BRUCELLOSIS
Brucellosis is a contagious disease that is a significant public health concern as it can be spread to humans and has serious economic and healthcare repercussions. It is in the World Organization for Animal Health (WOAH) Terrestrial Animal Health Code, making it a listed disease. It is also known as “rock fever”, “undulant fever”, “Mediterranean fever” or “Malta fever”.
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Cattle
Sheep
Goats
Swine
Horses
Dogs
Malta fever can also infect other animal species like camelids, buffalo, yaks, rodents and deer, as well as human beings.
Although prevention programs have reduced the incidence of brucellosis in many regions and it has been eradicated in various countries, it remains an uncontrolled issue in areas where it is highly endemic, like the Mediterranean, Middle East, Africa, Latin America and parts of Asia, due to the following factors:
Unknown origin of replacement animals
As external animals aren’t traceable, the bacteria can be introduced into farms that were previously disease free.
Inappropriate handling of abortions
Lack of hygiene and disinfection, as well as incorrect disposal of the remains of aborted fetuses is one of the main focuses of the infection.
Presence of other animal species
When the livestock is in constant contact with other animals and their waste, it makes it easier for the disease to spread, as is seen with herding dogs.
Contaminated environments
The most common pathway of infection is digestive, by consuming contaminated grass, fodder and water.
Artificial insemination
The use of infected bulls for artificial insemination poses a significant threat.
Brucellosis is caused by various bacteria in the Brucella genus, which affect a wide range of species. These bacteria can replicate and survive in the host’s cells, which is why brucellosis is so persistent.
PRINCIPAL HOSPEDADOR
B. abortus
Cattle
Goats
B. ovis
Sheep
B. suis
Swine
Many of them can be passed among different animal species, and all of them are highly contagious for humans, although B. mellitensis is the most common cause of human brucellosis, accounting for over 98% of infections reported.
Although cases of brucellosis in animals can occur all year long, the epidemic peak is from February to July, months associated with calving and abortions.
Infected species secrete large amounts of bacteria in their milk, the tissues and products of abortions, and genital secretions, which can contaminate their environment. Brucella bacteria can survive for a relatively long time in the environment, making it easy for the disease to be constantly circulating in the herd.
- Among animals: The disease is highly contagious among animals and spread mainly through ingesting infected tissues or milk, and to a lesser degree venereally. The main source of infection are fetuses, amniotic sacs and vaginal discharge, which contain a high concentration of these bacteria.
- From animal to human (zoonosis):
- Direct contact: The main pathway for the spread of this disease, mainly affecting professionals who are in direct contact with animals, like farmers and veterinarians. People working in the livestock sector can also be infected by inhaling aerosols when the animals kick up dust (respiratory) and through open cuts or mucous membranes (cutaneous). Laboratory technicians and veterinarians can also be infected accidentally.
- Oral transmission: Consuming unpasteurized milk or dairy products, or eating contaminated meat or products raw, can also lead to cases of brucellosis.
- From person to person: Very infrequent, although it could be possible through blood transfusions or organ or tissue transplants.
- Abortions or premature births
- Infertility
- Birthing weak offspring
- Placenta accreta
- Decreased milk yield
- Weight loss
- Limping
- Inflamed genital area in males
In more serious cases, brucellosis can lead to other illnesses like metritis, orchitis, epididymitis and, rarely, arthritis.
Brucellosis in humans presents initially as an acute fever (undulant fever or Malta fever). If left untreated, it can become chronic and have serious complications that affect muscles, the cardiovascular system and the central nervous system.
Financial losses from brucellosis
Low birth rate
Abortions and infertility lead to a significantly lower birth rate.
Weak offspring
Weak offspring require non-productive maintenance, increasing costs without contributing financially.
Reduction of estrus
The time between calving can be up to 20 months in infected animals due to 40%-50% decrease in estrus.
Decreased milk yield
Infected cows produce up to 20% less milk.
Cost of culling infected animals
Infected animals must be culled to prevent the disease from spreading.
Increased production costs
The presence of brucellosis in livestock can increase production costs by 8%, or up to 10% in dairy farms.
Costs due to livestock mobility restrictions:
The prevention and control measures some countries put in place may include restricting or completely closing domestic and international markets to prevent infected animals or contaminated products from entering or moving around the area.
Brucellosis is a disease that entails significant economic losses globally. Here are some examples of its economic impact in different countries:
- Colombia: According to FEDEGÁN-FNG calculations, the direct cost of bovine brucellosis is estimated at €19,500 ($21,000) per day. This amount doesn’t include additional expenses for diagnosing animals with reproductive syndrome, culling reactors without government compensation, or leave and medical treatment for staff affected.
- Ecuador: Bovine brucellosis is estimated to cause annual losses of €5.1 million ($5.5 million) due to abortions, reduced milk yield and livestock mortality.
- Brazil: In 2013, the direct losses due to bovine brucellosis totaled over €150 million ($161 million) a year.
- India: In 2018, brucellosis was estimated to cause average annual losses of €3.16 billion ($3.4 billion) in the livestock sector, with 96% of that from the dairy sector.
Humans can get brucellosis accidentally and Brucella melitensis is the most common cause (up to 98% of all cases). From a public health standpoint, brucellosis is considered an occupational disease because it mainly affects people who work in slaughterhouses, butcheries and veterinary clinics.
People tend to be infected through contact with infected animals or materials, or by ingesting contaminated foods. The Brucella bacteria enter the body through the digestive system, lungs, mucous membranes or skin and spread through the bloodstream and lymphatic system to infect other organs and provoke localized infections.
After a variable incubation period that can range from one week to several months, they show symptoms similar to the common flu, like fever, headache, aches and fatigue. In the initial phase, Brucella is easy to detect using a blood culture.
In numerous countries, especially those free of brucellosis, any cases detected must be reported in order to keep outbreaks to a minimum and stop them from spreading.
How to control and prevent brucellosis?
The wide diversity of species susceptible to brucellosis complicates prevention measures. However, having a prevention strategy is key to reducing the impact of the disease on livestock.
Control
Brucellosis control measures can be imposed by national governments, to eradicate it from a specific region, or by farmers and veterinarians, to limit their financial losses.
Authorities can adopt three different strategies to control endemic brucellosis:
- Not take any public action: This tends to happen in countries where human brucellosis is rare and that don’t export small ruminants, or when resources are scarce.
- Optional control program: Tend to offer privileges for farmers who follow them.
- Mandatory national strategy: A well planned long term strategy based on vaccination.
If the prevalence of the disease is high (>5-10% of flocks infected), the plan must have three successive phases:
- Mass vaccination campaigns: There tends to be two types of campaigns:
- Vaccinating the whole receptive population the first year and only young animals once a year after that.
- Vaccinating the whole population every two years.
- Combination of vaccination and culling of seropositive animals: Shouldn’t be started until after a successful long term vaccination period (10–15 years).
- Diagnosis and culling: Implemented when the prevalence is below 1% and there is a proven tracing system in place.
- Hygiene and disinfection: Strict sanitary control measures at all farms, regardless of their size.
- Quarantining new animals: When bringing a new animal into a farm without health tracing, it must be kept in quarantine.
- Correct handling and disposal of abortion waste: Strict biosafety measures when collecting samples are crucial for preventing infection. Plus, all abortion materials must be disposed correctly.
- Correct use of equipment by professionals: Farmers, veterinarians and slaughterhouse staff must wear suitable protective gear, such as gloves that cover the forearm, tall rubber boots, coveralls, aprons and masks. These items should be disposable or easy to clean and disinfect. Plus, all these professionals must adhere to rigorous personal hygiene and cleanliness rules.
- Pasteurizing milk: Both for direct consumption and for production of dairy products for human consumption.
- Rose Bengal Test: One drop of animal serum is mixed with one drop of Rose Bengal antigen on a slide and if agglutination (lumps) appear it is positive.
Definitive diagnosis of brucellosis requires isolation and identification of the bacteria causing it. Often the culture is taken in vivo from milk, vaginal swabs and affected tissues, but it is samples from abortions, infected full-term calves and fetal membranes that contain the highest concentration of Brucella, facilitating diagnosis.
- Direct culture of milk and tissues: A sample is taken from milk or animal tissues and cultured on slides for four weeks to detect bacteria growth. Suspicious colonies have to be identified through further testing.
- PCR: Bacteria DNA is extracted from samples using a special kit and then the DNA is amplified in a polymerase chain reaction (PCR) to detect Brucella.
Combining several diagnostic methods allows for quick, precise detection of brucellosis, helping control and prevent the disease. Females that have recently calved or aborted should not be sampled, as they can give false positives. Testing must be done at least 30 days after birth.
Brucellosis vaccination
Vaccination is the most effective way to prevent brucellosis in animals and, as a result, limit associated financial losses and healthcare issues.
There are three strains used most commonly in vaccination: B-19 and RB51 in brucellosis vaccine for cattle and Rev-1 for sheep and goats.
- Álvarez-Hernández, N.E., Díaz-Flores, M. & Ortiz-Reynoso, M. (2015) Brucelosis, una zoonosis frecuente. Revista Medicina e Investigación. 3(2):129-132. doi: 10.1016/j.mei.2015.07.002
- Arenas, N. & Moreno, V. (2016). Estudio económico de la infección por Brucella abortus en ganado bovino en la región del Sumapaz, Colombia. Revista de la Facultad de Medicina Veterinaria y de Zootecnia, 63(3), 218–228. doi: 10.15446/rfmvz.v63n3.62751
- Benkirane, A. (2006) Ovine and caprine brucellosis: World distribution and control/eradication strategies in West Asia/North Africa region. Small Ruminant Research, 62 (1–2);19-25 doi: 10.1016/j.smallrumres.2005.07.032.
- Córdova-Izquierdo, A. et al (2016) Importancia de la Brucelosis bovina y consecuencias económicas para el ganadero. Revista Entorno Ganadero, 78: 18-24.
- Deka, R. P., Magnusson, U., Grace, D., & Lindahl, J. (2018). Bovine brucellosis: prevalence, risk factors, economic cost and control options with particular reference to India- a review. Infection Ecology & Epidemiology, 8(1). doi: 10.1080/20008686.2018.1556548
- Gul, S. & Khan, A. (2007). Epidemiology and epizootology of brucellosis: A review. Pakistan Veterinary Journal. 27. 145-151.
- Organización Mundial de la Salud (OMS) Código Sanitario para los Animales Terrestres. Capítulo 8.4. Infección por Brucella abortus, B. melitensis y B. suis. Recuperado de: https://www.woah.org/es/que-hacemos/normas/codigos-y-manuales/acceso-en-linea-al-codigo-terrestre/?id=169&L=1&htmfile=chapitre_bovine_brucellosis.htm
- Santos, R., Martins, T., Borges, A. & Paixao, T. (2013) Economic losses due to bovine brucellosis in Brazil. Pesquisa Veterinária Brasileira. 33. 759-764. doi: 10.1590/S0100-736X2013000600012.
- SENACSA (2017) Brucelosis Bovina. Recuperado de: https://www.senacsa.gov.py/index.php/Temas-pecuarios/sanidad-animal/programas-sanitarios/brucelosis-bovina#:~:text=Es%20una%20enfermedad%20infectocontagiosa%20de,los%20%C3%BAltimos%20meses%20de%20gestaci%C3%B3n.
- Singha, B.B, Dhandb, N.K & Gilla, J.P.S. (2015) Economic losses occurring due to brucellosis in Indian livestock populations. Preventive Veterinary Medicine, 119 (3–4): 211-215
DR. JOSÉ MARÍA BLASCO
Jose María Blasco holds a PhD in Veterinary Medicine from the University of Zaragoza and is a researcher at the IA2 CITA-UNIZAR Institute. He is also a member of the research group on Bacterial Zoonoses (ZooBac), which focuses on brucellosis, salmonellosis, and streptococcus.
We talked to him to learn about the main characteristics of brucellosis and how to prevent its spread in cattle.
RB-51 CZV
Lyophilized live vaccine for active immunization of cattle against brucellosis caused by Brucella abortus.
Vaccine for active immunization of cattle against brucellosis caused by Brucella abortus.
B-19 CZV OCULAR
Ophthalmic vaccine for active immunization of cattle against brucellosis caused by Brucella abortus or Brucella melitensis.
CZV REV-1
Vaccine for active immunization of sheep and goats against brucellosis caused by Brucella melitensis.
OCUREV
Ophthalmic vaccine for active immunization of sheep and goats against brucellosis caused by Brucella melitensis.
Serological diagnostic test for Brucella infections in cattle, sheep and goats.