Epidemiology of brucellosis and Q fever in Togo and the risk of disease spread through cattle trade in West Africa

Abstract

Zoonotic diseases account for more than half of infectious diseases of humans and three quarters of all emerging infectious diseases. Most of this burden lies with poor, rural communities who rely on livestock for nutrition and income. In order to advocate on behalf of these communities and reduce the disease burden, there is a need for high quality epidemiological data acquired through transdisciplinary approaches involving the natural, health and social science fields. Brucellosis is one of the most common zoonoses in the world. This bacterial disease has a major impact on human health, livestock production and the economy. In recent years, Q Fever has become a bacterial zoonosis of increasing interest, in part due to an unprecedented, large-scale outbreak in the Netherlands in 2007-2010. However, there is an absence of high quality epidemiological data from West Africa for both brucellois and Q Fever. Member countries of the Economic Community of West African States (ECOWAS) are required to permit free movement of people and goods across borders. This mobility is important culturally, socially and economically. However, mobile populations in sub- Saharan Africa suffer from the least access to health services. Cross-border trade and seasonal transhumance are central to livestock production to West Africa, but these movements can facilitate the rapid spread of pathogens across large distances. The Savannah Region of northern Togo is the country’s main livestock raising area. This is a dynamic zone, with frequent movement of both people and livestock across its borders with Ghana, Burkina Faso and Benin. Aims -To assess the global burden of human brucellosis and identify data gaps -To provide the first data on the epidemiology of brucellosis and Q Fever in people and animals in Togo -To conduct the first quantitative assessment of cattle trade in Togo, including the potential impact on disease spread in West Africa -To assess the mobility of people and livestock and the access to health care and other social services in northern Togo -To foster intersectoral collaboration and transdisciplinarity in Togo Methods A systematic review and meta-analysis of the burden of human brucellosis was undertaken in the framework of the Global Burden of Disease Study 2010. Additionally, primary data collection was conducted in the Savannah Region of northern Togo. A brucellosis and Q Fever serosurvey was conducted in cattle, sheep, goats and people in 25 randomly selected villages in 2011 and 18 transhumant herds from Burkina Faso in 2012. The serological testing methods included the Rose Bengal Test (RBT), Enzymelinked Immunosorbent Assay (ELISA), Complement Fixation Test (CFT) and Immunofluoresence Assay (IFA). Multiple Loci Variable Number of Tandem Repeats Analysis (MLVA) was used to genotype Brucella strains isolated from bovine hygroma fluid. Semi-structured interviews were conducted in 2011 in parallel with the serosurvey to assess the mobility of the local population and their access to health care and other social services. In 2012, semi-structured interviews were conducted with cattle traders in the 9 principal cattle markets in the study zone. The data collected was used to simulate cross-border livestock flows and assess the potential risk of disease spread in West Africa through cattle trade. Principal Findings The systematic review quantified the severe and chronic impact of brucellosis on its sufferers and provided the first informed estimates of acute and chronic disability weights for brucellosis. Major knowledge gaps regarding the incidence of brucellosis are evident for Sub-Saharan Africa, Eastern Europe, the Asia-Pacific, and Central and South America. In Togo, the association between cattle seropositivity and a history of abortion in cows suggests that brucellosis and Q Fever have an important impact on livestock production. Given the absence of small ruminants seropositive for brucellosis, it is likely that only B. abortus, not B. melitensis, is circulating in the study zone. People of Fulani ethnicity were shown to have greater exposure to zoonoses than the rest of the population, suggesting that cultural factors may influence the disease epidemiology. These results represent the first epidemiological data for zoonoses in linked human and animal populations in Togo. The impact of these diseases on human health and the economy warrants further investigation. The B. abortus strains isolated from cattle hygromas are among the first Brucella genotypic data available from West Africa. The identification of three distinct strains from only a small geographical area highlights the genetic diversity of circulating strains in the study zone. The two deletions detected in the BruAb2_0186 gene have important diagnostic and, possibly, epidemiological consequences. More molecular and epidemiological data are needed from the region, in order to better understand transmission patterns and develop more suitable diagnostic assays. The use of a chaotrophic buffer to preserve and inactivate DNA was both a safer and more sensitive diagnostic method than culture, and is of particular relevance to countries with poor laboratory biosafety. The first quantitive assessment of the risk of disease spread in West Africa through cross-border cattle trade demonstrated that surveillance for emerging infectious diseases as well as control activities targeting endemic diseases are likely to be ineffective if only conducted at a national level. The trade network in northern Togo extended into Burkina Faso, Ghana, Benin and Nigeria, with their epidemiological systems likely to be intimately linked to one another. There is a need for greater collaboration between countries at the regional level in order to strengthen disease surveillance and control efforts. In addition to the large number of foreign herdsmen undertaking transhumance in northern Togo every dry season, one third of local herds were reported to be seasonally transhumant. Women were also shown to be a more mobile sub-group of the local population, and further investigation of the needs of these mobile groups is warranted. Although the level of satisfaction with the local health centres was generally high, the cost of services was an exception and may reflect a financial barrier. Increased distance to the local health centre reduced the utilisation of skilled birth attendants by women, and may be an important barrier to accessing health care. Livestock herding duties of Fulani children resulted in poorer school attendance, and the impact on physical, intellectual and social development should be explored.