final report - ARCHIVE: Defra

Environment and epidemiology
when badgers urinate or defecate away from latrines. In addition, one instance has been reported of
a cattle feeding-trough becoming heavily contaminated with badger faeces and urine (Garnett et al.,
2002). However, since almost all cattle become infected via the respiratory route, these scenarios require
a mechanism whereby Mb that is present on grass, soil or cattle feed is aerosolized and inhaled during
olfactory investigation, rather than ingested during feeding. Such mechanisms have been proposed but
it is unclear how realistic they are.
4.4.9 As noted above, badgers sometimes visit farm buildings to consume cattle feed, and when they do
so the feed in question can become contaminated with faeces, urine or other exudates (Garnett et al.,
2002, 2003; Tolhurst, 2006). If stored cattle feed is contaminated in this way, bacilli could become
aerosolized when the feed in question is transferred to feeding troughs.
4.4.10 Two lines of evidence suggest that badgers that are in the terminal stages of bTB infection, and that
are consequently highly infectious, may be especially likely to frequent farm buildings and hence to
come into direct or indirect contact with cattle. Firstly, there are anecdotal accounts of debilitated
badgers taking up residence in farm buildings including, in at least one case, a cattle shed (Cheeseman
& Mallinson, 1981; Garnett et al., 2002). Secondly, badgers found dead in or close to farm buildings
are more likely to have been infected with bTB than badgers killed by road traffic (Cheeseman &
Mallinson, 1981). Such animals could act as ‘superspreaders’. Although the ISG has expressed doubt
about the relevance of this idea on the grounds that bTB only progresses to an advanced stage in a small
proportion of badgers (Bourne, 2007; Jenkins et al., 2008b), we feel that the ‘superspreader’ concept
deserves further consideration, both through empirical work and by means of modelling studies.
4.4.11 Similarly, little attention has been given to the idea that some cattle may be more likely than others
to come into contact with badger-related sources of infection. In a test carried out in New Zealand,
dominant herd members were more likely to become infected after exposure to sedated tuberculous
possums, presumably owing to a stronger investigative tendency on the part of these individuals (Sauter
& Morris, 1995). If a correlation were found between dominance and infection in cattle in the UK, it
would imply that individual cattle play an active role in exposing themselves to sources of infection
such as badgers or badger excreta, rather than becoming infected purely passively via activities, such
as grazing, that are common to all members of the herd.
4.4.12 We conclude that further investigation is needed into behaviours that result in indirect or (especially)
direct contact between badgers and cattle, both while cattle are at pasture and while they are housed
on farm premises. Such research would shed light on the relative plausibility of different transmission
scenarios, the tendency of severely infected badgers to behave in ways that increase the probability
of transmission, and the possibility that dominant and subordinate cattle differ in their tendency
to display risk-prone behaviour. Ultimately, the results would enable control measures to be more
precisely targeted towards high-risk situations. Given that transmission is in absolute terms a rare event
and that direct observation or video surveillance are both highly labour-intensive, research is needed
into the use of automatic monitoring systems, such as contact sensors, as a means of acquiring the
requisite data.
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