Epidemiology of Brucellosis in Humans and Domestic Ruminants in Bangladesh

Abstract

Background

Brucellosis is an ancient and one of the world’s most widespread zoonotic diseases affecting both, public health and animal production. It is endemic in many developing countries of Asia, Africa and Latin America including Bangladesh. Since the first report in 1970, a lot of brucellosis seroprevalence reports are available in cattle, goats, sheep and humans in Bangladesh. Most of the previously reported prevalence studies were based on non-random samples, which may not give a true representation of the status of the disease in respective populations. Some authors also investigated the risk factors in cattle. The tests used for the diagnosis of brucellosis in domestic ruminants and humans are imperfect and their performance was not evaluated in Bangladesh. The true prevalence of brucellosis in domestic ruminants is not known and is essential for analyzing the impact of this disease in domestic ruminants in Bangladesh. Indeed, when diagnostic tests are used without evaluating their performance in a context usually generate unreliable results, which in turn may lead to wrong epidemiological inferences. In addition, information on risk factors of brucellosis in humans and animals is also scarce. Moreover, the different species of Brucella prevalent in animals is scarce and not known in humans in Bangladesh. The overall objective of this thesis was to investigate the epidemiology of brucellosis in humans and domestic ruminants in Bangladesh in terms of the evaluation of commonly used diagnostic tests, estimation of true prevalence, identification of risk factors and detection of Brucellaspecies in order to provide information that will guide the selection of appropriate control strategies.

Study design and data analysis

Sampling

To collect random samples of animals a system of map digitization and selection of one geographical point from selected unions (Sub-Upazilla) using a hand held GPS machine was used. Blood (milk also where applicable) samples were then collected from livestock farmers and their animals within 0.5 km of the selected points. A convenient blood sample of butchers, dairy hands and veterinary practitioners were collected from Dhaka and Mymensingh districts. The sera of pyretic humans were collected from Mymensingh Medical College hospital randomly once in a week. Random milk samples were collected from Sirajgonj and Chittagong districts.

Systematic random milk and blood samples of cattle including breeding bulls (semen also) of central cattle breeding and dairy farm (CCBDF) were also collected. Milk and blood samples of gayals of a herd in regional Bangladesh Livestock Research Institute at Naikhonchari, Bandarban were also collected. Convenient samples of placenta and vaginal swabs were also collected from Mymensingh district.

Data collection and Analysis

Data on serology was generated by using Rose Bengal test (RBT), Slow Agglutination test (SAT) /Standard tube agglutination test (STAT) (animals/humans) and indirect enzyme linked immunosorbent assay (iELISA). Animal, their herd level data and human data on potential risk factors were collected using a pretested questionnaire. The data was stored in Microsoft Excels worksheets and transferred to respective software for analysis.