Todayโs path rounds are on ๐๐ฅ๐๐๐ค๐ก๐๐๐, otherwise known as ๐ก๐ข๐ฌ๐ญ๐จ๐ฆ๐จ๐ง๐ข๐๐ฌ๐ข๐ฌ.
๐๐ก๐๐ญ ๐ข๐ฌ ๐ข๐ญ?
๐๐ฅ๐๐๐ค๐ก๐๐๐ is a parasitic disease caused by a ๐ฉ๐ซ๐จ๐ญ๐จ๐ณ๐จ๐๐ง, which are small single celled organisms. Interestingly, this protozoan is transmitted alongside another parasite, the roundworm ๐๐๐ญ๐๐ซ๐๐ค๐ข๐ฌ ๐ ๐๐ฅ๐ฅ๐ข๐ง๐๐ซ๐ฎ๐ฆ. So these poor animals end up with two parasitic infections for the price of one!
๐๐ก๐จ ๐ ๐๐ญ๐ฌ ๐ข๐ญ?
Any ๐ ๐๐ฅ๐ฅ๐ข๐ง๐๐๐๐จ๐ฎ๐ฌ (poultry and game birds) bird species can get it, but we most commonly think of this disease in turkeys. In turkeys, mortality rates can be up to 80-100%!
๐๐ก๐๐ญ ๐๐๐ฎ๐ฌ๐๐ฌ ๐ข๐ญ?
As mentioned before, this protozoan likes to hitch a ride on the roundworm Heterakis gallinarum. This roundworm is transmitted primarily by earthworms, who ingest the roundwormโs eggs as they go about their earthworm life. The turkey or chicken then eats this earthworm, the egg hatches, and the bird becomes infected.
๐๐ก๐ฒ ๐ข๐ฌ ๐ญ๐ก๐ข๐ฌ ๐ ๐ฉ๐ซ๐จ๐๐ฅ๐๐ฆ?
Once the protozoans are within the bird, they migrate into the wall of the ๐๐๐๐, part of the large intestine. Here, they cause damage to the intestinal wall causing inflammation and leakage of ๐ฉ๐ฎ๐ฌ (fluid filled with inflammatory cells) that forms a cheesy, firm mass in the ceca. Gross. These protozoans also like to migrate to the liver, where they cause ๐ง๐๐๐ซ๐จ๐ฌ๐ข๐ฌ (cell death) in characteristic circular shapes.
๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐๐ข๐๐ ๐ง๐จ๐ฌ๐๐?
Usually this disease is diagnosed by necropsy, specifically looking for the ๐๐๐๐๐ฅ ๐๐จ๐ซ๐ of pus in the ceca, and the liver spots. Seeing both of these lesions together is considered ๐ฉ๐๐ญ๐ก๐จ๐ ๐ง๐จ๐ฆ๐จ๐ง๐ข๐, meaning that no other diseases present like this. So if you see them, you know what youโre dealing with! If you want to further confirm the diagnosis, you can do testing to specifically identify the protozoans DNA, or look at the tissue under a microscope to see the protozoans directly.
๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐ญ๐ซ๐๐๐ญ๐๐? ๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐ฉ๐ซ๐๐ฏ๐๐ง๐ญ๐๐?
Unfortunately, there are currently no approved treatments for blackhead. So prevention is key! Turkeys should not be raised with other poultry species, because many of those species can have ๐ฌ๐ฎ๐๐๐ฅ๐ข๐ง๐ข๐๐๐ฅ (no presenting symptoms) infections, allowing the protozoan to transmit to the turkey before anyone knows whatโs going on. If possible, turkeys should also be kept in environments with no earthworms, to prevent them from acquiring the disease through roundworm infection.
๐๐ก๐จ๐ญ๐จ๐ฌ
1-2) Examples of the liver necrosis seen during necropsy. Kinda pretty!
3-4) Examples of cecal cores.
5) Both lesions together!
6) What a pathologist might see looking at liver tissue under the microscope. Those little pink blobs are the protozoa itself!
๐๐จ๐ฎ๐ซ๐๐๐ฌ
Beckstead, R.B. Histomoniasis in Poultry. Merck Veterinary Manual, 2019.
Photos 1-6 ยฉ Noahโs Arkive contributors Holshuh, Luginbuhl, Page, Reece licensed under CC BY-SA 4.0.
