**2. Malaria transmission in India: current distribution and parasite formula**

insecticide-treated netting materials for vector containment has once again renewed the optimism of malaria elimination globally. Malaria map is shrinking with more than 35 countries certified to be malaria free, and another 21 countries that are likely to reach zero indigenous transmission (categorized as E-2020) are set to be declared malaria free by 2020 [1, 2]. Many more countries are moving forward from control to elimination. The Global Technical Strategy for Malaria 2016–2030 envisages: (i) to reduce global malaria mortality rates and case incidence by at least 90% compared to 2015 levels, (ii) to make at least 35 countries malaria free that reported cases in 2015 and (iii) preventing re-establishment in countries with no indigenous transmission [3]. Among member countries of the Southeast Asia Region of WHO (SEAR), Maldives and Sri Lanka have already been certified malaria free in 2015 and 2016, respectively, and Bhutan is targeting elimination in the foreseeable future. In the past decade, India has registered drastic decrease in cases and have formulated National Framework for Malaria Elimination (2016–2030) in close alignment with the Global Technical Strategy for Malaria, Roll Back Malaria Action (RBM), Investment to defeat Malaria (AIM) and the Asia Pacific Leaders Malaria Alliance (APLMA) for shared experiences and coordinated action to eliminate malaria (zero indigenous cases) throughout the country by 2030 [4]. The said task is set to be accomplished in phased manner with the following objectives: (i) eliminate malaria in all 26 low-to-moderate transmission States/Union Territories (UTs) by 2022, (ii) reduce the case incidence to <1 per 1000 population by 2024 in all States/UTs, (iii) interrupt indigenous transmission throughout the country by 2027 and (iv) prevent re-establishment of local transmission and maintain malaria-free status by 2030

India is historically endemic for both *Plasmodium vivax* and *P. falciparum* malaria and has history of successes and resurgences [5, 6]. Malaria was on the verge of elimination postindependence in 1960s with 0.1 million cases and no death, yet it reared its ugly head again in 1970s with record number of six million cases and many deaths attributed to technical and operational constraints. Transmission is largely seasonal corresponding to rainy season with record of focal disease outbreaks characterized by high rise in cases and attributable deaths. In 2017, India reported 0.84 million cases, the highest disease burden in SEAR member countries of WHO [4, 7]. Almost all Indian States and UTs are reporting cases, which can be broadly stratified into three different categories based on Annual Parasite Incidence (API) per 1000 population, that is, Category—I (total of 15 States/UTs including districts with API < 1) that are targeted for elimination phase, Category—II (total of 11 States/UTs with API < 1 with one or more districts reporting > 1 API) marked for pre-elimination phase and Category—III (total of 10 States/UTs with > 1 API) targeted for intensified control operations. With the rolling out of the present day evidence-based intervention tools, disease transmission is on the steady decline presenting window of opportunity to accelerate toward universal coverage for malaria prevention and treatment. India is a huge country (population 1.3 billion) with majority populous (80%) living at risk of malaria. The task is enormous and daunting. Given the political commitment and National Framework developed by the National Vector Borne Disease Control Programme (NVBDCP) of Government of India, malaria elimination is foreseeable, yet there are multiple challenges which must

and beyond.

258 Towards Malaria Elimination - A Leap Forward

Malaria transmission is heterogenous across Indian landscape for its diverse ecology and multiplicity of disease vectors [8]. Malaria is a serious public health concern and almost all 36 States/UTs are consistently contributing cases, but transmission intensities varied ranging from low-to-moderate (**Table 1**). Among these, north-eastern, eastern and central Indian States consistently contributed 80% of the total disease burden having concentration of cases (API > 10) associated with large forest cover, ethnic tribes, poverty and high rainfall (**Figure 1**). These included States of Odisha (formerly Orissa) and Jharkhand (eastern India), Chhattisgarh and Madhya Pradesh (central India) and Meghalaya and Tripura (northeast India), which together contributed >65% of *P. falciparum* cases. Approximately a billion population of India resides in malaria endemic areas, however, 80% of malaria cases are reported by just 20% of the population living in the forest-fringe, tribal and foothills hardto-reach areas of the country little aware of disease prevention and access to treatment [9]. These areas are prone to periodic disease outbreaks resulting in flare up of cases and attributable mortality accounting for inter-annual variation in reported morbidity. From the epidemiological data for the past 17 years (2001–2017), disease transmission trends are observed to be declining from two million cases in 2001 to close to a million cases in 2017 (**Figure 2**). However, consequent to the introduction of artemisinin-based combination therapy (ACT) beginning 2010 coupled with insecticide-treated netting materials (ITNs); there has been drastic decrease in cases and deaths. *P. falciparum* and *P. vivax* are the predominant infections of which there has been steady increase in proportions of the former parasite species presently constituting >60% of total cases what was 50:50 in 2001. Every single death was attributed to *P. falciparum*, majority of which were contributed by high-risk States of north-eastern, eastern and central India (**Figure 3**). The distribution of *P. malariae* is patchy, recorded in indigenous tribes of eastern, north-eastern and central India [10–12], but transmission of *P. ovale* except for few sporadic reports could not be clearly ascertained [13–15]. There exists no record of *P. knowlesi* malaria in India making inroads in other Southeast Asian countries [16].

The reported cases and deaths; however, are far from acccurate for disease surveillance that can be best described as fragmented and there is no system in place to capture data from private and public sectors alike, least the asymptomatic cases [17]; WHO estimates are much higher to the tune of >10 million cases and deaths manifold [1]. Nevertheless, the presented data showed disease transmisison trends in relation to existing interventions, and monitoring and evaluation in practice.


**No**

**State/Union** 

**2014**

**2015**

**2016**

**2017**

**Territories**

**Total** 

*Plasmodium* 

**Deaths**

**Total** 

*Plasmodium* 

**Deaths**

**Total** 

*Plasmodium* 

**Deaths**

**Total** 

*Plasmodium* 

**Deaths**

**malaria** 

*falciparum*

**cases**

**cases**

**malaria** 

*falciparum*

**cases**

**cases**

**malaria** 

*falciparum*

**cases**

**cases**

**malaria** 

*falciparum*

**cases**

19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

Puducherry

All India total

\**Source*: Ref. [7].

**Table 1.**

1,102,205

722,546

562

1,169,261 Malaria-attributable morbidity and mortality in different States and Union Territories (UTs) of India during 2014–2017\*.

778,821

384

1,090,724

716,213

331

840,838

533,481

103

261

79

3

0

54

5

1

76

11

0

59

13

0

Lakshadweep 0

Delhi

98

0 0

0

4

0

0

2

0

0

1

0

0

http://dx.doi.org/10.5772/intechopen.77046

0

54

0

0

31

0

0

577

2

0

Daman & Diu 56

4

0

84

18

0

48

7

0

37

4

0

D & N Haveli

 669

90

1

418

46

0

375

30

0

297

16

0

Declining Transmission of Malaria in India: Accelerating Towards Elimination

Chandigarh

114

0

0

152

1

1

157

0

0

114

1

0

A.N. Islands

557

109

0

409

77

0

485

140

0

404

67

0

West Bengal

26,484

4981

66

24,208

5775

34

35,236

5928

59

30,008

4632

29

Uttar Pradesh

41,612

326

0

42,767

371

0

39,238

158

0

32,345

159

0

Uttarakhand

1171

89

0

1466

73

0

961

47

0

532

14

0

Tripura

51,240

49,653

96

32,525

30,074

21

10,546

9545

14

7040

6572

6

Telangana

5189

4602

0

10,951

10,206

4

3512

2617

1

2688

2170

0

Tamil Nadu

8729

339

0

5587

355

0

4341

242

0

5449

197

0

Sikkim

35

18

0

27

11

0

15

5

0

12

3

0

Rajasthan

15,118

603

4

11,796

662

3

12,741

1031

5

6837

377

0

Punjab

1036

14

0

596

13

0

693

8

0

808

12

0

Orissa

395,035

342,280

89

436,850

369,533

80

449,697

389,332

77

352,140

297,554

25

Nagaland

1936

647

2

1527

532

3

828

316

0

394

188

1

**cases**


**No**

**State/Union** 

**2014**

**2015**

**2016**

**2017**

**Territories**

**Total** 

*Plasmodium* 

**Deaths**

**Total** 

*Plasmodium* 

**Deaths**

**Total** 

*Plasmodium* 

**Deaths**

**Total** 

*Plasmodium* 

**Deaths**

**malaria** 

*falciparum*

**cases**

**cases**

**malaria** 

*falciparum*

**cases**

**cases**

**malaria** 

*falciparum*

**cases**

**cases**

**malaria** 

*falciparum*

**cases**

1

Andhra

21,077

15,511

0

25,042

18,709

0

23,613

17,443

0

16,913

11,944

0

260 Towards Malaria Elimination - A Leap Forward

Pradesh

2

Arunachal

6082

2338

9

5088

1714

7

3144

911

2

1538

487

0

Pradesh

3 4 5 6 7 8 9

Himachal

102

1

0

60

1

0

121

19

0

95

9

0

Pradesh

10

Jammu &

291

21

0

216

8

0

242

11

0

226

0

0

Kashmir

11 12 13 14

Madhya

96,879

41,638

26

100,597

39,125

24

69,106

22,304

3

46,176

15,554

3

Pradesh

15 16 17 18

Mizoram

23,145

21,083

31

28,593

24,602

21

7583

5907

9

5710

4978

0

Meghalaya

39,168

37,149

73

48,603

43,828

79

35,147

31,867

45

16,433

14,974

11

Manipur

145

72

0

216

119

0

122

58

0

80

22

0

Maharashtra

53,385

25,770

68

56,603

31,139

59

23,983

7815

26

18,133

5929

19

Kerala

1751

305

6

1549

400

4

1547

419

2

1194

317

2

Karnataka

14,794

1329

2

12,445

1598

0

11,078

1746

0

6529

1118

0

Jharkhand

103,735

46,448

8

104,800

54,993

6

141,414

83,232

15

92,770

42,047

1

Haryana

4485

45

1

9308

726

3

7866

552

0

6887

904

0

Gujarat

41,608

6253

16

41,566

7232

7

44,783

6298

6

37,801

3502

2

Goa

824

42

0

651

75

1

742

130

0

653

75

2

Chhattisgarh

128,993

108,874

53

144,886

123,839

21

148,220

121,503

61

141,310

115,153

0

Bihar

2043

699

0

4006

1286

1

5205

895

0

3175

356

2

Assam

14,540

11,210

11

15,557

11,675

4

7826

5686

6

5473

4131

0

**cases**

**Table 1.** Malaria-attributable morbidity and mortality in different States and Union Territories (UTs) of India during 2014–2017\*

.

Declining Transmission of Malaria in India: Accelerating Towards Elimination http://dx.doi.org/10.5772/intechopen.77046 261

**Figure 1.** Malaria stratification by Annual Parasite Incidence (API) in Indian States for data based on 2014. API 10 corresponds to 10 confirmed cases per 1000 population. *Source*: Ref. [4].

## **3. Multiple disease vectors and insecticide resistance**

India holds the distinction in malaria epidemiological research for Noble prize-winning discovery that malaria is transmitted by mosquitoes by Sir Ronald Ross on the day of August 20, 1897, and for monumental work on faunistic surveys dating back to 1930s [18]. Of the 58 anopheline species recorded in India [19], six major vector taxa are implicated in malaria transmission, including *Anopheles culicifacies s.l*., *An. fluviatilis s.l.*, *An. minimus s.l.*, *An. dirus s.l.*, *An. sundaicus s.l.* and *An. stephensi* [20]. All of these, except *An. stephensi*, are species complexes among which members

were repeatedly incriminated as vectors evidenced by detection of live sporozoites in salivary glands across range of their distribution [21, 22]. With added tools of molecular taxonomy; however, there have been significant advances in understanding sibling-species composition of these taxa [23–25], distribution and their bionomics helping target species-specific control interventions in place and time (**Table 2**). Among these, *An. culicifacies* is the most widespread and extensively

**Figure 3.** Distribution of malaria-attributed deaths in different geoepidemiological regions of India for data based on 2014–2017. NE refers to group of seven sister States of northeast India including Arunachal Pradesh, Assam, Meghalaya, Manipur, Mizoram, Nagaland and Tripura; Central States include Madhya Pradesh and Chhattisgarh; Eastern States include Bihar, Jharkhand, Odisha (formerly Orissa) and West Bengal; Western States include Maharashtra, Goa, Gujarat and Rajasthan. In the remaining Indian States and Union Territories, death cases were few and far (not shown). *Source*: Ref. [7].

**Figure 2.** Malaria-attributable morbidity and mortality in India during 2001–2017. Malaria positive cases denote confirmed diagnosis by presence of malarial parasite in finger-prick blood-smears; Pf cases denote positivity for

Declining Transmission of Malaria in India: Accelerating Towards Elimination

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263

*Plasmodium falciparum;* death cases are attributed to confirmed falciparum malarial infection. *Source*: Ref. [7].

Declining Transmission of Malaria in India: Accelerating Towards Elimination http://dx.doi.org/10.5772/intechopen.77046 263

**Figure 2.** Malaria-attributable morbidity and mortality in India during 2001–2017. Malaria positive cases denote confirmed diagnosis by presence of malarial parasite in finger-prick blood-smears; Pf cases denote positivity for *Plasmodium falciparum;* death cases are attributed to confirmed falciparum malarial infection. *Source*: Ref. [7].

**Figure 3.** Distribution of malaria-attributed deaths in different geoepidemiological regions of India for data based on 2014–2017. NE refers to group of seven sister States of northeast India including Arunachal Pradesh, Assam, Meghalaya, Manipur, Mizoram, Nagaland and Tripura; Central States include Madhya Pradesh and Chhattisgarh; Eastern States include Bihar, Jharkhand, Odisha (formerly Orissa) and West Bengal; Western States include Maharashtra, Goa, Gujarat and Rajasthan. In the remaining Indian States and Union Territories, death cases were few and far (not shown). *Source*: Ref. [7].

**3. Multiple disease vectors and insecticide resistance**

corresponds to 10 confirmed cases per 1000 population. *Source*: Ref. [4].

262 Towards Malaria Elimination - A Leap Forward

India holds the distinction in malaria epidemiological research for Noble prize-winning discovery that malaria is transmitted by mosquitoes by Sir Ronald Ross on the day of August 20, 1897, and for monumental work on faunistic surveys dating back to 1930s [18]. Of the 58 anopheline species recorded in India [19], six major vector taxa are implicated in malaria transmission, including *Anopheles culicifacies s.l*., *An. fluviatilis s.l.*, *An. minimus s.l.*, *An. dirus s.l.*, *An. sundaicus s.l.* and *An. stephensi* [20]. All of these, except *An. stephensi*, are species complexes among which members

**Figure 1.** Malaria stratification by Annual Parasite Incidence (API) in Indian States for data based on 2014. API 10

were repeatedly incriminated as vectors evidenced by detection of live sporozoites in salivary glands across range of their distribution [21, 22]. With added tools of molecular taxonomy; however, there have been significant advances in understanding sibling-species composition of these taxa [23–25], distribution and their bionomics helping target species-specific control interventions in place and time (**Table 2**). Among these, *An. culicifacies* is the most widespread and extensively


*Anopheles*

**Sibling** 

**Diagnostic** 

**Breeding habitats**

**Feeding behavior** 

**Resting** 

**Sporozoite** 

**Insecticide** 

**Distribution range**

**susceptibility** 

**infectivity** 

**(%)**

**status**

**habitats**

**(peak biting** 

**activity)**

**cytotaxonomic/**

**molecular tools**

**species/**

**species** 

**prevalent in** 

**India (total** 

**identified)**

*An.* 

Not

Domestic

Predominantly

Endophilic

Incriminated

Resistant to

Urban metropolitan

cities of India

DDT and

Malathion

anthropophilic

(22:00—24:00)

containers, building

construction sites,

overhead water

storage tanks,

underground

cement tanks, desert

coolers

\**Source*: Refs. [20, 23–25]; rDNA, ribosomal DNA; SCAR, sequence characterized amplified region; ITS2, internal transcribed spacer 2; PCR, polymerase chain reaction.

Bionomics, distribution and sibling-species composition of the dominant mosquito vector taxa of human malaria in India\*

.

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265

**Table 2.**

*stephensi*

applicable

**taxa**


*Anopheles*

**Sibling** 

**Diagnostic** 

**Breeding habitats**

**Feeding behavior** 

**Resting** 

**Sporozoite** 

**Insecticide** 

**Distribution range**

**susceptibility** 

**infectivity** 

**(%)**

**status**

**habitats**

**(peak biting** 

**activity)**

**cytotaxonomic/**

**molecular tools**

**species/**

**species** 

**prevalent in** 

**India (total** 

**identified)**

*An.* 

A,B,C,D and

Fixed paracentric

Rain water

Predominantly

Humandwellings

Incriminated

Resistant

Throughout rural

264 Towards Malaria Elimination - A Leap Forward

to DDT,

India

malathion and

pyrethroids

(0.3–20)

zoophilic except

'E' (A and B:

indoors and

cattle sheds

22:00–23:00; C and

D: 18:00–21:00; no

data for E)

collections, riverine

pools, rice fields,

seepage water,

streams, borrow

pits, irrigation

channels

inversions, PCR

based sequencing of

28S-D3 domain; ITS2-

PCR-RFLP; rDNA

ITS2

*An.* 

S, T, U and

Fixed paracentric

Seepage water

Sibling species

S—human

Incriminated

Highly

Throughout India

except north-eastern

susceptible to

all residual

States

insecticides

dwellings

indoors; T—

cattle sheds

'S'—highly

anthropophilic

(20:00–24:00);

'T'—zoophilic

foothill streams,

irrigation channels,

river ecology,

shallow wells

inversions; PCR

based sequencing

of rDNA ITS2; 28S

rDNA-D3

Form 'V' (4)

*fluviatilis* 

*s.l.*

*An.* 

*An. minimus* 

rDNA ITS2; 28S

Perennial foothill

Highly

Humandwellings

Incriminated

Highly

North-eastern of

Arunachala Pradesh,

Assam, Meghalaya,

Manipur, Mizoram,

Nagaland, Tripura,

and Eastern State of

Odisha

susceptible to

all residual

insecticides

(3.0)

anthropophilic

(01:00—04:00)

indoors

seepage water

streams

rDNA-D3

*minimus s.l.*

*An. dirus s.l.*

*An. baimaii*

Karyotypic

Jungle water pools,

Highly

Exophilic

Incriminated

Highly

North-eastern of

Arunachala Pradesh,

Assam, Meghalaya,

Manipur, Mizoram,

Nagaland, Tripura

susceptible to

all residual

insecticides

(1.9)

anthropophilic

(21:00—24:00)

Elephant foot-prints

studies, polytene

chromosome

analysis, geneenzyme variation, DNA probes, rDNA

ITS2; SCAR-PCR

*An.* 

*An. sundaicus*

Mitochondrial DNA

Brackish water

Predominantly

Both

Incriminated

Highly

Andaman & Nicobar

susceptible to

Islands

all residual

insecticides

indoors and

outdoors

zoophilic except

indoor resting

populations

(21:00—04:00)

including swamps,

salt water lagoons,

creeks as well as

fresh water

cytochrome oxidase

1 and cytochrome-b;

rDNA ITS2; 28S

rDNA-D3

*sundaicus* 

cytotype

D (4)

*s.l.*

(8)

*s.s*. (3)

*culicifacies* 

E (5)

*s.l.*

**taxa**

\**Source*: Refs. [20, 23–25]; rDNA, ribosomal DNA; SCAR, sequence characterized amplified region; ITS2, internal transcribed spacer 2; PCR, polymerase chain reaction.

**Table 2.** Bionomics, distribution and sibling-species composition of the dominant mosquito vector taxa of human malaria in India\* . studied for its sibling species composition (A, B, C, D and E), distribution range, seasonal prevalence, larval ecology, feeding and breeding behavior and disease transmission relationships [26]. Species E is the most efficient malaria vector of all having predilection for human host, while species B is a poor vector for its zoophilic characteristics. The other three species (A, C and D) are responsible for local transmission in areas of their predominance [27]. This taxon is the most abundant rural vector in plains of mainland India generating about 65% of cases annually and held responsible for focal disease outbreaks associated with build-up of vector density. It is regarded as highly adaptive species for its diverse breeding habitats and invading new territories in degraded forests of north-eastern India evidenced by records of rising density and incrimination [28–30]. Its control has become a formidable challenge for having grown multi-resistant virtually to all available insecticides including pyrethroids opening new vistas for research on newer interventions that are sustainable, cost-effective and community-based [31–33].

*An. stephensi* is the only urban vector species breeding in domestic containers and often associated with tropical aggregation of labor at construction sites in metropolitan cities [44]. The species is resistant to multiple insecticides and its control focused on 'source reduction' to contain urban malaria. Due to continued urbanization and associated labor migration, urban malaria is viewed as a growing menace contributing about 10% of cases in the country [5–7]. Besides these dominant vectors, member species of *An. maculatus s.l.*, *An. annularis s.l.* and *An. subpictus s.l.* are also implicated; however, these species are considered of lesser significance for being predominantly zoophilic [45, 46]. Vector control is an integral part of the malaria control strategy in India and huge investment is made annually to contain build-up of disease vectors averting epidemic malaria. What is tantamount to vector control is the entomological surveillance for developing malaria-risk maps, judicious application of insecticides, monitoring insecticide-resistance and residual efficacy, universal coverage for population at risk and continued research for newer interventions, which are community-based and sustainable. We strongly believe that judicious mix of technologies that are situation-specific and doable would help save operational costs in resource-poor settings. The country is in dire need of skilled entomologist/taxonomists (an expertise that is getting scarce) to meet the human resource requirements for control of malaria, and other vector-borne diseases, as well as vector surveillance post-elimination to prevent re-establishment of local transmission in malaria-free territories.

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267

Of the two prevalent malaria parasite species, the rising proportions of *P. falciparum* is of grave concern for presently constituting >60% of total reported cases in the country [5, 7]. Rising trends of *P. falciparum* are largely attributed to fast emerging drug-resistance over space and time in parallel with phenomenon happening in countries of the Greater Mekong Subregion (GMS) of Southeast Asia [47]. Historically, chloroquine (CQ) was the most commonly used drug for treatment ever since inception of the control program in 1953 for its efficacy and affordability. It had become obsolete since its first report of treatment failure in Assam (northeast India) way back in 1973 [48]. Subsequently, drug-resistant foci had multiplied for which northeast is considered corridor for spread to rest of peninsular India resulting in steady rise in proportions of *P. falciparum* what was 13% in 1978 to 65% in present day malaria [49]. Northeast India shares wide border with Myanmar contiguous with GMS countries which is porous for cross-border migration, facilitating entry of drug-resistant strains enroute to the rest of India and beyond. Malaria transmission along this border is intense vectored by *An. minimus* and *An. baimaii* (the two most efficient vector species), and healthcare access is inadequate resulting in indiscriminate and sub-optimal doses *inter-alia*, poor vector control, illiteracy and treatment-seeking behavior; all contributing to propagation and spread of drug-resistant malaria strains [50]. Chloroquine therapy was subsequently upgraded to sulfadoxine-pyrimethamine (SP) in 2004 as first-line treatment in selected districts reporting CQ-resistant malaria [51]. The therapeutic efficacy of SP was short lived resulting in substantial rise in cases in the following years [52]. It was in 1990s that the development of artemisinin-derivatives raised new hopes for treatment of drug-resistant malaria for its fast acting schizontocidal properties. Initially, artemisinin was used as monotherapy for treatment of severe and complicated clinical malaria, discontinued in 2009 due to high recrudescence

**4. Drug-resistant malaria**

*An. fluviatilis* complex is just as widespread and have overlapping distribution with *An. culicifacies* throughout India [20]. Among its sibling species, that is, S, T, U and form 'V'; it is species S which is highly anthropophilic and responsible for maintaining hyperendemic malaria predominantly in foothills of eastern India contributing ~15% of reported cases [34]. It shares similar bionomical characteristics with yet another efficient malaria vector species *An. minimus s.s* for breeding in foothill seepage water streams and resting indoors in human dwellings [35]. Both are highly susceptible to residual insecticides. *An. minimus* instead is the most predominant vector species of north-eastern States of India and has long history of disappearance and re-appearance stymying the control authorities. It is reckoned as the most efficient vector species for its high anthropophily (human blood index > 90%) and fulminating focal disease outbreaks taking heavy toll of human lives [36]. It is a perennial species and widely incriminated practically all months of the year with average sporozoite infection rate of 3% [37]. This species exhibits high behavioral plasticity for avoiding sprayed surfaces for weeks and establishing extra-domiciliary transmission in response to indoor residual spraying (IRS). While this species has staged comeback in eastern State of Odisha after lapse of 45 years [38], the populations of *An. minimus* once again are reported diminishing in erstwhile domains of its distribution in northeast India corroborated by evidence of reducing disease transmission [35]. It presents an unprecedented opportunity to strengthen interventions to keep populations of this species at bay helping achieve malaria elimination specific to the region at sub-national level.

Within the *An. dirus* complex, *An. baimaii* is the only vector occurring in India with a wide prevalence in the north-eastern States and has been recorded in high densities and incriminated in range of its distribution [39]. It is just as efficient vector species with strong predilection for human host but distinct from *An. minimus* for its breeding and resting characteristics [40, 41]. It is a forest dweller affecting forest-fringe human settlements along inter-country and inter-state border areas causing devastating disease outbreaks often in conjunction with *An. minimus*; together they contribute 10% of reported cases in the country [42]. Its control has become difficult for peak biting activity during second quartile (21:00–00:00) of the night as well as exophilic resting behavior avoiding sprayed surfaces. Its populations along with that of *An. minimus* are also depleting owing to deforestation and urbanization [29, 30]. However, niche thus vacated by both these species is accessed by *An. culicifacies s.l.* and has established foothold erstwhile recorded in lowdensity [26, 28]. Among sibling species of the *An. sundaicus* complex, cytotype species D has been characterized with a regional importance presently confined to Andaman and Nicobar Islands [43]. It is a brackish water species, largely zoophilic and susceptible to residual insecticides.

*An. stephensi* is the only urban vector species breeding in domestic containers and often associated with tropical aggregation of labor at construction sites in metropolitan cities [44]. The species is resistant to multiple insecticides and its control focused on 'source reduction' to contain urban malaria. Due to continued urbanization and associated labor migration, urban malaria is viewed as a growing menace contributing about 10% of cases in the country [5–7].

Besides these dominant vectors, member species of *An. maculatus s.l.*, *An. annularis s.l.* and *An. subpictus s.l.* are also implicated; however, these species are considered of lesser significance for being predominantly zoophilic [45, 46]. Vector control is an integral part of the malaria control strategy in India and huge investment is made annually to contain build-up of disease vectors averting epidemic malaria. What is tantamount to vector control is the entomological surveillance for developing malaria-risk maps, judicious application of insecticides, monitoring insecticide-resistance and residual efficacy, universal coverage for population at risk and continued research for newer interventions, which are community-based and sustainable. We strongly believe that judicious mix of technologies that are situation-specific and doable would help save operational costs in resource-poor settings. The country is in dire need of skilled entomologist/taxonomists (an expertise that is getting scarce) to meet the human resource requirements for control of malaria, and other vector-borne diseases, as well as vector surveillance post-elimination to prevent re-establishment of local transmission in malaria-free territories.
