Skip to main content

Table 2 Challenges identified and possible solutions for effective vector control

From: Biology and bionomics of malaria vectors in India: existing information and what more needs to be known for strategizing elimination of malaria

S. No.

Challenges

Recommendations—studies on vector biology and bionomics, choosing appropriate vector control tools from existing ones and identifying newer tools where needed

1

Changes in the ecosystem due to developmental activities, and continuous pressure of insecticides on vector species have led to changes in the vector species prevalence and also in their biological characters

Situational analysis of vector species prevalence and their bionomics especially to generate data on seasonal density of vector species, resting (indoor and outdoor) and biting (endophagy and exophagy) behaviour, biting rhythm, EIRs, insecticide susceptibility:

i. Desirable to carry out studies in all the districts which have more than one API in the Categories 2 & 3. Keeping in view the human and financial resource constraints, studies to be taken up in states with high incidence of malaria

ii. In these areas An. culicifacies and An. fluviatilis are major vectors and both are species complexes—(a) identification of sibling species of these complexes and (b) bionomics of vectors species as mentioned above at the sibling species level

iii. (a) In the north eastern states bionomics studies of An. baimaii and An. minimus in selected areas and (b) the relative role of An. culicifacies and its sibling species and their responses to LLINs main usage which is now the main control strategy

iv. In Andaman & Nicobar Islands detailed vector bionomics studies in the islands endemic for malaria

2

Early biting and seasonal variations in the biting rhythms

i. An. culicifacies species C and D

ii. An. baimaii

i. Indoor and outdoor all night biting rhythm studies during different seasons in the states where species C and species D are reported

ii. a. In all the states of north east—proportion biting indoors/outdoors during different seasons and during different quarters of the night in order to estimate the outdoor biting and seasonal variations if any

ii. b. Quarter-wise EIRs to quantify the magnitude of transmission

ii. c. If LLINs are being used and early biting is observed (indoors and outdoors), additionally IRS using different class of insecticide to which the species is susceptible to be done in the houses/cattle sheds to target the early biting mosquitoes which would go for resting indoors

ii. d. Promoting use of personal protection repellents during dusk time

3

Outdoor resting and transmission

i. Outdoor transmission in jhum cultivation areas—An. baimaii, An. minimus

ii. An. baimaii—predominantly exophilic found resting in forests

iii. Transmission in forest areas where people go to collect produce

i. Data on vector biting away from houses in forest areas/in jhum cultivation areas and establishing the quantum of transmission outdoors through EIRs

ii. Delimiting the areas where An. baimaii is the exclusive vector—introduction of vector control tools that can target exophilic mosquitoes

iii. a. Identification of vectors in the forest areas of Madhya Pradesh and estimation of transmission that is originating from forest areas. Other forest areas in central and eastern region (Chhattisgarh, Andhra Pradesh and Jharkhand states) are to be examined for peoples movement to forest areas and relate with epidemiology

iii. b. Selection of tools to target exophilic and forest dwelling vectors

4

Changes in the behavior of vectors

As saturation of areas with LLINs distribution is being used as main vector control strategy in high endemic states, and because of the properties of pyrethroids, changes in the vectors with respect to resting and biting times are expected as observed in Odisha

Regular surveillance of vector species in LLINs distributed areas for changes in the species and sibling species composition and in behavior with reference to resting sites, host feeding preference and biting time

5

An. subpictus in Goa and Chennai, and also in other coastal areas where malaria transmission is reported

Biology and bionomics study of this species, and assessment of its relative role in transmission in coastal areas

6

P. knowlesi transmission dynamics

P. knowlesi positive blood smears found in different islands of Andaman & Nicobar islands—Port Blair, Car Nicobar, Teresa and Campbell Bay. An. sundaicus has been found positive for P. knowlesi

i. Assessing the possible role of other vector species in the transmission of P. knowlesi. Establishing site of transmission and initiating in depth studies on biology and bionomics of vector species and identification of suitable strategies to control the vector

ii. The transmission cycle in the islands—Examination of Macaca fascicularis (the primary host for P. knowlesi) present on the islands for the presence of parasite, and establishing its transmission mode: zoonotic and/or human to human infections

7

IRS for the control of An. culicifacies and An. fluviatilis

An. culicifacies sibling species are predominantly zoophagic and cattle shed collections are high. Furthermore, with the use of LLINs An. fluviatilis has shifted its resting to cattle sheds.

As per the current strategy for IRS, only human dwellings are sprayed

Where IRS is the choice for the control of vectors, spraying in all the resting places including the cattle sheds

8

Development of resistance to pyrethroids

Primarily development of pyrethroid resistance should be avoided or delayed following WHO norms [78]. To decrease pyrethroids selection pressure, in areas where An. fluviatilis and An. culicifacies are sympatric and An. fluviatilis is susceptible to DDT, instead of LLINs, DDT can be sprayed to control An. fluviatilis effectively. To control An. culicifacies if is highly resistant to DDT, feasibility of spraying one round of pyrethroid in pre-monsoon months could be studied

9

Operational issues related to IRS

Quality and dosage of insecticide, poor coverage, following schedules etc.

i. Training to spray personnel for quality spraying

ii. Health education to the community on importance of spray coverage

iii. Use of compression sprayers

10

Number of spray cycles and time of spraying

As per the NVBDCP guidelines two rounds of spray one in May–June and another in July–August/September

In the areas where An. fluviatilis and An. minimus are vectors, and their prevalence extends into January and February and malaria cases are noticeably high, extra round of IRS i.e. total three rounds to interrupt the transmission. Spray cycles to be rescheduled to cover the transmission seasons/months

11

Insecticide resistance management

With the continuous and increasing use of pyrethroids in indoor sprays and in ITNs/LLINs, resistance to pyrethroids has been observed in the major vector An. culicifacies. IRS and LLINs distribution in the same areas is precipitating resistance to pyrethroids. In addition, continuous use of DDT and malathion has resulted in high levels of resistance to these insecticides in An. culicifacies, and also to some degree in other vectors

i. Regular surveillance of vector dynamics and resistance monitoring to plan resistance management strategies

ii. New insecticide classes are needed to manage resistance to existing insecticides. Avoiding simultaneous use of LLINs and IRS with pyrethroids or same class of any insecticides

12

i. An. stephensi in semi-arid rural areas of Rajasthan—exophily, exophagy and resting on house hold objects and avoiding resting on walls of houses

ii. At construction sites and at other developmental project execution sites that increase mosquito productivity

i. Bio-environmental methods—environmental management and manipulation, source reduction, larvivorous fish etc.; larviciding (wherever possible) replacing the current strategy of IRS or in addition to IRS

ii. IRS or LLINs can be used depending on the type of housing and people’s acceptance. Source reduction and use of larvicides or larvivorous fish in water storing containers

13

Protection to people in areas away from houses from mosquito bites

Providing protection to people (i) living in the forests (ii) who live away from their homes for short periods for the collection of forest produce (North-east and Madhya Pradesh) or for Jhum cultivation (north east) and (iii) who get bitten by mosquitoes outside away from the houses (iv) during early hours of morning or in the evening

At present there are no tools available in India to provide protection to those who live in forests and are not accessible to protection with the two main tools that are being used by the programme, IRS or LLINs

Following tools that have been tested in other malaria endemic countries could be evaluated for their efficacy and suitability in Indian settings

i. Insecticide impregnated tents, plastic tarpaulin, canvas polyethylene tents which could be used in special situations

ii. Insecticide impregnated sheets, blankets and personal clothes, hammocks etc.

iii. Spatial repellent dispensers

iv. Totally mosquito proof portable huts.

v. Attractive toxic sugar baits (ATSB)

vi. Eave tubes etc.