by Fiep de Bie
Trichomonosis or trichomoniasis disease in finches has been in the news a lot this summer, as there seem to be more cases than usual. Pathologists and technicians at the Canadian Wildlife Health Cooperative (CWHC) received many calls from concerned bird-watchers all over the Maritimes with reports of sick or diseased birds.
What are the signs of the disease?
Around the feeder, sick birds look puffed up and very lethargic, to the point where they will not even fly away. Frequently, affected finches are seen to have matted wet plumage around the face and beak. The birds’ throats are blocked by the characteristic cankers (nodules or plaques) composed of dead tissue and inflammatory reaction to the parasite. The cankers grow so large that they prevent the bird from swallowing and result in eventual starvation. Diagnosis of trichomonosis relies on post-mortem examination and follow-up laboratory testing. While the lesions of the disease at post mortem are fairly characteristic, confirmation of the presence of the parasite requires microscopic examination of tissues and sometimes additional tests.
This purple finch is showing signs of trichomonosis including wet feathers from spitting up food. (Sheryl and Doug Wilson / The Canadian Veterinary Journal)
Where did the disease come from?
Trichomonas gallinae is the protozoan parasite that cause trichomonosis. It is a well-known disease in the UK, where an epidemic affected birds (most frequently Greenfinch and Chaffinch) throughout much of the country in 2006 and 2007. Later, it spread throughout Europe. It is probable that the original parasitic infection in finches originated from pigeons and doves, which can carry the parasite but don’t usually become sick. However, it is likely that the majority of current transmissions are from finch to finch. The disease first emerged in the Maritime provinces in 2007 and has since caused summer to fall mortality in regional Purple finch and American goldfinch populations1. In 2016, we had the first confirmed cases from Newfoundland, making the disease present in all Atlantic provinces. It is notable that the Atlantic provinces have the closest geographical proximity to the UK and that finch trichomoniasis emerged immediately after the onset of epidemic mortality in British finches2. Research revealed that the genotype found in the parasite affecting Maritime finches is the same as the one that one caused the epidemic in the UK, but it is uncertain how it was transmitted, as bird migration from Europe is an unlikely route of introduction of the disease. The movement of captive birds by humans, whether deliberate (e.g. cage and aviary birds, game birds, zoological collections) or accidental (e.g. wild bird stowaways or stray racing pigeons) could have occurred; however, there is no available evidence to support or refute this hypothesis. Therefore it remains a big unknown as to why the disease emerged after the epidemic in the UK, an ocean apart.
How is the disease spread?
The parasite is spread by birds feeding at the same feeding station and dropping food from their mouth, or drinking water contaminated from an infected bird. Feeding platforms may spread the disease more quickly because affected birds will drop or regurgitate seeds. Other birds then end up eating the infected food. With hanging feeders, the food will fall away from the feeder, but it is still possible to spread the disease. Affected birds feed their offspring and will consequently spread the disease. Raptors can also acquire the disease by eating prey that is affected.
Amy Seymour took this photo of birds in her backyard in Mount Stewart, PEI, which appear to be showing signs of trichomonosis. (Amy Seymour)
At the Canadian Wildlife Health Cooperative, we had a number of “frequently asked questions” about the disease:
What do I do when there are sick finches at my feeder?
It is recommended to stop feeding for at least 2-4 weeks, as feeding stations encourage birds to congregate, thereby increasing the potential for disease spread between individuals when an outbreak occurs. Water can serve to promote survival of the organism. Consider leaving bird baths empty until no sick or dead finches are seen (drying kills the Trichomonas parasite). Discard remaining birdseed into the garbage; wash feeders and bird bath with a bleach and water solution, (then rinse thoroughly and air dry), to keep the birds safe.
When is it safe to start putting the feeders back up?
The number of outbreaks in our region typically peaks in the late summer to fall, but this year it already emerged at the end of June. Research done by the CWHC suggested that temperature and humidity play a role in the survival of the parasite. Transmission may be more likely during the summer months as trichomonads have better survival in warmer temperatures.
To feed or not to feed?
There is a lot of discussion about this and opinions are divided. We all love to see our birds and feeders allow us to see birds at close range. However, considering the risk of the spread of a disease such as trichomonosis or other diseases such as salmonellosis, it is probably better to not feed birds in the summer or perhaps not at all. In the summer, there are adequate food sources in our natural environment.
Is it there a health threat for humans and pets?
Trichomonas gallinae is a parasite of birds and there is no known health threat to people or to other mammals such as dogs and cats. But it is recommended to wear rubber gloves when cleaning feeders and avoid handling sick or dead birds directly. For instance, use disposable gloves or pick the bird up through an inverted plastic bag.
Let’s hope that with the help of sensible hygiene precautions as a routine measure and the help of considerate bird watchers, the disease won’t be as prevalent as it was earlier this year and years to come.
Fiep de Bie Wildlife Technician Canadian Wildlife Health Cooperative Atlantic Veterinary College