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