Brucellosis: Symptoms, Causes, and Treatment

Brucellosis is a disease caused by a zoonotic bacterium, that is, it's transmitted to humans by other animals. Learn more in today's article.

Written and verified by el biólogo Samuel Antonio Sánchez Amador.

Last update: 09 May, 2023

Brucellosis, also known as Malta fever, Mediterranean fever, or Bang’s disease, is an infectious disease with a worldwide distribution caused by the bacterial genus Brucella. It’s a zoonosis, meaning that it’s a disease that’s transmitted from other animals to humans.

In 1968, the World Health Organization (WHO) stated that brucellosis was responsible for more disease, poverty, and economic loss than any other known animal disease that affects humans, according to studies. The lack of integration between public and veterinary health in many countries makes this one of the most widespread zoonoses.

So, today we’ll introduce you to a genus of bacteria that’s troubling epidemiologists and livestock health specialists alike. In the following paragraphs, we’ll cover everything you need to know about brucellosis, from symptoms to epidemiology. Keep reading.

The global situation of brucellosis

The description of epidemiology, that is, the study of the distribution, frequency, and determinant patterns of the appearance of a disease is the first step to combat it. Therefore, we’ll present you with a series of relevant data as far as brucellosis is concerned, all of them collected by specialized portals on the subject:

• The incidence of brucellosis: The number of new cases in a given time and population—is 0.01 cases per year per 100,000 inhabitants in high-income countries. In low-income regions, this value increases to 200 cases per year per 100,000 inhabitants.
• In countries like Spain, 2,842 cases were detected each year before the start of the 21st century, that is, about 7 patients per 100,000 inhabitants.
• People who work directly with livestock are more likely to get it.
• According to the Center for Public Safety and Food Safety, only 1-2% of brucellosis cases typically end in the death of the patient. Some outbreaks have a lethality of up to 5%.

As we can see, we’re talking about a disease whose incidence is related to the country’s health infrastructure and the state of livestock animals. In Europe and the United States, food laws and protocols have become stricter.

Causal agent

We’re dealing with the genus Brucella, a rod-shaped taxon of gram-negative bacteria with a diameter of about 0.7 μm. They’re microorganisms without mobile capacity and are strictly aerobic, meaning that they require oxygen to live.

As indicated by the National Library of Medicine, the genome of this bacterial genus is made up of two chromosomes and lacks plasmids —regions of circular DNA. Unfortunately, the genetic pathogenic bases of Brucella haven’t yet been fully studied, so the factors that predispose one to the virulence of one or another host continues to be a secret.

Here’s a list of the different species of the genus and their hosts:

• B. melitensis: Its known hosts are goats, cattle, sheep, dogs, and humans.
• B. abortus: Its hosts are bovines, canids, and humans.
• Brucella suis: Known hosts are pigs, canids, and humans.
• Brucella canis: Known hosts are canids and humans.

There are six more species, those that affect everything from foxes to seals, but because they’re not transmissible to humans —or cases in humans haven’t been recorded— we’re not going to focus on them. It should be noted that B. melitensis is the most worrying agent of all, as according to studies already cited, it causes 98% of brucellosis. The remaining 2% is attributed to B. abortus.

The causes of brucellosis and transmission

Brucellosis is a zoonosis, meaning that it’s transmitted between animals and humans. According to the Centers for Disease Control and Prevention (CDC), there are multiple routes of infection. We’ll tell you briefly below.

1. Consuming poorly treated products

The consumption of raw, undercooked meats or unpasteurized dairy products is a risk factor for contracting the bacteria. As indicated by the World Health Organization (WHO), most brucellosis outbreaks are caused by the consumption of raw milk and untreated fresh cheese.

2. By inhalation

For this reason, workers in the livestock sector are more at risk. The bacteria can be directly inhaled by coming into contact with contaminated animal products, such as placentas, feces, urine, or fetuses. We’re dealing with a method of direct airborne transmission.

3. Entry through wounds and mucous membranes

Like the respiratory tract, open wounds or mucous membranes—such as the lining of the mouth—are excellent entry points for Brucella bacteria. For this reason, the following groups are most at risk:

• Veterinarians who work with sick animals
• Packers of meat products in factories or local businesses
• Workers in slaughterhouses and meat processing plants
• Hunters

Symptoms of brucellosis

The Mayo Clinic and other portals already mentioned help us to discern its clinical picture. In general, we can affirm that there are four forms of presentation. It can be evidenced by highly polymorphous clinical manifestations, many of them asymptomatic:

• Asymptomatic form: Caused by the accidental inoculation of the bacteria through vaccine material, that is, it’s typical in the veterinary field. Despite not being serious, the patient may present joint discomfort, fever, weakness, and fatigue.
• Localized forms: Affect a specific area of the body. An example of this is spondylitis, that is, swelling of the vertebrae of the spine due to infection.
• Septicemia: The bacteria pass into the blood and spread through the organs, so we’re talking about a more serious medical condition than the previous ones. The patient has a high fever, chills, profuse sweating, and severe headaches. Lymph nodes also swell (adenopathy).
• Chronic form: Only present in patients who’ve presented an evolution of the disease for more than six months.

Unfortunately, brucellosis has a certain tendency to relapse, that is, to reappear after an apparent cure. In some patients, the disease can last for years, although this isn’t so common with proper treatment. As indicated by the MSDmanuals portal, among the possible complications of the disease, we find subacute bacterial endocarditis —infection of the heart tissue—, meningitis, encephalitis, and osteomyelitis.

Diagnosis and treatment

The isolation of Brucella spp. is the definitive diagnostic method. To do this, samples of the patient’s blood or bone marrow fluid are obtained and cultivated in a prolific culture medium. The colonies usually begin to be observed after 2-4 days, the time it takes for confirmation.

There are also indirect diagnostic methods, such as seroagglutination and enzyme immunoassay, although we’re not going to dwell on them due to their exceptional nature.

Once the causative agent is confirmed, the patient should start taking antibiotics for at least six weeks. A series of non-specific symptoms—fatigue, joint pain, or headache—may be experienced several months after infection. In addition, there are no reliable serological or clinical criteria that confirm a complete cure.

The drugs of choice are usually doxycycline and rifampizin, applied orally for a period of 6 to 8 weeks. Pregnant women and people with allergies to antibiotics or a compromised immune system should notify their physician of their condition.

This is a very non-lethal disease, as we remember that less than 2% of patients usually die from it. Even so, the patient can show symptoms for several months and the chances of reinfection are higher than with other bacterial diseases.

A low-lethality disease

As you’ve been able to observe in this article, brucellosis is a not very lethal disease, but one that can be quite difficult to get rid of once the patient has been infected. Unfortunately, it’s a widespread zoonosis in low-income countries.

It’s clear that the best prevention against this disease is sanitation, both for healthcare professionals in contact with livestock and for products derived from it. The pasteurization of dairy products, the cooking of meat, and the application of special measures in veterinarians and slaughterhouses reduce the chances of contagion to a minimum.