Brucella species as potential biological weapons

Dr. Philip H. Elzer
Louisiana State University AgCenter and School of Veterinary Medicine
Department of Veterinary Science
Baton Rouge, Louisiana

          Brucellosis is a zoonotic disease with potential for use as a biowarfare agent. The genus Brucella contains six recognized species including B. abortus, B. melitensis, B. suis, B. canis, B. ovis, and B. neotomae. All of the brucellae are Gram negative, facultative intracellular pathogens, which survive and replicate in host macrophages. The hallmarks of animal brucellosis, in both domestic and wild animals, are abortion, infertility and reproductive failure. If used in an agroterrorist attack, these organisms could decimate a generation of livestock and companion animals. Fever, chills, malaise, arthritis, dementia, and possibly even death characterize the disease in man. Human brucellosis, also known as undulant fever or Malta fever, is caused by only four species of brucellae. B. melitensis is the most infectious to man in that 1-10 colony forming units are thought to cause disease followed by B. suis (1000-10,000), B. abortus (100,000), and finally B. canis (>1,000,000 in an immuno-compromised individual). There are several animal vaccines that are safe and effective; however, they are all pathogenic to man. Currently there are no vaccines approved for use in humans. Brucellae are characterized as BSL-3 organisms due to their ability to infect humans through aerosol exposure, which makes them an ideal bacterial agent for use by terrorists. If the general public were exposed to this biowarfare agent, medical resources would be stretched 10 fold to take care of the large number of people that would be debilitated by this organism. With the recent tragic events in the United States and throughout the world, three species of Brucella are considered "agents of mass destruction." The need for a human vaccine is paramount.
          There are six recognized species in the genus Brucella characterized by their host specificity and ability to cause chronic infections in many animals and man. Brucellae are know to cause abortion and infertility in wild and domestic ungulates [1,2,3]. In addition to the agricultural economic loss associated with brucellosis, several of the brucellae are zoonotic agents. After the tragic events associated with September 11, 2001, in the United States, three species of Brucella are also considered "agents of mass destruction." Therefore the development of a safe and efficacious vaccine for all ungulates and humans is a paramount goal for brucellosis researchers.
          The properties of the ideal biological weapon are that the agent should be highly contagious and consistently produce a known disease or syndrome. It is best if it can be disseminated throughout the environment, i.e. aerosolized; and it needs to be stable under production, storage, and delivery to target. However the organism should have a short survival time in the target area so it is not a threat at later time points to delivery personnel. It is preferable that the target populations have little or no natural resistance.
          Brucellae are the consummate biological warfare agents in that they meet all of these criteria. They are highly infectious (see Table 1), can be easily aerosolized, are stable during production; and due to its sensitivity to direct sunlight, it is destroyed in the environment over time. Since there are no human vaccines against brucellosis, most, if not all populations, have little or no natural immunity to this organism. Brucella species were weaponized in the United States following WWII. These species were field tested in cluster bombs in 1955. However all of the munitions using this agent were destroyed in 1969. If used in an agroterrorist attack, these organisms could decimate a generation of livestock and companion animals. With the concentration of livestock, lack of genetic diversity, increased farm sizes, importation of animals, and increased international travel, agriculture around the world is very vulnerable to a terrorism attack. The effects of agroterrorism would be immediate in that there would be mass hysteria manifested by panic buying of the stocked products. There would be demoralization due to the loss of food, plants, companion animals, and economic devastation. This economic destruction could become worldwide if a country's main agricultural export product or products were boycotted by numerous nations [4].
          All of the brucellae are Gram negative, facultative intracellular pathogens, which survive and replicate in host macrophages. In man, brucellosis, also known as undulant fever or Malta fever, is caused by only four species of brucellae (B. abortus, B. melitensis, B. suis, and B. canis). Human infection is caused by ingestion of infected raw milk products, exposure to infected animals, and aerosolization of the organism. Brucellosis in man is characterized by a cyclical fever that starts two to three weeks post-exposure. Night sweats, headaches, backaches, and general malaise are symptoms associated with acute infection. Chronic brucellosis can lead to a debilitating condition, including arthritis, dementia and even death. Patients with chronic brucellosis have frequent relapses, and 2/3 of these individuals develop psychoneurosis. Human brucellosis can be treated with the administration of tetracycline or doxycycline in combination therapy with rifampin or gentamicin [5].
          Due to the potential use of biowarfare agents, public health officials need to be constantly aware of possible intentional exposures to infectious agents. There are needs for rapid and specific detection devices for environmental releases and medical samples. Improved surveillance and diagnostics with effective communication amongst numerous regulatory and emergency agencies is necessary to contain and control an exposure or outbreak. An example of this is illustrated by a case report of a 38 yr old woman from New Hampshire, USA, who was thought to have been exposed to Brucella spp. This report highlights several aspects of the needed public health response to a possible biowarfare agent [6].
          The CDC classifies B. abortus, B. melitensis and B. suis as "agents of mass destruction" and as category B organisms. Brucella canis, a less virulent strain, can cause human disease but only when contracted by an immuno-suppressed individual. B. melitensis is the most infectious to man in that 1-10 colony forming units (cfu) are thought to cause disease followed by B. suis (1000-10,000 cfu), B. abortus (100,000 cfu), and finally B. canis (>1,000,000 cfu) in immuno-compromised individuals (Table 1). Brucellae are characterized as BSL-3 organisms due to their ability to infect humans through aerosol exposure, which makes them an ideal bacterial agent of mass destruction [7]. If the general public were exposed to this biowarfare agent, medical resources would be stretched 10 fold to take care of the large number of people that would be debilitated by this organism. Currently there is no approved vaccine for human use, and a vast majority of the animal vaccines are virulent to man. Thus, there is a need to find a safe and efficacious vaccine that can be used in humans [7].

Table 1. Human Susceptibility to Brucella spp.

References:

1. Timoney, J.F., J.H. Gillespie, F.W. Scott, and J.E. Barlough. 1988. The Genus Brucella. Hagan and Brunner's Microbiology and Infectious Diseases of Domestic Animals. 8th edition. Cornell Univ. Press, Comstock Publishing Assoc., Ithaca, New York.
2. Burrows, W. 1968. Brucella. In Textbook of Microbiology. 19th edition. W.B. Saunders Co.,Philadelphia, Pennsylvania.
3. Nicoletti, P. 1980. The epidemiology of bovine brucellosis. Adv. Vet. Sci. Compar. Med.24:70.
4. Huxsoll, D.L., W.C. Patrick III, and C.D. Parrott. 1987. Veterinary services in biological disasters. J. Am. Vet. Med. Assoc. 190:714-722.
5. Young, E.J. 1989. Clinical manifestations of human brucellosis. p.97-126. In:E.J. Young and M.J. Corbel (Ed.), Brucellosis: Clinical and laboratory aspects. CRC Press, Boca Raton, FL.
6. Suspected Brucellosis Case Prompts Investigation of Possible Bioterrorism-Related Activity-New Hampshire and Massachusetts, 1999. MMWR 49 (23); 509-512.
7. Acha, P.N., and B. Szyfres. 1980. Zoonoses and communicable diseases common to man and animals, p. 28-45. Pan American Health Organization, Washington, D.C.

Ed. Note: Bartolome and Espona show us that non-classical CB terrorism is practiced in Latin America and that the expertise and technologies used were and are imported.