Brucella infections in terrestrial wildlife

Previous authors: J GODFROID

Current authors:
J X L GODFROID - Faculty of Biosciences, Fisheries and Economics, UiT - The Arctic University of Norway, Hansine Hansens veg 18, Tromsø 9019, Norway and Faculty of Veterinary Science, University of Pretoria, Private, Bag X04, Onderstepoort, Gauteng, South Africa, 0081
J M BLASCO - Emeritus Researcher, DVM, PhD, Cita/Ia2/University Zaragoza Avenue, Montañana 930, Zaragoza, 50011, Spain
J RHYAN - U.S. Department of Agriculture, Animal and Plant Health Inspection Service, Veterinary Services, Fort Collins, CO, United States of America

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

Introduction

Brucellosis in wildlife is characterized by abortion, retained placenta, orchitis, epididymitis, and excretion of brucellae in semen, uterine discharges and milk.

The epidemiological link between wildlife and many of the diseases in livestock is now well recognized (see Infectious diseases of animals in sub-Saharan Africa: The wildlife/livestock interface). The long-standing conflict between livestock owners and animal health authorities on one hand, and wildlife conservationists on the other, is largely based on differing attitudes to controlling diseases of livestock that are or can be associated with wildlife. The creation of new interfaces between livestock and wildlife due to anthropogenic effects is the most important factor in disease transmission.⁹ Translocation or introduction of wildlife species into an area where they did not occur previously and a lack of surveillance in wildlife may increase these interfaces and consequently transmission of diseases.¹⁰

When studying brucellosis in wildlife, four main questions arise:³⁶

1. Is wildlife brucellosis a result of a spill-over from livestock or is it a sustainable infection in one or more wildlife host species?
2. Is wildlife brucellosis a reservoir of Brucella spp. for livestock?
3. Did the epidemiological situation of Brucella infection in wildlife change over time and, if so, what are the main drivers of change and does it have an impact on wildlife population dynamics?
4. Is wildlife brucellosis of zoonotic concern?

To avoid potential conflicts between ecologists, regulatory veterinary services, production animal and wildlife industries and veterinary public health authorities, the general approach has evolved from the diagnosis of brucellosis as a disease in wildlife to include the early detection of pre- or subclinical infections and to identifying routes of transmission of infection between different host species at the livestock/wildlife interface. This approach is aimed at initiating preventive control and management measures in order to decrease the disease risks in both livestock and free ranging/captive wildlife as well as the zoonotic potential.⁴⁰

Brucellosis is an ancient disease with a low fatality rate in humans (less than 2 per cent of untreated cases). Yet human brucellosis remains the most common zoonotic disease worldwide with more than 500 000 new cases annually. It is associated with substantial residual disability and is an important cause of travel-associated morbidity.⁶⁷ The vast majority of these cases are caused by B. melitensis and are linked to contact with livestock or consumption of mainly raw dairy products.³⁶ However, from a veterinary and public health perspective, the risk of spill-over of B. melitensis from ibex (Capra ibex) in the Alps to livestock and from there to humans is considered very low.²

It is worth noting that, to date, there is no report of the direct transmission of B. abortus from elk (Cervus canadensis) to humans in the Greater Yellowstone Area (GYA) in the USA. Although the Yellowstone Park service raises awareness about the risk for people in the GYA (https://www.nps.gov/yell/learn/nature/brucellosis.htm), the US Centers for Disease Control and Prevention only mentions hunting feral pigs (infected with B. suis biovar 1) as a zoonotic risk (https://www.cdc.gov/brucellosis/exposure/hunters.html).

Spillover of B. suis biovar 4 infections from semi-domesticated reindeer have been reported in indigenous people in Canada, Alaska, and Russia. In North America, the average number of cases is one per year.²⁶ The situation globally is comparable with that in Russia with the exception of Yakutia, in the Far East, where the  infection rate is high (4.8-5.6 per cent) among reindeer breeders.⁷¹ In contrast to B. suis biovars 1, 3 and 4, B. suis biovar 2 has rarely been isolated from humans.⁵⁶

In sub-Saharan Africa, no proof of direct transmission of Brucella spp. from wildlife to humans has been reported, although transmission resulting from preparing and consuming African buffalo (Syncerus caffer) bushmeat has been suggested.³

Aetiology and epidemiology

Brucellae are Gram-negative, facultative intracellular bacteria that can infect many mammalian species including humans. Twelve species are recognized within the genus Brucella:

1. a group composed of the six “classical” Brucella species, some of which include different biovars: Brucella abortus (biovars 1, 2, 3, 4, 5, 6, 7, 9), Brucella melitensis (biovars 1, 2, 3), Brucella suis (biovars 1, 2, 3, 4, 5), Brucella ovis, Brucella canis, and Brucella neotomae,⁴ and
2.  a group represented by the six "new" recently described species: Brucella ceti,²⁸ Brucella pinnipedialis,²⁸ Brucella microti...