Saturday, 15 July 2006

Is there a link between soil properties and anthrax outbreaks?.

Mabel Pazos1, Nuria Roca1, Ramón Noseda2, and Gustavo Combessies2. (1) Facultad de Agronomía - UNCPBA, Republica de Italia 780, CC 47, Azul, 7300, Argentina, (2) Laboratorio Azul Diagnóstico S.A., 25 de Mayo 479, Azul, Argentina

Interest in anthrax has increased recently due to its use in bioterrorism attacks. Anthrax is a rapidly fatal, infectious disease that affects many animal species, particularly herbivores and humans. The disease is caused by Bacillus anthracis, a spore-forming bacterium, and is most common in rangeland. These include South and Central America, Southern and Eastern Europe, Asia, Africa, the Caribbean, and the Middle East. When anthrax affects humans, it is usually due to an occupational exposure to infected animals or their waste products. The highly resistant spores can persist under favorable conditions for decades in the environment before infecting a new host. In Argentina, anthrax is a reportable disease that occurs sporadically in livestock and humans. Azul Co., in Buenos Aires province, is located in the center of the Humid Pampa with an area of 6615 km. Cattle raising occupies more than half of this area in a very flat plain with regional slopes of less than 0.5%, alkaline soils with slow permeability, and the area is subject to frequent flooding. The first vaccination against anthrax was performed in Argentina in 1886. However, only in the last thirty years are there detailed records of anthrax outbreaks in the area. Presently, 14% of the sudden cattle deaths are caused by the B. anthracis. An Alert Network of response facing epidemic outbreaks of natural, accidental or deliberate utilization of B. anthracis was established in Azul in 2002. With the leadership of a reference laboratory, a collaborator of the World Health Organization, only after confirmation of an anthrax outbreak are human and animal health institutions informed and soil samples of the site collected. Studies on the ecology of anthrax have found a correlation between the disease and specific soil factors such as, alkaline pH, high moisture, and high organic matter content. These soil characteristics are similar to those found in Azul and its surrounding areas. Besides sampling every site where recent outbreaks occur, a second soil sampling is performed on those farms with repeated outbreaks occur through the years. There are records of farms in which four outbreaks occurred within four to six years. These fields are locally called campos malditos(cursed fields). To evaluate the conditions that favor B. anthracis survival in soil, surface representative soil samples from fields with recent outbreaks and with a history of repeated epidemics were analyzed representing a total area of about 2000 ha. Results of organic matter, pH, electrical conductivity, CEC, exchangeable cations, and free carbonates will be given. Preliminary results indicate a wide range of properties, particularly pH, organic matter content, and ESP. From the total amount of analyzed samples, 15% show a pH above 8.5 which was suggested as the upper limit for the bacterium survival. Besides continuing with the soil characterization, further studies will concentrate on the evaluation of soil moisture, rainfall, and runoff direction prior and during outbreaks.

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