Brucellosis is a common bacterial zoonotic infection characterized by a wide range of non-specific influenza-like clinical manifestations in humans. Brucella spp. is transmitted from infected animals such as cattle, goats, and sheep to humans through consumption of raw dairy and meat products or by direct contact with tissues and fluids (1). Human-to-human transmission is rare (2). There are an estimated 500,000 new cases in humans annually (3). The highest burden of disease is in the Middle East and Central Asia. Large outbreaks are regularly documented in these regions, the majority of which are associated with consumption of raw dairy products from unvaccinated animals (4, 5). Although there are no approved vaccines to prevent human brucellosis, vaccination of animals is highly effective in reducing disease (6, 7). Pasteurization of milk destroys Brucella spp (8). but is not commonly done in Tajikistan.

Tajikistan ranks among the top 25 countries with the highest incidence of brucellosis (9). During 2005–2014, the average annual incidence of brucellosis in Tajikistan was 14.0 per 100,000 people (10). An estimated 74% of the population in Tajikistan lives in rural areas, with approximately 60% working in agriculture and/or animal husbandry. Brucellosis is considered endemic in most districts in Tajikistan, and the risk is particularly high in regions where the population predominantly works in agriculture and animal husbandry (10–12).

In May 2023, a sharp increase of brucellosis was observed in a district in northwestern Tajikistan (Figure 1). Incidence in the district was much higher than in surrounding districts. In addition, 12-month incidence in the district in 2022 was 1.0/100,000 people and 5-month incidence by May 2023 had already reached 32.7/100,000. The majority of cases, 84% (87/103), were concentrated in the same remote mountainous village with a population of 10,712.

A rapid response team composed of residents of the Field Epidemiology Training Program, epidemiologists and laboratorians from the Center for State Sanitary and Epidemiological Surveillance from the region, and specialists from the Committee for Food Security conducted an investigation. The aim was to identify risk factors for brucellosis infection and provide recommendations for preventing outbreaks.

In May 2023, a sharp increase in the incidence of brucellosis was observed in a small rural village in Tajikistan. The increase was associated with direct contact with unvaccinated livestock and consumption of their products. Effective measures were adopted in response to this outbreak, and cases subsided by September.

All participants in the study lived near livestock, none of which had been vaccinated against Brucella spp. in at least 5 years, and most participants owned livestock. Close contact with livestock is a major risk factor for brucellosis in humans (14–16). Most rural households in Tajikistan rely on the ownership of a small number of livestock for food consumption and for income. We found that more cases than controls in our study owned goats. In many countries, including in Tajikistan, goats and sheep are a particularly common source of human brucellosis (17, 18). Previous studies of goats in Tajikistan have found high seroprevalence of brucellosis, ranging from 5.5% to 6.7% (19).

None of the households in the village had vaccinated their livestock against brucellosis in the last 5 years. Vaccination of animals against brucellosis is critical to eliminating spread of disease in livestock (20, 21). Tajikistan ranks among the world's poorest countries, and nearly one-third of the population experiences food insecurity; rural Tajikistan is particularly affected by poverty (22). Rural communities not only lack the economic means to pay for vaccinating livestock, but also vaccines are not available in or near remote villages. The village in this outbreak was located in a mountainous area about 4 h from the nearest city.

Due to the favorable geographical conditions in the village, every year at the end of winter and beginning of spring, the surrounding areas of the village grow grass that is used as pastures for animals throughout the region. Residents of other neighboring villages lend their livestock to the residents of this village on a contractual basis until autumn. The residents of this village care for the cattle given on a contractual basis together with their own livestock. No passport or vaccination certificate is required when transferring animals. Village animals might have acquired Brucella during this period of increased contact with animals from other areas. Unfortunately, there were insufficient funds to test animals as part of this outbreak investigation.

The remoteness of villages, like the one from this outbreak, also makes its population heavily reliant on home- or locally- produced foods. We found that a high proportion of participants consumed home- or locally-grown food products, and that people who consumed homemade kaymak, home-grown goat or sheep meat, and locally-produced milk had increased odds of brucellosis. Importantly, people who ate both homemade kaymak and homemade meat had increased odds of brucellosis compared with those who ate neither, even after adjusting for consumption of raw milk, and engagement in animal slaughter and direct animal care. All of which are known risk factors for brucellosis. While meat consumption alone is not a risk factor, consumption of undercooked meat is a known risk factor for brucellosis (1). Kaymak is a homemade traditional cream, which is made with unpasteurized goat/sheep or cow milk. Kaymak is produced using a specialized equipment. The temperature is maintained between 30°C and 40°C throughout the preparation process, and the product is consumed raw. Consumption of unpasteurized dairy products from goats and/or cows are implicated in brucellosis outbreaks globally each year (14, 15, 23). Likewise, in our study, people who drank locally produced milk had increased odds of brucellosis, even when controlling for consumption of kaymak and meat. While we did not specifically ask whether the milk they had consumed was pasteurized or not, pasteurization is not common in rural areas of Tajikistan. In the village, due to reduced economic means, neighbors frequently share milk and other locally-produced dairy products with one another. Therefore, in such a setting, a single household with a sick animal could result in many households becoming sick.

Participants’ knowledge about methods of protection against brucellosis is very low. Since more than 90% of the participants had secondary education, after graduating from high school people were mainly engaged in agriculture and livestock farming. The lack of information about the symptoms of brucellosis and methods of its prevention was the reason that patients did not go to a medical facility on time. Previous studies have shown that insufficient knowledge about brucellosis further contributes to the spread of infection in the population and can lead to highly risky actions (24–26).

Our study is subject to some important limitations. Dairy and meat products were not tested using laboratory methods during the study due to budgetary constraints. Testing these products would have strengthened the findings of the study. Another limitation of the study was that due to a lack of laboratory capacity, blood samples were not tested for brucellosis species identification. Correct diagnosis and species identification are critical tools for targeted surveillance and control of brucellosis (27, 28). Our analysis is also limited by a lack of power to compare small sub-groups. Specifically, most cases consumed both kaymak and meat; and few consumed only kaymak. There is insufficient power to detect a statistical difference between those that only ate kaymak and those that had no kaymak and no meat. Our questionnaire did not include a question about the type of local milk participants had consumed, specifically, it was not asked if the milk was unpasteurized and if it was cow or goat milk. However, consumption of cow milk is more common, and home pasteurization of milk is uncommon. Lastly, the study is an outbreak investigation of a single village, the results are not generalizable beyond the village of study. Nevertheless, the risk factors for brucellosis identified in this study, have also been identified in other brucellosis outbreaks around the world. Brucellosis prevention measures can be applied to other regions to prevent brucellosis outbreaks.

Results of the study were shared with the head of the administration of the district and region, and brought to the attention of the national Ministry of Health and Social Protection of the Population of the Republic of Tajikistan. The Ministry of Health, established an Emergency Epidemic Control Commission in the district, which included all interested structures in order to prevent the spread of infection and carry out anti-epidemic measures, but the study team was not directly involved in this process.

Epidemic control measures taken by the emergency team included slaughter of diseased animals. The team also informed the public about the characteristics of brucellosis, proper animal care and safe consumption of dairy and meat products, including avoiding eating undercooked meat. The brucellosis outbreak was contained by August. To achieve long-term prevention, a brucellosis vaccination campaign for livestock was initiated in the village and district, and veterinary services increased monitoring of the quality of milk and dairy products. Over 5,000 animals were vaccinated in the district by the end of 2023.

Our study showed that brucellosis remains an important public health problem in northwest Tajikistan. Contact with unvaccinated livestock and consumption of their products played a key role in this outbreak in a remote mountainous village. Cases were likely higher than reported because one in ten randomly selected controls tested positive for a previous infection. Following our investigation, a brucellosis prevention education campaign and animal vaccination campaigns were carried out in the village and surrounding district. No more brucellosis cases were reported after September 2023.