Imported Malaria in Qazvin Province, Iran: A Retrospective Study From 2008 to 2023

1.Introduction
Malaria, caused by Plasmodium parasites, remains a significant issue for public health globally, significantly impacting children and pregnant women residing in tropical and subtropical areas of the world [1]. The transmission occurs via the bite of infected female Anopheles mosquitoes during their blood-feeding process [2]. Further modes of transmission include blood transfusions, congenital transmission (from an infected mother to a fetus during the acute phase of infection), and organ transplantation [3]. Five primary Plasmodium species, including P. vivax, P. falciparum, P. malariae, P. ovale, and P. knowlesi, are responsible for human malaria. Zoonotic Plasmodium parasites such as P. inui and P. cynomolgi can also infect humans [4]. 
Annually, the world malaria report published by the World Health Organization (WHO) offers a detailed and current assessment of malaria control and elimination trends worldwide. According to WHO’s 2023 report, malaria constitutes a considerable global health concern, with an estimated 249 million cases and 608,000 deaths reported across 85 endemic countries in 2022 [5]. 
The clinical presentation of malaria differs between children and adults. Symptoms can vary from mild febrile syndrome in uncomplicated cases to severe, life-threatening complications such as severe anemia, acute respiratory distress syndrome, hypoglycemia, shock, metabolic acidosis, acute kidney injury, or cerebral malaria [6]. 
Studies conducted in Iran have identified P. vivax as the predominant malaria species, while P. falciparum is primarily limited to the eastern and southeastern regions of the country [7, 8]. Historically, malaria was prevalent in Iran, with an estimated four to five million out of a population of 13 million reported to have been affected by the disease by 1924 [9]. The anti-malaria campaign launched in 1951 led to the interruption of malaria transmission in many regions. Reports from recent years have revealed a decreasing trend in malaria incidence in Iran [10]. 
In recent years, Iran has experienced a significant decline in malaria incidence rates. The 2009 WHO malaria report stated that Iran was in the pre-elimination phase. The ultimate goal of Iran’s malaria elimination program is to terminate local malaria transmission by 2025 [7]. 
During 2021 and 2022, political unrest in Afghanistan and floods in Pakistan caused a surge in malaria outbreaks and a notable influx of migrants and refugees. This situation heightened the risk of imported malaria cases in Iran [11]. Factors such as war, violence, drought, insecurity, and unemployment have led to Afghan migration to Iran [12]. On August 15, 2021, the Taliban captured Kabul, resulting in the collapse of the Islamic Republic of Afghanistan and prompting a considerable influx of refugees into Iran [13]. Many of them carried a range of infectious diseases, including tuberculosis, cholera, Crimean-Congo hemorrhagic fever (CCHF), leishmaniasis, hepatitis B, and malaria [14]. Moreover, recent reports indicate that a majority of Afghan migrants (74%) in Iran are individuals aged 24 and younger, frequently arriving to pursue employment opportunities. This demographic trend could potentially contribute to the spread of various infectious diseases [15].
Qazvin Province, situated in northern Iran, is home to a considerable population of Afghan refugees residing on the outskirts of Qazvin City [16]. As a result of the importance of this issue, we aimed to study the epidemiological features of imported malaria and investigate the cases reported between 2008 and 2023 in Qazvin Province, northwestern Iran. 

2. Materials and Methods
2.1. Study area
Qazvin Province, with a population of approximately 1,273,761, is an area of 15,821 km2 located in the Northwestern part of Iran. It is situated between longitudes 48° 45′ to 50° 50 E and latitudes 35° 37′ and 36° 45′ N. It is surrounded by the Zagros Mountains to the west and the Alborz Mountains to the northeast and southeast. Moreover, it shares borders with Mazandaran and Guilan provinces to the north, Hamedan and Zanjan provinces to the west, Markazi Province to the south, and Tehran Province to the east [17, 18]. 

2.2. Cases and data collection 
Patients referred to the health centers and the Vice-Chancellor of Health in Qazvin Province underwent blood sample collection using a sterile lancet. Subsequently, a drop of blood was placed on a slide to prepare peripheral blood smears, stained with Giemsa and examined under a light microscope to detect and identify parasites. All cases were diagnosed by the lab-confirmed method, and there was no mortality. A questionnaire capturing various demographic factors was created for each confirmed case. These included: Name, age, reporting year and month, forms of malaria (passive/active), gender, occupation, county, nationality, parasite species, parasitic stage in blood, and other pertinent information was recorded. 

2.3. Statistical analysis 
Microsoft Excel and Stata software, version 18 were used to perform the descriptive analysis. The chi-square (χ2) test was used to compare the data counts. A P<0.05 was regarded as statistically significant.

3. Results
Between 2008 and 2023, 41 imported malaria cases, including 40(97.56%) males and one (2.44%) female, were reported in Qazvin Province (Table 1).

In terms of age groups, the highest prevalence was observed in the 21-30 age group [16(39.02%)], followed by the 11-20 age group [12(29.27%)] (Table 1). 
The highest prevalence rate of malaria cases [15(36.59%)] was documented in 2008, followed by cases reported in 2023 [7(17.07%)]. Additionally, regarding the seasonal distribution, the highest number of cases was reported in May during 2008-2023, when malaria accounted for 9(21.95%) cases. The lowest monthly incidence of malaria, 1(2.44%), occurred in January (Table 1, Figure 1).

P. vivax was the most prevalent species, accounting for 36 cases (87.80%), while P. falciparum was the etiological agent diagnosed in 5 cases (12.20%) (Table 1). 
Regarding the two forms of the disease, passive malaria exhibited the highest prevalence, with 39 cases (95.12%). Additionally, among the different stages of the parasite in the blood, trophozoites were the most frequently observed stage, accounting for 18 cases (43.90%) (Table 1). 
The nationality-based analysis showed that the sources of the 32 imported malaria cases were countries outside Iran (Afghanistan and Pakistan), with Afghans constituting the largest proportion, accounting for 30 cases (73.17%) (Table 1). 
According to the occupation, workers had the highest prevalence, accounting for 27 cases (65.85%) (Table 1). 
The county-based analysis revealed that the highest and lowest prevalence values were documented in Qazvin [22(53.66%)] and Abyek [1(2.44%)], respectively (Table 1, Figure 2).

The analysis of disease severity and type of medical services indicated that the highest prevalence was observed in the group recorded as outpatients with no complications, comprising 14 cases (34.15%) (Table 1).
According to the χ2 test, a statistically significant association was observed between nationality and occupation (P=0.0001). The highest prevalence was found among Afghan workers [26(63.41%)] (Table 2).

Additionally, no significant differences were observed in other malaria-related risk factors (Supplementary Tables 1, 2, and 3).

4. Discussion
To our knowledge, this is the first report on imported malaria cases in Qazvin, Iran. In the current study, we analyzed longitudinal surveillance data of imported malaria collected between 2008 and 2023 to explore the epidemiological characteristics of the disease. Four principal epidemiological features were identified through our analyses. First, P. vivax was the predominant species among imported malaria cases, with the majority originating from Afghanistan, which accounted for the highest number of cases. Second, most imported malaria cases were concentrated in Qazvin, the province›s capital. Third, most cases involved workers, mainly adult men aged 21-30. Fourth, seasonal variations were observed in imported malaria cases; however, it is noteworthy that in 19.51% of cases, the month variable was not recorded. 
In Asia, particularly in Pakistan and Afghanistan, malaria remains a significant public health concern, with ongoing transmission of both P. falciparum and P. vivax [19, 20]. Afghanistan and Pakistan, which share borders with Iran, are malaria-endemic countries. The significant human migration from these countries to Iran facilitates malaria transmission and presents substantial political, social, operational, and technical challenges to the elimination of malaria in Iran [21, 22]. Despite efforts to control malaria, it remains a significant health issue in the southern regions of Iran. Most local malaria transmission occurs in Sistan and Baluchestan, Hormozgan, and Kerman provinces [23, 24]. 
A comparison of our findings with data from other Iranian provinces reveals distinct epidemiological patterns shaped by regional factors. In southern provinces such as Sistan and Baluchestan, Hormozgan, and Kerman, malaria transmission remains a mix of indigenous and imported cases, driven by proximity to endemic countries like Pakistan and Afghanistan, as well as favorable ecological conditions for Anopheles vectors [23, 24]. For instance, Sistan and Baluchestan reports the highest burden of P. vivax and P. falciparum due to cross-border movement and local transmission. The province accounted for 53% of all malaria cases in Iran in 2007. Its borders with Pakistan and Afghanistan facilitate considerable cross-border population movement, contributing to the malaria burden [25]. In contrast, Qazvin Province, located in the northwest, has no indigenous transmission and relies entirely on imported cases, primarily from Afghan migrants.
Notably, provinces bordering Afghanistan, such as Khorasan Razavi, report higher imported cases but also face sporadic local outbreaks due to vector presence. Accordingly, 61% of the cases were transmitted from outside the province, including immigrants from Afghanistan and Pakistan, while 34.6% of the cases were due to local transmission, particularly in Sarakhs City, where conditions support sporadic local outbreaks [26]. Unlike these regions, Qazvin’s colder climate and mountainous geography limit vector activity, reducing the risk of re-establishment despite imported cases.
Seven species of Anopheles mosquitoes, including Anopheles stephensi, An. culicifacies s.l., An. superpictus s.l., An. fluviatilis s.l., and An. maculipennis complex (An. sacharovi and An. dthali), are malaria vectors in Iran [27]. Imported malaria constitutes most of the disease cases in Iran (based on reports of imported cases in Iran). Our study showed that imported malaria was the reason for all cases in Qazvin Province during the study period. Imported malaria disseminates malaria parasites to a region and contributes to local transmission. This occurs when local Anopheles mosquitoes feed on individuals who have traveled to the area and are infected with malaria [28]. 
Malaria is endemic in Pakistan and is still one of the leading causes of illness and death in the region. The most significant increase in malaria cases from 2021 to 2022 was observed in Pakistan, with approximately 2.6 million cases reported in 2022 compared to 500,000 cases in 2021 [5]. More than 170,000 cases were laboratory confirmed, with 77% attributed to P. vivax and 23% to P. falciparum [29]. The surge in cases in Pakistan in 2022 followed devastating floods in the country between June and October, resulting in a fivefold increase in the caseload. Additionally, countries such as Iran, which had not reported indigenous cases for several years, recorded more than 1,000 cases in 2022 [5]. 
Extreme malaria transmission primarily occurs in districts situated along the borders with Iran and Afghanistan and along the coastal belt in the Sistan and Baluchestan Province. Moreover, there is a significant population movement between Pakistan and its neighboring countries, particularly Afghanistan and Iran. This movement is exceptionally high in Khyber Pakhtunkhwa Province, which hosts over one million Afghan refugees [29]. 
Since 2002, Iran has launched strict measures limiting the movement of refugees and has designated “no-go areas” for refugees. Initially limited to border provinces, these restrictions now extend to most of Iran’s 31 provinces, with Mazandaran Province being the most recent addition. Sixteen provinces have completely banned Afghans residing within their boundaries, while twelve provinces have restrictions on specific areas and cities. Tehran, Alborz, and Qom are the only provinces where Afghan refugees are not subject to residential restrictions [30]. It is noteworthy that all eight individuals of Iranian nationality included in our study had a history of traveling to the southern regions of Iran.
Our research has certain limitations. First, the study’s reliance solely on microscopic diagnostic techniques could constrain the precision of the findings. Further diagnostic methods, such as molecular or serological testing, may offer a deeper comprehension of the disease. Second, in some cases, patients’ histories—such as occupation, month of onset, severity of disease, and medical services, and forms of malaria (passive/active) —were not applicable or were not documented in detail. However, the present paper provides the most valuable information on imported malaria in Qazvin Province, which can offer new and significant insights for researchers in infectious and tropical diseases. This can help in further planning comprehensive and precise health programs to decrease the incidence of this infection in Qazvin Province.

5. Conclusion 
This study provides valuable insights into the epidemiological characteristics of imported malaria cases in Qazvin Province between 2008 and 2023. The challenge of imported malaria, particularly P. vivax, poses a significant obstacle to malaria elimination efforts in Iran. Although no mortality was reported in our study and P. vivax represented a higher prevalence than P. falciparum, it is still recommended to diagnose and treat imported P. falciparum infections promptly to prevent fatal cases. We observed that most cases were Afghans, with workers as the most affected group. Thus, to address this challenge, malaria prevention activities should mostly focus on imported Afghan workers. Furthermore, to sustain progress in the elimination of malaria in Iran, it is necessary to prevent the re-establishment of the disease caused by imported cases. Enhanced surveillance and preventive measures are imperative to mitigate the burden of imported malaria and prevent its spread in Qazvin Province. Finally, our findings emphasize the importance of targeted interventions and effective malaria prevention strategies, which must focus on populations involved in cross-border movements.

Ethical Considerations
Compliance with ethical guidelines
This study was approved by the Research Ethics Committee of Qazvin University of Medical Sciences, Iran (Code: IR.QUMS.REC.1402.429). The requirement for consent was waived by the ethics committee.

Data availability
The author confirm that the data supporting the findings of this study are available within the article.

Funding
This study was supported by the Medical Microbiology Research Center, Qazvin University of Medical Sciences, Qazvin, Iran (Grant No.: 402000518).

Authors' contributions
Study design: Milad Badri, Behzad Najafpour, Hadi Bagheri, and Aida Vafae Eslahi; Sample collection: Milad Badri, Aida Vafae Eslahi, Behzad Najafpour, Hadi Bagheri, Leila Modarresnia, Farhad Nikkhahi, Ali Asghari and Amin Karampour; Data analysis and visualization: Meysam Olfatifar, Aida Vafae Eslahi, and Milad Badri; Supervision and writing: Aida Vafae Eslahi, Giovanni Sgroi, and Milad Badri; Final approval: All authors. 

Conflict of interest
The authors declared no conflict of interest.

​​​​​​​Acknowledgements
We sincerely appreciate the staff of health centers and Vice-Chancellor of Health in Qazvin Province, as well as the Medical Microbiology Research Center, Qazvin University of Medical Sciences, Qazvin, Iran.

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