Bovine TB in Ireland and how it compares to that in the UK

The Irish Republic is the closest equivalent to the UK in that the Irish Republic has badgers (albeit at a lower density) and a bovine TB problem. Estimated badger populations in Great Britain, the Irish Republic and Northern Ireland are shown in the table below.

Country	Badger population	Year when estimated	Reference
Great Britain	300,000-350,000	2003	3
Irish Republic	72,000-95,000	2009	4
Northern Ireland	33,500	2007/08	5

This page illustrates the extent of bovine TB in the Irish Rebublic, illustrates how the situation changed between 1996 and 2006, compares this with the change in Great Britain and Northern Ireland, and gives a measure of what the Irish Republic have been doing to address the problem.

Cattle-related actions are similar in both the Irish Republic and Northern Ireland, focusing on surveillance (the detection of new cases, through field and factory surveillance) and control (the resolution of existing cases, through herd restriction, reactor removal, ongoing testing, etc.). However badgers are routinely culled in the Irish Republic but not in Northern Ireland.

The prevalence of bovine TB in cattle



The above images were taken from Reference 1, where maps are presented every 2 years, which can either show a reduction or increase every 2 years. These images suggest that the problem in Northern Ireland between 1996 and 2006 became more established whereas the problem in the Irish Republic reduced slightly.



The above maps have been taken from Reference 2. The problem has clearly deteriorated in South West England, Wales and the West Midlands, is becoming more established in Central and Northern England, and is spreading into new areas of Eastern England. New incidences in Eastern England which are remote from established areas are more likely to be due to cattle-to-cattle transmission than badger-to-cattle transmission¹⁸.


In the above graph the proportion of cattle culled was obtained by dividing the number of cattle culled by the total number of cattle which existed in each year as supplied in Reference 6 except for data labelled "Northern Ireland 2" where incidence numbers are used. Such incidences were calculated by dividing the number of reactors disclosed by the number of animals tested each year. Data was sourced as shown in the table below.

Northern Ireland	Request	Reply	Received data
Northern Ireland 2	Request, reply and received data
Irish Republic	Request	Reply	Received data
Great Britain	Request Request	Reply Reply	(See reply) Received data

It should be noted that there are likely to be anomolies between what data presented in these graphs represent. For instance some data include cases discovered in slaughterhouse inspections and other data do not. In Great Britain, slaughterhouse cases reported to Animal Health in 2009 and 2010 accounted for about 3% of the total number of animals reported to be infected by TB in each year.

Data for the year 2001 is not shown in the graphs for Great Britain and Northern Ireland because sufficient testing was suspended during this year due to Foot and Mouth as to cause significant under reporting of cases.

Northern Ireland operates an annual testing policy throughout the country so in theory the number of animals tested should equal the number of existing animals in the country. The differences between the two sets of numbers for Northern Ireland are more clearly shown in the graph below which shows data from the same sources as in the graph above but from 1998 only. Such data was re-downloaded from the above sites in May 2012 when data for 2011 were included for all countries. Regarding the above graph, cattle slaughtered pre 1990 in Northern Ireland do not include abattoir cases. Also cattle slaughtered in 2011 only includes cattle slaughtered up to the end of November.

In the Irish Republic, approximate values for the number of TB reactors between 1961 and 1964 were read off a graph shown in Fig 1 of Reference 19. Unlike all other years for which the number of existing cattle was taken from reported numbers for each year, the number of existing cattle between 1961 and 1964 was assumed to be constant and equal to 5,000,000. This number lies roughly half way between the reported numbers for 1960 and 1965.



Data shown in the above graph were sourced as follows.

Country	References
Northern Ireland	23,20,25
Northern Ireland 2	27
Irish Republic	21,26
Great Britain	22,20,24

The influence of Foot and Mouth

Foot and Mouth occurred in 2001 and, as can be seen in the above graph, in the following 3 years TB infection levels increased substantially in Northern Ireland whereas they noticeably reduced in the Irish Republic. The extent to which TB testing was interrupted due to Foot and Mouth and the percentage of cattle which were culled in each country due to Foot and Mouth are shown in the tables below.

Irish Republic	Request (Sent 30May11)	Reply (Received 30Jun11)
Northern Ireland	Request (Sent 07Apr11)	Reply (Received 22Apr11)

Country	Number of months over which testing was suspended or reduced	Number of cattle culled due to Foot and Mouth	Number of cattle in the country	Percentage of cattle culled due to Foot and Mouth
Irish Republic	1.5	1,181	6,408,000	0.02
Northern Ireland	1	50,565	1,679,100	3.01
Great Britain	911	581,80217	8,923,0006	6.52

In summary, TB testing was suspended for 4 weeks in Northern Ireland and 6 weeks in the Irish Republic. However Northern Ireland culled 3.01% of their cattle (50,565 cattle out of 1,679,100) whereas the Irish Republic only culled 0.02% of their cattle (1,181 cattle out of 6,408,000). It follows that there would have been a lot more cattle movements during restocking in Northern Ireland than in the Irish Republic. This probably caused significantly more cattle to cattle transmission of bovine TB in Northern Ireland and may explain why the prevalence of bovine TB increased much more in Northern Ireland than in the Irish Republic.

The influence of culling

The following graph shows the number of badgers (reported by DAFF) which have been culled in the Irish Republic each year between 1995 and 2010.

Irish Republic

Request (Sent 28Nov10)

Reply (Received 21Feb11)

Received data

Between 1996 and 2006 about 4,000 bagers were culled each year. If the badger population was about 80,000 and the average life expectancy of a wild badger is assumed to be 4 years, then there was a 16/80 chance of any one badger being culled during its lifetime during this 10-year period, that is, 1 in 5 badgers were culled.

Regarding the situation in Northern Ireland, the upper graph, which shows the proportion of cattle culled, does not add to the impression that the problem in Northern Ireland is deteriorating which comparison of the maps in 1996 and 2006 may have suggested. Consider the differences between the proportions of cattle culled in Northern Ireland and the Irish Republic in the 5 years between 2007 and 2011 as presented in the table below. If these differences are due to culling alone, culling badgers in the Irish Republic would have saved on average 4,454 cattle each year. Whilst this is significant and welcome, this saving is not substantial.

Year	Number of cattle in the Irish Republic	% of cattle culled in Northern Ireland	% of cattle culled in the Irish Republic	% difference	The number of cattle saved
2007	6084037	0.444	0.455	-0.01	-688
2008	6150163	0.517	0.486	0.03	1906
2009	6025656	0.513	0.395	0.12	7078
2010	5751564	0.399	0.351	0.05	2724
2011	5819281	0.512	0.318	0.19	11249

Average number of cattle saved each year = (-688+1906+7078+2724+11249)/5 = 4454

A possible explanation for why badging culling may not be giving the Irish Republic a substantial advantage is that the culling carried out by the interim culling strategy is too localised. The following gives some background as to why this may be considered to be the case. Cattle incidence in Great Britain between 1986 and 1998 significantly increased as is shown in the graph below taken from Reference 12. (Foot and Mouth occurred in 2001.)



In 1986 the culling strategy changed from that of 'clean ring' where badgers are first culled on land occupied by affected cattle herds, then on adjoining land, expanding outwards until no further infected animals were captured¹⁴, to one where badgers were only culled on the infected farm. (A history of English culling strategies is given on Page 5 of Reference 14 and also in Reference 10.) Records of the proportion of diseased badgers made during the RBCT¹⁰ showed that during the course of the trial, detected disease levels in culled badgers doubled¹⁵. The report in Reference 13 explains that in the Irish Republic, badger setts are first identified within 2 km of a tuberculosis-affected farm and then badgers are culled within a 500 metre radius of each sett. The aerial photographs shown on Page 13 of this report show that this distance is typically equivalent to about 3 or 4 medium size fields. If badgers migrate out from these areas and culling increases disease levels in remaining badgers, it is possible that this is overall offsetting most of the benefits which may be occurring due to a reduced badger population. It should be noted however that badger population densities in Ireland is thought to be considerably less than in Great Britain¹⁶ so social disruption may be different. [Editor note: However estimating a badger population is very difficult and estimates for Ireland have varied over a very wide range.] Also the way in which badgers are trapped in the Irish Republic differ in a number of ways from the way in which badgers were trapped during the RBCT. However it remains possible that removing badgers by the culling in Ireland is still disrupting their social organisation, causing remaining badgers to range more widely and to migrate to areas outside the culled areas. If this is happening, this is probably spreading infection, increasing TB prevalence in badgers, and hence transmission of TB to cattle.

References

1. An all-island approach to mapping bovine tuberculosis in Ireland by G McGrath et al published in 2009
2. Great Britain and Republic of Ireland badger culling trials: An initial comparative study by C.M O'Connor et al, University of Glasgow
3. Tuberculosis in cattle and badgers in United Kingdom. Report to the Standing Committee, 23rd meeting, Convention on the Conservation of European Wildlife and Natural habitats (Bern Convention). Strasbourg, 26 November, 2003
4. Sleeman et al., 2009. How many Eurasian badgers Meles meles L. are there in the Republic of Ireland? Eur J Wildl Res DOI 10.1007/s10344-008-0244-1
5. Department of Agriculture and Rural Development - Badger Survey of Northern Ireland 2007/08 - Quercus Project QU07-13
6. Number of cattle in England, Wales, Scotland, Northern Ireland, Great Britain and the UK for each year from 1866 to 2010
7. Functions of the Wildlife Administration Unit (WAU) in Johnstown Castle, Wexford
8. Scotland declared TB-free
9. Four Area Badger Culling Trial in the Irish Republic
10. Final Report of the Independent Scientific Group on Cattle TB
11. Number of animals tested and slaughtered due to bovine TB
12. Government Veterinary Journal
13. Eradication of bovine TB in the Irish Republic including a detailed description of badger culling and vaccination strategy. Released in April 2010.
14. The effects of annual widespread badger culls on cattle tuberculosis following the cessation of culling - Supplementary Information
15. A critique of the Randomised Badger Culling Trial (RBCT)
16. DEFRA consultation Sept 2010: Annex B - Scientific evidence on culling
17. Numbers of cattle slaughtered per month by county in Great Britain due to Foot and Mouth
18. Prevalence and transmission of bovine TB between cattle and badgers
19. Bovine tuberculosis eradication in Ireland
20. Cattle and calves in the UK from 1866 to 2011
21. TB stats in the Irish Republic in 2011
22. TB incidents in Great Britain to Jan 2012 - Animals
23. Reactors by month in Northern Ireland to Feb 2012
24. Incidence of Bovine TB in Great Britain to 2011
25. Incidence of Bovine TB in Northern Ireland to 2011
26. Incidence of Bovine TB in the Irish Republic to 2011
27. Number of bovine TB reactors slaughtered in Northern Ireland from 1961 to Nov 2011