Biology Public health importance Surveillance Control Prevention Health education

Rodents

Rat and mouse are rodents. The common species of commensal rodent in Hong Kong are:

  1. Rattus norvegicus (Rn), sewer rat; also known as norway rat.
  2. Rattus rattus (R2), house rat; also known as roof rat.
  3. Mus musculus (Mm), mouse.

Special Features about Rodents

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:

Some of the common rodent-borne diseases are:

Rodent Prevention and Control

Rodent Survey Purposes:

  1. Find out the rodent species, estimated rodent population, rodent harbourages, food attraction for the rodent and activity range of the rodent.
  2. 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).

Rat-flea Index = No. of rat collected from the rat examined
Total no. of rat examined

Please click here for the latest information on rat-flea index

It has been reported from World Health Organization (WHO) that a Rat-flea Index of greater than 1 represents an increased potential 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 disinfestation operation in places with Rat-flea Index greater than 1.

Rodent Infestation Survey

Since 2000, FEHD has been conducting the Rodent Infestation Survey (RIS) regularly by setting baits in designated survey locations to monitor rodent infestation.  The ratio of the baits gnawed by rodents to the number of baits collected from the survey location generates the Rodent Infestation Rate (RIR).  When RIRs for all survey locations under a particular district are available, the District RIR could be compiled.  When RIRs of all survey locations are available, the Overall RIR could be compiled.  The RIS adopts a scientific and objective method in assessing the extensiveness of rodent infestation in the survey location.  Based on the RIR and its trend, the RIS can gauge the general situation of rodent infestation in individual survey locations and form the basis for devising anti-rodent measures.  The results also serve as reference for assessing the overall efficacy of rodent prevention and disinfestation work. 

The surveys are conducted in rodent-infested areas or places which are likely to have rodent problems, in particular areas bustling with human activities.   The survey in each survey location is conducted every six months.

Rodent Infestation Rate = Number of baits gnawed by rodents in that survey location X 100%
Number of baits collected from a particular survey location
District Rodent Infestation Rate = Total number of baits gnawed by rodents in all survey locations of that district X 100%
Total number of baits collected from all survey locations of a particular district
Overall Rodent Infestation Rate = Total number of baits gnawed by rodents from all survey locations of all districts X 100%
Total number of baits collected from all survey locations of all districts

At present, there are a total of 50 survey locations in 19 districts.  The survey in each survey location lasts for three days.  During the survey period, the Department will place around 50 census baits (a piece of uncooked sweet potato) within each survey location.  Baits are set at a distance of about 50 m apart to avoid the same rodent from gnawing on two different baits (average activity range of a rodent is less than 50 m).  Daily checking and replacement of baits will be performed.  On the third day, all the baits will be removed, and the number of baits gnawed by rodents will be counted against the number of baits collected from the survey location to derive the RIR.

A census bait (a piece of uncooked sweet potato)
A census bait (a piece of uncooked sweet potato)

A census bait with gnawing marks (indicated by the arrows)
A census bait with gnawing marks (indicated by the arrows)

The department has, over time, tried out different methods.  Having regard to a number of factors including our local climate, environmental conditions and the habits of rodents, the department has come to the conclusion that adopting the ratio of baits gnawed by rodents as the infestation rate is the most suitable method for Hong Kong.  FEHD has been using uncooked sweet potato as bait because it is generally attractive to rodents and clear gnawing marks could be identified once rodents bit on it.

The RIR is divided into three levels.  Details of each level and follow-up action to be taken are summarised in the table below.

Range of Rodent Infestation Rate Level of Rodent Infestation Action(s) to be Taken
0% to < 10% Level 1
(Rodent infestation is not extensive during the survey period)
Targeted anti-rodent operations will be arranged mainly at locations where rodent activities are detected
10% to < 20% Level 2
(Rodent infestation is slightly extensive during the survey period)
Block / Area Control covering the activity areas of an entire rodent population will be conducted
≥ 20% Level 3
(Rodent infestation is extensive during the survey period and rodent colonies may have been formed)
An Inter-departmental working group will be set up to co-ordinate anti-rodent operations at district level, including strengthening cleansing services, assisting relevant departments in carrying out anti-rodent work in areas under their purview and promoting rodent prevention and control in the community

Once the RIR results are available, respective District Environmental Hygiene Offices (DEHOs) and other relevant government departments will be notified for the specific follow-up actions.

For survey locations with more serious rodent infestations, the FEHD has strengthened follow-up actions, implemented mitigation measures for a month to strengthen rodent prevention and control work at the relevant locations, and conducted a new round of Rodent Infestation Survey at these locations afterwards to closely monitor the rodent infestation and evaluate the effectiveness of the mitigation measures.   

FEHD adopts an integrated approach in monitoring rodent infestation.  Apart from making reference to the RIR, the frontline staff of FEHD will also conduct on-site rodent assessment to evaluate the degree of rodent infestation during regular inspections.  Targeted rodent prevention and control actions will also be implemented taking into account complaints and views from the local community and residents.  Moreover, management of housing estates, hospitals, schools, construction sites and other venues or properties are advised to take specific measures to monitor and contain rodent problems in their own properties once rodent infestation is detected.

To ensure the accuracy of survey results, members of the public are advised not to disturb the census baits.

warning notice
A warning notice (the white label) is displayed during the survey to remind members of the public not to disturb the census bait.

Rodent Infestation Rates for the 50 survey location in 2021 are provided below:

District Survey location First half of
2021
Second half of
2021
Overall of
2021
Hong Kong Island
Central / Western Wellington Street [Map] 0.0% 1.7% 0.8%
Queen's Road Central (Sheung Wan) [Map] 0.0% 1.6%

0.8%

Third Street [Map] 3.2% 6.6% 4.9%
District RIR 1.1% 3.3% 2.2%
Eastern Sheung On Street and Fung Yip Street [Map] 4.3% 4.5% 4.4%
King's Road (North Point) [Map] 9.4%
(3.9%)#
6.0% 7.8%
Tsat Tsz Mui Road [Map] 0.0% 0.0% 0.0%
District RIR 4.8% 3.6% 4.2%
Southern Lee Hing Street [Map] 2.9% 9.1% 6.0%
Wah Fu Road [Map] 0.0% 0.0% 0.0%
Aberdeen Praya Road (Aberdeen and Tin Wan) [Map] 0.0% 3.8% 1.9%
District RIR 0.7% 3.5% 2.1%
Wan Chai Lockhart Road (Wan Chai) [Map] 5.6% 5.5% 5.5%
District RIR 5.6% 5.5% 5.5%
Islands
Islands San Hing Street (Cheung Chau) [Map] 0.0% -- --
Yu Tung Road [Map] 0.0% 0.0% 0.0%
District RIR 0.0% -- --
Kowloon
Kowloon City Ma Tau Wai Road [Map] 3.6% -- --
Nga Tsin Wai Road (Kowloon City) [Map] 0.0% 4.3% 2.1%
Muk Chui Street [Map] 0.0% 4.7% 2.3%
District RIR 1.4% -- --
Kwun Tong Yee On Street and Shui Wo Street [Map] 0.0% 0.0% 0.0%
Hoi Yuen Road and Hung To Road [Map] 0.0% -- --
Lei Yue Mun Road (Yau Tong) [Map] 0.0% 0.0% 0.0%
District RIR 0.0% -- --
Mong Kok Nathan Road (Mong Kok) [Map] 1.7% -- --
Prince Edward Road West (Prince Edward) [Map] 5.1% -- --
District RIR 3.4% -- --
Sham Shui Po Shun Ning Road [Map] 11.1%
(7.0%)#
-- --
Kwong Lee Road [Map] 0.0% -- --
Pei Ho Street [Map] 9.8%
(4.8%)#
-- --
District RIR 7.3% -- --
Wong Tai Sin Clear Water Bay Road (Choi Hung) [Map] 3.3% 1.7% 2.5%
Po Kong Village Road (Wong Tai Sin) [Map] 0.0% 4.7% 2.3%
Tai Yau Street [Map] 2.0% 18.0%
(14.0%) #

9.9%

District RIR 1.9% 7.9% 4.9%
Yau Tsim Nathan Road (Tsim Sha Tsui) [Map] 18.2%
(3.6%)#
7.0% 12.5%
Shanghai Street [Map] 5.7% -- --
District RIR 12.0% -- --
New Territories (East)
North On Kui Street [Map] 0.0% 1.9% 0.9%
San Hong Street [Map] 3.6% 5.8% 4.7%
Pak Wo Road (Sheung Shui) [Map] 0.0% -- --
District RIR 1.2% -- --
Sai Kung Po Ning Road [Map] 1.9% 1.8% 1.8%
Po Tung Road [Map] 1.8% -- --
Po Lam Road North [Map] 1.9% -- --
District RIR 1.8% -- --
Shatin Hang Hong Street [Map] 1.8% 0.0% 0.9%
Sha Kok Street [Map] 0.0% -- --
Wo Che Street [Map] 1.8% -- --
District RIR 1.2% -- --
Tai Po Kwong Fuk Road [Map] 3.5% -- --
On Po Road [Map] 5.6% -- --
District RIR 4.5% -- --
New Territories (West)
Tsuen Wan Chung On Street and Sha Tsui Road [Map] 1.9% -- --
Chai Wan Kok Street [Map] 6.7% -- --
District RIR 4.1% -- --
Tuen Mun Tip King Road [Map] 0.0% -- --
Pui To Road (Tuen Mun Industrial Area) [Map] 4.9% -- --
Tsing Tin Road and Ming Kum Road [Map] 5.1% -- --
District RIR 3.4% -- --
Yuen Long Castle Peak Road - Yuen Long [Map] 3.4% -- --
Tin Shui Road [Map] 0.0% -- --
Hung Yuen Road [Map] 2.5% -- --
District RIR 1.9% -- --
Kwai Tsing Tsing King Road and Tam Kon Shan Road [Map] 4.1% -- --
Tai Wo Hau Road [Map] 0.0% -- --
Cheung Wing Road and Wo Yi Hop Road [Map] 1.6% -- --
District RIR 1.9% -- --
Overall RIR 2.8% -- --

Starting from the second half of 2020, for survey locations with RIRs of 8% or above, FEHD will, after implementation of improvement measures in rodent infestation, conduct a second survey (the reassessment) to assess the effectiveness of remedial control measures.  Figures of the reassessment are in brackets.

RIR (by type of locations) First half of 2021 Second half of 2021 Overall of 2021
Rear lanes/public places 3.6%
[details]
Industrial Area 2.7%
[details]
Residential Area 1.5%
[details]
Recreational Area 2.0%
[details]

Rodent Control and Prevention

  1. Direct disinfestations
    • Use poisonous bait or traps
    • Temporary effect
      1. 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
      2. Traps
        • Cage trap
        • Snap trap/break back trap

    (Note: Sticky traps such as glue trap and glue pad will make the captured live rodents struggle and startle, causing them to discharge urine and faeces due to excessive fright. The excrement of rodents may contain pathogens such as bacteria and viruses, increasing the risks of the public and pest control operators contracting rodent-borne diseases. Trapped rodents will also suffer from unnecessary pain when they struggle to escape. Therefore, FEHD does not use and does not recommend the use of sticky traps for rodent control.)

  2. Fundamental control

    Improve the sanitary condition of the environment and deprive rodents of :

    • Food
    • Harbourage
    • Passages

Purposes of rodent prevention

Disposal of dead rodents

The following procedures can be used for handling dead rodents found:

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

Photo of Norway rat
Rattus norvegicus, body length (head to tail) 34-46cm, body weight 150-600g

Photo of Roof rat
Rattus rattus, body length (head to tail) 35-46cm, body weight 80-300g

Photo of mice
Mus musculus, body length (head to tail) 12-21cm, body weight 10-21g

Photo of rat flea
Xenopsylla cheopis (Rat Flea), about 2-4mm long

Photo of rat flea
Ctenocephalides felis, about 2-4mm long

R. sanguineus
R. sanguineus, a tick, is a rodent-borne disease vector for the transmission of Boutonneuse fever

L. deliense
L. deliense, a mite, is a rodent-borne disease vector for the transmission of scrub typhus