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The Pigeon Cote: The Emerging Problem Of Pigeon Circovirus |
A new disease concern for pigeon fanciers is being recognized with increasing
frequency. With reports of infected flocks in northern and southern California,
Canada, and Australia, it now appears that Pigeon Circovirus may become a
major problem among mixed-aged flocks. This is an example of a disease that
has been around for at least a decade, but that went unrecognized until recently.
1. |
Circoviruses are a newly described group that includes Pigeon Circovirus,
Psittacine Beak and Feather Disease (PBFD) and Chicken Anemia Agent (CAA).
Detailed laboratory studies confirm that these viruses are similar to one
another (they share some portions of their DNA), but there is no known cross-over
of disease agents from one group of birds to another. PBFD is certainly the
best known of the three, affecting more than 35 species of "hookbills" (parrots,
macaws, cockatoos, and their allies). This disease results in characteristic
abnormalities in feather growth, beak lesions and long-term loss of body
condition. It is known that both PBFD and CAA cause disruption of the tissues
comprising the lymphoid system. This system (including the spleen, thymus,
Bursa of Fabricius, and both gut- and bronchial-associated lymphoid tissues)
houses cells that are responsible for most immune functions of the body:
making antibodies, recognizing disease organisms, processing antigens, and
so forth. Because CAA and PBFD viruses harm the lymphoid organs, birds having
these diseases are "immunosuppressed". That is, these viruses cause a form
of acquired immunodeficiency (like human AIDS). One result is that secondary
infections with other viruses, bacteria and fungi are common among birds
with PBFD and CAA, even when birds are vaccinated against the secondary problems.
In other words, Circoviruses compromise the birds' ability to benefit from
vaccination! |
Disease symptoms seen in birds with Pigeon Circovirus somewhat resemble
those seen with PBFD and CAA. Pigeons initially show respiratory symptoms,
weight loss, diarrhea, and stop eating, often dying after a short (2 to 5
day) period of illness. Many symptoms seen in Circovirus - infected birds
are really attributable to disease caused by secondary infections that take
hold because Circovirus has suppressed the bird's immune responses. Among
these secondary infections, researchers have found Chlamydia
(Ornithosis/Psittacosis), Herpes virus, Pasteurella (Cholera), Paramyxovirus
- 1, Trichomonas (Canker), and Aspergillus (among others). Interestingly,
in some Circovirus - infected flocks, there will be illness, but no mortality,
while in other flocks, 100% of the squabs will die. |
When these pigeons are presented for post-mortem exam, the most common
findings are destruction of cells in the spleen, thymus and Bursa. The latter
two organs normally shrink in size after hatching and are tiny or absent
in the adult bird. In the youngster, however, they are very important as
sites for immune system tissues. With these primary target organs, it is
not surprising that all pigeons with confirmed Circovirus infections thus
far have been one year or less in age. Infections have occurred both in racing
lofts (in one case a bird returned two days late from a race and other
individuals were performing poorly.), and in squab operations; a variety
of breeds are represented. The relatively high frequency of infections among
racing pigeons suggests that inadequate attention has been paid to shipping
conditions and quarantine. Dr. Leslie Woods, of U.C. Davis feels that if
Pigeon Circovirus holds true to the pattern set by PBFD and CAA, then infection
may be by a fecal-oral route. As yet, there are no known wild bird reservoirs
for the virus, so it is uncertain how racers are encountering the disease. |
Several factors conspire at present to hinder the prevention and diagnosis
of Circovirus in Pigeons. So far, researchers have not been able get the
virus to replicate in the lab. This step is required before rapid diagnostic
tests can be developed or vaccine trials can be done. Additionally, the presence
of so many secondary infections in Circovirus - positive flocks can lead
to errors in treatment and diagnosis. Unfortunately, the other Circoviruses
are very resistant to treatment with heat, disinfectants and detergents.
2. If this also holds for Pigeon Circovirus, it may be that the only way
to salvage an infected flock is to eliminate all young birds for at least
a year (ie, let the virus die - out naturally). Even this measure may fail,
however, if the virus is able to exist in a "carrier state" in some adult
birds. These and other details of the epidemiology (natural history and patterns
of infection) of Pigeon Circovirus are completely unknown. |
Our advice is to pay careful attention to hygiene and quarantine procedures
when shipping birds, especially racers. Fanciers who import squabs, particularly
into flocks that already have many young birds, should observe strict quarantines
for 2 to 4 weeks after arrival. Until flocks can routinely be vaccinated,
this newly recognized, immunosuppressive virus represents a real threat to
'open - entry' flocks and racing lofts. |
| Dave J. Rupiper DVM
Kenneth T. Briggs DVM, Ph.D. |
References
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