female vet with cat Zuku Winter NAVLE® Sale

NAVLE® Question of the day

MO TU WED TH FR

August 28, 2024

NAVLE

A 12-week-old chicken from a young backyard flock is presented for evaluation because of weight loss, decreased appetite, and diarrhea.

The irises in the affected bird are lighter than normal with irregular pupillary margins, and the hen does not have a normal pupillary light reflex. Several other young birds appear to be growing poorly compared to the rest of the flock.

The image below is an example of what the affected bird's eye looks like, vs. a normal eye on the left.

Based on the presumptive diagnosis, how can this problem be prevented going forward?

A - Use only mycoplasma-resistant bloodlines for new additions to flock

B - Isolate unaffected animals; breed from survivors of disease

C - Cull birds from the same genetic line

D - Buy only vaccinated chicks

E - Collect pharyngeal swabs from affected birds; Tx for entire flock with antimicrobials based on culture and sensitivity

Sorry. You chose "B - Isolate unaffected animals; breed from survivors of disease" but the correct answer is "D - Buy only vaccinated chicks"

Buy only chicks vaccinated against Marek disease. This chicken has ocular evidence of Marek disease. There is no treatment, but the problem is preventable when chicks are vaccinated at hatching or before 2 weeks of age.

Diffuse infiltration of mononuclear cells can turn the irises of affected chickens from a normal yellow color to a pale tan to gray color (a.k.a. “gray eye”). Cellular infiltration can also occur in many other tissues (skin, nerves, viscera), and there may be palpable tumors in the muscle and skin.

Marek disease is common in commercial poultry. Dx usually based on enlarged nerves and lymphoid tumors in the viscera. Lymphoid leukosis is a key differential.

Absence of bursal tumors helps distinguish Marek disease from leukosis. But if you find bursal tumors, Marek disease is still on the DDX list pending other tests, like immunochemistry. Chicks as young as 3 weeks can show Marek disease, but lymphoid leukosis is typically seen in chickens more than 14 weeks old.

Image courtesy of the USDA.