Epidemiologische Auswertung der BHV1-Bekämpfung in Milch- und Mutterkuhbetrieben in Nordrhein-Westfalen von 2010 bis 2015
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Beschreibung
"History of the reaching of the BHV1 freedom in North Rhine-Westphalia from 2010-2015: Epidemiological analysis of the BHV1 fight for dairy and suckler cows"
In several member states of the European Union, BHV1 has been eradicated through control programs. Germany has been officially free from BHV1 since June 2017 and may benefit from additional guarantees.
The aim of this study was to present the progress of gaining freedom from BHV1 in North Rhine-Westphalia in the period from 01/01/2010 to 31/12/2015. Another purpose of the study was to identify possible risk factors for re-infection with BHV1 in cattle farms.
In order to work as cost-effective and resource-saving as possible, the data already available in the German “Herkunfts- und Informationssystem für Tiere” (HIT) were used for the analysis. However, the status of freedom of a farm cannot simply be assessed retrospectively in HIT: To assess the process of gaining freedom of BHV1 on herd-level, the test results entered in HIT for the individual animals had to be aggregated, summarized and classified at herd level.
To this end, classification criteria for the BHV1 status were developed for each farm based on the diagnostic test results of individual animals. Afterwards, two veterinarians categorized the cattle farms independently according to the categorization schemes.
To validate the manual categorization, the agreement between the two veterinarians was determined as 87.6%. The existing differences referred mainly to farms that were not BHV1-free. Due to irregularities in the implementation of the investigation scheme at the farm level, the presence of “reactors” (i.e. cattle that had tested positive for BHV1) in some herds, or missing tests, the classification criteria of the categorization could only be applied with some difficulties. In principle, however, the manual categorization of the farms proved to be a suitable working tool.
The results showed that a large proportion of the farms in North Rhine-Westphalia was free already at the beginning of the study period or gained freedom from BHV1 during its course. Only 3 % of the holdings were not free by the end of the study period.
Within the study period, 158 farms suffered a re-infection with BHV1.
The biggest risk factor for reinfection seems to be latent carriers that were still present in the herds: the proportion of farms with BHV1-free status was much higher among those, in which reactors were still present in comparison with farms without existing reactors.
Another risk factor for a BHV1 introduction was cattle density: the higher the density of cattle in an area, the higher the proportion of farms with an introduction of BHV1. Seasonal differences were also observed. The season with the highest risk for a re-infection with BHV1 was winter.
Future studies may examine, to what extent the purchase of cattle represents a risk factor for infection with BHV1. The data available for the current study did not allow addressing this question.
In summary, the manual categorization is applicable, and can, for most of the cattle holdings, be switched to an automatic procedure, i.e. an algorithm based on the established and validated rules. This opens up new opportunities for risk-based surveillance to maintain Germany's status as officially free from BHV1 with reduced resources.
Autor*in
Magalie Eisele
Themen in »Epidemiologische Auswertung der BHV1-Bekämpfung in Milch- und Mutterkuhbetrieben in Nordrhein-Westfalen von 2010 bis 2015«
Epidemiologie Gesundheitsschutz Milchkühe NRW Nordrhein-Westfalen Seuchenbekämpfung bovine Herpesviren bovine herpesviruses diary cows disease control epidemiology health protecion north rhine-westfalia