Rapid insecticide resistance bioassays for three major urban insects in Taiwan.

BACKGROUND: Taiwan's warm and humid climate and dense population provide a suitable environment for the breeding of pests. The three major urban insects in Taiwan are house flies, cockroaches, and mosquitoes. In cases where a disease outbreak or high pest density necessitates chemical control, selecting the most effective insecticide is crucial. The resistance of pests to the selected environmental insecticide must be rapidly assessed to achieve effective chemical control and reduce environmental pollution. METHODS: In this study, we evaluated the resistance of various pests, namely, house flies (Musca domestica L.), cockroaches (Blattella germanica L. and Periplaneta americana), and mosquitoes (Aedes aegypti and Ae. albopictus) against 10 commonly used insecticides. Rapid insecticide resistance bioassays were performed using discriminating doses or concentrations of the active ingredients of insecticides. RESULTS: Five field strains of M. domestica (L.) are resistant to all 10 commonly used insecticides and exhibit cross- and multiple resistance to four types of pyrethroids and three types of organophosphates, propoxur, fipronil, and imidacloprid. None of the five field strains of P. americana are resistant to any of the tested insecticides, and only one strain of B. germanica (L.) is resistant to permethrin. One strain of Ae. albopictus is resistant to pirimiphos-methyl, whereas five strains of Ae. aegypti exhibit multiple resistance to pyrethroids, organophosphates, and other insecticides. CONCLUSIONS: In the event of a disease outbreak or high pest density, rapid insecticide resistance bioassays may be performed using discriminating doses or concentrations to achieve precise and effective chemical control, reduce environmental pollution, and increase control efficacy.

Effectiveness and acceptance of total release insecticidal aerosol cans as a control measure in reducing dengue vectors.

The effectiveness of regular application of insecticidal fogging in reducing dengue is questionable, since delays occur between peak time of outbreak and insecticide administrations. Moreover, many residents do not accept indoor application because of concern about insecticide contamination of household items. The study described in this article was designed to evaluate the effectiveness and acceptance of insecticidal aerosol cans to reduce dengue vectors inside and outside of homes. Residents in Kaohsiung City of South Taiwan were provided with two formulations of aerosol cans (permethrin 3.75% weight/weight [w/w] and cypermethrin 1.716% w/w) and were requested to use these aerosol cans. Although the indoor ovitrap index of the permethrin group returned to the original level in week 3, the index of the cypermethrin group decreased 60% to 20%. The residents accepted the insecticidal aerosol cans but complained of unfavorable effects caused by traditional insecticidal fogging. Results indicate that the insecticidal aerosol cans may serve as a supplementary household control measure for dengue vectors during the time period between the peak of outbreak and the administration of government-organized insecticide fogging.

Multidrug resistant bacteria isolated from cockroaches in long-term care facilities and nursing homes.

Residents in long-term care facilities and nursing homes have a relative higher risk for infections. The nocturnal and filthy habits of cockroaches may be ideal disseminators of pathogenic microorganisms in these institutions. This study was designed to determine the infestation and vector potential of cockroaches under this institutional environment. Cockroaches were collected from 69 long-term care facilities and nursing homes in Kaohsiung City. Risk factors related to cockroach infestation were determined by questionnaire survey. In addition, bacteria were isolated and identified from the alimentary tract and external surface of these insects. Antibiotic resistances of these microorganisms were then determined. Cockroach infestation was found in 45 (65.2%) institutions and 558 cockroaches (119 Periplaneta americana and 439 Blattella germanica) were collected. A significant association was found between cockroach infestation and indoor environmental sanitation. From 250 adult cockroaches, 38 species of gram-negative bacteria, 20 species of glucose non-fermenter bacilli and 6 species of gram-positive bacteria were isolated. Moreover, antibiotic resistances were found among the bacteria isolated. These findings indicate that cockroaches have the potential in transmitting pathogenic bacteria with multidrug resistances in long-term care facilities and nursing homes.

Seasonal abundance of vectors at outdoor environments in endemic and nonendemic districts of dengue in Kaohsiung, South Taiwan.

This study was designed to determine the seasonal variation in abundance of dengue vectors at open spaces, empty houses, parks, and markets in endemic and nonendemic districts of dengue. Ovitraps were placed in these sites from March 2003 to January 2004 in Kaohsiung Area (Kaohsiung City and Kaohsiung County), South Taiwan. The index peaked in May, June, and September in the endemic districts and in May and October in nonendemic districts. The egg production of the vectors increased from April on and peaked in September. Aedes albopictus had a significant higher proportion than A. aegypti throughout the study period and in both districts. Although ovitrap indices at open spaces, empty houses, and parks were significantly higher than those in nearby households, no significant difference was found between markets and households. Moreover, the outdoor ovitrap index was significantly higher than the indoor one. No significant difference was found between the endemic and nonendemic districts in egg production, vector maturation, vector abundance at the outdoor environments, or nearby households. These findings indicate the importance of the environmental conditions surrounding the human dwelling sites in the transmission of dengue. Measures applied to remove dengue vectors should include these sites but also outdoor environments as well.

Health problems among international travellers: from a subtropical region to tropical and non-tropical regions.

International travel may be associated with the risk of a wide range of infectious diseases. This study was designed to obtain information on the health problems among international travellers from a subtropical region to the neighbouring tropical, subtropical, and temperate regions. Health problems among international travellers from Taiwan to the Philippines, Malaysia, Indonesia, Singapore, Vietnam, Thailand (tropical group), Hong Kong, Macao, China and Japan (non-tropical group) were surveyed through the telephone. Of 649 travellers surveyed, 8.2% had one or more health problems and insect bite (3.4%) and coughing or sore throats (3.2%) were the most important symptoms. The rate of coughing or sore throats was significantly higher among those returned from the non-tropical regions. However, no associations were found between health problems and the demographic factors, travel style or travelling duration of travel.

Seaport as a source of hantavirus: a study on isolated isles.

Since small mammals from seaports have relative higher seroprevalences of hantavirus, this seroepidemiologic study was conducted on the isles in Kinmen and Lienchiang Counties along the coast of southern mainland China to determine whether seaport may play the role as a source of hantavirus. Among six species of small mammals trapped in Kinmen County, only male Mus musculus (6.7%) and Rattus losea (5.3%) were found to be positive. In Lienchiang County, five species of small mammals were trapped and positive findings were obtained only in male R. norvegicus (9.3%), male M. musculus (7.7%), and female R. losea (1.6%). There was no significant difference in the seroprevalence between the two counties (Kinmen 3.8% vs. Lienchiang 3.9%). The positive rate in Liaolo (17.9%) of Kinmen County was significantly higher than the remaining trapping stations and those in Matsu Distillery (10.3%) and Fushing (5.8%) of Lienchiang County were significantly higher than the remaining ones. Moreover, a significant inverse correlation was found between the seropositive rate and the distance of small mammal sampling sites to the seaport (p < 0.01). These findings suggest the role of seaport as a source of hantavirus.

Impact of a short-term community-based cleanliness campaign on the sources of dengue vectors: an entomological and human behavior study.

In June 2002, a considerable number of cases of dengue fever/dengue hemorrhage fever were reported in South Taiwan. To effectively reduce the sources of dengue vectors, the government conducted a weeklong community-based cleanliness campaign. The study reported here was designed to evaluate the effectiveness of the campaign. The sources of dengue vectors were evaluated according to changes in the ovitrap index. This index significantly decreased from 66.7 percent before the campaign to 39.3 percent three months later. Human knowledge and behavior were investigated by a survey questionnaire. Although the respondents had sufficient knowledge about dengue as well as its transmission and prevention, only 57.4 percent knew that the dengue vector breeds in clean water. After the campaign, this percentage significantly increased, to 88.4 percent, and the percentage of those properly handling artificial containers also significantly increased. On the basis of these findings, the authors conclude that short-term community-based cleanliness educational programs may change behavior to eliminate container habitats of the dengue vectors and in turn reduce the ovitrap index. This control strategy is a feasible alternative to rapidly reduce sources of dengue vector in urban areas, especially at the onset of a new epidemic.

The differences of dengue vectors and human behavior between families with and without members having dengue fever/dengue hemorrhagic fever.

Dengue vectors, human knowledge and behavior have been reported to play an important role in the transmission of dengue. This study was designed to understand the differences of dengue vectors and the behavior between families with (target group) and without (control group) members having dengue fever/dengue hemorrhagic fever. Population density of dengue vectors were determined by ovitrap index. The living conditions, knowledge, and behavior related to dengue were investigated by questionnaire survey. Long-term ovitrap indices obtained in the target group was significantly higher than those obtained in the control. Most of the respondents had sufficient knowledge about the transmission and prevention of dengue. However, only low percentages of the families frequently cleaned water-filled containers and ditches around their residence, especially in the target group. These findings indicate that higher indices of dengue vectors and dengue-related behavior are important in the transmission of indigenous dengue.

Insecticide resistance in German cockroaches (Blattella germanica) from hospitals and households in Taiwan.

Since a high percentage of cockroach infestation has been determined in hospitals in Kaohsiung, South Taiwan, insecticide resistances may have developed in the cockroach populations. To determine the resistances in cohorts of German cockroach (Blattella germanica) from hospitals and households to organophosphates, carbamates and pyrethroids, cockroaches were trapped from 30 hospitals and 30 households in this area. Bioassays by topical application were then carried out on the first generation bred in the laboratory. Resistance ratio (RR) was determined by comparing the LD50 of the collected cohorts with that of a susceptible cohort. RR ranges of chlorpyrifos, propoxur and cypermethrin in the hospitals were 2.04 - 28.80, 2.86 - 30.86 and 1.95 - 14.05 and those in the household were 1.92 - 17.72, 6.93 - 62.50 and 2.80 - 27.35 respectively. Significant correlations among the RRs of the three insecticides were separately found in the hospitals and households, indicating the existence of cross resistance among the three groups of insecticides. The patterns of propoxur > chlorpyrifos > cypermethrin in hospitals and propoxur > cypermethrin > chlorpyrifos in households reflect that chlorpyrifos is more frequently used in hospitals than in households. In contrast, cypermethrin is used more frequently in households.

Isolation of bacteria with antibiotic resistance from household cockroaches (Periplaneta americana and Blattella germanica).

Cockroaches may harbor and disseminate microorganisms to the environment. In this study, Periplaneta americana and Blattella germanica were collected from 40 households in Kaohsiung City and Kaohsiung County, Taiwan. Cockroach infestation was found in 50% of the studied households and 226 cockroaches (123 P. americana and 103 B. germanica) collected by trapping. P. americana was more often found in the kitchen (70.7%) whereas B. germanica in the storage room (51.5%) and kitchen (36.9%). There was no significant difference between the percentages of P. americana (99.9%) and B. germanica (98.0%) carrying bacteria. A total of 25 species of bacteria was isolated from P. americana and only 21 from B. germanica. Antibiotic resistance was found in Staphylococcus aureus, Enterococcus species, Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, Serratia marcescens, and Proteus species isolated from the cockroaches. These findings suggest a potential role of cockroaches in the transmission of pathogenic bacteria with antibiotic resistance in households.

Cockroaches as potential vectors of nosocomial infections.

OBJECTIVE: To determine the possible role of cockroaches in the epidemiology of nosocomial infections. DESIGN: Epidemiologic investigation of bacteria and fungi in cockroaches and evaluation of the antibiotic resistance of the bacteria isolated from the insects. SETTING: Ninety hospitals in Kaohsiung City and Kaohsiung County in Taiwan. METHODS: Cockroaches were collected in clinical and nonclinical areas and microorganisms were isolated from their external surface and alimentary tract. The susceptibilities of Staphylococcus aureus, Enterococcus species, Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, Serratia marcescens, and Proteus species to 17 antibiotics were tested. RESULTS: Cockroach infestation was found in 46.7% of the hospitals studied. Two hundred three cockroaches were collected (139 Periplaneta americana and 64 Blattella germanica). Periplaneta americana was found more often in nonclinical areas (64.5%) and B. germanica in clinical areas (78.1%). There was no statistically significant difference between Periplaneta americana (98.6%) and B. germanica (96.9%) regarding overall isolation rate (P > .05). However, 33 species of bacteria and 16 species of fungi were isolated from Periplaneta americana and only 23 and 12, respectively, from B. germanica. Resistance to ampicillin (13.7% to 100%), chloramphenicol (14.3% to 71.4%), tetracycline (14.3% to 73.3%), and trimethoprim-sulfamethoxazole (14.3% to 57.1%) was found in two gram-positive and five gram-negative bacteria. CONCLUSION: Because cockroach infestation occurred in more than 40% of the hospitals and nearly all of the cockroaches harbored bacteria with multidrug resistance and fungi, cockroaches may play a potential role in the epidemiology of nosocomial infections in those hospitals.

Developing a safety and health training model for petrochemical workers.

The production processes of the petrochemical industry expose workers to high potential hazards. Our previous study showed that hazard recognition was closely related to worker safety and health training activities. The purpose of this study was to establish and validate a safety and health training model. It is expected that the training model will help workers to recognize hazards, thereby lowering their operating risks. The training model, which included a complete training course and follow-up scoring using a questionnaire, was applied to three groups of subjects for comparison. Group A had joined our study previously and took the training course again at this time. Group B had also joined our previous study but did not take this training course. Group C was new to our study and took this training course for the first time. Groups A and C (who took the training course) had higher cognition and attitude scores than group B (who did not take the training course). The training course was a significant factor that positively influenced both cognition and attitude scores among managers and workers. The training course was more significant for managers while the duration of education was more significant for workers.

Cockroaches (Periplaneta americana and Blattella germanica) as potential mechanical disseminators of Entamoeba histolytica.

Since cockroaches feed on feces, they may disseminate infective agents with the fecal-oral route. A field survey and experiments were conducted to determine the role of cockroaches in the dissemination of Entamoeba histolytica. Periplaneta americana (n=299) and Blattella germanica (n=29) were collected from 11 primary schools in an urban area of South Taiwan. E. histolytica/E. dispar cysts were found on the cuticle and/or in the digestive tract of P. americana (25.4%) whereas cysts were only isolated from the digestive tract of B. germanica (10.3%). E. histolytica cysts were found on the cuticle and/or in the digestive tract of both species after exposure to 1000 or 100 cysts/g feces for 24 h. These findings indicate that cockroaches may harbor the E. histolytica cysts and play a role as potential mechanical disseminators.

A community-based surveillance on determinants of rodent infestation.

Rodent infestation is an important factor in the transmission of infectious diseases of public health importance. From October to November 1998, surveillance stations were established in 110 boroughs of Kaohsiung City in southern Taiwan. Boroughs were chosen by random sampling 10 boroughs from each of 11 districts (464 boroughs) in the city. The extent of rodent infestation was determined by cage trapping. The possibility of applying a community-based control program was evaluated by investigating associated demographic and environmental factors as well as related knowledge, attitudes, and behaviors. A total of 90 rodents were trapped in 41% of the 110 boroughs. Using univariate analyses, 17 factors were significantly associated with rodent infestation. A lack of knowledge that rodent control relies on community cooperation was the most important factor among the seven variables associated with the extent of rodent infestation (OR 3.1) by logistic multiple regression. This revealed the importance of community cooperation in controlling rodent infestation. Moreover, improvement of environmental hygiene associated with garbage problems, such as cleanliness of storage rooms and closets, and the hygiene of empty space and resource recycling stations should not be ignored.