing organisms. In addition, conditions are not favourable for host insects, which also need water (e.g. mosquitoes) and damp decomposing organic matter (e.g. flies), for propagation.
The rains bring down the temperature and create wet & humid conditions, creating an ideal ground for pests and diseases. Given the general unhygienic surroundings we live in, it is then no surprise that we find ourselves staring down the barrel of one epidemic or the other.
Flies
Flies thrive in moist places where there are garbage and faeces. They are active in daylight or in artificial light and rest at night on walls, fences, wires or other objects. The high humidity and abundance of moist, decomposing organic matter and garbage provide flies with perfect breeding grounds, in which fly larvae complete their development, explaining their large number seen buzzing around during the rains.
Common and filth flies are attracted by the smell of fermenting, rotting material or faeces and feed primarily on liquids or moisture from these. Dry food is dissolved by a secretion from the salivary glands and by regurgitating. They also seek food on moist skin surfaces such as the mouth, eyes, sores and wounds. Flesh flies breed by laying their eggs on decomposing flesh, which the larvae eat.
Flies spread various infectious diseases such as cholera, shigellosis, typhoid, salmonellosis, diarrhoea and dysentery by contaminating food. They also transmit parasitic worms which cause skin infections.
Flies can contaminate food just by sitting on it and they will sit as easily on both filth and human food; disease causing organisms and germs stuck to parts of their body (mouth, legs, body hairs) thus find their way into our stomachs. Flies also have a particularly disgusting habit when they land on our food; they regurgitate or vomit onto to it. This vomitus contains strong enzymes which break down the food into an easily digestible soup which the flies then suck up. Speaking of table manners, flies have another ace; they defecate while eating, yet another way of spreading contamination.
Fly Prevention Tips
- Ensure garbage is collected and disposed off in time
- Collect garbage in containers and these should have tight fitting lids
- Clean out and dry garbage containers regularly
- Doors closers should work properly and gaps around doors and windows should be sealed
- Broken glass and damaged insect screens in doors and windows should be replaced
- Identify and screen all vents & openings which could serve as fly entry points
- Fly breeding in surrounding areas should be prevented by eliminating garbage and organic debris
- Night illumination should shine onto buildings rather than from buildings
- Switch from mercury vapour to sodium vapour lamps
- Install adequate number of insect light traps and ensure they are five feet or below from ground level
- Check if air curtains, where installed, are fully functional
- Check if puddles form around the building after rain; these are to be eliminated
- Ensure drains are cleaned regularly and free from solid wastes
- Engage a professional pest management company for fly management in and around your (commercial) building.
Mosquitoes
Mosquito belongs to the fly family, with the mouth-parts modified into a piercing-sucking organ called the proboscis. Only the female of the species bites as she needs the blood-meal to complete development of her eggs. The males do not bite but live on plant nectar instead.
This biting behaviour is responsible for the spread of different diseases; when a mosquito bites an infected person, the protozoan, virus or bacteria travels to the mosquito’s body and this cycle is completed when the mosquito bites a healthy person, transmitting the disease.
Some major species of mosquitoes found in and around human habitation and their common breeding sites are:
Anopheles Spp. or the Malaria Mosquito breeds in stagnant collections of clean water such as ponds, lakes, overhead reservoirs, underground tanks, etc., in urban and rural areas. This mosquito is active after dusk and aptly called the ‘midnight-biter’.
Culex Spp. breeds prolifically in stagnant collections of polluted water such as drains, cess pools, gutters, septic tanks, etc., in urban surroundings. It is the common house mosquito and a major nuisance after dusk, biting heavily and causing sleepless nights.
Aedes Spp. the Yellow Fever or Asian Tiger Mosquito breeds in man-made collections of stagnant water such as water coolers, pots, old tyres, cans, empty bottles, flower vases, etc., in urban areas. This variety is a day biter causing a characteristic itchy red lump over the bitten area.
Armigeres Spp. a large mosquito and a vicious evening biter. It is not a major transmitter of any human disease, but its bite is very irritating and scratching the bitten area can lead to secondary infections. A day biter, with peak period of dawn and dusk, it attack a person in large numbers and even follows him if he moves away. A. subalbatus breeds profusely in septic tanks, entering through the vent pipes and laying eggs inside. Thanks to unplanned development and ill-constructed buildings, it has become a major nuisance pest in urban and rural areas.
While there is medical therapy for Malaria and Chikungunya, there is no known cure for Dengue. In the past few years, these diseases have been reported from many states in India and grabbed major headlines on TV and Newspapers.
Every responsible citizen should contribute in containing these diseases by simple measures that prevent breeding and multiplication of mosquitoes. These mosquitoes breed in clean stagnant water present in overhead tanks, discarded plastic containers, empty cans, old tyres, mud-pots, trays below refrigerators and in air-conditioning units, water coolers, flower vases, drain trays below potted plants, overhead tanks, empty coconut shells and open cisterns where rainwater may collect. Eggs laid are attached to wet surfaces of the container and can survive without water, hatching after a long dry spell. The best way to prevent breeding of mosquitoes is by keeping our surroundings free of discarded containers that could become a potential breeding site.
Other mosquito control measures such as anti-larval treatment and fogging against adult mosquitoes are also useful, but will have to be carried out by the Municipal Corporation or professional pest management companies.
Some Tips for combating mosquitoes
- Changing water every week in flower vases and drain trays of potted plants
- Covering overhead tank to prevent access to mosquitoes
- Preventing indoor or outdoor water stagnation even in smallest of containers
- Using mosquito nets at home
- Preventing mosquito entry by keeping doors closed and windows screened
- Using mosquito repellent on skin during day and night at mosquito infested sites
- Not storing water in open containers & covering all water containers with lids
- Scrubbing and cleaning margins of containers used for water,
- Ensuring regular cleaning of water tanks
- Storing old drums or barrels inverted to prevent water accumulation
- Ensure wearing of full sleeved and long legged clothes for protection against mosquito bites, especially at dusk.
Rodents
The Indian Mole-Rat is the most important pest in both urban and rural areas in India. It is one of the most destructive pests to crops and cultivation; in addition to consuming or spoiling stored produce, it a very active burrower and is responsible for much structural damage to storage buildings as well. It is a very good swimmer, able to live in deep water rice fields, where it can cause much damage to the crop.
Burrows are usually made in paddy field embankments or “bunds” and also in areas where crops like tubers, vegetables, coconut and young rubber are cultivated. It is an aggressive animal and erects its long guard hairs scattered over the back, emitting harsh pig-like grunts when disturbed.
The Bandicoot Rat is a truly giant rat. The dark, greyish-brown adult grows to 30-40cms with an equally long tail. It looks similar to the Mole-Rat, but is much larger, weighing as much as 1.4kg! It is found in fields but usually occupies the outskirts of human dwellings such as compounds and gardens, commonly found rummaging near garbage bins. Its burrowing habits cause great damage to grounds, flooring and pavements as it can also tunnel through brick and masonry.
The characteristic large burrow gives away its presence. It is a totally non-fussy eater, equally comfortable feeding on household refuse, grain & vegetables and is a very serious pest in poultry farms. This large, aggressive animal erects guard hairs on its back and emits pig-like grunts when disturbed. If caged with others, it is likely to fight to death within a few hours.
Bandicoot Rats act as carriers of several human and animal diseases such as Bubonic Plague, Murine typhus, Weil’s Disease, Leptospirosis, Salmonellosis and Rat-bite Fever (Leishmaniasis). Compounded by ignorance and low levels of civic hygiene, the recent outbreaks of the rat-borne diseases: Plague (Surat, 1996) and Leptospirosis (Mumbai, 2003-04), highlight the seriousness of the rat menace in today’s modern cities.
Rodent management tips
- Ensure garbage is collected and disposed in time
- Collect garbage in containers and these should have tight fitting lids
- Clean out and dry garbage containers regularly
- Doors closers should work properly and gaps around doors and windows should be sealed
- A proper rodent management programme should be in place; contact a reputed pest management company for the same.
As we can see, the control of pest-borne diseases is directly linked to control and management of the pest itself. Thus, large-scale public health pest control programmes are imperative and given the financial, manpower & other constraints of local municipal authorities, individuals themselves need to contribute by adhering to the basic tenets of hygiene and cleanliness. We cannot control the vagaries of nature, but we can enjoy the rains, through some basic hygiene & prevention tips and proper pest management programmes provided by reputed pest managers, to ensure pest-free and disease-free localities during the monsoon.
The author is a Pest Management professional, involved in the industry in various capacities for more than a decade