Anopheles subpictus is a species of Anopheles mosquito, and the vector of malaria, which is scattered via the eastern regions of Asia and Australia(1). Afghanistan, Bangladesh, Australia, China, Cambodia, India, Iran, Indonesia, Maldives, Malaysia, Nepal, Myanmar (Burma), New Guinea, Pakistan, Sri Lanka, Philippines, Vietnam, Thailand, and India are among the most common areas of activity of this carrier(2). An. subpictus is generally considered a potential vector in Southeast Asian countries(3, 4).. The activity of An. subpictus is more in the central regions of India and its activity decreases in the east. An. subpictus is known as a potential vector of malaria, especially in coastal areas of India and Sri Lanka(5, 6). The variable vector potential of An. subpictus in different geographical areas has led to the presence of different biological species. An. subpictus has four subspecies, A, B, C, and D, and they are identified based on paracentric inversions in X chromosome. However, the status of species identification in most countries remains ambiguous (2). A, B, C, and D subspecies were found in Sri Lanka, whereas A and B subspecies were found in India. But according to research, species B is a typical malaria vector, particularly in the coastal regions of India and Sri Lanka (1, 6). Anopheles subpictus is the primary vector of malaria in India, and the secondary vector in Sri Lanka(7, 8). Japanese encephalitis virus has been isolated from this vector. Consequently, the control of this vector is very important to prevent the transmission of diseases. Malaria transmission can be reduced by adopting vector control measures, such as indoor residual spraying with insecticides, larval control measures, and personal protection measures (9). Installing insecticide-treated nets impregnated with persistent insecticides, treating patients simultaneously, continuously spraying with insecticides, and intermittent preventative treatment during pregnancy are some of the current malaria prevention strategies. Thus, preventive spraying is the main approach to control the vector, and prevent the spread of malaria, which protects about 40% of the population at risk (10, 11). The World Health Organization has recommended 12 types of insecticides, in four categories: organochlorines, organophosphates, carbamates, and pyrethroids, for spraying and fighting vectors (12). Organochlorine insecticides, DDT, malathion, and synthetic pyrethroids are the most common insecticides used to fight malaria. However, the continuous and widespread use of insecticides, especially organochlorine insecticides, resulted in the development of resistance in many malaria vectors in the world (2, 7, 13, 14).
The mechanism of action of insecticides on carriers, especially organochlorines, and pyrethroids insecticides, is that by acting on sodium channels, they lead to the disturbances in the opening and closing of sodium channels and the death of carriers (15, 16). Therefore, genetic mutations in target locations cause resistance in sodium channels and then resistance to insecticides. Target site insensitivity is in terms of a mutation in the voltage-sensitive sodium channel gene (Vssc). The most important of these mutations is Knockdown resistance (Kdr). Kdr mutations reduce neurosensitivity to organochlorines and pyrethroids in insects and prevent their effects on insects (17–19). Given that one of the primary methods for combating malaria is vector control. Insecticide resistance impedes efforts to control vectors and accelerates the development of malaria. Organochlorine insecticides are among the insecticides that are widely used in the fight against malaria in the world. As a result, resistance to them makes it difficult to fight malaria (2, 20, 21).
In general, the presence of resistance of Anopheles subpictus against insecticides, especially organochlorine insecticides, was reported. The mutations that led to Kdr in this vector are one of the most important causes of resistance to this group of insecticides. However, the level of resistance and its extent in different regions of the world are unclear (22, 23). Considering the importance of Anopheles subpictus as one of the main vectors of malaria and also the importance of resistance to insecticides that hinders the fight against this vector, knowing the type of resistance, and the ratio of resistance to insecticides is important for making the right decision to fight. Based on this, a study was carried out to assess the proportion of Kdr resistance to organochlorine insecticides in Anopheles subpictus and to look into the mutations discovered globally in this area using a systematic review method.