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 flea 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

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 at or 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. As the RIR of a district only assesses the rodent problem of the surveillance areas within the district couple of days when the census baits have been laid, the RIR do not reflect fully the actual situation of rodent infestation of the districts concerned. FEHD would also take into account the complaints and requests for services on rodent control made by the public in deploying the resources for carrying out the relevant work.

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
    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
      • the use of glue traps can scare rodent that are caught live and cause them to urinate. Since their urine may contain germs, this may increase the risk of being exposed to rodent-borne diseases
  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