Introduction
Rodents and Public Health
Rodents and Mice in Natural Disasters
Management and Control of Rodent Populations
Recommendations
Prevention of Diseases Transmitted by Rodents
Rodent Control
Introduction
Rodents are mammals of the order Rodentia, with
rats and mice belonging to the suborder Myomorpha. Members of the Muridae
family are the dominant species in every region of the world, due to
their ability to adapt to and exploit new situations. Commensal rats
and mice, that is those that live at the expense of humans, invade their
dwellings, eat their food, upset their comfort, and frequently transmit
diseases to them, belong to this family. Three species of commensal
rodents are the most widely distributed: the Norwegian rat, Rattus
norvegicus; the roof rat, Rattus rattus; and the common mouse,
Mus musculus.
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Rodents and Public Health
Rats and mice (commensal and wild) have significance
for public health chiefly due to their role as carriers or reservoirs
for infections and diseases that can be transmitted to humans (zoonoses).
The diseases present in the Americas include: the plague (Yersinia
pestis), salmonellosis (S. typhimurium; S. enteritidis);
leptospirosis (L. icterohaemorragiae); murine typhus (Rickettsia
typhi); rickettsialpox (R. akari); lymphocytic choriomeningitis
(arenavirus); rat-bite fever (Spirilum minus, Streptobacillus
monilifomis); Hantavirus hemorrhagic pulmonary syndrome; hemorrhagic
fevers (Arenavirus); Venezuelan equine encephalitis (alphavirus); Powassan
encephalitis (Flavivirus); rabies; Rocky Mountain spotted fever (R.
rickettsii); and tularemia (Francisella tularensis),
as well as parasitisms, such as trichinosis (Trichinella spiralis);
eosinophilic meningitis (Angiostrongylius cantonensis); and taeniasis
(Hymenolepis nana or H. diminuta).
The transmission of these infections to humans occurs
by indirect contact. Some are transmitted through contact with infected
rodent urine or feces, others through fleas and lice, and still others
through mosquito bites.
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Rodents and Mice in Natural Disasters
When natural disasters strike, rats and mice endure
the same suffering as humans do. Many of them are crushed to death or
drowned, die of starvation, or fall prey to infections. Their populations
are frequently decimated. Moreover, there is often displacement among
the survivors, who wander to new areas in search of protection, shelter,
and food. Fearful and disorganized, it takes time for them to regroup
and reorganize their social behavior, become familiar with their new
environment, find safe havens, locate food and water, and memorize their
movements. All this occurs before they reproduce again. Reproductive
activity among wild rodents and commensal rats usually declines during
the rainy season.
Colony building and reproduction only will begin when
their new ecosystem has stabilized. Thus, the reestablishment of a rodent
population after a disaster will take six to ten months under favorable
conditions.
The infections carried by the new populations can be transmitted to
people when the conditions favor contact with contaminated rodent urine
or feces or with their ectoparasites, vectors of the infections. This
contact also occurs between various species of commensal and wild rodents,
permitting transmission and cases of emerging or heretofore unknown
infections in new geographical areas.
In conclusion, during the emergency the spread infection
by rodents will not be an immediate concern. However, the activity and
growth of rodent populations should be monitored as part of the surveillance
of these diseases.
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MANAGEMENT AND CONTROL OF RODENT POPULATIONS
Decisions on rodent control after a natural disaster
should be analyzed within an epidemiological and economic context, and
steps to eliminate rodents should not be taken impulsively and haphazardly
with the mass application of rodenticides. This measure takes time and
money and exposes other animals (domestic animals) and people to an
additional risk, which may be the chemical or biological components
of the product. The indiscriminate elimination of rodents poses a greater
risk, since the ectoparasites of these species, the vectors of the infections
they carry, immediately seek out other hosts--among them humans-and
transmit the infections to them. This is what happens with the plague
and rickettsiosis.
Moreover, the disease vectors for people are not necessarily
rodents. For example, the last leptospirosis outbreaks occurred in Peru
and Ecuador during El Niño; in Nicaragua, after Hurricane Mitch, where
the leptospire involved was L. canicola, whose principal reservoir
is the dog; and in Belize, where the predominant leptospire was L.
harjo, for which cattle are the principal reservoir. Consequently,
the mass application of rodenticides would not be an appropriate measure.
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What to Do:
- Keep an up-to-date epidemiological map of the geographical area,
indicating the areas where infections have been detected where rodents
are the reservoir.
- Identify the areas most vulnerable to access by rodents and contact
with people--in particular, shelters, food storage sites, garbage
dumps, and abandoned buildings.
- Determine the presence of fleas, lice, and other vectors for their
immediate control.
- Search for indications of the growth of rodent populations: burrows,
droppings, tracks and pawprints, gnawed food and materials.
- Monitor the health status of rat populations in specific areas.
The capture and study of specimens should be the responsibility of
specialized personnel.
- Control the rodent population. (Described below)
PREVENTION OF DISEASES TRANSMITTED BY RODENTS
- Community participation in both rural and urban areas is fundamental
for the prevention of infections carried by rodents. A number of measures
are recommended.
- Protect food from rodents. Insofar as possible, use containers
(metal boxes, clay or ceramic pots with lids, silos). Large volumes
of food or sacks should be placed on wooden benches in an orderly
fashion to facilitate inspection of the sacks.
- Proper refuse and waste disposal. All materials that serve as
a refuge for rodents--for example, cardboard boxes, idle machinery,
wooden or brick troughs--should be removed from dwellings.
- In areas where leptospirosis has been detected, shoes must be
worn. Keep people from bathing in stagnant water.
- General hygiene and sanitation. Dark, humid rooms and areas
are undesirable; ensure that they receive adequate ventilation
and light.
- Application of pesticides for fleas and lice.
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Rodent Control
Rodent control activities should consider the epidemiological
implications, ecology, and dynamic population of the rodents. When selecting
the control methods, safety as well as public health and environment
protection will be taken into account.
- Environmental sanitation. This is the best way to keep rodents out
of housing and the neighborhood. It involves cleanliness, the proper
storage and handling of food products, the proper disposal of organic
products, and the elimination of everything that can serve as a refuge
for rodents.
- Traps. These are used in situations where the use of rodenticides
is undesirable or poses a risk. Traps are also used for scientific
purposes or for the surveillance of disease and can be of the spring
type or cages for the capture of live specimens. Traps are of little
use in controlling major rodent infestations.
- Rodenticides. Rodenticides are rodent poisons. Toxic gases, as well
as chemical and biological products, are available on the market.
Rodenticides are not a solution in themselves. They should be accompanied
by changes that permit an improvement in environmental sanitation.
The application of rodenticides of any type should
be carried out by specialized personnel and only when there is a recognized
risk of a rodent population explosion
The application of rodenticides of any type should be carried out
by specialized personnel and only when there is a recognized risk
of a rodent population explosion and the risk of zoonosis transmission
from rodents to people and domestic animals in rural or densely populated
urban areas. In any case, the following is recommended:
- Conduct an analysis of the risks mentioned above. Identify the
predominant species of rodent (habits and behaviors differ; thus,
the control measures can differ);
- Conduct a situational diagnosis. Insofar as possible, use traps
to determine thedegree of infestation. Identify the localities where
the infestation is greatest;
- Select the bait and determine where it is to be placed;
- Decide on the safety measures and inform the community;
- Conduct an evaluation two or three months later to determine the
effectiveness of the measure.
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