After 27 years with no detected cases, an outbreak of anthrax occurred
in a beef cattle herd in the south of Sweden. The outbreak was unusual
as it occurred in winter, in animals not exposed to meat-and-bone meal,
in a non-endemic country.
The affected herd consisted of 90
animals, including calves and young stock. The animals were kept in a
barn on deep straw bedding and fed only roughage. Seven animals died
during 10 days, with no typical previous clinical signs except fever.
The carcasses were reportedly normal in appearance, particularly as
regards rigor mortis, bleeding and coagulation of the blood.
Soil samples
Subsequently,
three more animals died and anthrax was suspected at necropsy and
confirmed by culture and PCR on blood samples. The isolated strain was
susceptible to tetracycline, ciprofloxacin and ampicillin. Subtyping by
MLVA showed the strain to cluster with isolates in the A lineage of
Bacillus anthracis. Environmental samples from the holding were all
negative except for two soil samples taken from a spot where infected
carcasses had been kept until they were picked up for transport.
Contaminated roughage
The
most likely source of the infection was concluded to be contaminated
roughage, although this could not be substantiated by laboratory
analysis. The suspected feed was mixed with soil and dust and originated
from fields where flooding occurred the previous year, followed by a
dry summer with a very low water level in the river allowing for the
harvesting on soil usually not exposed. In the early 1900s, animal
carcasses are said to have been dumped in this river during anthrax
outbreaks and it is most likely that some anthrax spores could remain in
the area. The case indicates that untypical cases in non-endemic areas
may be missed to a larger extent than previously thought. Field tests
allowing a preliminary risk assessment of animal carcasses would be
helpful for increased sensitivity of detection and prevention of further
exposure to the causative agent.