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Background <p>In the northeastern region of India, perennial malaria transmission persists in certain hotspots in areas geographically adjacent to the international borders with Bhutan, Bangladesh, and Myanmar, where both <i>Plasmodium vivax</i> and <i>Plasmodium falciparum</i> coexist, particularly in remote, forested, and inaccessible areas. This northeastern landscape harbors a wide diversity of anopheline vector species; <i>Anopheles minimus</i> and <i>Anopheles baimaii</i> are the traditional primary vectors of malaria. The extensive deployment of long-lasting insecticidal nets (LLINs) and indoor residual spraying as traditional vector control strategies has resulted in regional and temporal changes in species composition, specifically <i>An. minimus</i> and <i>An. baimaii</i>, and their resting and feeding behavior. Despite the reduced abundance of these primary anopheline vectors, the persistence of malaria suggests the involvement of additional anopheline species. Secondary malaria vectors may also play a role in transmitting malaria, along with primary malaria vectors, and are widely distributed across northeastern India. Secondary malaria vectors have significantly lower sporozoite rates compared with primary malaria vectors, yet are capable of sustaining malaria transmission in a specific region. This study aimed to investigate the sporozoite positivity of secondary anopheline species in the high-malaria-endemic district of Kokrajhar, Assam, in northeastern India.</p> Methods <p>During the study period, 1794 female mosquitoes representing five genera in <i>Anopheles</i>, <i>Culex</i>, <i>Aedes</i>, <i>Mansonia</i>, and <i>Armigeres</i> were collected using three methods: CDC light trap collection, indoor resting collection using the mouth aspiration method, and pyrethrum spray captures. Morphologically identified <i>Anopheles maculatus</i> group specimens were validated by polymerase chain reaction targeting the Internal Transcribed Spacer 2 region within the nuclear ribosomal DNA and referred to as <i>An. maculatus,</i> a species of the Maculatus Group of subgenus Cellia (Diptera: Culicidae)<i>.</i></p> Results <p>The <i>Plasmodium</i> positivity (Percent, number/total number) was highest in <i>An. maculatus</i> (4%; 5/80), followed by <i>An. minimus</i> (4.8%; 1/21), and <i>Anopheles kochi</i> (4.6%; 1/22)<i>.</i> These results suggest that anopheline species beyond the traditionally recognized primary vectors, such as <i>An. minimus</i> and <i>An. baimaii</i>, may play a role in sustaining malaria transmission in endemic areas of northeastern India.</p> Conclusions <p>Recognizing and integrating the behavior and ecology of secondary vectors into malaria control programs is essential for the development and deployment of more targeted and sustainable vector control strategies.</p> Graphical abstract <p></p>

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Evidence of secondary anopheline vectors in sustaining malaria transmission in Kokrajhar District, Assam, Northeastern India

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年11月21日

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  • Kuldeep Singh,
  • Ajeet Mohanty,
  • Waseem Akram Malla,
  • Ritesh Ranjha,
  • Jugal Gam,
  • Rahim Ali,
  • Praveen Kumar Bharti,
  • Anup R. Anvikar,
  • Himmat Singh

摘要

Background

In the northeastern region of India, perennial malaria transmission persists in certain hotspots in areas geographically adjacent to the international borders with Bhutan, Bangladesh, and Myanmar, where both Plasmodium vivax and Plasmodium falciparum coexist, particularly in remote, forested, and inaccessible areas. This northeastern landscape harbors a wide diversity of anopheline vector species; Anopheles minimus and Anopheles baimaii are the traditional primary vectors of malaria. The extensive deployment of long-lasting insecticidal nets (LLINs) and indoor residual spraying as traditional vector control strategies has resulted in regional and temporal changes in species composition, specifically An. minimus and An. baimaii, and their resting and feeding behavior. Despite the reduced abundance of these primary anopheline vectors, the persistence of malaria suggests the involvement of additional anopheline species. Secondary malaria vectors may also play a role in transmitting malaria, along with primary malaria vectors, and are widely distributed across northeastern India. Secondary malaria vectors have significantly lower sporozoite rates compared with primary malaria vectors, yet are capable of sustaining malaria transmission in a specific region. This study aimed to investigate the sporozoite positivity of secondary anopheline species in the high-malaria-endemic district of Kokrajhar, Assam, in northeastern India.

Methods

During the study period, 1794 female mosquitoes representing five genera in Anopheles, Culex, Aedes, Mansonia, and Armigeres were collected using three methods: CDC light trap collection, indoor resting collection using the mouth aspiration method, and pyrethrum spray captures. Morphologically identified Anopheles maculatus group specimens were validated by polymerase chain reaction targeting the Internal Transcribed Spacer 2 region within the nuclear ribosomal DNA and referred to as An. maculatus, a species of the Maculatus Group of subgenus Cellia (Diptera: Culicidae).

Results

The Plasmodium positivity (Percent, number/total number) was highest in An. maculatus (4%; 5/80), followed by An. minimus (4.8%; 1/21), and Anopheles kochi (4.6%; 1/22). These results suggest that anopheline species beyond the traditionally recognized primary vectors, such as An. minimus and An. baimaii, may play a role in sustaining malaria transmission in endemic areas of northeastern India.

Conclusions

Recognizing and integrating the behavior and ecology of secondary vectors into malaria control programs is essential for the development and deployment of more targeted and sustainable vector control strategies.

Graphical abstract