Pigeon Forum

by Dr.Gord Chalmers » Thu Feb 09, 2012 12:18 pm

I have been involved peripherally in an interesting case involving a loft of racing pigeons in the northwest USA. In this loft, a number of breeding birds were found unable to fly up from the floor. In brief, detailed post mortem examinations showed the presence of a parasite in brain, breast and other muscles - which accounted for the presenting signs. This microscopic parasite has been identified as a species known as Sarcocystis (sarco-sist-is) found commonly in domestic and other animals. There are about 130 recognized species in reptiles, birds and mammals (most are in mammals). Some have even been found in snakes. This parasite in birds requires 2 hosts, an intermediate stage in a bird such as pigeons, etc. and a final stage in a mammal.
In North America, a common final stage of one species is found in the Virginia opossum and the intermediate stage is found in a number of wild and domestic birds. In the opossum, the final stage is characterized by the passage (in its droppings) of organisms that very much resemble coccidia*. Opossums acquire the infection by eating dead birds that carry the cyst form in their muscles. Birds acquire the infection when they pick through these droppings and swallow what they have picked up. In birds like pigeons, cowbirds, grackles, etc. this parasite goes through a number of developmental changes in the intestines, lungs, brain, etc., and finally ends up in body muscles in the appearance of a cyst. The presence of many of these cysts in muscle results in sufficient damage that pigeons for instance are unable to fly or to fly very well. When many organisms reach the brain, the signs can be similar to those of PMV, paratyphoid, herpes, etc.. Since birds like infected cowbirds, grackles, etc. appear to have evolved with the opossum over time, they have apparently become very resistant to the effects of this parasite and appear completely normal. The owner of the affected racing pigeons indicates that opsossums are not common in his area but at one point when the problem began he did find a weasel in the loft. Now whether this weasel was like the opossum and carried the organisms in its intestines just isn't known at this time. Another important point is that cockroaches are a good mechanical transport host for the coccidia-like stage and may have been a key factor in this outbreak.
Each year for about 3 years the owner has had about nine birds affected. Recent treatment of affected birds in 2011 with a drug called Deraprim (pyrimethamine) in capsules (prepared by a pharmacist in a dosage of 0.2 mg per capsule) for a couple of days appears to have been quite helpful.
This is a very brief outline of the problem in the affected loft. In the last 10 days or so, I have had several Emailed copies of a very recent report of this condition in a wild pigeon. As well, there are several fairly recently published studies of this condition in 3 lofts of racing pigeons in Germany where it was determined that the final host in this disease was the Northern Harrier hawk.
What are the risks for most of us? It's just my view that we don't have a great deal to be concerned about, but this case does point up the value of having a number of pigeons with nervous signs and failure to fly, examined at post mortem, and importantly, to have a variety of tissues including the breast and other muscles examined microscopically at the laboratory level. When similarly affected pigeons are found in areas where opossums are common, it's likely a good idea to consider sarcocystis infection as one reasonable possibility, also to include herpes,PMV and paratyphoid among the possible causes. Gord.
*PS - Fanciers are often familiar with 'cocci' counts in their birds, and the stage passed by the infected opossum very much resemble coccidia. As an aside, waterfowl hunters are often familiar with one particular species of Sarcocystis when they strip the skin off the breast of ducks they have shot. What they see with the naked eye are what appear to be many yellowish or white rice grain-like structures in these breast muscles. In this case, the striped skunk is the intermediate host and ducks are the final host.)