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CASE NOTES

Relevance of historical anthrax data in current property risk assessments

Barbara Moloney, NSW DPI Orange and Dan Salmon, LLS Murray (formerly SDV Riverina)

Posted Flock & Herd August 2015

Introduction

The first known case of anthrax in Australia occurred near Leppington near Sydney in 1847. It was originally called Cumberland Disease after the county where it was first found.

It was not until 1888 that scientists from the Pasteur Institute confirmed that Cumberland Disease was in fact anthrax. The likely source of infection into Australia was contaminated bone manure used as fertiliser. Some of the subsequent spread from the 1890s was likely to be due to increased use of bonemeal as a mineral supplement, some of which was imported from India. Most spread into the rest of NSW and other eastern states occurred due to stock movements.1

Of interest an outbreak of anthrax in the Wide Bay area of Queensland in the late 20th century was also linked to the importation of bone meal from India.

Data sources

Very early reports of anthrax cases can be found in the Sydney Morning Herald (1851)2 and the Department of Mines Annual Reports going back to at least 1886.3 In 1922 and 1936 Max Henry listed summaries of annual anthrax cases from 1909 to 1921 and 1924-25 to 1935-36.4-15 Seddon lists summaries of annual anthrax outbreaks in NSW from 1924-25 to 1949-1950 and 1947-48 to 1961-62.1, 16 Department of Agriculture Livestock Diseases Reports list cases of anthrax from 1924-25 to 1947-48 with some years missing due to WWII, and continuing as Livestock Health and Husbandry reports up until about 1974-75.

David Kennedy's Masters Thesis tabulated anthrax occurrences in NSW for the period 1925-25 to 1974-75.17 Annual outbreak summaries from 1969 up to 1981 have been listed by Beveridge18 and NSW Agriculture annual reports from 1975-76 to 1986-87.

Individual case records were kept by Pastures Protection Boards on occurrences of anthrax. In 1958 DVO South RH Falk compiled a summary of anthrax outbreaks occurring in southern PP Districts during the period 1931 to 1957 including individual outbreak dates.

Periodically staff from NSW Agriculture have requested details of anthrax cases from individual Boards. This data has been compiled and stored in a number of different formats which makes collation from all years and all districts difficult. More recently many DVs are now entering anthrax case data against PICs in the Livestock Health Management System (LHMS). Individual cases have also been recorded in various spreadsheets. Since 2001 details of all anthrax cases have been stored in a DPI Access Database, which can be used for cross-validation and checking with LHMS. An additional database of historical cases is currently being compiled which can be used for the same purposes. This includes information provided previously by LHPAs and Departmental paper files.

Results

Case reports for anthrax are reasonably complete since 1990. More work needs to be done to compile data for the 1970s and prior. One hundred and fifty nine cases have been found for the 1980s which is consistent with the number reported in summaries. About 126 cases have been found for the 1970s and there were 166 according to the annual summaries.

Discussion

The spatial and temporal patterns in the anthrax occurrences in NSW will be analysed to compare the past occurrences with more recent occurrences. This may inform risk assessments for the likelihood of future cases.

Field comments from the sdv riverina

My experience with anthrax as a diagnostician and case manager as well as interested observer has given me some facts, and several opinions that might not necessarily be based on fact.
Anthrax behaves differently in different areas. In the southern Riverina anthrax is a sporadic disease that has rarely been diagnosed twice on the same holding despite poor vaccination cover. On the other hand in the northern Riverina the disease occurs much more commonly and several holdings have deaths if vaccination cover is incomplete.
The seasonal conditions that precede anthrax incidents are usually hot dry weather followed by rain. Conventional wisdom has it that the rain washes away soil to expose anthrax spores that have survived in the soil. The nature of the paddocks in the Riverina where anthrax occurs makes this explanation highly unlikely. The land is flat and the rainfall events are rarely heavy enough for any water to move let alone move with sufficient force to wash soil away from previously covered anthrax spores.
An exception to this pattern occurred during the very wet, mild winters of the early 1970s. There were several incidents during those winters, all in cattle. This fits in more with the conventional model because the feet of the cattle were penetrating the soil to considerable depth making it possible for them to have contact with spores buried deep in the soil. This fits the pattern seen in many other parts of the world where anthrax occurs in swampy areas.
My personal hypothesis for the seasonal pattern is that the hot dry conditions kill most of the other soil microbes leaving the anthrax spores with a competitive advantage when it rains. This hypothesis is disputed by microbiologists who contend that the nutritional demands of B anthracis are so high that it is unlikely that they could multiply in soil.
Morbidity from anthrax is also quite variable. We have had incidents where hundreds of sheep or dozens of cattle have died but they are in the minority.
Particularly in the southern Riverina most anthrax incidents only involve a handful of deaths. Sometimes this is because the disease is diagnosed in the index case and vaccination gives immunity before the second wave of infection. Another factor is that many anthrax incidents do not progress to a full-blown epidemic.
Most managers of properties where we diagnose anthrax for the first time report that there had been occasional deaths in the paddock involved for many years.
Once again my hypothesis for this sporadic incidence is the nature of the disease. Autolysis of carcasses in anthrax is extremely rapid and comprehensive and the vegetative form of B anthracis is quite fragile. Spores do not form unless the organisms are exposed to the air so despite the unimaginable number of organisms in a carcass at the time of death there are not a commensurate number of spores formed in an unopened carcass. This means that in the absence of scavengers (including humans) individual anthrax cases do not produce a lot of contamination so that the progress from an individual death to an outbreak is the exception rather than the rule.

Acknowledgements

Charles Sturt University students for compiling some of the anthrax case data. LHPA staff for providing information from their records.

References

  1. Seddon HR, Albiston HE. Anthrax. Part 5 Bacterial diseases. 2 edn. Department of Health, Canberra, Australia, 1965:12 - 26
  2. Walker RJ. The Cattle Disease. Sydney Morning Herald, 1851:1
  3. Stanley E. Anthrax. Splenic Apoplexy (Cumberland Disease). Department of Mines: Annual Report of the Stock and Brands Branch, 1885:15-16
  4. Henry M. Livestock Disease Report. 1945-46, Department of Agriculture, Division of Animal Industry. Sydney, 1946:12
  5. Henry M. Livestock Disease Report, 1944-45, Department of Agriculture, Division of Animal Industry. Sydney, 1945:7
  6. Henry M. Livestock Disease Report, 1943-44, Division of Animal Industry. Department of Agriculture. 1944:7
  7. Henry M. Live Stock Diseases Report 1940/41. 1942:4
  8. Henry M. Live Stock Diseases Reports-Stock Branch, Department of Agriculture, New South Wales, 1938-39. 1940:2
  9. Henry M. Live Stock Diseases Report (No. 13).Recording Control Work during the Year ended 30th June, 1937. David Harold Paisley, Govt Printer, Sydney, 1938:24
  10. Henry M. Live Stock Diseases Report (No. 12). Recording Control Work during the Year ended 30th June, 1936. David Harold Paisley, Govt Printer, Sydney, 1937:24
  11. Henry M. Live Stock Diseases Report (No. 11) Recording Control Work during the Year ended 30th June, 1935. Alfred James Kent Govt Printer, Sydney, 1936:25
  12. Henry M. Department of Agriculture. Live Stock Diseases Report (No. 10) Recording Control Work during the Year ended 30th June, 1934. Govt Printer, Sydney, 1935
  13. Henry M. Live Stock Diseases Report (No. 8), Recording Control Work during the Year ended 30th June, 1932. Alfred James Kent, Sydney, 1933
  14. Henry M. Live Stock Diseases Report (No. 6) Department of Agriculture, Recording Control Work during the Year ended 30th June, 1930. Live Stock Diseases Report (No 6) Department of Agriculture, Recording Control Work during the Year ended 30th June, 1930. Sydney: Alfred James Kent, 1931:6, 18
  15. Henry M. Live Stock Diseases Report Recording Work During the Year ended June 30th, 1929. Live Stock Diseases Report Recording Work During the Year ended June 30th, 1929 1930. Sydney, 1930
  16. Seddon HR. Anthrax. Part 5 Bacterial diseases. Department of Health, Canberra, Australia, 1953:8 - 40
  17. Kennedy DJ. A study of Anthrax in Grazing Livestock. University of Melbourne, 1979
  18. Beveridge W. Anthrax. Australian Government Publishing Service, Canberra, 1983

 

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