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Blog · Disease ID

Sick chicken? The backyard disease ID cheat sheet

11 minute read · published 2026-04-10

Backyard flocks face a small set of common diseases. Most are preventable with NPIP-clean stock, vaccination, biosecurity, and a clean coop. When a bird gets sick anyway, fast diagnosis matters. Here's a symptom-first guide to the eight conditions that account for most backyard losses, plus when to call your state vet.

This is reference material, not veterinary advice. Notifiable diseases (HPAI, Newcastle, Marek's outbreaks) MUST be reported to your state veterinarian (USDA hotline: 1-866-536-7593). Don't move birds while you suspect disease.

1. Coccidiosis

Who: chicks 3-8 weeks. Symptoms: bloody droppings, lethargy, ruffled feathers, hunched posture, sudden drop in feed consumption. Cause: Eimeria protozoa in damp bedding. Treat: Corid (amprolium) in drinking water for 5-7 days. Prevent: medicated chick starter for first 8 weeks unless your chicks are vaccinated for cocci.

2. Marek's disease

Who: birds 3-8 months. Symptoms: one-leg paralysis (classic), wing droop, gray eye, sudden weight loss, tumors on internal organs (post-mortem). Cause: herpesvirus, airborne via feather dander, no cure. Treat: none - infected birds shed virus for life. Prevent: vaccinate at hatch (most NPIP hatcheries offer this). Source vaccinated chicks from NPIP breeders.

3. Respiratory infections (MG, infectious bronchitis, coryza)

Who: any age. Symptoms: sneezing, nasal discharge, swollen sinuses, gurgling, drop in egg production, foamy eye discharge. Cause: Mycoplasma gallisepticum, infectious bronchitis virus, Avibacterium (coryza). Treat: tylosin or oxytetracycline (vet prescription required). Cull carriers - MG persists for life. Prevent: Mycoplasma-clean (MS Clean) flocks. Quarantine all new birds 30 days.

4. Fowl pox

Who: any age. Symptoms: wart-like scabs on comb, wattles, eyelids (dry form) or yellow cheesy lesions in mouth/throat (wet form, more serious). Cause: avipoxvirus, transmitted by mosquitoes. Treat: supportive only - clean scabs with iodine, keep wet-form birds on soft food. Prevent: vaccinate in mosquito-heavy areas. Eliminate standing water.

5. Avian influenza (HPAI)

Who: any age. Symptoms: sudden death in multiple birds, swollen face/wattles, dark comb, neurological signs (twisted neck), diarrhea. Cause: H5N1 / H5N8 viruses from wild waterfowl. Treat: NONE - notifiable, flock will be culled. Prevent: rigorous biosecurity (guide), keep birds away from wild waterfowl, AI-monitor your flock.

6. External parasites (mites + lice)

Who: any age. Symptoms: feather loss around vent and base of neck, scratching, dust-bathing more than usual, lice crawling near feather base, mites visible at night under wings. Cause: direct bird-to-bird or via wild birds. Treat: permethrin dust (one application, repeat in 10 days). Clean and re-bed coop the same day. Prevent: dust bath box with food-grade DE + wood ash. Quarantine new birds.

7. Internal parasites (worms)

Who: any age, free-range more often. Symptoms: weight loss despite eating, pale comb, watery diarrhea, drop in egg production, worms visible in droppings. Cause: roundworms, tapeworms, cecal worms. Treat: fenbendazole (Safe-Guard) or ivermectin. Discard eggs during treatment + 14-day withdrawal. Prevent: rotate pasture. Test fecals annually.

8. Egg-bound or vent prolapse

Who: laying hens, especially overweight or first-year layers. Symptoms: straining, sitting puffed up, exposed reddish tissue from vent (prolapse), no egg laid for 24+ hours. Treat: warm bath for 20 minutes, lubricate vent, gently massage abdomen. Prolapse: clean tissue with iodine, push back in, isolate bird (others will peck). Vet if it recurs. Prevent: avoid overfeeding scratch grain, ensure calcium (oyster shell free-choice), light schedule control (max 14 hours light).

The diagnostic flow

  1. Isolate the bird in a separate area away from the flock.
  2. Take vitals: alert vs. lethargic? eating? drinking? breathing normally?
  3. Check externally: mites/lice (look at base of feathers near vent), comb color, eye discharge, leg condition, wounds.
  4. Check droppings on a clean surface: blood, worms, watery, normal.
  5. Check the rest of the flock for similar symptoms - one bird vs. flock-wide changes the urgency.
  6. If multiple birds sick + sudden onset: call your state vet. HPAI testing is free and fast.
  7. If one bird: match symptoms to the cheat sheet above. Start supportive care (water, electrolytes, isolation).

The "stock the medicine cabinet" list

Source birds from NPIP-certified breeders to dodge half of this list. Pair with our biosecurity guide.