Bovine brucellosis (Brucella abortus infection)

GENERAL INTRODUCTION: GRAM-NEGATIVE AEROBIC OR CAPNOPHILIC RODS AND COCCI Brucella spp. infections

Introduction

Bovine brucellosis is a highly contagious disease caused mostly by Brucella abortus, a bacterium which occurs intracellularly in its mammalian host. Apart from causing characteristic mid- to late-term abortion and infertility in cows, B. abortus also occasionally causes orchitis and inflammation of the accessory sex glands in bulls. Other livestock and wild animal species (see Brucella infections in terrestrial wildlife), though of varying susceptibility, are sometimes infected.⁷⁷ Bovine brucellosis is also an important zoonosis.⁸ In some countries, particularly in southern Europe and western Asia, where cattle are kept in close association with sheep or goats, infection and abortion can also be caused by Brucella melitensis.¹⁹⁵ Occasionally, Brucella suis may cause an infection in cattle but has not been reported to cause abortion.^{69, 74}

By visiting the OIE (World Organisation for Animal Health) website and using the WAHIS interface,¹⁵³ information on the worldwide brucellosis status as well as those animal diseases listed by the OIE due to their implications for international trade or public health can be obtained. This information is regularly updated and is based on the emergency level of the situation and on monthly and annual reports sent to the Central Bureau of the OIE by national veterinary administrations and other official sources. In sub-Saharan Africa, brucellosis is an important disease in both humans and livestock. In general, the assessment of the occurrence of brucellosis is restricted to few published studies based on serological surveys and it is considered to be the highest in pastoral production systems.¹²⁹ Recent studies show that brucellosis is highly prevalent among dairy herds in peri-urban areas of several sub-Saharan African countries.^{79, 139} The surveillance and control of brucellosis in sub-Saharan Africa is rarely implemented outside southern Africa. The rate of infection in humans is virtually unknown and public awareness is extremely low. Hence, the impact of brucellosis in terms of public health and social importance is rarely correctly addressed.¹²⁹

It is suspected that bovine brucellosis was introduced into southern Africa with cattle imported from Europe,⁸⁸ but there is also a possibility that it was introduced into the subcontinent much earlier during the migration of people and their cattle herds from other African countries.¹²³ The first reliable record of its existence in South Africa was that of Gray in 1906 when he reported a serious outbreak of abortion among cattle near Johannesburg.⁸⁸ Its presence was finally confirmed by Hall in 1913 when he isolated B. abortus from the stomach of an aborted bovine foetus.⁸⁸ Outbreaks of abortion thought to be bovine brucellosis were first observed in Zimbabwe in 1906, and the presence of brucellosis was confirmed in that country in 1914. According to an obituary notice by Bevan in The Veterinary Record of 1957, Zimbabwe was the first country to show that B. abortus-infected cattle could transmit the pathogen to humans and that goats were not the source of the infection.⁷

The disease has a relatively high prevalence in southern Africa, especially in intensively farmed areas, and it is the most important bacterial cause of abortion on the subcontinent. It has an important economic impact on the beef and dairy cattle industries, especially as in 1990, 14,7 percent of the herds in South Africa were known to be infected and the losses to cattle farmers exceeded R300 million per annum.¹³

In recent decades, developing countries, particularly India, have increased their share in global dairy production. In India, brucellosis in cattle and water buffalo accounted for more than 95 percent of the total losses occurring due to brucellosis in livestock populations, and has been responsible for a median loss of US $ 3.4 billion in 2015.¹⁷⁹  The impact of brucellosis and other zoonoses affecting livestock production has to be globally assessed by their impact on human health. Of note, worldwide, brucellosis is not ranked among the top diseases based on disability-adjusted life years (DALY) losses.¹²⁹

Aetiology

Brucella abortus is a small, Gram-negative, non-sporulating, non-encapsulated coccus...