CHAPTER ONE

INTRODUCTION

1.1 BACKGROUND

Brucellosis is a global zoonotic disease associated with significant morbidity that can lead to

increased rates of spontaneous abortions in livestock and also poses a serious human health

hazard.1 Brucellosis is a disease of mainly cattle, swine, goats, sheep and dogs. The disease is

widely distributed throughout the developing world, considered to be a serious problem in at

least 86 countries.2 It is a severe zoonosis in North African countries3 and the Near East4

causing economic and livestock losses and affecting industrial production.5

The infection is transmitted to humans by animals through direct contact with infected

materials like afterbirth or indirectly by ingestion of animal products and by inhalation of

airborne agents. Consumption of raw milk and cheese made from raw milk (fresh cheese) is

the major source of infection in man. Most of the fresh cheeses are sheep and goat cheese.

Next to this it is considered to be an occupational disease for people who work in the livestock

sector. Human-to-human transmission is however very rare.6

Infections are caused by various bacteria of the genus Brucella, which tend to be host-

specific. However, most species of Brucella are able to infect other animal species as well and

some of them have zoonotic potential.7 In humans, brucellosis can be caused by B. abortus, B.

melitensis, B. suis biovars 1-4 and, rarely, B. canis or marine mammal Brucella. B. ovis, B.

neotomae, and B. suis biovar 5 have not been associated with human disease. The disease

affects cattle, swine, sheep and goats, camels, equines, and dogs. It may also infect other

ruminants and marine mammals. The disease in animals is characterized by abortions or

1

reproductive failure. While animals typically recover, and will be able to have live offspring

following the initial abortion, they may continue to shed the bacteria. Brucellosis in cattle (B.

abortus) in sheep and goats (B. melitensis) and in swine (B. suis) are diseases listed in the

World Organization for Animal Health (OIE) Terrestrial Animal Health Code.8

In endemic areas, human brucellosis has serious public health consequences. Worldwide,

Brucella melitensis is the most prevalent species causing human brucellosis, owing in part to

difficulties in immunizing free-ranging goats and sheep. In countries where eradication in

animals (through vaccination and/or elimination of infected animals) is not feasible,

prevention of human infection is primarily based on raising awareness, food-safety measures,

occupational hygiene and laboratory safety. In most countries, brucellosis is a notifiable

disease.2

1.2 STATEMENT OF THE PROBLEM

Brucellosis is a zoonosis of both public health and economic significance in most developing

countries. In many developed countries, the animal disease has been brought under control,

which has led to a subsequent decrease in the number of human cases. The occurrence of the

disease in humans is largely dependent on the animal reservoir. Where brucellosis exists in

sheep and goats, it causes the greatest incidence of infection in humans.10

Brucellosis, especially caused by Brucella melitensis, remains one of the most common

zoonotic diseases worldwide with more than 500,000 human cases reported annually9. In the

U.S., there are up to 200 new cases of human brucellosis annually.10

2

Investigations and reports have shown that brucellosis is endemic in Nigeria and evidence of

infection as well as frank outbreaks have occurred both in cattle11, 12and in human beings.13

An investigation also showed serological evidence of infection in goats in certain parts of the

country.14 Brucellosis in small ruminants (sheep and goats) has been reported in northern

Nigeria.13

Previous work on isolation of brucella in Nigerian livestock has indicated that Brucella

abortus has been the major species isolated from cattle13,14,15 and from sheep and goats.16-18

However, Brucella melitensis had been isolated from sheep and goat milk in Nigeria.19 There

were also serological reports of brucellosis in small ruminants in various parts of Nigeria.20