Black spot…. to be
continued.
In the
land of the blind the one-eyed man is king. By this I mean as long as a problem
is not solved, everyone is right. Of course, this can be of no excuse for
constructive thinking and trying to find solutions for problems. Black spot in
canaries is one of them. Everybody will ask why?
We know
black spot is caused by the circovirus, which attacks the immune system.
Secondary infections kill the chicks. But if this is really true, we don’t
know. Why?
-
There have
been some studies identifying the circovirus in canaries, but only the one of
Goldsmith (1995) points to a relation between black spot and the circovirus.
Other studies prove the presence of the circovirus in canaries, but without a
link to the black spot.
-
Dr. Grífols
(2008) studied a flock of canaries with a high mortality rate. He confirmed the
presence of the circovirus with electron microscopy (gold standard!). But when
asking for the presence of black spot, the fancier told him he has never had
one. Dr. Grífols states: ‘The description
of Goldsmith (1995) of a typical condition for canary circovirus called “Black
Spot” should be discarded as these signs are probably produced by secondary
infections, and posterior description of infections. Circovirus infections should
be suspected if an increased mortality is seen, even without the presence of
black spot’.
From this we
have to conclude black spot is not the hallmark of circovirus infections and
canaries can be carrier birds, even without signs of black spot.
-
Research on
circovirus infections in pigeons (young pigeon disease) has shown
experimentally infected pigeons do indeed carry the virus, but secondary
infections were not seen. (Duchatel, 2011).
-
Prof. Sheykhi (2018) noted 25% of all canaries are carriers of
the circovirus. If this was true, and circovirus infections are the only reason
for black spot, we all would face catastrophe.
-
Usage of preventive
antibiotics to prevent secondary infections is disappointing.
But
recently some new research has been done. This research concerns some facts
about Isospororis, known to us as Lankesterella or Atoxoplasmosis, all synonyms.
We all
know the disease in young birds (2-9 months) with symptoms like: ruffled
feathers, anorexia, weight loss, tachypnoea, balance problems, diarrhoea and
death. Some birds do show these symptoms but a lot of birds do not show any
clinical signs. Stress can make flair up the infection and the disease become
symptomatic.
Infection
occurs in the intestines but also in the blood, through the white blood cells
circulating all over the body and in this way infecting liver, spleen, lungs
and brain.
Transmission
is via the faecal-oral route, meaning stools containing parasites from an
infected bird and ingested by another bird do cause infection. This is called
horizontal transmission.
Diagnosis is live birds is hard.
The parasites do resemble coccidiosis and most vets cannot distinguish between
parasites from coccidiosis or lankasterella on microscopic examination of
stools. Full diagnosis only can be done on post mortem examination. Also,
infected birds do not shed parasites all the time in their stools, which
complicated diagnosis.
Till now we all thought this was a
disease of young birds being infected after birth, so hatchlings and fledglings.
We have never known this is wrong.
Recently it has been proven vertical transmission is also possible. Vertical transmission means an infected hen lays an egg with the infection in it.
If one understands this, one can
imagine Lankasterella can infect the unborn chick in the egg. In this way black
spot could be explained, as black spot chicks are born with it, so infection
has to start in the egg during incubation. This way of transmission was
recently proven in a study, never before!
This also can explain why all kinds
of “preventative” antibiotics don’t help at all. Most antibiotics don’t cure
lankasterella!
So, what can we do?
Husbandry and sanitation are
extremely important. Regular cleaning, covered feeding and drinking stations
are of the utmost importance. Minimising stress and disturbance of breeding
birds may aid in prevention of flairing up the disease and increase of shedding
parasites.
As to medication, till now, no cure
has been proven to eliminate 100% this disease from infected birds. Even long
duration of treatments, up to 3 months, do reduce shedding, but after this
period the infection re-appears. Fecal shedding of parasites have been shown to
return to pre-treatment levels in as little as 10 days!
If we look at the medications for
Lankasterella, historically sulpha drugs, like ESB3, have been used for years.
We all know we cannot us these in the breeding in the breeding season because
they cause reduced fertility and thin egg shells.
Experiments are being done with the
newer drugs like diclazuril (Appertex) and toltrazuril (Baycox).
Most
of the experience has been done with diclazuril
and it has been proven no negative effects were seen when administered to
breeding birds. No negative effects were shown as to fertility, number of eggs,
egg shell quality, dead in shell. It is important it is given prior to egg
laying and being continued in pulsed form as long as the birds are breeding.
Dose is 2 mg/kg soft food.
New
experiments are being done with toltrazuril (Baycox). This seems to be one of the most potent drugs as to
Lankasterella, but it has to be used with care. If given at higher dose a
negative correlation has been shown with clutch size and laying frequency. But
when I asked the question to an avian vet, she told me Baycox can be safely
used in the breeding season. But only for one day a week at a dose of 3 ml/L
and this during the whole breeding season. This dose seems high but birds do
drink less when administering Baycox.
I
hope this can help some fanciers being confronted with black spot chicks in
high numbers.
To
be continued…. Science never stops.
Dr.
Jan Vanderborght
