Principal FindingsAnalyzing the spatiotemporal distribution of human brucellosis is important in understanding the epidemiology of the disease in the country and helps forecast the future situation. There has been a decline in human brucellosis cases since 2012, which may be due to veterinary protective and control measures through vaccinating livestock that have been implemented since 2007. However, vaccination rounds were disrupted during Islamic State in Iraq and the Levant (ISIL) events that negatively affected the control program [11,12]. Nevertheless, animal health campaigns were relaunched soon after liberation in 2017, with several vaccination rounds having been completed since then [13].
The number of female individuals who tested positive for brucellosis has been constantly higher than the number of male individuals, with increased reporting frequency since 2015. This can be due to increased exposure of female individuals to infected animals and animal products through housekeeping and farming activities [11]. This contradicts what has been found in research from Germany [1], Italy [14], and Iran [8]. Therefore, the potential differences should be investigated further to detect whether the difference is due to different proportions of male individuals in different countries or biological differences that enhance contracting brucellosis. Nearly two-thirds (30,977/50,621, 61.19%) of the patients were between 15 and 45 years old, which can negatively affect the economic status of the patients and their families and the quality of life for the patients [9]. People in this age group may consume more locally made dairy products due to a lack of knowledge regarding the importance of pasteurized milk and milk products. However, this age category was very broad and could have been classified into 2-3 age groups to detect the most commonly affected age group [15-18].
Most human brucellosis cases were in the northern provinces during the first period (2007‐2012), especially in Salah Al-Din, Sulaymaniyah, Nineveh, Erbil, Kirkuk, and Dahuk. Northern provinces share an extensive border with Iran, Turkey, and Syria and direct borders with other Iraq provinces, which, in turn, share borders with Jordan, Saudi Arabia, and Kuwait [16,17]. Sheep and goat husbandry has been practiced in the northern region of Iraq since the earliest times due to the nature of these provinces, which is characterized by broad grass-covered terrain, undulating hills steep, and craggy mountains well suited to sheep and goat grazing [19]. Livestock and its products dominate northern Iraq’s economy and represents an important food resource for its inhabitants [5]. Therefore, the high clustering of brucellosis in this area could be due to area grazing strategy, animal population density, owner’s ignorance of the hazards of the disease, unhygienic disposal of infected animals as well as aborted fetuses or placental membranes, and uncontrolled movement of diseased animals [18]. Because there is no curative medical therapy for animal brucellosis, the infected animals should be slaughtered and disposed of properly. However, these animals are expensive in Iraq; therefore, farmers firmly refuse to slaughter and dispose them. As a result, the infection will persist through transmission from the infected animals to their offspring by breastfeeding. Likewise, humans may consume this infected, unpasteurized milk, resulting in infection and areas endemic with brucellosis in animals and humans [15]. One potential control method in this case is the isolation of the infected animal from healthy animals and milk pasteurization to prevent animal-to-animal and animal-to-human transmissions. Preventive measures such as health education activities should be performed in high-risk areas. Adopting the Quarantine-Slaughter-Immunization strategy and One Health Approach is crucial in controlling the disease. This can be achieved through multisectoral coordination and coordination with neighboring countries in the control programs.
The seasonal variation in the occurrence of human brucellosis in Iraq, that is, the decline in the number of human brucellosis cases in winter and the rise in spring and summer, could be explained by high exposure to the disease during spring and summer when the deliveries of animals, increased milk production, and contamination occur [19,20].
The human brucellosis cases were clustered in the north and northeastern regions of Iraq, mainly in areas in the vicinity of the Zagros mountains, which contain dense oak forests and fertile soil with a high density of sheep and goats; the main economic activity in the area is animal farming. The Zagros Mountains are also the route of seasonal migration for nomads [19]. Human-to-human transmission is rare and clusters of human cases are most likely a result of animal processing, more intensive agricultural production zones, and similar sociocultural practices [14].
On the contrary, the low cluster areas may be due to having economic superiority, standardized industrial manufacturing for cow- or sheep-related products, good sanitary habits, awareness of human brucellosis, and easy access to immediate treatment after infection [4,21]. In addition, several changes in the surveillance case definition, the diagnostic methods, and the reporting of human brucellosis that occurred during the second period of the study could have also contributed to the low numbers reported compared to the first period. For example, the primary diagnostic method during the first period was the Rose-Bengal test, which has variable sensitivity and specificity based on the exposure history, stage of infection, and prior infection history. In contrast, the diagnostic test used during the second period was ELISA for immunoglobulin M, immunoglobulin G, and culture. Although all suspected cases are initially reported to the Surveillance Section, their final classification as suspected or confirmed may vary by governorates based on their testing and interpretation capacity (Surveillance Section, CDC, Public Health Directorate, MoH in Iraq; unpublished data; 2024). As another example, the data were collected in an aggregate format based on sex, age group, and province in the first period of the study. In contrast, the data were collected in a case-based format during the second period of the study (Surveillance Section, CDC, Public Health Directorate, MoH in Iraq; unpublished data; 2024).
This study has several strengths. First, this is the first study to include data across 12 years in a detailed spatiotemporal analysis. The consistency of the epidemiological characteristics across 12 years can lead to public health interventions in areas where effort should be spent. That is, due to the fact that the infection is consistently more frequent among female individuals, health promotion activities may be directed to design educational materials on dealing with animals and their products and delivering them using personal protective measures that target female individuals working in the animal husbandry industry. The second strength is the use of an innovative statistical approach to detect whether the clustering of cases is significant or random, in addition to follow-up of the progress of clusters over 7 years, which clearly showed a continued increase in the north and northeastern areas and a continuous decline in the southern areas.
This study also has limitations. Data regarding important risk factors of human brucellosis, such as occupation, rural or urban areas, comorbidities, and treatment protocol, were lacking. Had this information been available, it would have facilitated a better understanding of the epidemiology and characteristics of human brucellosis in Iraq (Surveillance Section, CDC, Public Health Directorate, MoH in Iraq; unpublished data; 2024).