Brucella

Brucella
Scientific classification
Kingdom:	Bacteria
Phylum:	Proteobacteria
Class:	Alphaproteobacteria
Order:	Rhizobiales
Family:	Brucellaceae
Genus:	Brucella
Species
B. abortus B. canis B. ceti B. inopinata B. melitensis B. microti B. neotomae B. ovis B. pinnipedialis B. suis

Brucella is a genus of Gram-negative bacteria. They are small (0.5 to 0.7 by 0.6 to 1.5 µm), non-motile, non-encapsulated coccobacilli, which function as facultative intracellular parasites.

Brucella is the cause of brucellosis, which is a zoonosis. It is transmitted by ingesting infected food, direct contact with an infected animal, or inhalation of aerosols. Transmission from human to human, for example through sexual intercourse or from mother to child, is exceedingly rare, but possible. Minimum infectious exposure is between 10 - 100 organisms. Brucellosis primarily occurs through occupational exposure (e.g. exposure to cattle, sheep, pigs), but also by consumption of unpasteurized milk products.

There are a few different species of Brucella, each with slightly different host specificity. B. melitensis which infects goats and sheep, B. abortus which infects cattle, B. suis infects pigs, B. ovis infects sheep and B. neotomae. Recently new species were discovered, in marine mammals (B. pinnipedialis and B. ceti ), in the common vole Microtus arvalis (B. microti ), and even in a breast implant (B. inopinata ). One unnamed strain (Brucella sp. NVSL 07-0026) has been isolated from a baboon.

However, the new NCBI taxonomy has named all Brucella species Brucella melitensis. They include Brucella melitensis 16M and 5 other biovars: abortus, canis, neotomae, ovis, and suis.

Diagnosis

Brucella is isolated from a blood culture on Castaneda medium. Prolonged incubation (up to 6 weeks) may be required as they are slow-growing, but on modern automated machines the cultures often show positive results within seven days. On Gram stain they appear as dense clumps of Gram-negative coccobacilli and are exceedingly difficult to see. In recent years molecular diagnostic techniques based on the genetic component of the pathogen have become more popular.

It is crucial to be able to differentiate Brucella from Salmonella which could also be isolated from blood cultures and are Gram-negative. Testing for urease would successfully accomplish the task; as it is positive for the Brucella and negative for the Salmonella.

Brucella could also be seen in bone marrow.

Laboratory acquired brucellosis is common. This most often happens when the disease is not thought of until cultures become positive, by which time the specimens have already been handled by a number of laboratory staff. The idea of preventive treatment is to stop people who have been exposed to Brucella from becoming ill with the disease.

There are no clinical trials to be relied on as a guide for optimal treatment, but a three week course of rifampicin and doxycycline twice daily is the combination most often used, and appears to be efficacious; the advantage of this regimen is that it is oral medication and there are no injections; however, a high rate of side effects (nausea, vomiting, loss of appetite) has also been reported.

Human brucellosis

Sir David Bruce isolated B. melitensis from British soldiers who died from Malta fever in Malta. The disease is characterized by acute undulating fever, headache, night sweats, fatigue and anorexia. Human brucellosis is not considered a contagious disease and people become infected by contact with fluids from infected animals (sheep, cattle or pigs) or derived food products like unpasteurized milk and cheese. Brucellosis is also considered an occupational disease because of a higher incidence in people working with animals (slaughterhouse cases). The real worldwide incidence of brucellosis is unknown because there is a low level of surveillance and reporting in Brucella endemic areas.

Possible Pathogens Responsible for the Plague in Thebes

The following text is edited from: Kousoulis AA, Economopoulos KP, Poulakou-Rebelakou E, Androutsos G, Tsiodras S. The plague of Thebes, a historical epidemic in Sophocles’ Oedipus Rex. Emerging Infectious Diseases. 2012 Jan. http://dx.doi.org/10.3201/eid1801.AD1801

"The pathogen of the plague described in Oedipus Rex reflects the complexity of every historically emerging zoonosis. Any proposed pathogen should be a highly contagious, zoonotic disease of cattle that causes stillbirth, miscarriages, and infertility, is characterized by high mortality rates, and has the potential to have caused an epidemic in the 5th century bc.

After a close inspection of the characteristics, the pathogens that include most (5 of 7) of the features described by Sophocles in Oedipus Rex are Leishmania spp., Leptospira spp., Brucella abortus, Orthopoxviridae, and Francisella tularensis. Among the diseases caused by these pathogens that can affect humans are the following: 1) tularemia, which is a disease mainly transmitted through rabbits; 2) smallpox, which is not a cattle zoonosis; 3) leishmaniasis, which is not a highly contagious disease; and 4) leptospirosis, which has been associated with epidemics after rainfall and flooding in relation to rodent infestation. Thus, the most probable cause of the plague in Thebes is B. abortus. Brucellosis is a highly contagious zoonosis caused by ingestion of raw milk or meat from infected cows or close contact with their secretions. Τhe mortality rate for untreated brucellosis is difficult to determine from the literature of the preantibiotic era (Durack DT, Littman RJ, Benitez RM, Mackowiak PA. Hellenic holocaust: a historical clinico-pathologic conference. Am J Med. 2000;109:391–7); nevertheless, an 80% rate has been reported in situations of comorbidity with endocarditis (Langmuir AD, Worthen TD, Solomon J, Ray CG, Petersen E. The Thucydides syndrome. A new hypothesis for the cause of the plague of Athens. N Engl J Med. 1985;313:1027–30). Epidemics, stillbirths, and miscarriages caused by B. abortus have been reported since the time of Hippocrates, which is when this disease was initially described.

However, taking into account that in modern times brucellosis in humans is a severe granulomatous disease characterized by extremely rare direct transmission from person-to-person, insidious onset in sporadic cases (mainly among veterinarians), and low mortality rates, it may be difficult for 21st century physicians and veterinarians to accept B. abortus as the causative agent of the plague of Thebes. Alternatively, the plague of Thebes could be a composite of >2 causative agents, as it has been suggested for the contemporary plague of Athens (Durack et al., 2000; Langmuir et al., 1985). In this case scenario, we could assume that cattle in Thebes may have been having brucellosis, leptospirosis, or listeriosis, while humans could have been affected by a different pathogen such as Salmonella enterica serovar Typhi (Papagrigorakis MJ, Synodinos PN, Yapijakis C. Ancient typhoid epidemic reveals possible ancestral strain of Salmonella enterica serovar Typhi. Infect Genet Evol. 2007;7:126–7; Papagrigorakis MJ, Yapijakis C, Synodinos PN, Baziotopoulou-Valavani E. DNA examination of ancient dental pulp incriminates typhoid fever as a probable cause of the Plague of Athens. Int J Infect Dis. 2006;10:206–14). It should be noted that exploring the diseases of history requires examining the social, economic, and demographic aspects of each era because this is the only way to better understand how diseases work over centuries (Littman RJ. The plague of Athens: epidemiology and paleopathology. Mt Sinai J Med. 2009;76:456–67). Finally, we cannot reject the possibility of dealing with a Brucella strain that has evolved to become less deadly than a more lethal ancestor (Durack et al., 2000)."

Blue light study

In a study published in Science in August 2007, it was revealed that Brucella reacts strongly to the presence of the blue spectrum in natural light, reproducing at a great rate and becoming infectious. Conversely, depriving Brucella of the blue wavelengths dropped its reproductive rate by 90%, a result one of the co-authors called "spectacular."

External links

• Microbiology of Brucella | Medchrome
• Brucella genomes and related information at PATRIC, a Bioinformatics Resource Center funded by NIAID
• Brucellosis
• Brucella Genome Projects (from Genomes OnLine Database)
• Comparative Analysis of Brucella Genomes (at DOE's IMG system)
• Brucella Bioinformatics Portal