To the Editor—Brucellosis, or Mediterranean fever, is an important zoonotic disease caused by various species of the gram-negative bacteria Brucella. The well-known species of Brucella are B. abortus, B. melitensis, B. ovis, B. canis, and B. suis, which infect cows, goats, sheep, dogs, and pigs, respectively.^{Reference Olsen and Palmer1} This infectious disease can be transmitted from infected animals to humans through direct contact, tissues (placenta or aborted tissues), or animal products (dairy products). Human to human transmission is rare.^{Reference Köse, Senger and Akkoçlu2} Brucellosis imposes considerable economic losses in many countries each year via damage to livestock through reduced fertility, abortion, and decline in milk production and via humans through significant loss of work days of infected persons and their families and long-term treatment costs.^{Reference McDermott, Grace and Zinsstag3} According to the World Health Organization, >500,000 new cases of brucellosis are reported annually worldwide; however, undetected cases are estimated to be 4× this number.^{Reference Asiimwe, Kansiime and Rwego4,Reference Corbel5} The incidence rate of this infection varies from <0.01 to >200 cases per 100,000 population in different parts of the world, depending on geographical area, hygiene level, eating habits, occupation, and other factors.^{Reference Al-Anazi and Al-Jasser6} Notably, the incidence rate of this disease (per 100,000 population) is very low in many countries: the United States (0.04), Italy (0.9), Spain (1.3), Russia (0.4), Chile (0.006) France (0.05), South Korea (0.1), and China (0.4). It has even been eradicated in some countries: Sweden, Denmark, Finland, Germany, the United Kingdom (excluding Northern Ireland), Austria, Netherlands, Belgium, Luxembourg, Norway, and Switzerland. Unfortunately, the infection is still endemic in Middle East countries, where high incidence rates (per 100,000 population) prevail: Iran (23.8), Turkey (26.2), Syria (160.3), Saudi Arabia (21.4), and Iraq (27.8).^{Reference Pappas, Papadimitriou, Akritidis, Christou and Tsianos7} In Iran, ~16,000 cases of brucellosis are reported annually.^{Reference Pakzad, Hosseinzadehgan and Abtahi8,Reference Mirnejad, Jazi, Mostafaei and Sedighi9} According to data from the National Commission on Communicable Diseases Control, in 1989, the annual incidence exceeded 100 cases per 100,000 population, but in 2013, the annual incidence had fallen to 23.8 cases per 100,000 population. Despite this decline, human brucellosis remains an important health issue in Iran.^{Reference Pappas, Papadimitriou, Akritidis, Christou and Tsianos7} Distribution of the disease is uneven across the country, and although cases of the disease have been reported in all provinces of the country, the incidence is higher in the western and northwestern provinces, in the Zagros Mountain region.^{Reference Pakzad, Pakzad and Safiri10} In an analytical study in 2011, Pakzad et al^{Reference Pakzad, Pakzad and Safiri10} reported the highest incidence rate of brucellosis in Coohrang County of Chaharmahal-Bakhtiari province, with 317 cases per 100,000 population. In subsequent years, Charuymaq County of East Azerbaijan province had rates of 384 cases per 100,000 population in 2012, 534 in 2013, and 583 in 2014, which was at most 14575 and 25 times higher than the average incidence rate of brucellosis in the USA and Iran, respectively.^{Reference Pakzad, Pakzad and Safiri10} In 2012, Almasi et al^{Reference Almasi, Hashemian and Azizi11} also reported that the incidence rate of brucellosis in Kermanshah is ~275 per 100,000 cases, and in 2009, Bokaie et al^{Reference Bokaei, Heydari and Abbaszadeh12} reported that the incidence rate in Western Azerbaijan was ~175 per 100,000. In Hamadan, the incidence rate has been reported to be 130 per 100,000 cases. In provinces outside the Zagros Mountains, such as Qom and Tehran, the incidences rate were 7 and 10 per 100,000 cases, respectively.^{Reference Mirnejad, Jazi, Mostafaei and Sedighi9} Overall, the incidence rate of brucellosis in the Zagros Mountains is significantly higher than other provinces. This region may be also related to high incidence rates of brucellosis in Iran, Iraq, and Turkey. Thus, we investigated the factors that affect the rate of brucellosis in the Zagros Mountains to recommend ways to reduce the prevalence of this disease.

The Zagros Mountains, with a total length of 1,600 km, spread across Iran, Iraq, and Turkey. They begin in northwestern of Iran, continue along i western borders, and end at the strait of Hormuz. They encompass the provinces of West Azerbaijan, Lorestan, Hamadan, Markazi, Isfahan, Fars, Kurdistan, Kermanshah, Ilam, Kohgiluyeh and Boyerahmad, Chaharmahal and Bakhtiari, Khuzestan and Kerman, Bushehr and Hormozgan.¹³ The earliest agriculture and animal husbandry began here thousands of years ago in Susa and Anshan, the ancient cities located in these mountains.^{Reference Bahmanimehr, Nikmanesh and Yepiskoposyan14} The people of the Zagros Mountains have been sheep and goat (boazer goat) herders since ~10,000 b.c.e. The Zagros people have always been in contact with animals and livestock through hunting and migratory or rural life; therefore, they have continually been at risk for zoonotic diseases.^{Reference Vigne15}

The high incidence of brucellosis in this area has many causes.^{Reference Corbel5,Reference Esmaeili16–19} Several studies have reported a higher density of livestock in these areas. The Zagros region has ~43% of the total population (>34 million people) of Iran, and it is home to 52% of all livestock in the country, including cattle, sheep, and goats. Most of the country’s nomadic and rural population resides in the Zagros Mountains, with close and continual contact with animals. These residents often assist in animal deliveries and come into contact with placenta and related discharges, which are the most potential agents for transmission of Brucella bacteria. These nomadic areas have a low level of hygiene and lack of access to antibacterial detergents and disinfectants. The population in these rural areas, especially nomads, lack sufficient education regarding transmission, manifestation, and complications of brucellosis. They have high and continuous consumption of nonpasteurized dairy products, and they consume raw and semi-raw dairy products (eg, milk and cream). Due to continued movement and living in areas with difficult accessibility, monitoring and vaccination of nomad herds is very difficult and not very effective. Often, several nomads come together in one place, causing cross transmission of Brucella from one herd to another. Transmission also occurs from livestock to wild animals living in the Zagros Mountains, which makes them reservoirs of infection. Other reasons for the high brucellosis rate include unauthorized animal trafficking from neighboring countries and lack of a quarantine system at the borders; lack of appropriate identification system for infectious disease in livestock; traditional, unauthorized, and unsanitary slaughter of animals; and lack of funds.

Despite all these obstacles, we believe that reducing or even eradicating this infection in the Zagros region and more generally in Iran in the long term is possible. We need more effective plans, efforts, cooperation, and especially aid from international organizations such as WHO. Education is a low-cost but very effective measure that increases awareness of and information about brucellosis, its transmission, complications, manifestations, and risk factors. Personal hygiene when assisting animal delivery, boiling milk, and disuse of raw dairy products are other areas of education that can be relatively easily accomplished. Allocating free or cheap drug and health supplies to aid with hygiene can help reduce this infection in nomadic and rural areas. Monitoring and conducting regular vaccination of livestock, preventing animal trafficking, and creating a quarantine system at the borders to identify sick animals are other examples of appropriate measures that will contribute to achieving this valuable goal.^{Reference Asiimwe, Kansiime and Rwego4}