Lewerin et al. Acta Veterinaria Scandinavica 2010, 52:7 http://www.actavetscand.com/content/52/1/7 Due to the long persistence of anthrax spores in soil, no country can claim absolute freedom from the agent, but regular outbreaks usually occur in limited geo- graphic regions. Endemic foci exist in most parts of the world, including Africa, Asia, United States and Austra- lia [8,9] and regular vaccination is practised in many of these areas. The susceptibility to infection varies among host spe- cies, with cattle and sheep being the most susceptible, followed by goats and horses, humans are regarded as intermediate in susceptibility and swine and carnivores relatively resistant [1]. Spores from the environment enter the host via inges- tion or inhalation, are taken up by macrophages and transported to lymph nodes where the spores germinate into vegetative bacteria that multiply quickly and escape into the bloodstream, causing systemic reactions due to the release of toxin [1]. Cutaneous infection also occurs (this is the most common form in humans) and may give rise to a local oedema that develops into a necrotic lesion and/or progress to a systemic infection [4]. The acute form of the disease, the most common in cattle and sheep, is seen only as sudden death, where the car- cass is typically characterised by dark non-coagulated blood oozing from orifices, lack of rigor mortis and quick decomposition [1]. Prior symptoms, if observed, may include fever, listlessness, oedema and bleeding from mucous membranes [4]. The signs observed in subclinical cases vary but may include oedema of the throat and neck and/or gastrointestinal symptoms. In some less susceptible host species, gastrointestinal infec- tion may occur without systemic involvement and symp- toms caused by toxins released in the intestinal canal, by bacteria that multiply in the intestines [1]. B. anthracis is susceptible to several antimicrobials, but therapy has to be administered early in the course of infection, since the toxin effects are not influenced by antimicrobials and symptoms caused by already released toxin will per- sist in spite of therapy. The incubation period varies by host species, route of infection and other factors but is estimated to 1-14 days in natural infection of cattle [4]. The infectious dose also depends on host species and route of infection and estimates vary [4]. Cattle may be difficult to infect by the parenteral route while readily infected when given anthrax spores in feed [10]. The number of spores required for oral infection of cattle has not been reliably determined and the assessment of risks from environ- mental exposure is therefore difficult. Now that meat and bone meal is no longer fed to ruminants and swine, this formerly common route of infection has been practically eliminated. The most common cause of infection these days is exposure of grazing animals to environmental spores persisting in Page 2 of 8 soil, but rare outbreaks in cattle housed in barns have been reported [4]. The successful prevention of anthrax in many parts of the world has led to the disease almost being forgotten by both farmers and veterinarians, a fact that may lead to failures in clinical surveillance and thus underreporting of occurrence [4]. The occurrence of anthrax is closely linked to climate [4,8]. Changes in climate with warmer temperature and more incidents of extreme weather that interfere with soil surface may cause more frequent exposure of rumi- nants to old anthrax spores and thus new outbreaks in areas currently regarded as “free”. The risk of re-occur- rence of anthrax is hard to assess, due to lack of detailed information about where infected carcasses have been buried and lack of data on infectious doses required for inhalation and ingestion by grazing animal species. In spite of the long-standing knowledge of the disease some crucial data on pathogenesis is still missing and a lot of what is known relies on theory rather than scienti- fic data [4]. As in most European countries, anthrax was com- mon in Swedish livestock in the first half of the 20th century. A large outbreak, associated with imported meat-and-bone meal, occurred in the county of Hal- land in the 1950s [11]. However, in the latter part of the 20th century the disease was regarded as practically extinct. In most areas in Sweden, the soils are not very alkaline [12] and the general conception has been that soil contamination may not be a major risk in this country. However, the level of environmental contami- nation is also likely to depend on the management of previous anthrax cases. Anthrax is included in the Swedish Epizootic Act [13], which means that any sus- picion is notifiable and that the veterinary authorities are obliged to undertake control and eradication mea- sures in case the infection is detected. The absence of detected cases for several decades has strengthened the perception that eradication measures along with favourable environmental conditions may have suc- ceeded in reducing soil contamination to a negligible level. A search for old data has revealed a very high number of anthrax cases in several parts of the country not so long ago and most carcasses appear to have been buried. Thus, the perceived risk from soil may have been underestimated. In 1981, a single case occurred in a dairy farm in the county of Uppland, most likely associated with exposure to spores from a soil heap that had been moved just before the onset of symptoms in the cow. Twenty-seven years later, an outbreak occurred in a beef herd in the county of Halland, in the South of Swe- den. The outbreak was unusual as it occurred in winter, in animals housed on deep straw and fed only roughage, in a non-endemic country.