January 31, 2012 | 3
One of the reasons I love my job as a wildlife veterinarian so much is the variety of my days. No two days are the same; each is filled with different animals with different problems, and I love the anticipation of what my day may bring. I never know what kind of animal will come through the door, what challenges I’ll face, and what skills I’ll get to use – it’s very unpredictable and that makes it so fun and exciting! My job is very fast-paced, keeps me on my toes, and there’s never a dull moment – emergency medicine at its finest! It is also full of new discoveries, as I found out last spring.
Last April I was examining a wild male adult Rock Pigeon that couldn’t fly. The person who found the pigeon suspected a broken wing. On the initial physical exam, I didn’t find any broken bones but the bird was exhibiting odd neurologic behaviors, including ataxia (lack of coordination) and torticollis (head tilt).
My differential diagnoses included head trauma, aberrant parasite migration (a parasite that’s normally found in the gastro-intestinal system migrates to other parts of the body, like the central nervous system), and a viral or bacterial infection causing encephalitis (inflammation of the lining of the brain).
I started the bird on anti-inflammatories and moved it into our isolation ward in case he was potentially contagious to other birds. Over the next five to seven days, the bird’s neurological symptoms progressively worsened. He literally started standing on his head and spinning in circles (see video). The torticollis also worsened. Because of his decreasing status and poor prognosis I humanely euthanized him.
Normally, when we euthanize an animal or when an animal dies, it’s disposed of or saved under a salvage permit for a licensed organization to use in their collections, for research, etc. Sometimes though, we send animals out for additional testing to help pinpoint the cause of the animal’s illness or death. This is done via a necropsy (just like an autopsy but for animals).
Since Paramyxovirus, a highly contagious viral disease in pigeons that manifests as neurological symptoms, including ataxia and torticollis, was high on my list of possible diagnoses, I sent this bird to the University of Minnesota (UMN) Diagnostic Lab (D-Lab) where they would do a necropsy and test for the virus.
In the past WRC has had several pigeons showing similar signs and Paramyxovirus was always suspected. To my knowledge, however, none had ever been sent in for necropsy. A pattern was there, but what was it? What is going on with these neurologic pigeons, I wondered.
Well, the bird tested negative for Paramyxovirus. However, what the D-Lab did find was shocking. A parasite, named Sarcocystis calchasi, was found in cysts in the bird’s skeletal muscles. The really neat thing? This parasite had never been identified in the United States! It actually hadn’t been identified anywhere outside of Germany (where it was identified in 2009)!
When the pathologists contacted me to tell me this news, I was very excited (as were they!). Tissue samples were sent to Germany to confirm identification of the parasite, and sure enough it was S. calchasi.
The parasite is passed from bird to bird via infected feces, likely from the Northern Goshawk or Cooper’s hawk, which acts as final host in the lifestage of the parasite (does not cause symptoms in those birds). The parasite then migrates from the GI tract into the muscles of the bird. The aforementioned bird had a severe case of meningoencephalitis (inflammation in the brain); however, the parasite was not found there. The parasite’s role in causing neurologic symptoms is still unknown but the UMN’s pathologists are busy researching other birds.
With these amazing results, we promptly collaborated and published the findings in “Transboundary and Emerging Diseases.” My first paper as a wildlife veterinarian has been published!
Dr. Arno Wunschmann, a veterinary diagnostician at UMN who discovered the S. calchasi cysts, speaks of what impact this discovery has on the global transmission of diseases:
“This case demonstrates that diseases can spread very quickly and how the use of modern diagnostic tools can help diagnose diseases (in this case PCR). The disease was first described in 2009 in Germany and showed up 2 years later already in Minnesota.
“I was only to able to put the pieces together because somebody in Germany had worked hard to get his cases published in a timely fashion (because the first cases were only seen two years before the paper was in print) and I used the literature resources (including the internet). It is a beautiful example of how the scientific community as a whole is meant to function and can function. Alternatively, one can speculate that the disease went undiagnosed for some period of time but that seems unlikely because the lesion is very obvious (if a pathologist examines the muscle).”
S. calchasi is now recognized as an important differential diagnosis in neurologic pigeons.
How many pigeons possibly have it and have been misdiagnosed? That’s hard to say, but since S. calchasi was discovered, we’ve submitted every pigeon (all wild birds, not domestic) that dies while in our care or is euthanized. Nearly 20% have tested positive for this parasitic infection. This is huge news in the tracking of wildlife diseases on a global level.
One of the best parts of this discovery? My curiosity paid off! Wunschmann states: “The case demonstrates nicely how important it is that curious clinicians do not just accept the status quo and submit animals for necropsy. Compliments to you!”
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