Mosquito larva distribution and natural Wolbachia infection in campus areas of Nakhon Ratchasima, Thailand

Objective: To determine the prevalence of mosquito larvae in campus areas and the infection rate of endosymbiotic bacteria, Wolbachia in mosquito larvae. Method: The mosquito larvae samples were collected in residential areas and academic buildings of Suranaree University of Technology located in Northeastern Thailand during 2017-2018. Mosquito species identification was performed using GLOBE mosquito protocols and Rattanarithikul & Panthusiri's keys. The gene encoding for the surface protein of Wolbachia was amplified by PCR and confirmed by DNA sequencing. Results: Armigeres sp. is the highest proportion of mosquito larvae followed by Culex spp., Aedes albopictus, Aedes aegypti, and Toxorynchites spp., respectively. Aedes aegypti have breeding sites mostly in the containers found indoors, whereas the main breeding sites of Aedes albopictus were found in both outdoors and indoors. The House Index and Breteau Index for Aedes spp. was more than 5% and 20%, respectively, in both areas, indicating that these areas are dengue sensitive. The highest proportion of Wolbachia infection was found in the larvae of Culex spp. (86.21%), followed by Aedes albopictus (69.23%) and rarely detected in Aedes aegypti (9.09%). Conclusion: The present study reported the first natural infection of Wolbachia in mosquito larvae in Thailand. Our result suggested that the mosquito species containing higher proportion of Wolbachia are less likely to be vectors for dengue. Therefore, Wolbachia transfection in mosquito larvae could be applied as a biocontrol for dengue and other mosquito-borne disease prevention.

Mosquito density in rural Kerala: a study on the trend of Aedes larval indices over monsoon in a rural area of Thrissur district, India

Background: Dengue is one of the most rapidly spreading mosquito-borne viral diseases in the world. Aedes aegypti mosquito is the main vector of dengue and Chikungunya. Entomological surveillance on Aedes mosquito has been standardized on different indices like House index, Container index, Breteau index. Larval indices are important predictors of outbreaks and are valuable in taking preventive measures. The objectives of the present study was to study the trend of larval indices over four months in selected wards of Kaiparambu Panchayat, Thrissur, Kerala, India and to identify the major breeding sources.Methods: A series of surveys were conducted from May to August of 2017 in Kaiparambu Panchayat under the field practice area of Amala Institute of Medical Sciences Thrissur. Houses were selected serially from 4, 5 and 6 wards with roughly 120 houses being covered each month.Results: A total of 489 houses were surveyed over 4 months. Overall, positive containers (with larvae) were present in 375 of 4055 potential containers showing a calculated House index (HI) is 44.4%, Container index (CI) is 11.5% and the Breteau Index is 76.7%. All three indices increased from May to June, peaked in July and dropped by August. Plastic containers were the most common source of breeding.Conclusions: The indices indicate risk even in the pre-monsoon season and there is a marked rise during monsoon. Hence, control measures need to be adopted during the pre-monsoon season so as to reduce the impact of the impending outbreak.

A study on mosquito density in rural Kerala before and after floods

Background: Mosquito borne diseases are a major public health problem in Kerala. Mosquito density assessed by larval surveys is easier and quicker to perform. The larval indices are an important practical predictor of outbreaks of mosquito borne disease and are valuable in taking preventive measures. This study is done to calculate standardized larval indices namely house index, container index and Breteau index and to identify the major breeding sources of mosquitoes in the residential environment in a rural of Thrissur, Kerala.Methods: A cross-sectional study selecting 80 houses from 1 wards of Konnikara village under Thrikkur Panchayath under the field practice area of rural training centre, Amala Institute of Medical Sciences Thrissur. Every water holding container indoors and outdoors was counted and searched for larval presence and noted on a pretested format.Results: In this study, 80 houses were surveyed in 2 days initially in June and in September. All the entomological indices were found to be above the critical level in the initial survey in June. House index=36% container index=44%; Breteau index=143% showing high chances for outbreaks of mosquito borne diseases. In September though the indices were very low house index 1.25% container index 2.77% and Breteau index.Conclusions: The area is prone for mosquito borne disease outbreaks like dengue fever and after interventions the vector indices and potential risks came down

The effects of a behavioral change program in reducing the house index of mosquito larvae in households in Phetcabun province, Thailand.

Introduction: The purpose of this quasi-experimental research was to study the effectiveness of a behavioral change program in reducing house index of mosquito in Village Baan-Wangpong, Lomsak district in Phetcabun province, Thailand. Methods: The sample size of experimental and control group was 42 representatives of household in each group. Representatives of each sampled household were tested for knowledge, perception and behavioral practice in prevention of dengue fever before and after the program intervention. The program included training on dengue fever prevention by health personnel, demonstration of making mosquito repellents from local product, organising an awareness contest, broadcasting health messages through media and surveying households for mosquitoes’ larvae. Results: The study found that most households in village Baan-Wangpong had low knowledge (60.4%), perceived risk (60.4%), perceived severity (64.6%) and behavioral practice (77.1%) in the prevention of dengue fever prior to the program, with comparability in intervention versus control. The results showed that after the program intervention, the experimental group had a significantly higher level of knowledge (p=0.001), perceived risk (p=0.042), perceived severity (p=0.002) and behavior (p=0.028) in preventing dengue fever than before the program intervention and higher than the control group post-intervention. The experimental group’s house index was also significantly (p=0.001) lower than before the program and lower than the control group post-intervention. Conclusions: This study suggests that a proactive program about knowledge, perceptions and behaviors on prevention of dengue fever with support from public health personnel and community participation, can positively change health behavior, resulting in reducing the house index of mosquito larva.

Updating the geographical distribution and frequency of Aedes albopictus in Brazil with remarks regarding its range in the Americas

The geographical distribution of Aedes albopictus in Brazil was updated according to the data recorded across the country over the last eight years. Countrywide house indexes (HI) for Ae. albopictus in urban and suburban areas were described for the first time using a sample of Brazilian municipalities. This mosquito is currently present in at least 59% of the Brazilian municipalities and in 24 of the 27 federal units (i.e., 26 states and the Federal District). In 34 Brazilian municipalities, the HI values for Ae. albopictus were higher than those recorded for Ae. aegypti, reaching figures as high as HI = 7.72 in the Southeast Region. Remarks regarding the current range of this mosquito species in the Americas are also presented. Nineteen American countries are currently infested and few mainland American countries have not confirmed the occurrence of Ae. albopictus. The large distribution and high frequency of Ae. albopictus in the Americas may become a critical factor in the spread of arboviruses like chikungunya in the new world.

Clinico-Epidemiological Profile of an Outbreak of Dengue Fever in Rural Area of Ambajogai Mandai, District Beed.

A c1inico-epidemiological study of fever cases was carried out in three villages of Ambajogai Mandal, Beed, Maharashtra. Out of 123 fever cases studied, most common affected age group was 21-45 years with more number of females i.e.55.28%. The patients mainly presented with fever and joint pain with no any evidence of haemorrhagic manifestation. Of the 36 blood samples tested 03 samples were found positive for IgM antibodies to dengue virus. Larval survey showed highest breeding preference in domestic water container like earthen pots. Entomological indices were found out to be higher as house index 19.76%; container index 19.02%; Breteau index 22.31%. Clinico-epidemiological, laboratory and entomological investigations indicate present episode of fever outbreak was due to dengue fever. It demands for strengthening the surveillance activity and alert reporting of peripheral health staff along with IEC activities for community participation and involvement of other departments.

Vector density and the control of kala-azar in Bihar, India

Bihar, India has been in the grip of kala-azar for many years. Its rampant and severe spread has made life miserable in most parts of the state. Such conditions require a comprehensive understanding of this affliction. The numbers coming out of the districts prone to the disease in the north and south Ganges have provided us with several startling revelations, as there are striking uniformities on both sides, including similar vegetation, water storage facilities, house construction and little change in risk factors. The northern areas have been regularly sprayed with DDT since 1977, but eradication of the disease appears to be a distant dream. In 2007 alone, there were as many as 37,738 cases in that region. In contrast, the southern districts of Patna and Nalanda have never had the disease in its epidemic form and endemic disease has been present in only some pockets of the two districts. In those cases, two rounds of spraying with DDT had very positive results, with successful control and no new established foci. In addition, an eleven-year longitudinal study of the man hour density and house index for the vector Phlebotomus argentipes demonstrated that they were quite high in Patna and Nalanda and quite low in north Bihar. Given these facts, an attempt has been made to unravel the role of P. argentipes saliva (salivary gland) in the epidemiology of kala-azar. It was determined that patchy DDT spraying should be avoided for effective control of kala-azar.