1. Role of Artificial Containers as Breeding Sites for Anopheline Mosquitoes in Malaria Hypoendemic Areas of Rural Bandarban, Bangladesh: Evidence from a Baseline Survey
Mohammad Shafiul Alam1*, Sumit Chakma1, H M Al-Amin1, Rubayet Elahi1, Abu Naser Mohon1, Wasif Ali Khan1, Rashidul Haque1, Gregory E. Glass2, David A. Sack2, David J. Sullivan2 and Douglas E. Norris2
1ICDDR,B, GPO Box 128, Dhaka 1000, Bangladesh 2Johns Hopkins Malaria Research Institute, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205, USA
Presentation no.
210
Materials and Methods
Abstract
Within the framework of our Mapping Malaria Epidemiology of Bandarban project, a survey was conducted for breeding habitats of vector mosquitoes during September-October The survey was carried out in seven of the 24 study clusters in two unions (Kuhalong and Rajbila), based on malaria incidence. The survey team screened mosquito larvae from natural reservoirs irrespective to their size and artificial or natural containers where natural water (e.g. rain) can stand for few days following standard protocols. Twenty larval habitats from each selected cluster were surveyed. A total of 3,696 immature mosquitoes (larvae and/or pupae) representing five mosquito genera were recorded from 122 habitats. The collection was dominated by Culex spp. (n = 2082; 46 single and 28 mixed occupancy) followed by Aedes spp. (n = 1469; 36 single and 14 mixed occupancy). Immature stages of Anopheles species (n = 128) were collected from 25 habitats, nine of which were single occupancy whereas, 14 habitats were shared with Culex spp and the remaining two with Aedes species. Anopheline larvae were reared to adult before identification and seven species were recorded. Median temperature and PH of Anopheline larval habitat were 35°C (IQR: 32.5°C -36.0°C) and 7.4(IQR: ) respectively. Rice fields have been implicated as the most preferred breeding site for Anopheles spp. Anopheline breeding sites also include puddle, irrigation canal, animal hoof print, artificial container and livestock wallow. Among the collected anophelines, An. kochi and An. vagus were found in containers (abundant plastic buckets and cement tanks respectively). An. vagus is considered an important malaria vector in Bangladesh. However, the preferences of An. vagus to artificial container needs further attention and should consider an alarming sign to malaria control in Bangladesh.
Mosquito larval survey was carried out in seven clusters (four from Kuhalong and three from Rajbila)
These clusters were selected based on malaria incidence
Two teams consist of two members each sampled one cluster in a given day
The team screened Anopheles larvae from natural reservoir irrespective to their size and artificial or natural containers where natural water (e.g. rain) can stand for few days
Twenty collections of different habitats from each selected cluster were surveyed. Thus, a total of 140 collections (of different habitats) were done during the period
Mosquito larvae and pupae were sampled using standard dipping techniques
In case of small reservoir (animals hoof/foot print, leaves, pit etc) maximum amount of water was sampled using serological pipette
All larval samples were passed through a mesh sieve and placed with water into labeled plastic container and were taken to the laboratory placed at the Bandarban field office for further processing
Larvae were reared to adult. Standard taxonomic keys were used for identification
Searching Mosquito Larvae by the side of a Rice field
Sampling Mosquito Larvae from Animal hoof print
Sampling Mosquito Larvae from Bamboo pole
Rearing Anopheles Larvae in cages at Bandarban Field office
Results
Among the collection, mosquito larvae (and/or pupae) of any species was found in 122 habitats represented by immature of five mosquito genera
The collection was dominated by Culex spp. (46 single and 28 mixed occupancy) followed by Aedes spp. (36 single and 14 mixed occupancy)
Immature stages of Anopheles species were collected from 25 habitats, nine of which were single occupancy whereas, 14 habitats were shared with Culex spp and remaining two with Aedes species (Table 1)
A total of 3,696 different immature stages of mosquitoes were collected
More than half of those were from Culex species (2082) followed by Aedes (1469) and Anopheles (128)
Seven species Anopheles mosquitoes were identified
Most frequent mosquito breeding site was bamboo pole which was found to harbor all five genera of mosquitoes
Bamboo is used as a fence in most of the tribal houses which temporarily reserves rainy water and served as a breeding site for mosquitoes preferably for Culex spp. and Aedes spp. However, An. jamesii and An. vagus were found to share bamboo pole as their breeding sites either with Culex spp. or Aedes spp
Rice field has been implicated as the most preferred breeding site for Anopheles spp. Other Anopheline breeding sites include puddle, irrigation canal, animal hoof print, artificial container and livestock wallow (table 2)
Larvae of An. kochi were collected from artificial containers (abundant plastic bucket) which is unusual for Anopheles mosquitoes. In another occasion larvae of An. vagus were collected from a type of large artificial container
Median temperature and PH of Anopheline larval habitat (water body) were 35°C (IQR: 32.5°C-36.0°C) and 7.4(IQR: ) respectively
Sampling Mosquito Larvae contained water from a large artificial container (Cement tank)
Sampling Mosquito Larvae from puddle
Table 1. Distribution of Mosquito species according to larval habitats
 Larval habitat
Anopheles
Aedes
Culex
Armigeres
An+Ae
An+Cx
Ae+Cx
Cx+Tx
Ae+Cx+Ar
Lake/Pond Margin -
Rice Field +
Puddle
Irrigation Canal
Sluggish Stream
Animal Hoof Print
Large Artificial Container
Small Artificial Container
Tree Hole
Livestock Wallow
Bamboo hole
Others
Malaria is a major health burden in this remote, mountainous south-eastern region of Bangladesh bordering India and Myanmar
Malaria in Bangladesh is mainly caused by two Plasmodium species: Plasmodium falciparum and Plasmodium vivax
Out of 35 anopheline species reported in Bangladesh, 16 have shown evidence to have some role in transmitting human malaria parasites
Among those, An. aconitus, An. annularis An. baimaii, An. jeyporiensis, An. minimus, An. nivipes, An. philippinensis, An. sundicus and An. vagus are vectors
A total of 25 Anopheles spp. have been reported
Anopheles breeding ecology is an important component to formulate effective control strategies
Unfortunately, there are very few reports available on Anopheles breeding habitats in Bangladesh
Introduction
Table 2. Anopheles larvae identified up to species level according to study unions
Species
Rajibila
Kuhalong
Total
An. baimaii 1
An. barbirostris 16
An. karwari 5
An. kochi 10 14 24
An. jamesii 11
An. philippinensis-nivipes 4
An. vagus 51 7 58
Unidentified 3 86 42
128
Map of study area showing the Larval habitats of different Anopheles mosquitoes
This entomological investigation was carried out as a part of a collaborative research project between ICDDR,B and Johns Hopkins Malaria Research Institute entitled “ Mapping malaria epidemiology in Bangladesh”.
The main study includes:
A Demographic Surveillance System (DSS) which includes KPC survey
GIS with coordinates of all houses and other key features
Active surveillance from a random sample of persons
Passive surveillance of malaria cases as and when they are identified
Mosquito vector surveillance
Data management system which integrates all data
Objectives for this Mosquito breeding sites investigations were:
To record the preferred breeding habitats of different Anopheles species
To observe the distribution of breeding sites maintained by dominant Anopheles species
To correlate the malaria epidemiology with the larval abundance in both peak and off peak transmission season
Objectives
Table 3. List of larval habitats of Anopheles species in Bandarban
Species
Larval Habitat
An. baimaii
Puddle
An. barbirostris
Irrigation canal, puddle, Rice field
An. jamesii
Bamboo hole, Irrigation canal, Puddle
An. karwari
An. kochi
Small artificial container, livestock wallow, puddle, rice field
An. philippinensis/nivipes
Rice field
An. vagus
Animal hoof print, large artificial container, Bamboo hole, Puddle
Conclusion
Bandarban has high diversity in anopheline species with a wide range of larval sites
Rice field has been implicated as the most preferred breeding place for Anopheles spp.
Anophelines found to breed in the artificial containers, though they are not usual nor expected breeding habitat
More detailed longitudinal data is required to reveal larval habitats of the major vector species present in CHT in order to design effective vector control strategies
*For correspondence: Mohammad Shafiul Alam,