The initial 534 records and 4 from other sources are highlighted (Fig. 1). After duplicates were removed 449 records were left. A further 363 records (irrelevant) were excluded based on the inclusion criteria discussed above. A total of 86 abstracts were accessed based on the PICO, of which a further 62 were excluded after full reading. A total of 24 papers were left for review and further citation search yielded no new articles.
With various approaches, malaria transmission in South Africa has been linked to climatic conditions. For instance, 14 studies (58.3%) out of 24 presented in supplementary table highlighted the significant roles that climate plays on the resurgence. Although some of the 14 studies also mentioned other factors, emphasis was more on climate. Furthermore, it is noted in line with Adeola et al (2017) that climatic factors affecting malaria transmission in South Africa cannot be generalized across the epidemic regions . For instance, temperature seems to be the major factor in KwaZulu-Natal province as highlighted in 4 of the 14 studies [21-24]. However, two of the four studies [21, 23] also acknowledge the importance of rainfall on malaria transmission over the province. Rainfall seems more significant on malaria resurgence in Limpopo than temperature as indicated by four other studies [5, 6, 25, 26]. Also, two of the four likewise pointed to the significance of temperature. [5, 26] In addition, Behera et al (2018) attributed malaria resurgence over the province to El Niño/La Niña and sea surface temperature (SST) from the south-western Indian Ocean . We found only three studies [5, 8, 27] linking the resurgence to climate in Mpumalanga province over the study period. Kapwata and Gebreselassie (2016) and Adeola et al (2017) believe that transmission over the province is associated with surface land temperature and other non-climatic factors [5, 27], while Abiodun et al (2018c) found that rainfall and relative humidity are more significant .
Similar findings were established over some South African neighbouring countries such as Zimbabwe [28, 29], Mozambique [30, 31], Botswana  and East African highlands [33-35].
Half of the 24 papers highlight the importance of mosquito abundance on malaria resurgence across the epidemic regions in South Africa [5, 8, 15, 21, 22-24, 36-40]. For example, using climate-based mathematical models, the impact of mosquito (mainly An. arabiensis) population dynamics on malaria transmission was investigated over KwaZulu-Natal [21, 22, 24, 36, 39]. Limpopo and Mpumalanga provinces . With statistical approach, other studies confirm mosquitos’ impact on the resurgence [5, 38, 40]. More importantly, the resurgence has been traced to arrival of new mosquito species across the epidemic regions .
Similarly, the importance of mosquito abundance on malaria transmission has been investigated in Zimbabwe [41, 42], Mozambique [43, 44] and Namibia .
Six (25%) out of the 24 selected studies have connected malaria resurgence in South Africa with socio-economy factors [6, 37, 46-49]. For instance, it has been established that migration from neighbouring countries were found to be the cause of malaria over Limpopo  and KwaZulu-Natal provinces . Most researchers and stakeholders working on malaria in South Africa believe that South Africa’s 2018 malaria elimination target was not realistic due to lack of new tools, resources and the capacity to fight malaria; coupled with poor cross-border collaborations; overreliance on partners to implement; poor community involvement; and poor surveillance [46, 47]. Inadequate communication channels on malaria control, such as Sterile Insect Technique (SIT) also play significant roles on malaria transmission . Practicing animal husbandry, residing in household structures that had not been sprayed were greatly found to be associated with malaria infection over KwaZulu-Natal province . It has also been established that the odds of malaria infection are lower in modern, improved housing compared to traditional housing in sub-Sahara Africa .
The impacts of socio-economic factors on malaria transmission have also been highlighted in Malawi  Gambia  and Ghana .
Four studies (16.7%) linked the resurgence to environmental factors. The resurgence in Mpumalanga province has been associated with normalized difference vegetation index (NDVI) [5, 53] normalized difference water index (NDWI), altitude, water body and irrigated land [5, 54]. Malahlela et al (2018) concluded that the resurgence in Limpopo province is traceable to vegetation moisture and vegetation greenness. We found no study in this regard over KwaZulu-Natal within the study period .
Environmental factors such as vegetation index, water body, among others have been similarly linked to malaria incidence in Kenya , Zimbabwe [56, 57], Botswana  and Eritrea .
In general, climate variables play major roles in malaria transmission across all the epidemic provinces. For instance, four of the papers suggested that both temperature and rainfall are equally responsible for the transmission in KwaZulu-Natal, while two suggested similar findings over Limpopo. However, three additional papers concluded that the impact of temperature on the transmission is more significant than that of rainfall on KwaZulu-Natal and Mpumalanga provinces. This implies that effect of temperature is more pronounced over the two provinces. Rainfall is seen to be more significant than temperature over Limpopo province.