The persistent threat of malaria in Bishoftu Town: twelve-year trends and their implications for Addis Ababa

Abstract

Bishoftu town, located about 40 km from the largely malaria-free Addis Ababa, remains malaria-endemic. Factors that possibly heighten exposure risk include abundant water bodies, increased visitors during events such as the Irreechaa festival, climate change, and changing land-use around the town. Frequent travel and strong interconnections raise concerns about spillover to Addis Ababa via infected people or mosquitoes. The potential spread of the invasive urban vector Anopheles stephensi is an additional concern, although there is currently little evidence of its introduction in Bishoftu. Future surges in transmission could be facilitated by infrastructure projects most particularly the construction of a major new airport in Bishoftu that will increase visitor traffic. Analysis of 252,610 blood films from the Bishoftu Town Health Office (January 2011 - December 2022) revealed 5,696(2.3%) malaria cases, with Plasmodium vivax at 63.8% and P. falciparum at 31.0%. The highest incidence (804 cases) occurred in 2017, with individuals > 14 constituting 66.3% of cases. Findings indicate persistent malaria with a fluctuating trend, highlighting the need for aggressive surveillance and targeted control measures to combat malaria in Bishoftu and prevent its spread to Addis, considering demographic shifts, increased mobility, and the development of recreational water pools associated with development projects.

Introduction

Globally, significant progress in malaria control occurred between 2000 and 2015 [1], with an increasing number of countries eliminating malaria [2]. This involved reducing cases and deaths through vector control and effective case-management using rapid diagnostics and artemisinin combination therapies [3], as well as licensing the first malaria vaccines for children [4]. However, the post-2019 situation is concerning, marked by a resurgence of malaria [5]. The latest World Malaria Report [6] estimated 282 million malaria cases and over 600,000 deaths, figures slightly higher than those reported in 2023 [5].

Ethiopia mirrors this, showing marked declines in malaria burden since 2000 [7, 8], which facilitated plans for elimination in select areas [9]. The country also introduced a childhood malaria vaccine [10]. Nevertheless, from January 1 to October 20, 2024, Ethiopia reported over 7.3 million malaria cases and 1,157 deaths, the highest annual count in seven years [11]. Evidence is mounting on the determinants explaining the current global malaria resurgence [12–16]. Urbanization is recognized as a key factor in malaria transmission, particularly in sub-Saharan Africa [17]. In Ethiopia, rapid urbanization and extensive development projects are occurring nationwide. Given these changes, malaria must be closely monitored, both prospectively and retrospectively. Understanding the fluctuations of malaria cases is crucial for determining effective interventions tailored to each locality. Local urban centers are vital to monitor, as they can become hotspots for malaria spillover into previously non-endemic areas. Retrospective trend analysis identifies patterns in malaria incidence over time. By examining historical data, public health officials can understand factors contributing to resurgence, evaluate past interventions, and adjust current strategies. Assessing the epidemiological patterns in specific health facilities is essential for monitoring progress toward malaria containment and elimination.

This study evaluated twelve-year malaria trends in Bishoftu town (formerly Debre Zeit), central Ethiopia, addressing a critical gap in knowledge. Bishoftu poses significant risks to Addis Ababa, a largely malaria-free city just 40 km away. The study provides insights for public health authorities to develop targeted strategies against the rising threat of malaria in urban contexts, highlighting Bishoftu’s vulnerability and potential spillover to Addis Ababa.

Methods

Study setting and design

Bishoftu town is located at 1900 m altitude (8°45′ N, 38°58′ E), with a population of 207,383 (109,106 females) [18]. The population density is 40.02 individuals per km², with a 5% annual growth rate between 2007 and 2022. The town has five public health centers and one hospital.

Data extraction and analysis

The study population included malaria suspects visiting Bishoftu health centers and hospital (January 2011 - December 2022) whose blood samples were examined microscopically per WHO guidelines. Laboratory technicians reported data annually to the Bishoftu town health office. A checklist compiled twelve-year data on year, demographics, slide status, and Plasmodium species. The chi-square test and Student’s t-test assessed relationships between malaria and demographics, with statistical significance set at p < 0.05.

Results

Annual trends

A total of 252,610 patients were examined during the study period, with 5,690 positives (3.2%). Data from individual facilities were not accessible. The highest number of cases was in 2017 (804), followed by 2012 (704) and 2014 (548), while the lowest was in 2015 (165). Similar case numbers were reported in 2011, 2019, 2020, and 2021. An upward trend in malaria cases was observed from 2011 to 2022, with declines in 2013, 2015, and 2018. The highest percentage of slide positives was in 2019 (3.7%), followed by 2020 (3.4%) and 2012 (3.2%), while the lowest were in 2018 (0.95%) and 2015 (1.1%). Overall, the annual cases fluctuated (Table 1).

Table 1.

Patients examined for malaria, slide-positive cases, and Plasmodium species distribution in Bishoftu Town (2011–2022)

Year	Slide	Positives	Percent (%)	P. vivax	P. falciparum
2011	24,343	487	2.0	390	97
2012	21,963	704	3.2	363	341
2013	23,785	359	1.5	261	98
2014	23,478	548	2.3	362	186
2015	15,243	165	1.1	77	88
2016	21,345	386	1.8	226	160
2017	29,365	804	2.7	710	94
2018	25,656	243	0.95	185	58
2019	12,450	458	3.7	257	201
2020	14,685	502	3.4	358	144
2021	16,808	497	2.9	390	107
2022	23,489	537	2.3	347	190
Total	252,610	5,690	2.3	3,926	1,764
p-value	< 0.001	< 0.001	< 0.001	0.002	0.003

Distribution of Plasmodium species

Plasmodium vivax (3,629 cases, 63.8%) and P. falciparum (1,764 cases, 31.0%) were co-endemic (Table 1). P. vivax incidence was consistently higher, except in 2015, peaking at 710 cases in 2017, with similar counts in 2011, 2021, 2012, 2014, and 2020. P. falciparum cases peaked in 2012, followed by 2019, 2022, and 2014, with the lowest in 2018 and 2015. Years 2017, 2011, and 2013 had similar cases for both species. In 2012, P. vivax cases were lower than in 2015. The differences were significant (p < 0.001).

Malaria distribution by age and gender

Malaria cases varied by demographics. In the under-five group, there were 322 males and 349 females; in the 5–14 group, 667 males and 578 females; and in the over-14 group, 2,122 males and 1,652 females (Table 2). An upward trend in malaria cases was observed with age, peaking in the over-14 group, with a statistically significant difference (p < 0.001). The proportions of malaria-positive individuals were significant for age groups < 15 (1,916 cases, 33.7%) and ≥ 15 (3,774 cases, 66.3%) (p < 0.001). Males had a higher number of positive cases than females, except in 2021. The highest incidence for both sexes was in 2017, followed by 2012 and 2014, with the lowest in 2015. Overall, males accounted for 54.7% and females 45.3% of cases, though the difference was not significant (p = 0.387). However, the number of tested individuals by sex or age category is unknown, preventing calculation of specific proportions.

Table 2.

Malaria cases by year, gender, and age groups in Bishoftu town (2011–2022)

Year	Tested	Pos	< 5 M; n, %	< 5 F; n, %	5-14 M; n, %	5–14 F; n, %	> 14 M; n, %	> 14 F; n, %
2011	24,343	487	21, 0.09	22, 0.09	51, 0.21	46, 0.19	220, 0.9	127, 0.52
2012	21,963	704	38, 0.17	43, 0.20	97, 0.44	85, 0.39	244, 1.1	197, 0.90
2013	23,785	359	24, 0.10	18, 0.08	44, 0.18	38, 0.16	145, 0.6	90, 0.38
2014	23,478	548	25, 0.11	26, 0.11	81, 0.35	70, 0.30	176, 0.8	170, 0.72
2015	15,243	165	10, 0.07	17, 0.11	15, 0.10	21, 0.14	67, 0.4	35, 0.23
2016	21,345	386	23, 0.11	22, 0.10	54, 0.25	42, 0.20	144, 0.7	101, 0.47
2017	29,365	804	58, 0.20	99, 0.34	108, 0.37	63, 0.21	285, 0.9	191, 0.65
2018	25,656	243	14, 0.05	8, 0.03	33, 0.13	25, 0.10	103, 0.4	60, 0.23
2019	12,450	458	48, 0.39	45, 0.36	21, 0.17	17, 0.14	158, 1.3	169, 1.4
2020	14,685	502	35, 0.24	26, 0.18	60, 0.41	78, 0.53	175, 1.2	128, 0.87
2021	16,808	497	15, 0.09	14, 0.08	39, 0.23	35, 0.21	147, 0.9	247, 1.5
2022	23,489	537	11, 0.05	9, 0.04	64,0.27	58, 0.25	258, 1.1	137, 0.58
Total	252,610	5,690	322	349	667	578	2122	1652
p-value	< 0.001	< 0.001	0.039	0.04	0.04	< 0.001	0.001	0.005

Discussion

The slide-positivity of 2.3% is lower than reports from various Ethiopian settings [19–25]. This could be due to better bed net distribution, larval source management, and community awareness campaigns. Differing community awareness and intervention implementation, and variations in socio-demographic status and intervention utilization influence malaria transmission [26]. The low malaria frequency may also be due to species variation, with more prevalent P. vivax potentially leading to false-negative microscopy diagnoses due to lower parasite density [27]. The dominance of P. vivax may also be due to hypnozoites [28].

Despite lower overall prevalence, attention is needed for malaria in Bishoftu, particularly P. vivax. Studies [29–34] have reported chloroquine resistance in P. vivax, raising concerns about controlling this species. Globally, malaria prevention often focuses on P. falciparum, seen as more prevalent and fatal, risking neglect of P. vivax, which also contributes to morbidity and complicates control efforts. Ignoring P. vivax may lead to a resurgence, hindering elimination strategies and requiring comprehensive monitoring and interventions for both species. Studies [35–37] indicate substantial P. vivax prevalence in Ethiopia, suggesting a potential surge in specific areas, necessitating increased awareness and targeted interventions.

The inter-annual malaria case count fluctuated in Bishoftu over 12 years. The rise in incidence in 2019 aligns with findings from 25 urban towns in Ethiopia [38]. Similarly, increased cases in 2020 are consistent with [39], potentially linked to the COVID-19 pandemic, which redirected resources away from malaria. A significant association was found between age and malaria, with those > 14 most affected, followed by ages 5–14, while under 5 were least affected. Males showed higher incidence than females, though not significantly. The elevated incidence among males > 14 may be due to outdoor activities and travel, consistent with other studies in Ethiopia [40–42].

Bishoftu faces a significant health challenge from malaria, particularly P. vivax, amid rapid urbanization. Located 40 km south of Addis Ababa, the town is set for growth with the upcoming launch of Africa’s largest airport, expected to initially accommodate 60 million passengers, potentially increasing to 110 million [43]. This surge in travel may facilitate malaria spread between Bishoftu and Addis Ababa. The phenomenon of ‘urban malaria travelers’ poses a serious risk, as evidenced by a recent Saudi Arabian study linking nearly all malaria cases in 2022 and 2023 to travel [44].

Bishoftu’s growing reputation as a recreational center, with hotels and resorts, attracts diverse visitors, including Ethiopian weekenders and international tourists. Population and economic growth are primarily driven by rural-urban migration rather than natural fertility [45]. Many residents commute between Bishoftu and Addis Ababa for work, increasing malaria risk in previously safe areas. Urbanization, while promoting economic growth, also facilitates the spread of infectious diseases like malaria [46–47]. Additionally, urbanization in Africa leads to lifestyle changes that heighten the risk of non-communicable comorbidities [48], complicating malaria management.

Climate change exacerbates the malaria landscape, as rising temperatures expand the habitat of malaria vectors [49]. This shift increases transmission risk in Bishoftu and threatens Addis Ababa, where conditions are becoming more favorable for malaria. Indigenous cases were reported in the southern suburbs of Addis Ababa two decades ago [50]. Recent reports of indigenous malaria near Bishoftu heighten concerns. Retrospective analyses show a rising trend in malaria cases in Addis Ababa, with a notable increase in outpatient treatments since 1996. A significant outbreak occurred in Akaki in 1998/1999, with clinical cases more than tripling during the peak [51]. This surge indicates that malaria is becoming a major contributor to morbidity, straining health services. The 1998/1999 epidemic is thought to be linked to climate change, as climatic data indicate rising regional temperatures [52]. The ongoing threat from P. vivax stresses the urgent need for effective surveillance and control measures in urban settings. Bishoftu’s cultural significance as a center for the Irreecha festival [53] may further complicate malaria risk. This major event attracts large gatherings during the peak malaria transmission season, increasing exposure to mosquito bites.

While our study does not specifically investigate Anopheles stephensi, its emergence as an urban-adapted malaria vector in Ethiopia poses a significant threat to control efforts. Reports indicate that An. stephensi has established itself in urban environments of Ethiopia [54], where conditions in Bishoftu, such as increased population density and changes in land-use, may facilitate higher transmission rates. Water development projects are known determinants of malaria transmission in Ethiopia and elsewhere [55, 56]. Additionally, Lake Hora, a major tourist attraction just north of the town center, is suitable for mosquito breeding. This largest of Bishoftu’s lakes [57], alongside other crater lakes, creates favorable microecologies for mosquitoes.

The existing and emerging risks of malaria transmission in Bishoftu necessitate urgent attention, particularly regarding P. vivax and An. stephensi. Scaling-up malaria control and elimination efforts is essential to reduce the potential for outbreaks in Addis Ababa and surrounding areas. Recognizing the interconnectedness of urban areas allows effective public health measures to protect both Bishoftu and Addis Ababa from an escalating malaria crisis. Addressing this issue is critical for safeguarding public health on a larger scale. Our findings highlight the urgency for targeted interventions and strategic resource allocation to augment malaria prevention efforts in Bishoftu and beyond. The study’s limitations include the absence of seasonal data and details on examinations by age or sex. Additionally, information on mixed infections, mortality cases, other Plasmodium species, levels of disease severity, and spatial distribution is lacking.

Conclusion

In this twelve-year retrospective analysis, P. vivax was the dominant species and individuals aged ≥ 15 years represented the largest proportion of reported cases. Although Bishoftu’s overall slide-positivity was lower than many other Ethiopian settings, the town faces important and evolving risks for urban malaria. Factors such as abundant water bodies, large seasonal gatherings (e.g., the Irreecha festival), rapid urbanization, increased mobility related to tourism and infrastructure developments, and the documented regional expansion of the urban-adapted vector An. stephensi raise the possibility of increased transmission and potential spillover to nearby Addis Ababa. Importantly, we did not perform entomological surveys in this study and do not claim confirmed An. stephensi presence in Bishoftu. Instead, we describe An. stephensi as a potential and plausible threat given its regional spread and Bishoftu’s ecological and socio-demographic characteristics. We recommend immediate targeted entomological surveys and larval-habitat mapping including molecular species identification and insecticide-susceptibility testing. Overall, integrated malaria control measures will enable timely, evidence-based interventions to prevent outbreaks and protect both Bishoftu and nearby Addis Ababa.

Abbreviation

WHO

World Health Organization

Author contributions

BCD conceptualized the study, collected and analyzed the data, interpreted the findings, drafted the manuscript. HM critically reviewed the manuscript. Both authors have read and approved the final version of the manuscript for publication.

Funding

This study did not receive any specific financial support.

Data availability

The data used to prepared this manuscript is fully presented here.

Declarations

Ethics approval and consent to participate

The College of Natural and Computational Sciences Institutional Review Board (CNCS-IRB) at Addis Ababa University states that ethical approval is not needed for studies that do not involve human or animal subjects and do not collect biological samples. Instead, we obtained approval letters from the Department of Microbial, Cellular and Molecular Biology and Bishoftu Town Health Office.

Competing interests

The authors declare no competing interests.