I am so nervous about diseases that run under the radar that Quercus has never been integrated with the main flock. The coccidia that he developed at three weeks old told me that I'd taken in a small peeping ecosystem, and I swore to myself that I would be very, very careful with this bird. The coccidia, arrgh, did make its way into the main flock after all, but so far has been little more than a nuisance. I wince with every new batch of chicks that hits the ground, though, and fret over them until they get past the danger window.
Then, last November, Quirk broke with scaly leg mite. I flipped out. His legs had been fine for nearly a year, and all of a sudden the scales began rucking up over spongy, crumbly growths. We stomped on the situation good and hard: since he wasn't a laying hen and wasn't a meal, Ivermectin time baby! A few weeks later the lesions were gone, but given the tenacious nature of the mite, and the blowup out of nowhere, I can't really believe that the mites are vanquished. No doubt they've gone back to a carrier state. I now inspect legs in the barn a couple evenings a month, dreading to see the mites appear.
I'm not the least bit surprised about the coccidia and the mites. That feral flock adds and subtracts stray birds all the time, healthy and sick. A rather tarnished ray of sunshine in the situation is that without human intervention, the feral flock practices survival of the fittest in its most elemental form: when a new bug comes through, susceptible birds sicken and some die, while the resistant ones survive. It selects for hardiness, and it does it old-school: no medications, no sympathy, no second chances. But the thing about hardiness is that it's rather fussy. There are three major points to remember:
- A hardy bird can look perfectly healthy and still be a carrier of diseases (the Typhoid Mary principle)
- The hardier the bird, the greater chance that he will have survived some really funky bugs, some of which he may now carry (the Eclectic Collector principle)
- Hardiness is not forever (Time wounds all heels)
Quirk has lived long enough without symptoms to make me less concerned about many of the diseases on the list, but I still worry about Marek's disease (range paralysis), which is a viral disease that attacks the nerve tissue and is famous for lying doggo in the body for years before making its presence known. Marek's is alive and well in the feral flock, flaring up periodically in young birds and older carriers. Marek's can even travel on stray feathers from a carrier bird, and we have several older hens who like to eat feathers, so during the molting season I spend a lot of time picking up shed feathers and making sure that Quirk's enclosure stays where the prevailing wind will sweep any stray bits away from the others.
The best defense is a good offense: quarantine. Generally it is recommended to quarantine new birds completely for a full month, and watch them with extreme care. Even when it comes time to begin introducing them to the main flock, it may be practical (if rather cold-hearted) to first introduce them to a few expendable, more susceptible birds for another month. This gives most diseases plenty of time to show up (except for a few jokers in the deck, like Marek's). Knowing the source of your new birds is another important defense. A "closed" flock (one that doesn't add new birds) is safer than an "open" one. Likewise, birds that attend shows or otherwise interact with unfamiliar chickens are at higher risk for exposure. Day-old chicks from a reputable hatchery are another means of adding birds that are disease-free.
<chuckle> When I started this post, I thought that I would only discuss subclinical disease, but of course one train of thought leads to another, and there's a lot more to disease control than simply being aware that some bugs are good at hiding from you. With that thought in mind, I may just have to come back to this!