Brief overview of bovine brucellosis: The Kenyan perspective

Introduction

Brucellosis is the most common and widespread of all bacterial zoonotic infections affecting man, livestock and wild animals (OIE., 2012; Corbel., 2006 and FAO., 2003) with significant socio-economic impacts and human suffering in endemic areas (Young., 1995; Boschiroli et al., 2001; McDermott., 2013). In Kenya, the nationwide prevalence of brucellosis in animals is unknown (ZDU., 2015) but the Zoonotic Disease Unit (ZDU) is in the process of determining the national prevalence and incidence through the current and ongoing study at Kajiado county in Kenya. Previous work by ZDU on brucellosis has been published on June this year 2015 as, “Sero-prevalence of Brucellosis in Humans and their Animals: A Linked Cross-sectional Study in Two Selected Counties in Kenya“

Epidemiology

Bovine brucellosis, caused by Brucella abortus, is a contagious disease with a worldwide distribution, except in regions where it has been eradicated (Robinson., 2003). It is less often caused by Brucella melintesis and seldom by Brucella suis, all of which are intracellular, facultative, Gram-negative, coccobacilli or short rod bacteria (OIE., 2012) of which nine biotypes have been recognized (Radostits et al., 2000).

Transmission

As a herd problem, it is primarily spread by contact and ingestion of contaminated material (Boschiroli et al., 2001; Radostits et al., 2000), while spread between herds is facilitated by introduction of asymptomatic animals (Nicoletti., 2013). The primary routes of infection are through the mucous membranes of the conjunctiva, oral and nasal surfaces (Abernethy et al., 2006) and supposedly through vertical transmission or colostrum (Aparicio., 2013). Humans get infected by direct or indirect contact with infected animals, their products or by-products (Corbel., 2006; Dean et al., 2012; Karadzinska-Bislimovska et al., 2010) and therefore humans play a role in its persistence and transmission (Aparicio., 2013).

Risk factors

Susceptibility of cattle to Brucella abortus infection is influenced by: management factors such as artificial insemination (Boschiroli et al., 2001), herd sizes and population density; animal factors such as age, sex, reproductive status; and biological factors such as herd immunity (Crawford., 1990). Infection occurs in cattle of all ages but persists commonly in sexually mature animals (Radostits et al., 2000). Young animals are more resistant to infection and often clear infections but latent infections may occur (Walker., 1999).

Factors contributing to brucellosis in Kenya include:

• The available data on brucellosis is not adequate enough to inform effective control processes.
• The free range production system practiced in most parts of the country helps to maintain the disease in both animal and human populations
• The cultures of some community that encourages consumption of raw livestock products e.g. whole blood an raw milk
• Inadequate and non-sustainable resources for effective brucellosis control i.e. for the implementation of test and cull policy (currently not practiced); for skill improvement and equipping of the existing surveillance personnel/ staff; for the hiring of adequate skilled personnel
• Livestock-wildlife interaction (especially during free grazing), cattle rustling and porous borders limiting control efforts
• Inadequate diagnostic techniques which by extension do not give a true picture of Brucellosis presence/absence (the current study by ZDU will validate the existing testing kits and provide alternative, better and tested diagnostic options

Clinical features

In cattle it is manifested by elevated incidences of third trimester abortions (Crawford et al., 1990), placental retention, stillbirths, infertility, carpal hygromas (McDermott., 2002) and potential sterility in males (Halling and Boyle., 2002), resulting in huge negative economic impacts (Schelling et al., 2003; OIE., 2012). Clinical signs are not pathognomonic for the disease (Corbel., 2006) and therefore diagnosis is by demonstrating Brucella pathogens through laboratory techniques. The same organism also causes undulant fever in man (Mantur et al., 2007), which presents as febrile flu-like illness and is common among pastoralists in Africa (Seifert., 1996) and also Kenya (Muruki et al., 1994).

Diagnosis of bovine brucellosis

There are basically three main groups of diagnostic methods for detecting Brucella species: Identification of the agent, serological tests and other complementary tests. Identification of the agent can be achieved through microscopy, isolation and inoculation (OIE., 2012; Weidmann., 1991); Serology achieved through: Milk Ring Test-MRT, Serum agglutination Test-SAT, buffered Brucella antigen tests-BBATs, and Complement Fixation test-CFT (Radostits et al., 2000) while complementary tests used are: enzyme-linked immunosorbent assay-ELISA (Fadeel., 2006), fluorescence polarization assay-FPA and Polymerase Chain Reaction-PCR (Romero et al., 1995). For control strategies at national/local level, the BBATs as well as the ELISA and FPA, are suitable screening tests (OIE., 2012).

In Kenya the RBPT, ELISA and CFT are conducted at the central Veterinary Laboratories with prospects of starting PCR testing for brucellosis.

Treatment

Generally, treatment of infected livestock is not attempted because of the high rates of treatment failure, cost, (Walker., 1999; Nicoletti., 2013) and potential problems of residues to public safety when high doses of antimicrobials are used as chemotherapy. Man can be treated with a combination therapy of Doxycycline and Rifampicin antimicrobials, however, relapses may occur (Corbel., 2006).

Prevention and control of bovine brucellosis

This can be achieved through public health education and awareness among consumers and farmers on proper animal husbandry practices, sanitation and food-borne risks associated with brucellosis. Vaccinating all breeding animals to raise herd immunity (OIE., 2012). Strengthen and endorse strategies to control cross-border animal movement coupled with routine surveillance that provides accurate epidemiological information about the disease. Test, segregate and eliminate infected animals (Weidmann., 1991) but it should be noted that this approach is not a viable option in developing countries due to the high implementation costs.

Surveillance and control strategies for brucellosis available in Kenya:

• Surveillance of brucellosis is carried out by Veterinary Epidemiology and Economics Unit (VEEU) team but this is restricted to seroprevalence studies of particular areas in Kenya. There are about 7 veterinarians in the VEEU unit each of whom is in charge of particular diseases but work hand in hand in diseases surveillance collaboratively.
• Each county in Kenya has at least one veterinarian to implement disease control measures in that county
• Laboratory infrastrusture which comprise of:
  •  National referral laboratories, namely: Central Veterinary Laboratories (CVL) at Kabete and the National Veterinary Quality Control Lab at Embakasi
  • Regional laboratories, namely: Nakuru (serves southern Rift Valley region), Kericho (serves Nyanza, Western, and western Rift Valley region), Eldoret (serves Northern Rift Valley region, which has a satellite lab at Lodwar), Karatina (serves the Central and Eastern regions, which have a satellite lab at Isiolo), Mariakani(serves Coast region, having two satellite labs at Ukunda and Witu) and Garissa (serves North Eastern region)
• Brucellosis was included in the Integrated Diseases Surveillance and Reporting system on March 2011 (reported on a monthly basis)
• On 17th June of 2011 (Legal notice No. 68), Brucellosis was gazetted as a notifiable disease in Kenya under the animal diseases act (Cap. 364). This means that all identified cases of brucellosis must be reported to the department of veterinary services. Prior to this gazettement, cases of brucellosis were not necessarily reported and therefore it was difficult to determine the occurrence, prevalence and spread nationwide.
• Establishment of Disease Free Zones (DFZ): These are zones to be established around the country to be free from diseases such as: FMD, RVF, CBPP, Brucellosis, CCPP, PPR, BSE. This will be done in three zones. The first phase is currently on-going and the area for the first DFZ is the coastal area
• Research conducted by various universities in Kenya such as University of Nairobi as part of Msc and PhD projects and by various research institutes such as Kenya Agricultural and Livestock Research organisation (KALRO-previously KARI) and the International livestock Research Institute (ILRI).
• The Zoonotic Disease Unit (ZDU) which was set up in 2011 by the Ministry of Livestock Development (MoLD) and the Ministry of Public Health and Sanitation (MPHS) with the main objective of establishing and maintaining active collaboration at the animal, human and ecosystem interface towards better prevention and control of zoonotic diseases (learn more about the activities of ZDU, by clicking here)

 Impact of brucellosis on the Kenyan animal population

Analysis of passively collected data between the years 2003 to 2010 by the Zoonotic Disease Unit in Kenya demonstrate that brucellosis is wide spread throughout Kenya (ZDU., 2015) and that hundreds of Brucella-associated abortions in livestock are reported every year, suggesting that the disease is a major source of morbidity and mortality.

Economic losses due to brucellosis in Kenya are due to: abortion; birth of weak calves; reduced milk production; impaired fertility; major impediment to trade and export; loss of man hours, high treatment cost and government costs on research and surveillance schemes.

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