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(Article by Dr Rob Conradie)
Our first experience with YBD was birds showing vomiting and diarrhoea which we diagnosed as ADENO E.COLI syndrome. This virus was found first because it was the easiest to find.
The PCR test later developed for CIRCO VIRUS enabled us to also list this as a cause of YBD.
This virus has now been accepted world-wide to be the PRIMARY cause of YBD with all the other viruses, including Adeno virus, bacteria and other pathogens being secondary.
At a pigeon veterinary congress held in Poland last year CIRCO virus was discussed at length.
The data given was collected from universities all over the world. Varying percentages shown below depended on the country where the tests were done.
Interestingly, they found Circo virus in:-
• 53% – 63% of supposedly healthy youngsters. These youngsters could have become ill when placed under stress or when mixing with birds that were perhaps carriers of other pathogens (infectious agents).
• 80%- 98% in sick young birds.
• 36% in healthy old birds
This virus acts similar to Aids where a person is HIV positive but not necessarily ill or has full blown Aids where they become very ill.
They discovered that the 36% healthy old birds are able to pass it onto their youngsters.
The virus in these carriers was found in the sperm of cocks and the ovaries of hens. The virus was found in the egg and later in one-day-old babies.
Here we have a situation where the Circo virus is passed into the egg in the same way as we get mother to child transmission with AIDS.
We find that these youngsters stay healthy in the stock loft until they are weaned and put under stress and come into contact with other birds.
To demonstrate this an experiment was done where Circo virus was injected and dosed to babies reared under clean, spacious, stress free laboratory conditions. During the experiment lasting a year none of the birds became ill during the experiment.
The following year, in the same laboratory, a new batch of babies were reared and infected in the same way but at weaning were placed in race lofts where they were managed in the same way as our own pigeons.
All became ill.
Stress and mixing with other sub clinically ill or carrier birds, had caused it to flare showing how big a role stress and the other disease conditions play with the development of YBD associated with Circo virus.
Another interesting trial was one done by the Taiwanese Pigeon Federation. They worked with a university that tested all their birds that had not performed during the year.
98% were found to be positive for Circo virus.
Another example of how prevalent the virus is in lost or poor-performing racing pigeons, came from an article originating from a pigeon clinic in Belgium. They tested 41 stray birds that had been brought in by members of the public.
All were positive for Circo virus.
Circo virus is not the only problem found in this YBD complex. This world-wide study also looked at tests for secondary problems.
83% of Circo virus cases had one or more secondary problems.
The Circo virus, plus all the secondary problems found, form the YBD complex.
The more prevalent ones are:-
• Adeno virus was found commonly. It was often associated with E.coli. Vomition and diarrhoea were common symptoms in these cases.
• Bacteria were found in nearly 100% of cases.
Lists of antibiotics and efficacy levels were given. Of the Medpet products Avivet and the Mediprim/Medicox combination showed good efficacy.
• Herpes virus 17% – the main symptom seen here was yellow cheesy “growths” in the mouth that look very similar to Canker.
• Paramyxo 19%
• Canker 35%
• Candida in 19%
Veterinarians world-wide now agree that YBD is the name given to most young birds that are ill and that it is a complex multifactoral disease with Circo virus being the primary problem in most cases. Everything else found revolves around the Circo virus.
The reason why this has only more recently been accepted is that the diagnostic methods for Circo virus have improved.
Researchers that had kept samples from many YBD cases years back found Circo virus using the new techniques that are available today. Samples that were positive for Adeno virus were also found to be positive for Circo virus.
SYMPTOMS
Symptoms vary depending on what secondary pathogens are involved.
The significant symptoms are:
No, or poor, appetite. Listlessness, ruffled feathers, excessive thirst, weight-loss and death in a high percentage of cases (high mortality). Acute deaths can occur.
Vomiting and diarrhoea is seen when Circo virus and/or Adeno virus are involved. This is accompanied or caused by crop stasis. The crop is always full of water and does not appear to empty. These virus conditions cause a paralysis of the upper digestive tract. The condition is worsened when the bird drinks a lot of water as a result of a fever or as a result of primary or secondary Paramyxo.
These viruses known to cause paralysis of the crop would also cause paralysis of the oesophagus, leading to those symptoms we sometimes see where the birds have difficulty in swallowing. They have to maneuver their necks to push the food down.
Retention of food or “slow crop” is similar in many ways. It is often as a result of these virus infections, but it can also be Canker or Candida. Both can also cause difficult swallowing.
Another symptom that we see is feathering defects. These take the form of a grizzling type of effect as a result of multiple fret marks or stunted feather growth. If these feathers fall out it looks as though the feather root has shriveled up. These feather abnormalities can be seen in youngsters in the nest.
Paramyxo is known to do this as well.
Today, laboratories often use these feathers to isolate Circo virus from these cases.
When Herpes virus and bacterial infections are involved, yellow-grey lesions are often seen in the mouth. These look like Canker type lesions.
Postmortems and microscopic pathology have shown lesions in most organs of the body but mainly in the Bursa of Fabricius and Thymus which are the two main organs responsible for providing immunity in the first few weeks of life. The bursa is a mass of lymphoid tissue at the end of the intestine near the anus.
Lesions are also seen in the lungs, crop, intestines, pancreas, oesophagus and trachea.
The most recent article on Circo virus came from Taiwan. Here, apart from the organs already mentioned, inclusion bodies, which are the footprints of the virus, were found in the eyelids.
Does Circo virus, as well as possibly Herpes not play a role in the eye problems we all have in our birds from time to time?
PREVENTION
Circo virus destroys the lymphoid or tonsillar tissue in the body especially the Bursa of Fabricus and Thymus but other lympoid tissue that is so important in the protection of young birds in the early stage of life.
The main objective of treatment of YBD, whatever the cause, is to protect and stimulate the surviving lymphoid tissue. This tissue must produce the maximum number of white blood cells (lymphocytes) and antibodies which are responsible for fighting any infection in the body.
The intestine being the largest internal organ in the body would have the largest lymphoid system.
A healthy intestine would mean a healthy lymphoid system. The objective of treatment here, would therefore be the following.
• Control those conditions that damage the intestines (Coccidiosis and worms for example). You cannot achieve intestinal health without controlling these first.
• Regular use of Probiotics. The advantage of these cannot be overestimated.
We tend to overlook the importance of intestinal health.
The lymphoid system of the intestine, being the largest can provide assistance to all the other organ systems by sending “reinforcements” throughout the body.
Look after this system with PROBIOTICS and stimulate the lymphoid tissue all over the body with IMMUNE STIMULANTS.
• PROBIOTICS to use would be Entero-Plus, Intestum and Protein Boost.
A few IMMUNE STIMULANTS that have been scientifically proven to stimulate antibody and lymphocyte production are:-
• Beta Glucan found in Entero-Plus, Intestum and Medimune.
The advantage we have here is that Entero-Plus and Intestum contain Beta Glucan as well as probiotics. The probiotic fraction helps keep the intestinal content healthy and the Beta Glucan stimulates antibody production from a healthy intestinal immune system.
• Circo virus has been found in one-day-old babies. When the baby is old enough, give a Medimune tablet every day.
This serves three purposes:
1. It boosts the general immunity
2. When the bird is vaccinated against Paramyxo for the first time these tabs give the baby chance to develop optimum immunity.
3. Daily handling makes the birds tame.
While the babies are getting Medimune tabs the parents can be given Entero-Plus or Intestum on the food and Medi-Brew in the water. These products would help the babies being fed by the parents.
• Levamisol found in Factor 5 could be used when the youngsters are weaned at over 4 weeks.
• Herbs. These are found in pigeon teas like Medi-Brew.
TREATMENT
• REST is important. No athlete with flu for example will recover if he does not stop training for a while.
• Probiotic/Immune booster combinations. Five products that can all be given in various combinations together or in rotation at various times would be Medimune, Viroban, Medi-Brew, Intestum, Entero-Plus or Protein Boost. Intestum and Entero-Plus need not be given together.
Regular use of these products throughout the season is recommended.
• Antibiotics.
• Canker and Candida treatments would be needed if diagnostic tests show that they are indicated. Both are common secondary infections.
• Vitamins like Viroban or Vitaton34.
• Vaccinate against Paramyxo. The reasoning behind this is two-fold:
1. Subclinical Paramyxo may be playing a role in the YBD complex because an inferior vaccine has been used. Boost the bird’s immunity by using a good quality vaccine.
2. When a virus vaccine is injected a chemical called Interferon is released by the bird’s system. This has a non-specific effect on ALL pathogens but mainly viruses in the system at that stage, whether it be Paramyxo, Circo, Herpes or any other virus.
Paramyxo possibly plays a bigger role in SA than in other countries. We should have control over this but why are we still getting more Paramyxo than we should?
• Poor vaccines are being used.
• The vaccines were possibly handled badly – the cold chain was broken.
• We are vaccinating babies too late. Babies can be born with Circo virus. Vaccinate at 3 weeks of age to give the baby maximum chance to develop an immunity before the virus becomes a full-blown problem which happens when the bird is placed under stress. It is important to give a booster 4 weeks later.
The best vaccines to use for Paramyxo are NobilisParamyxo and the poultry vaccines, Nobilis ND, Avipro 105 and Avivac.
In SA we appear to get two periods of the year where we have an increased incidence of the disease:
1. In the off-season mainly December /January when the youngsters are 2 – 5 months old. This is more likely to happen when the youngsters are trained on the road. This additional stress placed on them causes flare ups of the disease.
2. The second wave of infection that we see is when the youngsters start training in May/June. It becomes particularly prevalent when they are trained with other birds in the Federation/Union transporters. Many fanciers with sick birds have to miss the first few races because of this.
Following a preventative treatment outlined above would reduce the chances of having a problem with YBD.
For more information on Young Bird Disease and other ailments experienced by pigeons, see our article on Common Avian Diseases.