Regarding various factors related to chance of getting malaria infection in district Swabi, being male, married, having water tanks and tube wells as water source, working in irrigated fields and sleeping outside during night significantly increase the risk of having malaria. On the other hand, living in households with meshed windows seemed protective and significantly lower the malaria risk (Table 2). In district Charsadda, the univariable analyses revealed that working in irrigated fields, living in mud walled houses, sleeping outdoors, presence of animals in houses, sleeping outdoors and roaming at night results in significantly higher odds of acquiring malaria. Similarly, having past infection of malaria and living with family members with history of the disease have been associated with increased risk of malaria. Ownership of meshed windows and use of protective means such as bed nets, repellents and residual sprays apparently reduce malaria risk (Table 2). In Charsadda sleeping habits (OR = 4.05), irrigated fields (OR = 3.37), mud house type (OR = 1.53), late night roaming (OR = 1.52) and family malaria history (OR = 1.27), while in Swabi drinking water source (OR = 1.77), irrigated fields (OR = 1.7) and sleeping habits (OR = 1. .29) are playing more important role in malaria transmission.
In this study, prevalence rate of malaria and risk factors associated with malaria transmission were studied in two ecologically distinct districts: Charsadda and Swabi, of Khyber Pakhtunkhwa, Pakistan. Ecology of an area greatly influence the mosquito density due to availability of breeding habitats and ultimately transmission of malaria. In Charsadda as well as in Swabi majority of the cases were of Plasmodium vivax. Plasmodium vivax and Plasmodium falciparum are transmitted by Anopheles species, but Plasmodium falciparum has been deemed responsible for 99% of the deaths due to malaria [2, 13]. During current study, in majority of malaria cases the causative agent was reported to be Plasmodium vivax which is similar to other findings which report that 80% of the cases reported in the country belong to Plasmodium vivax while 20% are caused by Plasmodium falciparum [3].
Current study shows that proper use of barriers like windows screening, housing types and bed nets significantly reduce the incidence of malaria. Window screening though a simple method but offered a formidable barrier to the vectors of malaria and indoor sleeping has been considered beneficial in minimizing the transmission of malaria [14, 15]. Studies have shown a 50% reduction in indoor vector density and ultimately reduction in malaria due to screening of doors and windows [16]. Present study showed that in both districts; Charsadda and Swabi, a significant reduction in malaria cases (143 and 365 cases having windows mesh as compared to 930 and 520 cases having no windows mesh) have been observed due to use of window screening, though this factor has little contribution to the malaria transmission in both districts (OR = 0.144 and 0.379 for Charsadda and Swabi respectively). Majority of positive malaria cases have been observed among households not having windows mesh to prevent entry of vector mosquito into the house and reduce malaria transmission in the area. Thus, presence of windows mesh plays an important role in reducing malaria case burden in malaria endemic areas.
Along with screening windows and doors, modifying the building architecture [17] and good house construction [18] may help in minimizing risks of malaria infection in disease endemic areas. These strategies could also minimize human-vector interaction, thus resulting in reduction of the disease burden in the endemic areas. In our study malaria cases were also found to be significantly associated with house type. The odds of malaria infection were found to be twice as high among houses made of mud (OR = 1.53) in Charsadda, while no association have been observed in Swabi. Houses having good construction (brick made) were having significantly low malaria cases as compared to houses having mud walls and thatched roofs. Mud walled and thatched roof houses provide favourable conditions to vector mosquitoes for resting and taking refuge in the cracks, crevices and thatched roofs. Living in towns and in indoor setting significantly reduce the malaria transmission [19]. House construct plays an important role in determining the frequency of mosquito bites and their vectoral potential because such houses provide less resting and refuge places for the vector [20]. People in rural settlements and peripheral populations of towns have been found more vulnerable to malaria due to inadequate house construct and improper sanitation [21]. Both our study districts have more rural settlements but district Charsadda is almost all rural except the town of Charsadda, which may be the reason that houses having mud wall construction play a significant role in malaria transmission in Charsadda.
Using insect repellents, indoor residual spray (IRS) and insecticide treated bed nets reduce the chances of getting infected with malaria [22]. In Pakistan Deltamethrin wettable powder is used for IRS and temephos is used as larvicide as per WHO guidelines while the only insect repellent available is in the name of Mospel (Diethyltoluamide) by Abbott laboratories Pakistan. However, the use of these insecticides was variable in both districts. In Charsadda the odds of getting malaria infection was low but significant for those who use repellents, IRS and bed nets (OR = 0.116, 0.062 and 0.166 respectively). Charsadda being waterlogged provide abundant sites for mosquito breeding resulting in high abundance of mosquitoes, therefore using insect repellents, bed nets and IRS is a common practice in the area, which helps in reducing mosquito densities thus resulting in low transmission of the disease in households using these strategies. On the contrary Swabi have canal irrigation and dry areas, not providing abundant breeding sites like Charsadda, so insecticide use in various form was found infrequent in the people of the study area and no association has been observed between them and malaria occurrence. In addition, in Charsadda government organization like roll back malaria program and international organizations like global fund carry out IRS programs and distribute bed nets among the locals [23] which may be contributing towards the reduction in disease burden. On the other hand, no such organized activity either by government or NGOs happened in Swabi and locals carry out their own IRS activity, which may be the reason of these factors not playing any significant role in malaria transmission in Swabi.
Ecology of an area effects the vector abundance by providing breeding habitat for the mosquitoes [24]. Water storage activity has been associated with malaria occurrence [25] and has been found significant in Swabi only. The odds of malaria infection were found to be twice as high (OR = 1.8) for those households using water storage containers in Swabi. Charsadda being water logged provide enough breeding sites for mosquitoes so presence of water storage container does not have significant effect on the occurrence of malaria in the study area, on the contrary, lack of abundant breeding sites due to arid area and canal system does not provide enough egg laying opportunities all the year around for mosquitoes, diverting them to breed in water storage containers [26]. Irrigated fields also play an important role in breeding of the mosquitoes and has been observed to increase the odds of getting malaria three times in Charsadda (OR = 3.37) and twice in Swabi (OR = 1.7). It has been reported that stream bed pools used for irrigation act as an important source of Anopheles culicifacies breeding during dry period resulting in seasonal peak of malaria cases [27]. Charsadda and Swabi being agricultural districts depends upon canals and streams for irrigation, which can provide breeding grounds for vector mosquitoes thus playing significant role in malaria transmission in both districts. Sleeping outside has been observed to play a major role in malaria transmission in Charsadda by getting the odd ratio of malaria four times (OR = 4.05) higher for sleeping outside at night as compare to Swabi (OR = 1.3). Sleeping habits was also found significantly associated with malaria incidence in the study area. Outdoor sleeping increases the incidence of malaria due to exposure to vector mosquitoes as use of window mesh can prohibit mosquito entrance into the rooms thus decreasing mosquito-human interaction.
Domestic animals may minimize disease transmission in the sense that they provide an alternative host for the mosquito vector to meet its blood meal requirement. It has been noted in a study in Keerom, Indonesia where most of the people keep their animals around their houses [28]. In Swabi presence of domestic animals has not been significantly associated with malaria risk but significant association has been observed in Charsadda where presence of domestic animals increases the occurrence of malaria. As it has been discussed afore that domestic animals attract vector mosquitoes and house construction type provide refuge to indoor resting mosquitoes, both these conditions have been found associated with malaria in Charsadda only, thus house type and domestic animals combine effect increase the risk of malaria in the district.