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A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
[1]
Date: 6 May 2009
Source: 6minutes.com.au [edited]
[There is an ASP error, and one can only get this report by going in
through the 6minutes home page. - Mod.MHJ]
An unexpected side effect of climate change is the reemergence of
anthrax in rural areas, as flood waters uncover long buried spores,
New South Wales (NSW) researchers have suggested.
The 1st major outbreak of anthrax in cattle in the Hunter Valley
[NSW] in almost 70 years occurred in late 2007, they note in the
journal Emerging Infectious Diseases (15:5:840-42), this month [May
2009]. Initially, the outbreak in which 53 cattle died on 11
properties was blamed on waterborne dispersal of anthrax, but this
was ruled out when cases were found to spread upstream and to
properties without contiguous streams.
Now epidemiologists are pointing the finger at a "1-in-100-year rain
event" in June 2007, when the drought-ravaged area experienced
rainfall of 259 mm in 3 days, flooding which removed topsoil and
unearthed anthrax spores, washing them into streams and gullies.
They say the resurgence of anthrax underlines the decades-long
durability of the spores, which are resistant to biological extremes
of heat, cold and desiccation. Their experience is a timely reminder
that public health authorities should be on high alert for possible
anthrax when unexpected livestock deaths follow flooding in areas
where anthrax has historically occurred.
[Byline: Jared Reed]
--
Communicated by:
ProMED-mail Rapporteur Susan Baekeland
******
[2]
Date: May 2009
Source: Emerging Infectious Diseases [edited]
Anthrax was introduced into Australia in 1847 near Sydney, New South
Wales and spread along stock routes throughout New South Wales and
southern Queensland. Anthrax was considered endemic to the Hunter
Valley, New South Wales during the 1890s. The last recorded
anthrax-related stock losses there occurred on 3 properties in the
Upper Hunter Valley in 1939. During the past 4 decades, anthrax has
become uncommon in Australia. Clinical cases are seen only
sporadically in sheep, cattle, and (rarely) horses. Annually, 6-12
properties are affected in unrelated incidents; where cattle are
involved, generally only 1-3 animals per property are affected.
Anthrax is confined almost exclusively to a belt running through the
center of New South Wales.
From 14 Dec 2007, through 3 Jan 2008, a total of 53 cattle (_Bos
taurus_) with peracute anthrax and one horse died on 11 properties in
the Rouchel area, 20 km east of Aberdeen in the Hunter Valley and 350
km from the anthrax belt [The figure is worth accessing as it shows
the Rouchel location well to the east of the traditional NSW anthrax
belt. - Mod.MHJ]. The area is hilly, rising to 550 meters, with
alluvial soils alongside a stream and rocky basaltic and sandy soils
on the slopes. Most properties feature gullies that flow
intermittently after rain. The affected properties covered 60 square km.
The animals that died in this area were of all ages. Anthrax was not
suspected because of a long history of no local activity, but
_Bacillus anthracis_ was initially confirmed by microscopy of blood
smears and subsequently by PCR of blood or other carcass fluid smear
scrapings taken when animals were decomposed and microscopy was
unreliable (4). Dates of discovery of the index case on each property
ranged from 14-29 Dec 2007; 1-26 deaths (median 2) occurred per
property. Property attack rates varied from 0.9 percent (1/110
cattle) to 10.7 percent (3/28 cattle). All stock on infected and 24
neighboring properties were vaccinated in late December 2007;
carcasses were burned to ash; movement control, including quarantine,
was implemented; and all subsequent stock deaths in the area were
investigated to rule out anthrax. One subsequent case occurred when
an unvaccinated bull was introduced onto an infected property in late May 2008.
Detailed record review excluded importation of infected feed from
known anthrax-endemic areas before the outbreak, and no deaths
occurred in stock introduced from these areas during the previous
month. Many of the animals died near streams, and waterborne spore
dispersal with infection was initially hypothesized. However, the
temporal pattern of properties affected, with downstream properties
affected before upstream properties, the fact that properties without
contiguous streams were affected, and the dilution effect of rapidly
flowing streams argued against this transmission route. Because they
are septicemic, terminally ill animals with anthrax often seek water.
The mysterious contemporaneous reemergence of anthrax in this area is
unlikely to be explained by mechanical vector-borne transmission,
because only one animal had eye damage, suggesting a crow attack.
There was no additional evidence of scavenger attack. No tabanid
species (biting) flies were seen on any carcass, and the small number
of carcasses and relatively large distances between some properties
made mechanical transmission with ocular inoculation by non-biting
flies unlikely.
Both the remarkable survival capability of anthrax spores and a
1-in-100-year rain event probably contributed to the
near-simultaneous reemergence of anthrax on multiple properties in
this area. Anthrax spores are resistant to biological extremes of
heat, cold, pH, desiccation, chemicals, and irradiation, persisting
in this state for decades awaiting conditions that favor germination
and multiplication (6). In June 2007, drought-ravaged Hunter Valley
experienced intense flooding; most rain fell in just 3 days (259 mm
in the Aberdeen area, compared with the previous 3-year June average
of 43 mm), and massive amounts of topsoil washed into gullies and
streams. During late 2007, rainfall also was excessive: 132 mm and
129 mm in November and December 2007, respectively, compared with the
3-year average of 87 mm and 65 mm.
The June floods are likely to have unearthed anthrax spores in the
area. The question remains whether these spores had been present for
more than 6 decades, concentrating in depressions that collected
water and dead vegetation, potentially providing a milieu for
germination and multiplication (i.e., incubator areas), a mechanism
that has been implicated in wildlife epidemics of anthrax.
Alternatively, low-grade sporadic infection may have been ongoing
since the 1940s, and infrequent stock mortality may not have been
investigated for anthrax because of a low local index of suspicion,
resulting in environmental contamination The extreme weather
conditions in the area may have unearthed spores from undiagnosed
carcasses, providing simultaneous exposures on multiple properties.
We are currently unable to resolve this epidemiologic conundrum.
However, our experience is a timely reminder that veterinary public
health authorities should be on high alert for possible anthrax when
unexpected livestock deaths follow flooding in areas where anthrax
has historically occurred.
[Byline: David N. Durrheim, Paul Freeman, Ian Roth, and Michael Hornitzky]
--
Communicated by:
ProMED-mail Rapporteur Susan Baekeland
[This set of outbreaks characterizes 2 old problems: [1] If the
outbreaks follow heavy rains, erosion, and flooding, how do the
spores maintain a sufficient concentration to trigger new cases; and
[2] how does one explain outbreaks in an area where the disease has
not been recorded previously. Frankly, there are no easy answers
except that both situations occur and sometimes together, as in this
instance. Soil multiplication of _B. anthracis_ is now regarded as
being, at best, unlikely and epidemiologically meaningless if it
occurs. Spore survival can explain essentially all such events. The
situation of "unobserved cases" is best exemplified by last year's
[2008] bison outbreak in southwest Montana, where sporadic deaths had
for decades been put down to hemlock poisoning. Seemingly random
single livestock and wildlife deaths rarely trigger the suspicion
that they might be anthrax when anaerobic clostridial causes are much
more common.
For a map of Australia, go to:
for a map showing NSW in greater depth, see interactive map (of
Scone, the affected area) at
- Mod.MHJ]
[see also:
2008
----
Anthrax, bovine - Australia (04): (NSW) 20080116.0205
Anthrax, bovine - Australia (03): (NSW) 20080105.0061
Anthrax, bovine - Australia (02): (NSW) 20080103.0032
Anthrax, bovine - Australia: (NSW) 20080102.0015
2007
----
Anthrax, bovine - Australia (03): (NSW) 20071231.4193
Anthrax, bovine - Australia (NSW) (02) 20071229.4168
Anthrax, bovine - Australia (NSW) 20071227.4148]
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