Oorsig/Review
overall prevalence of EBL in the country, but it
certainly seems likely that it is high amongst
dairy herds. If the within herd prevalence is very
high (more than around 70%) it is very difficult
to eradicate the disease as a certain degree of
transmission still occurs even if you do all you
can to reduce the spread. If a herd has a lower
prevalence it is certainly possible to eradicate the
disease if you can reduce the spread (by not re-
using needles, rectal gloves etc) and ensure that
EBL free heifers are introduced into the herd,
while gradually culling out the infected cows.
If a herd is lucky enough to be free from the disease
(and we don't know how many of these there are,
especially in the big dairy areas) it is well worth
them taking care to prevent its introduction by
either buying from EBL free herds or quarantine
and testing of brought in cattle. In terms of the
cost of the disease, a large study in the US found
a 3% reduction of milk yield in infected herds as
well as increased culling so it is certainly worth
eradicating if possible. NYSCHAP has some
useful resources on reducing BLV spread (google
NYSCHAP BLV). There is a very sensitive BLV
ELISA which can detect a single infected cow in
250 and is a useful screen to find out if herds are
negative, but as far as I know it is not currently
available in South Africa, although if awareness
of the disease and demand for testing were to
increase then maybe that might change?
TC - 4 May 2017
In KZN and especially our inland dairy herds,
the incidence of EBL positive titres is anything
between 20 and 80% of a herd!! With herds
milking between 400 and 2000 cows we are
daunted by the idea of initiating a culling
programme. Our practice also wonders just
how effective the single-glove approach is when
there are so many other possible fomites. In tiny
European herds the elimination of EBL is another
ballgame. I recall sitting alongside a German
colleague and his looking at me “extremely skeef”
when I told him our herd sizes and the number of
rectals (yes some of us still palpate!) a day/week/
lifetime. Frankly we aren’t convinced – despite
some stern papers and lectures by illustrious
colleagues – that the EBL disease warrants too
much attention, especially when compared to
several far more costly conditions. Nevertheless,
were someone to market a vaccine, we’ll be near
the front of the queue!
ECONOMIC IMPACT
PI - 21 Aug 2002
A decent analysis of the disease under SA
circumstances needs to be done before this
24
question can be answered. This must take into
account economic impact of the disease (data from
elsewhere in the world), plus the demographics
and economics of the industry/herd plus the
epidemiology of the disease (including what
we know about it in SA). What I can say is that I
looked at the available literature a few years ago
when we were designing the new BSE certificate,
and there was a spectrum of opinion from “severe
economic impact” to “no discernible impact” to
“you can't do anything about it anyway”.
There was enough evidence there to convince
us that some consideration of the disease is
warranted, thus its inclusion for insurance and
AI bulls. Ernst Arndt felt very strongly about the
latter if I remember correctly. My gut feel at this
stage is that it's too late for our dairy industry as
a whole to 'nip it in the bud', and that it would
take a major eradication campaign. We have
bigger fish to fry at the moment, so I just can't see
this happening.
However, your question was on a specific herd.
One approach which I see getting quite a lot of
support is simply to eliminate transmission
opportunities wherever possible. With the high
turnover rate of most high-producing herds this
can lead to a marked reduction in the disease
incidence within 2 to 4 years. Practical steps
would be:
•
•
•
•
•
Use needles only once
Use rectal gloves only once (or disinfect
between cows)
Disinfect all dehorning, tagging, claw
trimming and other similar equipment
between uses
Break transmission via colostrum: This one's
controversial, but recommendations are
to test cows and only use colostrum from
negative cows, or use some commercial
substitute (Any available in SA??)
Segregating the herd into neg and positives
would also help, but may not be possible.
AH - 21 Aug 2002
I tend to agree that there is much more EBL out
there than we think (my opinion). The feedback
from the KZN will be interesting. What we need
to ask is what economic impact does it have?
Once an economic impact/value is tagged to it,
the importance can be quantified. Embrio Plus,
Taurus and other semen exporters will put a
different value on EBL than a dairy. For example,
I have seen it clinically in Dairy breed bulls >7 yrs
old. Most of the time one sees it clinically in older
(7-8 yrs) animals and I don’t know if most dairy
cows last that long. I think one needs to consider
the insect/biting flies as well.