range of movement: 30-50m
for rats, 5-10 m for mice
good swimmer
can dive
rat takes 15-30 gm food
and consumes about 30 gm water daily,
mouse takes only 3 gm
of food and small amount of water everyday.
5-8 litters per year,
5-14 per litter
average life span is
1 year
Public
Health Importance and Rodent-borne Diseases
Rodents are carriers
of viral, rickettsial and bacterial diseases.
The causative agents could enter our body
by four different ways:
through the ectoparasites
of rat like fleas, ticks and mites
by food or water contaminated
by rodent excreta
through direct contact
with rodent excreta
by rat bite
Some
of the common rodent-borne diseases are:
plague
a disease of
rodents caused by the bacterium,
Yersinia pestis
rat
fleas feeding on a bacteria-infected
rodent would transmit the disease
to the next host (rat or human)
through biting
Urban typhus
a rickettsial
disease transmitted by rat fleas
flea faeces
are rubbed or scratched into the
wound or abraded skin
also possible
by the inhalation of dust or ingestion
of food contaminated with flea
excreta
Spotted fever
a rickettsial
disease transmitted by rickettsia-infected
ticks feeding
on human through biting
larvae feed
on rodents; adults feed on dog
as their host
Scrub typhus
a rickettsial
disease transmitted by rickettsia-infected
mites feeding
on human through biting
transmitted
by mites amongst rodents in scrubby
areas
accidental
infections in man: campers, hikers
Personal Preventive
Measures for Scrub Typhus While
Hiking/Camping
Wear long
trousers and clothes with
long sleeves
Avoid resting
in scrubby area or on grasses
Apply insect
repellents to exposed skin
surfaces
Do not
leave clothes in scrubby area
or on grasses
Hantaan disease
a disease of
rodents caused by Hantaan virus
transmitted
by air-borne droplets and faecal
particles of infected rodent under
poor ventilation
Rat-bite fever
a disease of
rodent caused by bacteria
usually transmitted
to human through rat biting
Rodent
Prevention and Control
Rodent Survey Purposes:
a) Find out
the rodent species, estimated rodent population,
rodent harbourages, food attraction for
the rodent and activity range of the rodent.
b) Assist
in planning of rodent disinfestation operation
and long-term rodent prevention measures.
Rodents provide
the essential link in the spread of rodent-borne
diseases which are of public health importance.
Our Department has carried out study on
rat flea and rodent infestation survey to
monitor the situation of flea and rodent
infestation in 18 districts.
Rat Flea Survey
The number
of rat flea collected from the rat examined
per each rat examined gives Rat-flea Index
(Number of rat flea collected from the rat
examined/Total number of rat examined =
Rat-flea Index).
It has been
reported from World Health Organization
(WHO) that a Rat-flea Index of greater than
1 represents a potentially dangerous situation
with respect to increased plague risk for
human. Although Hong Kong does not have
human plague transmission since the middle
of 1920s, our Department would carry out
flea and rodent infestation operation in
places with Rat-flea Index greater than
1.
Rodent Infestation Survey
To monitor rodent infestation, our department has since 2000 conducted yearly Rodent Infestation Rate (RIR) surveys throughout the territory by setting baits in selected areas. The ratio of the baits bitten will indicate the RIR. The surveys adopt a scientific and objective method in assessing the degree of rodent infestation in the selected areas.
Rodent Infestation Rate =
No.
of bait consumed by rodent
X 100%
Total no. of bait collected from the specific area
When the RIR of a district is higher than 10 per cent, our department will strengthen rodent disinfestation operations there. For a district with an RIR reaching 20 per cent or higher, the relevant Government departments will form a joint task force and launch a special rodent control operation to strengthen rodent disinfestations, environmental improvement and cleansing services comprehensively, and to promote rodent control in the community.
The district RIR which reflects the rodent problem of a district changes with the environmental and sanitary conditions as well as the level of active participation of the community in rodent control.
Participation of all parties concerned is the key to success in sustaining effective rodent control.
Rodent Control
and Prevention
(1) Direct
disinfestations
Use poisonous bait
or traps
Temporary effect
(a) Stomach
poison
Mix rodenticide with
bait for rodent consumption
The rodenticides used
by our department are chronic anti-coagulants
(vitamin K as the anti-dote)
The anti-coagulants
take 4-5 days to give effects
(b) Traps
Cage trap
Snap trap/break back
trap
(2) Fundamental
control
Improve the
sanitary condition of the environment and
deprive rodents of :
Food
Harbourage
Passages
Purposes
of rodent prevention
Eliminate harbourages
for rodents and confine the rodent activity
area for enhancing the rodent disinfestations
work
Prevent re-infestation
of rodent
Disposal of dead rodents
The following procedures can be used for handling dead rodents found:
using tools such as tongs to put the dead rodents into a tough plastic bag (e.g. rubbish bag);
spraying the carcasses with general household disinfectant or diluted bleaching solution until they are soaked thoroughly;
sealing the bag tightly and placed it into another plastic bag. The second plastic bag should also be sealed;
putting the bagged material properly in covered rubbish bin or disposing of it to the nearest refuse collection point.
When handling dead rodents, attention should be paid to personal and environmental hygiene. Wear gloves and face mask, if necessary, when handling dead rodents and avoid direct contact with them. All areas, clothes and items contaminated by the dead rodents should be disinfected thoroughly using general household disinfectant or diluted bleaching solution. Before taking off gloves, wash them with water and then cleanse with general household disinfectant or diluted bleaching solution. Hands should be washed thoroughly with soap and water after removing the gloves.
Figure
X. cheopis,
a flea, is a rodent-borne disease vector for
the transmission of plague
R. sanguineus,
a tick, is a rodent-borne disease vector for
the transmission of Boutonneuse fever
L. deliense,
a mite, is a rodent-borne disease vector for
the transmission of scrub typhus
Last revision date: 02-04-2009