Email (slightly edited) from Sabine Zentis Jan 12 2008
With regard to the slaughtered cow whose herd is now reported to be infected - one needs to know whether this animals have been sampled on a routine basis weekly/monthly because they might have been infected very early in the epidemic.
I have no idea about the climatic factors in this region and I don't know why people are now so surprised; we have got the first blood tests back from the suckler cow survey in our region and so far the cattle tested ( ca. 120) were all positive.
We will not have many more results back till the end of March but so far it looks as if, dependent on the region, between 93-100 % of adult cattle test positive for antibodies. Most of the farmers pretend not to have seen any BT related problems. But at close look, pregnancy rates are pretty low, in some cases up to 85 % of cattle are barren.
I have been discussing the inconsistencies between "scientific knowledge" and the findings in the field with colleagues a couple of times now. All of us are still puzzled about the reality. It was established as a fact that
a) the vector is not active below 12 Ca) I am rather sure that these findings only relate to C. Imicola as our midges involved (and suspected) in transmission of BT are active at much lower temperatures.
b) virus replication does not occur below 15 C
The question remains why they bite at low temperatures - because the female midge only needs a blood meal for egg laying.
But whether the midges actually lay eggs during the colder time of the year must be researched.
I think one of the problems is that this research can't be done in the lab easily because not all species of midges can be bred and reared artificially. I have learned from Intervet that they tried to set up a field trial on the use of Butox pour on some place in Spain. They had to bring different species of midges to this place and interestingly the midges refused to cooperate.
They didn't attack the animals, not even the ones that hadn't been treated.
b) We have had at least 3 months now with temperature below 10 C but there have still been plenty of clinical cases of BT during December. It is known that a midge will stay infected for her whole life so the question is : how old do our midges get? This can be only established for sure in species that are kept under laboratory conditions but the real world is completely different. It is known that midges survive longer at lower temperatures, but how long and at what temperatures no one can say with certainty.
Vector research is very important to answer all these questions but we don't have the time to wait until someone kicks into gear.
Top priority is getting vaccination off the ground - and later they can do their research till the cows come home....
I have been running the trap inside again since last week; the night temperatures were around 5 C and I didn't catch one single midge. It seems the frost in December has at least reduced the lot.
It will be interesting to see under which conditions the first midges re emerge from hibernation, I will run the trap every night now (if there is no frost) to find out.
Back to the paperwork, I have to do plenty of reading as I will go to Brussels for the conference on Tuesday.