Seroprevalence and associated risk factors of human Brucella infection in selected provinces in Sri Lanka

Brucellosis is a systemic zoonotic bacterial infection. We studied the seroprevalence and risk factors for human Brucella infection in 1,294 healthy people from 4 provinces: Central, North-Western, North-Central and Western Provinces. Farmers in contact with farmanimals, veterinary staff, abattoir workers, and noncontact urban-dwellers were tested against B. abortus and B. melitensis antigens by SAT. Seroprevalence was 8.4% of the study population. Farm-animal owners and working full-time with livestock have a significantly higher risk of acquiring Brucella infection. Enhanced laboratory support and surveillance is necessary to control brucellosis in Sri Lanka. This is the first report on human Brucella infection.


Introduction
Brucellosis is a systemic bacterial zoonosis. It is transmitted by ingestion through food products, direct contact with infected animals and inhalation of aerosols. Transmission through blood transfusion or tissue transplantation and sexual transmission are rare possibilities. Although the disease has been well known for decades, it continues to be a major public health issue worldwide [1].
The true incidence of human brucellosis is unknown globally, as many countries known to be endemic for brucellosis, such as India and South Africa, do not have reliable data on the disease [2]. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. in humans. Although B. melitensis is thought to be the most virulent species, B. abortus is the most commonly distributed species worldwide [1]. Livestock farmers, slaughterhouse workers and veterinarians are at high risk of developing the disease. Travelers and urban residents usually acquire the infection through the consumption of contaminated food especially raw milk or milk products [3]. The disease was introduced to Sri Lanka during the second world war, through the importation of cattle. The first clinical outbreak in livestock was reported in 1956 [4,5]. The North-Western and North-Central Provinces with the highest density of cattle, were implicated as endemic areas for brucellosis [4]. However, a meta-analysis in 2013 has shown that data is not available for human brucellosis in Sri Lanka [6].
We studied the seroprevalence of human Brucella infection and associated risk factors among high-risk occupations such as farmers, veterinarians and abattoir workers in Central (CP), North-Western (NWP), North-Central (NCP) and Western (WP) Provinces.

Methods
The study was conducted in 2014/2015 among 9 districts in the 4 Provinces. The 41 veterinary divisions and their farms were randomly selected by probabilityproportional-to-size sampling technique. Veterinary staff, abattoir workers and non-contact urban-dwellers were recruited by convenient sampling.
A total of 1,294 blood samples were collected from farmers in contact with farm animals (818), veterinary staff (190), abattoir workers (137) risk categories and noncontact urban-dwellers (149). The study used a nonrandom purposive sampling method. Standard tube Agglutination Test (SAT) was performed using B. abortus and B. melitensis antigens (MAST TM Assure febrile stained antigen, UK) according to manufacturer 's guidelines at clinical bacteriology laboratory, Medical

Brief report
Research Institute. A titer of 1:80 was considered for seropositivity (past infection). Socio-demographic data were collected using an interviewer-administered questionnaire.

Statistical analysis
Data entry and statistical analyses were performed using SPSS version 21. Quantitative data were obtained in the form of percentages and figures. Cross tabulations were generated between seroprevalence and sociodemographic factors, and the Pearson  2 test was used to express the statistical significance of any associations. P-values of 0.05 or less were considered to be significant. The potential risk factors for seropositivity were also assessed using bivariate analyses and presented as Odds Ratio (OR).

Results
A total of 1,294 healthy adults were screened. Sample size was sufficient to estimate sero-prevalence of brucellosis at 50% in the study population. The level of precision is 95% with confidence interval 3% and the nonresponse rates was 15%. Males constituted 81.9% and the mean age was 45.6 years (

Discussion
Brucellosis has been recognized as a re-emerging zoonosis due to growing international tourism, migration and potential use as a biological weapon. In Sri Lanka, animal brucellosis is an endemic disease, causing economic impact to the livestock industry [4].
One clinically suspected case of human brucellosis has been briefly described in a Sri Lankan patient from Monaragala four-decades ago [7]. Since then, no reports were available on human disease in Sri Lanka. Our study shows a seroprevalence of 8.4% for human Brucella infection and the most common species detected serologically was B. abortus.
In animal brucellosis, B. abortus has been reported as the common species in Sri Lanka [4]. In the 1980s, cases of caprine brucellosis due to B. melitensis were reported and more recently, in swine in Sri Lanka [6,8]. High incidence of animal brucellosis was reported from Eastern, NCP and NWP [5].
Close contact with animals and raw milk ingestion has been attributed as the major risk factors in Karnataka in India [9]. In our study, farm animal owners and full-time handlers of livestock showed significant seropositivity than part-time livestock handlers and non-contact groups and only 53 persons ingested raw milk [ Table 2,3]. This signifies the variations in risk factors for brucellosis in different countries.
In conclusion, the seroprevalence for human Brucella infection is 8.4%. Farm-animal owners and those working full-time with animal husbandry have a significantly high risk of acquiring the infection. This is the first report on human Brucella infection in Sri Lanka.
Awareness of the disease among clinicians, and enhanced laboratory diagnostic support and surveillance in human and animal brucellosis are recommended to control brucellosis in Sri Lanka.