Dealing with Rodents
A number of rodents are of public health significance. During my professional career, I have been involved in the identification, trapping, testing and controlling Norway rats, roof rats, house mice and deer mice. The following three activities have importance:
Norway Rats That Would Not Die
Norway rat.
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In 1970, the Boise City-Ada County Health Department failed to reduce a Norway rat (Rattus norvegicus) population on a farm west of Boise, Idaho, after a six-week control program using the anticoagulant warfarin. Considering that the failure to kill the rats may have been due to warfarin resistance, tests were conducted with albino laboratory rats, urban rats and a rural rat population from a farm near the above-mentioned farm. Utilizing bait containing 0.025 percent warfarin, the rats were allowed free choice of lab chow or poisoned bait and the amounts consumed were measured.
Test results revealed that the laboratory, urban, and most of the rural rats died within the expected time limits for non-resistant rats (consuming less than 50mg warfarin/kg body weight within 10 days of free feeding). Two of the rural rats, however, survived for more than 50 days after consuming more than 265mg warfarin/kg body weight. These rats met the definition of warfarin resistance. |
Trapped Norway rat to be tested.
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Concurrently, similar investigations were being conducted in North Carolina and warfarin resistance was found there also. These two investigation were the first reports of warfarin resistance in North America. Subsequently, additional tests throughout the countries found more resistant rats. As a result, improved rat baits were produced for rodent control programs. For more information, the following references are recommended:
- Brothers, DR. 1972. A case of anticoagulant rodenticide resistance in an Idaho Norway rat (Rattus norvegicus) population. Calif. Vector Views. 19(6):41-44.
- Brooks, JE and AM Bowerman. 1975. Anticoagulant resistance in rodents in the United States and Europe. J. Env. Health. 36(6):537-541.
High Wire Roof Rat Control
Roof rats.
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From 1966 to 1971, annual roof rat (Rattus rattus) complaints in Santa Clara County, California, increased five-fold to more than 1,000, whereas Norway rat (Rattus norvegicus) complaints decreased. An analysis of roof rat complaints revealed that more than 13 percent reported rats traversing utility pole telephone cables and wires. An investigation was initiated to determine if a control program would work at that level of activity.
Twenty-nine residential blocks (containing 146 utility poles) were baited with 0.005 percent diphacin (an anticoagulant rodenticide) at the telephone cable level. |
Installing a rat bait station on a utility pole.
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For the most part, roof rat activity could be found on all telephone cables if the residential block had an infestation at all. Of significance was the increased rat activity on poles with vegetation around them at the cable level and in close proximity to fruit and nut trees. Portable bait stations with diphacin bait blocks were placed on the utility poles above the cable clamp. Of the total poles baited, 65.8 percent had bait consumption and a substantial kill was suspected as a result of dead rats found and a significant reduction in bait consumption thereafter. The procedure appeared to be an effective means of roof rat reduction and has the potential of long range effectiveness.
References:
References:
- Brothers, DR. 1972. An innovation in roof rat control. Proceedings of the Fifth Vertebrate Pest Conference:161-167.
- Ecke, DH, MT Vinatieri and JJ Krug. 1975. Advances in Roof Rat Control in Santa Clara County, California. Bul Soc of Vect Ecol 2:6-12.
Hantavirus in Idaho
Deer mouse.
The first case of hantavirus pulmonary syndrome (HPS) reported in the United States was in May 1993 in the Four Corners area of the southwest. With the primary vector being the deer mouse (Peromyscus maniculatus) which has a large distribution in the United States, federal and state health agencies immediately considered the potential risk of the disease nationally. For 1993, there were 48 cases with 27 fatalities (56 present). Of these, Idaho had one case and it was fatal. Having the one human case and since 15 percent of the deer mice collected in the area were also positive for hantavirus, a trapping and testing campaign was initiated. Positive identification of the rodents tested was necessary. Since trappers and laboratory personnel were not familiar with rodent identification, an identification key and training were provided. The following reference and identification key are provided:
Brothers, DR. 1994. Pictorial key for the identification of Idaho mice and rats and similar rodents: for laboratory personnel and other public health workers. IDHW. 3 pp.
Brothers, DR. 1994. Pictorial key for the identification of Idaho mice and rats and similar rodents: for laboratory personnel and other public health workers. IDHW. 3 pp.
