Saturday, September 8, 2012




The term “pest” refers broadly to any organism that is troublesome, noxious or destructive. Pest includes a variety of birds species, mites, ticks, nematodes, ants, swaps, bees locust, termites, plant and animal pathogens and parasite, nuisance wild animals (e.g. venomous snakes and Elephants) Rats and Mice, snails, cattle, weeds etc.
For the purpose of this lecture our concentration will be on the Pest widely known as Rat because of it strategic significance in pest and vector control and the Public Health importance.

Rats are various medium-sized, long-tailed rodents of the superfamily Muroidea. “True rats” are members of the genus Rattus, the most important of which to humans are the black rat, Rattus rattus, and brown rat, Rattus norvegicus. Many members of other rodent genera and families are also referred to as rats, and share many characteristics with true rats.

Rats are typically distinguished from mice by their size; rats are generally large muroid rodents, while mice are generally small muroid rodents. The muroid family is very large and complex, and the common terms rat and mouse are not taxonomically specific. Generally, when someone discovers a large muroid, its common name includes the term rat. While if it is small, the name includes the term mouse. Scientifically the terms are not confined to members of the Rattus and Mus genera, for example, the pack rat and cotton mouse.

The best-known rat species are the black rat (Rattus rattus) and the brown rat (Rattus norvegicus). The group is generally known as the Old World rats or true rats, and originated in Asia. Rats are bigger than most Old World mice, which are their relatives, but seldom weigh over 500 grams (1.1 lb) in the wild.

The term “rat” is also used in the names of other small mammals which are not true rats. Examples include the North American pack rats, a number of species loosely called kangaroo rats, and others. Rats such as the bandicoot pat (Bandicota bengalensis) are murine rodents related to true rats, but are not members of the genus Rattus. Male rats are called bucks unmated females are called does, pregnant or parent females are called dams, and infants are called kittens or pups. A group of rats is either referred to as a pack or a mischief.

The common species are opportunistic survivors and often live with and near humans; therefore, they are known as commensals. They may cause substantial food losses, especially in developing countries. However, the widely distributed and problematic commensal species of rats are a minority in this diverse genus. Many species of rats are island endemics and some have become endangered due to habitat loss or competition with the brown, black or Polynesian rat.

Rats are either terrestrial or arboreal in nature, although rats preferring one habitat are capable of inhabiting others. The Norway rat and roof rat are the two most common North American rat species. They are terrestrial and arboreal, respectively.
Norway rats are most commonly burrowers. They build their nests outside the walls of homes or in various clumps of vegetation. Norway rats may also construct their homes beneath the edges of sidewalks or patios.
As is implied by their name, roof rats prefer arboreal habitats. They live in yucca, palm and cypress trees, as well as in elevated areas of human homes. Roof rats can be found living in attics, rafters, eaves and on roofs. They may also choose to nest in non-arboreal vegetation, such as shrubs, honeysuckle and tall grasses.

Wild rodents, including rats, can carry many different zoonotic pathogens, such as Leptospira, Toxoplasma gondii, and Campylobacter. The Black Death is traditionally believed to have been caused by the micro-organism Yersinia pestis, carried by the tropical rat flea (Xenopsylla cheopis) which preyed on black rats living in European cities during the epidemic outbreaks of the Middle Ages; these rats were used as transpdort hosts. Other zoonotic diseases linked to pest rodents include classical swine fever and foot-and-mouth disease.
The multimammate rats transmits Lassa fever, a fatal disease that has caused several epidemic episodes in some parts of the country.
The average lifespan of any give rat depends on which species is being discussed, but many only live about a year due to predation.

Specially bred rats have been kept as pets at least since the late 19th century. Pet rats are typically variants of the species brown rat, but black rats and giant pouched rats are also known to be kept. Pet rats behave differently from their wild counterparts depending on how many generations they have been kept as pets. Pet rats do not pose any more of a health risk than pets such as cats or dogs. Tamed rats are generally friendly and can be taught to perform selected behaviours.

Subjects for scientific research
A laboratory rat strain, known as a Zucker rat, is bred to be genetically prone to diabetes, the same metabolic disorder found among humans.
In 1895, Clark University in Worcester, Massachusetts (United State) established a population of domestic albino brown rats to study the effects of diet and for other physiological studies. Over the years rates have been used in many experimental studies, which have added to our understanding of genetics, diseases, the effects of drugs, and other topics that have provided a great benefit for the health and well-being of humankind. Laboratory rats have also proved valuable in psychological studies of learning and other mental processes (Barnett, 2002), as well as to understand group behavior and overcrowding (with the work of John B. Calhoun on behavioral sink). A 2007 study found rats to possess metacognition, a mental ability previously only documented in humans and some primates.

Domestic rats differ from wild rats in many ways. They are calmer and less likely to bite; they can tolerate greater crowding; they breed earlier and produce more offspring; and their brains, livers, kidneys, adrenal glands, and hearts are smaller (Barnett 2002).

Brown rats are often used as model organisms for scientific research. Since the publication of the rate genome sequence, and other advances, such as the creation of a rat SNP chip and the production of knockout rats, the laboratory rat has become a useful genetic tool, although not as popular as mice. When it comes to conducting tests related to intelligence, learning, and drug abuse, rats are a popular choice due to their high intelligence, ingenuity, aggressiveness and adaptability. Their psychology, in many ways, seems to be similar to humans. Entirely new breeds or “lines” of brown rats, such as the Wistar rat, have been bred for use in laboratories. Much of the genome of Rattus norvegicus has been sequence.

Derattisation is one of the various methods of disinfestations. Derattisation can simply be described as every controlled measures taken or adopted in the elimination extermination or control of rats in an environment where they are not wanted or desired. There are various methods involved in derattisation and the use or adoption of any is based on:
(i) Purpose (ii) Types of rat (iii) level of infestation (iv) Habitat.

(a) Chemical Control: - This involves the use of Chemicals known as Rodenticides (Rat Poison) in exterminating rats. Rodenticides can either be “single feed baits or Anti coagulants” they are poison that have been developed specifically to kill rats and mice. They consist of first generation poisons such as Brodifacoum, Bromadiolome and Difenacoum.
Rodenticides are a category of pest control chemicals intended to kill rodents.
Single feed baits are chemicals sufficiently dangerous that the first dose is sufficient to kill.

The use of rodenticide baits for the control of rats is the only method by which most amateurs can be reasonably certain of eliminating a colony quickly and completely. With rats around, you should put aside any negative feelings you might have about using poisons for the sake of achieving swift and complete control. (The only exception to this advice is where rats are living inside your home, when a poisoned rat dying under the floor in the wall can produce a vile smell) In this case break back traps should be used as a first method of control.
Rodents are difficult to kill with poisons because their feeding habits reflect their place as scavengers. They will eat a small bit of something and wait, and if they don’t get sick, they continue. An effective rodenticide must be tasteless and odorless in lethal concentrations, and have a delayed effect.

Anticoagulants are defined as chronic (death occurs after one to two weeks after ingestion of the lethal dose, rarely sooner), single-dose (second generation) or multiple-dose (first generation) rodenticides, acting by effective blocking of the vitamin K cycle, resulting in inability to produce essential blood-clothing factors – mainly coagulation factors II (prothrombin), VII (reconverting).
In addition to this specific metabolic disruption, massive toxic doses of 4-hydroxycoumarin and indandione anticoagulants cause damage to tiny blood vessels (capillaries), increasing their permeability, causing diffuse internal bleeding (haemorrhagia). These effects are gradual, developing over several days, but claims that they are painless are unfounded: in humans both warfarin poisoning and hemophilia commonly cause moderate to severe pain from bleeding into muscles and joints. In the final phase of the intoxication, the exhausted rodent collapses in hypovolemic circulatory shock or severe anemia and dies calmly. However, because of the duration of discomfort and pain before death it has been suggested that the use of rodenticides can be considered as inhumane.

The main benefit of anticoagulants over other poisons is that the time taken for the poison to induce death means that the rats do not associate the damage with their feeding habits.
• First generation rodenticidal anticoagulants generally have shorter elimination half-lives, require higher concentrations (usually between 0.005% and 0.1%) and consecutive intake over days in order to accumulate the lethal dose, and less toxic than second generation agents.

• Second generation agents are far more toxic than first generation. They are generally applied in lower concentrations in baits – usually on the order of 0.001% to 0.005% - are lethal after a single ingestion of bait and are also effective against strains of rodents that became resistant to first generation anticoagulants; thus, the second generation anticoagulants are sometimes referred to as “superwarfains”.

Class Examples
* First generation: warfarin, coumatetraly Coumarings/4- Hydroxycoumar * Second generation: difenacoum, brodufacouM flocoumafen and bronmadiolone diphacinone, chlorophacinone, pindone

1,3-indandiones These are harder to group by generation. According to some sources, the indandiones are considered second generation. However, according to the U.S. Environmental Protection Agency, examples of first generation agents include chlorophacinone and diphacinone.

Other Difethialone is considered a second generation anticoagulant rodenticide.

Metal phosphides have been used as a means of killing rodents and are considered single-dose fast acting rodenticides (death occurs commonly within 1-3 days after bait ingestion). A bait consisting of food and a phosphide (usually zinc phosphide) is left where the rodents can eat it. The acid in the digestive system of the rodent reacts with the phosphide to generate the toxic phosphine gas. This method of vermin control has possible use in places where rodents are resistant to some of the anticoagulants, so that sometimes, in the case of large infestation by rodents, their population is initially reduced by copious amount of zinc phosphide feeding on anticoagulant bait. Inversely, the individual rodents, that survived anticoagulant bait poisoning (rest population) can be eradicated by pre-baiting them with nontoxic bait for a week or two (this is important to overcome bait shyness, and to get rodents used to feeding in specific areas by specific food, especially in eradicating rats) and subsequently applying poisoned bait of the same sort as used for pre-baiting until all consumption of the bait ceases (usually within 2-4 days). These methods of alternating rodenticides with different modes of action gives actual or almost 100% eradications of the rodent population in the ara, if the acceptance/palatability of baits are good (i.e. rodents feed on it readily).

Zinc phosphide is typically added to redent bait in a concentration of 0.75% to 2.0.0% to 2.0%. the baits have strong pungent garlic-like odor characteristic for phosphine liberated by hydrolysis. The odor attracts (or, at least, does not repulse) rodents, but has repulsive effect on other mammals. Birds, notably wild turkeys are not sensitive to the smell, and will feed on the bait, and thus become collateral damage.
The tablets or pellets (usually aluminium, calcium or magnesium phosphide for fumigation/gassing) may also contain other chemicals which evolve ammonia, which helps to reduce the potential for spontaneous ignition or explosion of the phosphine gas.

Phosphides do not accumulate in the tissues of poisoned animals so the risk of secondary poisoning is low.
Phosphides are rather fast – acting rat poisons, resulting in the rats dying usually in open areas, instead of in the affected buildings.
Phosphides used as rodenticides are:
• aluminium phosphide (fumigant only)
• calcium phosphide (fumigant only)
• magnesium phosphide (fumigant only)

• zinc phosphide (in baits)
Other Chemical poisons include:
• ANTU (a-naphthylthiourea; specific against Brown rat, Rattus norvegicus
• Arsenic
• Barium (a toxic metal) compound
Barium carbonate
• Bromethalin (which affects the nervous system, no antidote
• Chloralose (narcotic acting condensation product of chloral and glucose)
• Crimidine (2-chloro-N, N,6-trimethypyrimidin-4-amine; a synthetic convulsant poison, antivitamin B6)
• 1,3-Difluoro-2-propanol (“Gliftor” in the former USSR)
• Endrin (organochlorine cyclodiene insecticide, used in the past for extermination of voles in fields during winter by aircraft spraying)

• Fluoroacetamide (“1081”)
• Phosacetim (a delayed-action organoophosphorous rodenticide)
• White phosphorus
• Pyrinuron (an urea derivative)
• Scilliroside
• Sodium fluoroacetate(“1080)
• Strychnine
• Tetramethylenedisulfotetramine (“tetramine”)
• Thallium (a toxic heavy metal) compounds
• Zyklon B (hydrogen cyanide absorbed in an inert carrier)

These are poisons that have been developed specifically to kill rats and mice. They consist of ‘first generation’ poisons such as Warfarin and Coumatetraly and ‘second generation’ poisons such as Brodifacoum, Bromadiolone and Difenacoum.

Most of our rodenticides contain either Bromadiolone or Difenacoum, which are anti-coagulants.
These poisons affect the rodents blood clotting response, so after a few days the rodents will die as a result of internal hemorrhaging. The poison effectively thins the blood to the extent that blood seeps internally from tiny blood vessels and organs quickly resulting in heart failure which ultimately kills the rat.

You may know someone who takes minute amounts of prescription warfarin (a first generation rodenticide) in order to thin their blood to help prevent strokes. Strokes
are caused by thick blood clotting and stopping the flow of blood to vital areas like the brain. Often people under this medication can bruise very easily and this is because the tiny blood veins next to their skin break easily when damaged and blood seeps from the veins causing the bruising. These people are completely unaware of this process in their bodies in exactly the same way as the rodent is completely unaware of the process in action.
The rodents feel fine, suffering no pain and therefore they continue to feed as normal, consuming a lethal dose before succumbing to the effects of the poison. This is important, as rats in particular will quickly stop eating anything that they associate with danger, in the latter stages of poisoning, the rodents feel lethargic and tend to stay in their nests, where most of them die. The occasional one may die above ground, and you should always search for bodies whilst you are conducting a poisoning campaign.

Bait stations are a highly effective way of swiftly dealing with mice in buildings or in the home. Bait should always be placed within approved bait stations and difenacoum is the bait of choice. However, if you prefer not to use rodenticides, mice-unlike rats-are very easy to trap and trapping is generally our preferred method of control.

Break back rat traps are similar in appearance to normal break back mouse traps, but much more powerful. They are cheap to buy and easy to set.
Rats are notoriously difficult to trap. It is most unlikely that even a professional will manage to trap all the rats in a colony because, apart from being very cautious of new objects in their territory, they also learn very quickly from other rat’s experiences. So, if see a rat being caught in a trap, the older rats in particular tend to avoid similar situations and quickly become ‘trap shy’.
Leave the traps unset but baited for a couple of days before you activate the traps. You should quickly catch two or three, but after that things will get difficulty.

Mice are inquisitive creatures and will quickly check out any new objects in their territory. They don’t seem to learn from the experiences of their chums so they are amongst the easiest of all creatures to trap. The key is to use lots of traps, two in a single kitchen cupboard, four under the sink, ten in loft, those sorts of numbers. Bait the traps with a little peanut butter and you are off. Check them twice a day and don’t be surprised if you catch a lot of mice, there are probably many more than you at first think.

Spring traps like the Mark 4 Fenn trap can be quite effective when set correctly. They are much more powerful than the break back traps and must be handled with great care. Always remember to flip on the safety catch until you have the trap in the right position and then flip off the catch with a long stick or similar. By law these traps may only be used when covered by a tunnel to prevent access by cats and other animals. They are usually set with the treadle plate flush to the ground and then camouflaged with a small amount of soil. They should be secured to the ground by their chain.

Everyone seems to be selling these sticky glue traps but the is rarely any justification for using this inhumane method of control. Have a look at our video vault to see a rat being caught in a glue trap. The glue boards do cause the animal considerable stress and suffering.
Electronic traps do work, and kill rats. However, they are expensive and they will only ever take out the occasional bold rat. They won’t kill any more than cage or break-back traps and they require expensive batteries to run them.

This is the way to catch rats in electronic kill traps.
• Don’t expect these units to deal with an entire colony because they won’t do so any more than any other live or kill trap will succeed.
• For an occasional intruder they work OK.
• Set the trap pretty much anywhere that the rat frequents. Bait it with peanut butter stuck to the back wall of the trap. Don’t switch the trap on until the rat has started to take the peanut butter. Next evening switch the trap on.
• The next day you should have your rat, and you can be sure it will not have suffered for long, a couple of minutes at the most.
• I would still rather use a break back trap (cheaper and quicker to kill).
Rats are extremely cautions of traps of any kind; they just seem to know when danger is around.
You may catch a few rats with cages, provided you follow this guide but I can pretty much guarantee that you will not catch the whole colony.
- Use several cage traps unless you are just dealing with one or two invaders.
- Place the traps in position, open, unset, but baited and leave for several days until rats are feeding confidently from inside the cages.

Set all the traps one evening.
Next day you should have a rat or two.
- Continue to bait and set the traps, but if no success start again leaving the traps open but baited.
- Be patient, this exercise can take several weeks, by which time you could have safely and humanely eliminated the whole colony by using poison baits.
If you chose to use cage traps, I assume that is because you don’t want to kill the rat but would rather release it into the fields.
When you release the rat, make sure that it is several miles away because the moment it is out of the cage is only intention it’s to get back home – and it will soon work out in which direction home is.

On its way back home it will almost certainly die from stress, starvation or it will become a meal for some predator just looking for a little lost creature. It will not be allowed to join any other rat colonies; rather it will be viciously driven from each rat territory it crosses on its way home.

Catch and release is the least humane and most ineffectual option for controlling a small colony of rats, and is utterly useless with a large colony.
Mice, on the other hand are most obliging and will readily go into any sort of live capture trap. Bait it with a bit of peanut butter, check twice a day and just keep trapping and removing.

The same applies to catch and release mice at to rats above. It is not humane, but if it makes you feel better, well at least it will be providing some predator out there with an easy meal, so you can feel good about that.
Make sure you release a mile or so from home or you will just keep on catching the same mice as they wearily arrive home.
Check your traps twice a day don’t forget them and leave the occupants to die of starvation.

Control of rats in our premises can be effected environmentally. This involves the control of all factors that may encourage the breeding or propagation of rats and mice in our environment.

Such factors include:-
- Maintaining a very clean environment devoid of overgrown weeds
- Proper stacking/storage of food items in our environment
- Grating of entrance doors with metals to discourage gnawing for entrance by rats.
- Proper disposal of our domestic refuse
- All holes/hollows/channels/drainages within our environment should be properly constructed to discourage burrowing by rats or mice.
- Indiscriminate stacking of unserviceable articles/junks in our environment should be discouraged.
- Screening of our windows to disallow rat entrance etc.

This in recent times have not proved to be very effective in our living environment. The method involves the use of Predators (e.g. cats) who feed on rats to exterminate them. It is now a common occurrence that rats and cats are co-habitors of living premises.

Extermination or control of rat is inevitable particularly when their natural habitat is being threatened day in and out due to infrastructural developments. There is hardly a premises without raes particularly in the cities where ‘Rats’ are now being seen diurnally as against their nocturnal nature.
This poses a challenge to the Environmental Health Practitioners who are professional in pest and Vector Control.


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2. Meerburg BG, Singleton GR, Kijlstra A (2009). “Rodent-borne disease and their risks for public health”.
3. Merk Veterinary Manual Global Zoonoses Table” Retrieved 2006-11-24.
4. Rats Capable Of Reflecting On Mental Processes
5. Gibbs RA et al: Genome sequence of the Brown Norway rat yields insights into mammalian evolution,: Nature. 2004 April 1; 428(6982):475-6
6. “Individual differences and a spatial learning factor in two strains of mice (Mus musculus)’
7. “Novelty-Seeking in Outbred Mice Covaries with General Learning Abilities Irrespective of Stress Reactivity, Emotionality and Physical Attributes”
8. “Domain-Specific and Domain-General Learning Factors are Expressed in Genetically Heterogeneous CD-1 mice”
9. National Environmental Sanitation Policy & guidelines developed by the
Federal Ministry of Environment, Abuja.