Malaria is one of the most important vector-borne diseases that causes morbidity and mortality throughout the world [8]. Worldwide cases of acute illness due to malaria are estimated to be 300–500 million; however, much of the burden is laid on African children under five years of age [27] and pregnant women [1, 27]; even the health problem is worsening in SSA countries. In Ethiopia, malaria is the leading health problem due to three-fourths of the total area of the country is malaria, and more than two-thirds of the total population lives below 2,000 m of altitude [10, 11].

Potentially, this study district is one of the malaria hotspots/ hubs in Ethiopia [24, 25]. In the present study, the overall slide-positive rate of malaria was 4,626 (10.4%) in nine-year period. This result was lower as compared with other reports such as 39.6% [28], 48% [29], 33.8% [30], 21.8% [31], and 21.8% [32] done in various parts of Ethiopia. However, it was higher than 7.15% [14], 8.4% [33], 5.4% [34], and 5% [35], which were reported elsewhere in Ethiopia. This difference could be due to the presence of studies time variation, variations in geographical locations and climate, differences in population awareness about malaria bed net application, the skill of the laboratory personnel to detect and identify malaria parasites, differences in insecticide application in the districts, expansion of irrigation, insecticide and drug resistance, and differences in health-seeking behavior of suspected individuals [26, 31, 36, 37].

The Ethiopian Ministry of Health gave great attention to achieving zero indigenous malaria in districts with annual parasite incidence less than 10 and preventing the reintroduction of malaria in districts reporting zero indigenous malaria cases by 2025 via ensuring early diagnosis and prompt treatment, strengthening vector control, improving malaria surveillance and response systems, etc. [5]. However, in the current study, malaria cases were recorded throughout the year, though fluctuation was a characteristic. The highest peaks of total malaria cases were observed in 2016 (33.2%), and the lowest peaks were observed in 2018 (2%). This result agreed with a study conducted at a Bichena primary hospital, higher and lower malaria cases were recorded in similar years [38]. Similarly, a 7-year retrospective study conducted in Dembia district by Addisu et al. [31]. indicated that the highest prevalence was observed in 2016 (30.2%), followed by 2015 (24%). However, it contradicts the Ethiopian 2011 malaria indicator survey, which reported a malaria prevalence of 1.3%. This makes our finding very higher than the 2011 Ethiopian malaria indicator report [39]. This contradiction might be associated with the employed sample size, the difference in malaria control and prevention activities implemented by stakeholders, climatic factors (rainfall and temperature), the expansion of irrigation, insecticides and drug resistance. Moreover, in this study, the second peak malaria case was seen in 2020 (20.4%). The rebound-back of malaria cases this year, probably linked to the recent impact of COVID-19 on malaria control and elimination efforts. The spreading of disease across the country was collapsing the country’s malaria control and prevention strategy [5]. Consistent with this, Eshetu et al. [18]. reported the second peak malaria case in the year 2020 in Maksegnit health center, central Gondar zone, Ethiopia.

During this survey, males were more affected by malaria parasites than females (p < 0.0001). This finding is in line with many studies conducted in different parts of Ethiopia [14, 18, 29, 31, 35, 38, 40], India [41, 42], and South Africa [43].

The presence of more infectious males than females in the present study is probably related to male work experiences and lifestyle (e.g., day labor). Males were often engaged in early night outdoor agricultural activities because irrigation activity is common in Addis Zemen. Moreover, males usually sleep outdoors to look after farms. Therefore, all these practices made males have a higher chance of exposure to be infected by the anopheles malaria vector as compared to female counterparts, who are mostly at home for taking care of children and homework purposes and protected from such infective bites. Evidence showed that much greater mosquito human-biting activities occurred outdoors than indoors during the early parts of the night, suggesting higher outdoor malaria transmission potential in Ethiopia [44]. To the reverse of our finding, a higher proportion of malaria-positive females were reported than males in Ethiopia [34] and Mozambique [45]. This variation could be coupled with the presence of low immune status of the females compared with males [46]. The presence of female house-tasks/ responsibilities/ or cooking the evening meal outdoors or reaching childbearing age or waking up before sunrise to fetch water may also put them at great risk of malaria infection [47, 48].

Regarding age, all groups were found to be infected with the malaria parasite; however, the majority of the cases were between 15 and 45 years (57%) followed by between 5 and 14 (18.3%). This was in agreement with a study conducted in Kola Diba [28], Kombolcha [14], Wolkite Health Center [49], Bichena Health Center [38], and Maksegnit Health Center [18]. However, in contrast to this finding, the study conducted in Wolita [50] and Metema Hospital [51] showed high malaria positivity in 5–14-years older than the rest age groups. The presence of more malaria infected between the 15–45 age groups in Addis Zemen town is probably linked to the regular practice of irrigation activity in the town and its surroundings [52,53,54]. All these practices are more exposed to productive age groups and males to anopheles mosquito bites, which can transmit Plasmodium parasites.

This study revealed the prevalence of P. falciparum (80.1%), P. vivax (18.5%), and mixed infections (1.4%). The existence of these two parasites is comparable with the previous documents made in Ethiopia, which were the most common parasites across the country [28, 29, 31, 38, 55]. P. falciparum was the most predominant species than P. vivax, which it exceeded about fourfold. This finding was in agreement with other previous studies conducted in Metema (P. falciparum, 90.7% and P. vivax, 9%) [51], Kola Diba (P. falciparum, 75% and P. vivax, 25%) [56], Woreta town (P. falciparum, 69.7% and P. vivax, 26.5%) [29], and selected Amhara region (Central, North and West Gondar zones) (P. falciparum, 73.4% and P. vivax, 26.6%) [55]. A previous report from WHO [57] supported this reality too, P. falciparum and P. vivax accounted for 70% and 30% of all laboratory-confirmed cases, respectively in Ethiopia. The exclusive predominance of P. falciparum over P. vivax could be that the P. falciparum parasite can multiply rapidly by involving more than one parasite in a single red blood cell, colonizing all ages of the red blood cells without any selection, parasite-infected red blood cells can accumulate in various organs, and the availability of P. falciparum-infected cases in communities [58, 59]. Furthermore, the drug resistance nature [60,61,62], misdiagnosed and inappropriate therapy [63], and gaps of programme performance could be the other possible reasons for such dominance.

Contrary to the current study, many other studies reported a higher proportion of P. vivax, than P. falciparum in many parts of Ethiopia [64,65,66,67,68,69]. Additionally, in Butajira P. vivax was 62.5% [70], in Hallaba health center P. vivax was 70.41% [71], in Adim Tullu district P. vivax was 84.6% [72], and in Wolkite health center P. vivax was 69.7% [49], Ethiopia. The possible explanation for this trend shifts from P. falciparum to P. vivax might be due to the public health importance of P. vivax, i.e., frequently overlooked and left in the shadow of the enormous problems (headache, shivering, appetite loss, anemia, nausea, vomiting) caused by P. falciparum [63]. In addition, the prevention and control activities of malaria as guided by the national strategic plan (2006–2010) mainly focus on P. falciparum because it is assumed to be more prevalent and fatal malaria in the country Ethiopia [73]. Another possible reason might be climate variability [65].

In our study, the proportion of both P. falciparum and P. vivax showed a slight increment from 2013 and reached a peak level in 2016, and then declined and reached the lowest level in 2018. Again, they showed an alarming rise in 2020. Consistent with this finding, Minwuyelet & Aschale [38] reported high and low prevalence levels of P. falciparum and P. vivax in Bichena primary hospital in 2016 (6.81%, 2.67%) and 2018 (2.13%, 1.65%), respectively. On the contrary, other retrospective studies [16, 32, 55, 74, 75] done in various parts of Ethiopia indicated that there was an overall decline in malaria incidence associated with a decrement of P. falciparum and P. vivax. The lack of smooth reduction in the present study could be connected with COVID-19 [5] and the absence of better practices of malaria prevention and control strategies, i.e., the use of LLINs alone, IRS alone, or the use of improper insecticide-treated bed nets [76]. Besides, in Addis Zemen town irrigation is common and farmers may spend most of their time in the field, which exposes them to mosquito bites [77].

Malaria cases were occurring throughout the months of each year and showed significant variation (χ2 = 60.904, d.f.=11, p < 0.0001). The highest peaks of total malaria cases were observed during September, October, and November, and the lowest peaks were observed during March and April. In particular, the highest P. falciparum cases were recorded in September, October, and November and the minimum cases were recorded in April and then March. Likewise, the highest P. vivax cases were documented during September, November, October, and the least cases were observed in April, January, and February. Our findings are consistent with other studies conducted in Bichena Primary Hospital [38], Woreta Health Center [34], and Boricha district [32]. Moreover, other previously made studies [14,15,16] in various parts of Ethiopia also documented the presence of increased total malaria cases in September, October, and November. These months are considered the peak malaria transmission period in Ethiopia after the heavy rain in July and August [5, 78].

Regarding the seasonal distribution of malaria, in our findings, the highest and the lowest cases of malaria were observed during spring (40.20%) and autumn (17.40%), respectively. In line with this, Getacher et al. [15], Alkadir et al. [16], and Minwuyelet & Aschale [38] reported highest and lowest peak of total malaria cases in spring and autumn in Bichena primary hospital and Ataye district, Ethiopia, respectively. Moreover, Alemu et al. [65]. in Jimma town, Gemechu et al. [79]. in Sibu Sire district, Alelign et al. [29]. in Woreta town, and Gebretsadik et al. [14]. in Kombolcha health center, Ethiopia, had reported peak malaria cases in spring than in other seasons. This season is preferable for mosquito breeding because it provides appropriate temperature and enough rainfall for them. In Ethiopia, the peak malaria transmission occurs between September and December following the June to September long rains [73, 78]. Different from this result, Eshetu et al. [18]. reported highest malaria cases in Autumn than in other seasons in Maksegnit Health Center. The review of Alelign et al. [29]. also indicated that Autumn was the second peak malaria season in Woreta town. This would be an important indication that the area needs due attention and further concerted malaria interventions.