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Brucellosis: Endemic and re-emerging zoonosis
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During the first week of August, the Syrian Ministry of Health and the WHO Early Warning Alert and Response System reported a significant increase in the number of suspected brucellosis cases in humans, with, reportedly, an average of 100 new cases recorded each week in Damascus and rural Damascus alone.
A hundred new cases per week seems, in an urban or semi-urban environment, a relatively high figure for a disease that does not spread between humans. Taking a look at Syria’s records will, however, reveal similarly concerning situations in the not too far past. During 2007 and 2008, 39,838 and 25,315 annual human cases, respectively, were reported by Syria to the World Organization for Animal Health (OIE). This means, for 2007, more than 766 new cases per week. The numbers had declined during the preceding years.
Decline in veterinary service
The Food and Agriculture Organization of the United Nations ascribed this apparently re-emerging epidemic in the war-stricken country to the deterioration in the agricultural sector. As a result of the current unrest in the Syrian Arab Republic, the government’s veterinary service has become significantly eroded. Vaccines are in short supply and sanctions prohibit imports.
Most private companies that were producing prophylactic medications have gone out of business because of damage to their premises and because of the difficulty to import. Power outages have also led to the deterioration of the dairy and cheese vendor industry; this may have affected the quality of the products, particularly pasteurization, and may have led to the sourcing of dairy products from uncontrolled dairies. Infected goats, sheep and cattle are the main source of human infection with brucellosis in the Middle East and in most affected countries. It is a bacterial zoonosis, infecting humans either directly or indirectly by means of contaminated milk and dairy products.
Arnon Shimshony
Official reportable disease
Brucellosis is one of the diseases listed as “WHO’s seven neglected endemic zoonoses” (the others are anthrax, bovine tuberculosis, cysticercosis and neurocysticercosis, cystic echinococcosis or hydatid disease, rabies, and zoonotic sleeping sickness or human African trypanosomiasis).Brucellosis is one of the zoonotic diseases officially addressed by the international health agencies, WHO on the human side and the OIE on the animal side. Bovine brucellosis, caprine and ovine brucellosis and porcine brucellosis are three disease entities included in OIE’s official list of compulsorily reportable animal diseases. The prescribed internationally approved requirements for their respective notification procedures and control measures are laid out in the Terrestrial Animal Health Code. The methods for diagnosis and prevention, and the requirements related to the manufacture of vaccines and their testing, are handled in the Manual of Diagnostic Tests and Vaccines for Terrestrial Animals 2013.
On top of the prescribed notification of listed diseases in animals, OIE’s member countries are required to report annually the incidence in humans of listed zoonotic diseases.
The animal hosts of B. melitensis are sheep, goats, cows and camels (biovars 1, 2, 3). B. melitensis biovar 3 has also been found in Nile catfish and dogs. B. abortus (biovars 1, 2, 3, 4, 5, 6, 9) naturally infects cattle, bison, buffalo, elk, yak and camels.
The animal hosts of B. suis are horses (biovar 1), pigs and wild boars (biovars 1, 2, 3), the European hare (biovar 2), caribou and reindeer (biovar 4), and rodents (biovar 5). B. suis biovars 1, 3, 4 have been reported to cause human disease.
Humans can also be infected from marine mammals (B. ceti in whales, dolphins, porpoises) and, rarely, from canines (B. canis).
Occupational exposure
There is an occupational risk to veterinarians, farmers, slaughterhouse personnel and others who handle infected animals and aborted fetuses or placentas. Infection is essentially acquired by the mucosal routes.
Brucellosis is one of the most easily acquired laboratory infections, and strict safety precautions should be observed when handling cultures and heavily infected samples, such as products of abortion.
To enhance the control of this devastating disease, which continues to cause important medical, veterinary, socioeconomic and conservation problems, professionals in veterinary public health, human health, wildlife health and environmental health are expected to apply a One Health approach at local, regional and global levels.
Signs of disease
Brucellosis in susceptible animals is generally characterized by one or more of the following signs: abortion, retained placenta, orchitis, epididymitis and, rarely, arthritis, with excretion of the organisms in uterine discharges and in milk. Diagnosis depends on the isolation of Brucella from abortion material, udder secretions or from tissues removed at postmortem. There are several serologic and other diagnostic techniques.
The WHO laboratory biosafety manual classifies Brucella in risk group III. The bacterium readily infects humans, causing acute febrile illness — undulant fever — which may progress to a more chronic form and can also produce serious complications affecting the musculoskeletal, cardiovascular and central nervous systems. Ingestion of dairy products constitutes the main risk to the general public where the disease is endemic.
Brucellosis origins
First discovered in the 1850s in Malta, brucellosis reportedly remains one of the most common chronic bacterial infections in the world, despite ongoing efforts, in many countries, to prevent, control and eventually eradicate it. Although relatively effective diagnostic tests for brucellosis have been in existence for more than 100 years, it remains a serious, embedded and also a re-emerging disease in many parts of the globe, mainly in the Middle East, Asia, the Balkans and Latin America. Several countries in northern and central Europe, Canada, Japan, Australia and New Zealand are believed to be free from the agent. Israel, reportedly, eradicated one species, Brucella abortus.
Brucella bears the name of Surgeon-Captain David Bruce of the British Army Medical Staff who, in 1887, isolated Micrococcus melitensis, now Brucella melitensis, the causal organism of brucellosis (also known as Mediterranean, Malta or undulant fever). About 18 years later, in 1905, similarly in Malta, it was discovered that the goat was the animal reservoir. Since then, several additional Brucella species have been recognized, seven of which are currently known to infect humans.
Despite estimates of more than 500,000 new human cases annually, brucellosis remains frequently under-diagnosed and neglected among livestock diseases in many endemic countries. Most reported human cases are caused by transmission of B. melitensis, B. abortus and B. suis from livestock. The pathogenicity for humans of newly described species and atypical strains is also currently being reported.
References:
One Health Initiative. www.onehealthinitiative.com. Accessed August 20, 2013.
World Organization for Animal Health. www.oie.int/manual-of-diagnostic-tests-and-vaccines-for-terrestrial-animals. Accessed August 20, 2013.
For more information:
Arnon Shimshony, DVM, is associate professor at the Koret School of Veterinary Medicine Hebrew University of Jerusalem, Rehovot, and is the ProMED-mail animal diseases zoonoses moderator. Shimshony was chief veterinary officer, State of Israel, from 1974 to 1999. He is also a member of the Infectious Disease News Editorial Board.
Disclosure: Shimshony reports no relevant financial disclosures.