Flock health

Chicken Respiratory Diseases Chart: Signs, Spread, Vaccines and Reporting

Field guide · Updated November 4, 2026 · about 9 min read

Sneezing, a runny nose or a hen gasping for air can come from at least six different infections, two of which are federal emergencies. This chart sets the six side by side as the Merck Veterinary Manual, USDA APHIS and extension poultry specialists describe them: avian influenza, virulent Newcastle disease, infectious bronchitis, infectious laryngotracheitis (ILT), Mycoplasma gallisepticum (MG) and infectious coryza. It covers signs, spread, carriers, whether a vaccine exists, and which ones are reportable. It summarizes official guidance only; HenClass does not give treatment instructions or doses.

Short version: the signs overlap so much that a flock owner cannot tell these diseases apart by looking; a veterinarian or diagnostic lab has to test. Sudden deaths, swelling or purple color on the head or legs, a twisted neck and greenish, watery diarrhea are on APHIS's warning-sign lists for avian influenza and virulent Newcastle disease, both "notifiable" emergencies on the 2026 national list. Report sick or dying birds right away to your State veterinarian or to USDA toll-free at 1-866-536-7593 (USDA APHIS).

The six at a glance

Disease, cause, 2026 national list	Signs that stand out
Highly pathogenic avian influenza (HPAI, bird flu) Influenza A virus; highly pathogenic strains (APHIS) National list: notifiable, emergency	Sudden death; swelling of eyelids, comb, wattles and shanks; purple wattles, comb and legs; breathing difficulty; neurological signs; fewer eggs (APHIS). APHIS says HPAI strains are deadly to poultry and can wipe out whole flocks quickly.
Virulent Newcastle disease (vND) Virulent strains of avian paramyxovirus type 1 (Merck) National list: notifiable, emergency	Sudden death; sneezing, gasping; greenish, watery diarrhea; tremors, drooping wings, head or neck twisting; swelling around the eyes and neck; sharp drops in egg numbers and quality (APHIS). Merck gives up to 100% morbidity and mortality for the viscerotropic velogenic form, especially in flocks with no immunity.
Infectious bronchitis (IB) Avian gammacoronavirus (Merck) National list: monitored	In chicks, coughing, sneezing and rales for 10–14 days. In layers, egg production can drop by up to 70%, with thin, soft, wrinkled or pale shells and watery whites; recovery can take up to 8 weeks (Merck).
Infectious laryngotracheitis (ILT, LT) Herpesvirus (Minnesota) National list: monitored	Watery eyes first; birds stretch the head and neck forward to breathe, with wheezing and gurgling (Kentucky). Severe cases cause open-mouth breathing and often bloody mucus (Tennessee).
Mycoplasma gallisepticum (MG, chronic respiratory disease) Bacterium (mycoplasma) (Merck) National list: monitored	Rales, coughing, sneezing, nasal discharge and conjunctivitis (Merck); sticky nostrils, foamy eyes, swollen sinuses, or no outward signs at all (Kentucky). A slow, chronic disease.
Infectious coryza Avibacterium paragallinarum, a bacterium (Merck) National list: not listed	Facial swelling, nasal discharge, sneezing; swollen sinuses can keep the eyes shut (Merck). Kentucky describes a foul-smelling, thick, sticky discharge.

Low pathogenicity avian influenza is different: APHIS says these strains "typically cause few or no signs of illness," although some can turn highly pathogenic in poultry. The national list's avian influenza entry covers any influenza A in poultry.

Sneezing, nasal discharge: listed for all six (APHIS; Merck; Kentucky).
Gasping, hard breathing: all six (APHIS; Merck; Kentucky; Tennessee).
Swollen face or eyes: HPAI, vND, ILT, MG and coryza; in IB "sometimes," especially with a sinus infection at the same time (Merck).
Fewer eggs: all six; up to 70% fewer in IB (Merck), 10–40% fewer in coryza (Minnesota).
Sudden deaths: HPAI and vND (APHIS). APHIS says many vND birds die before showing any symptoms.
Purple comb, wattles or legs: HPAI (APHIS).
Twisted neck, tremors: vND (APHIS); "neurological signs" in HPAI (APHIS).
Misshapen or thin-shelled eggs: IB and vND (Merck); soft-shelled or misshapen eggs in avian influenza (AVMA).
Bloody mucus: severe ILT (Tennessee; Minnesota).
Foul-smelling discharge: coryza (Kentucky).

Chart drawn by HenClass from USDA APHIS, the Merck Veterinary Manual, the AVMA and the Kentucky, Tennessee and Minnesota extension publications listed below; reporting colors follow the 2026 USDA national list. A dot means a source lists that sign; an empty cell does not rule a disease out, and none of this replaces a lab diagnosis.

Why it takes a lab

The University of Kentucky's overview of respiratory diseases lists coughing, sneezing, rales, gasping and discharge from the eyes and nose under viral, bacterial and mycoplasma diseases alike. University of Tennessee Extension says mild ILT can look like other respiratory diseases. Confirming the cause needs testing: Merck names bacterial culture or PCR for coryza and real-time PCR on swabs for MG. For coryza, Minnesota Extension says the preferred sample is 2 to 3 heads from freshly dead birds that showed signs, kept cold and taken directly to a veterinary diagnostic lab, with results in at least 2 days. How to find a lab and send birds is on the hen health check page.

Spread, carriers and vaccines

Disease	How it spreads	After recovery
HPAI	Bird-to-bird contact; contaminated manure, equipment, clothing, shoes and hands. Wild birds can carry it without appearing sick (APHIS).	APHIS: there is no treatment, and the only way to stop the disease is to depopulate all affected and exposed poultry.
vND	Exhaled air, respiratory discharge and feces; between farms mainly through moving birds, poultry products, people, equipment and litter (Merck)	The sources here describe no carrier state; APHIS says it moves quickly through flocks and many birds die before showing symptoms
IB	Aerosols, contaminated feed or water, equipment and clothing (Merck)	Infected or live-vaccinated birds can shed virus on and off for up to 20 weeks; chicks infected young may never lay normally (Merck)
ILT	Respiratory secretions; litter, dust, darkling beetles, water-line biofilm, clothing, shoes and tires; survives up to three weeks on carcasses and equipment (Tennessee; Kentucky)	Carriers for life (Kentucky); infected flocks assumed to be lifelong carriers (Tennessee); up to 16 months (Minnesota). Stress such as a show can reactivate the virus (Tennessee).
MG	Through the egg in a small share of hatching eggs; aerosols within the flock; shoes, equipment and carrier birds between flocks (Merck)	Infected birds and flocks "remain infected for life" (Merck)
Coryza	Direct contact, airborne droplets, contaminated drinking water (Merck); "most outbreaks occur as a result of mixing flocks" (Kentucky). Not passed through eggs (Merck).	Recovered birds remain carriers and may shed the bacteria occasionally (Kentucky)

Vaccines

A vaccine existing is not a recommendation to use it: Tennessee ties ILT vaccination to veterinary supervision, and Minnesota says to work with your veterinarian on a coryza vaccination plan. No doses are given here.

HPAI: The AVMA's backyard-flock page says no vaccine is currently authorized for animals in the U.S.
vND: Live low-virulence vaccines are widely used; they prevent signs but not infection (Merck). APHIS: vaccinated poultry can still get sick and die.
IB: Live and killed vaccines exist, but types do not cross-protect, so the vaccine has to match local types (Merck).
ILT: Eye-drop, spray and drinking-water vaccines exist (Minnesota); see the disagreement below.
MG: Three live vaccines are licensed in the U.S. for the growing phase, plus inactivated bacterins (Merck). Minnesota suggests buying chicks from NPIP Mycoplasma certified-free flocks instead, because of vaccine reactions.
Coryza: Bacterins exist; serovars A, B and C do not cross-protect (Merck). Kentucky notes several doses are needed.

Merck notes that antimicrobials reduce MG signs but "do not eliminate infection," and Kentucky says antibiotics do not clear coryza carriers. Antibiotics do not work against the viruses (Kentucky). Treatment decisions belong with a veterinarian; the hen health check page explains how to find one.

Where the sources disagree

How long ILT carriers stay infectious. Kentucky says recovered birds "should be considered carriers for life," and Tennessee assumes infected flocks are lifelong carriers. Minnesota says recovered birds can carry the virus for up to 16 months.
Whether small flocks should vaccinate for ILT. Kentucky says a vaccine is available and describes eye-drop vaccination of each bird for small flocks. Minnesota rarely recommends it for small flocks, because the vaccine virus can spread to unvaccinated birds. Tennessee says to vaccinate only under veterinary supervision in areas where ILT is endemic, not to show birds within 30 days of the TCO vaccine, and to check state vaccine rules with the State veterinarian.
How deadly coryza is. Kentucky gives mortality of up to 50%, with 20% more common. Minnesota says death is uncommon.
How deadly ILT is. Tennessee gives 0.1–2% for mild forms and 5–70% (about 10–20% on average) for severe forms; Minnesota gives 5–70%.

Which are reportable, and who to call

USDA's National List of Reportable Animal Diseases (2026 version) sorts diseases into two groups. Veterinarians, labs and other animal health professionals report notifiable diseases within 24 hours and monitored diseases within 30 days (APHIS FAQ).

Status	Respiratory diseases on this page	What it means
Notifiable, emergency	Avian influenza (any influenza A in poultry), Newcastle disease (domestic poultry)	Reported within 24 hours of a suspected or confirmed case
Monitored	Infectious bronchitis, infectious laryngotracheitis, Mycoplasma gallisepticum (also M. synoviae)	Endemic in the U.S.; State officials and labs report monthly so APHIS can track trends
Not on the national list	Infectious coryza	No national reporting category; ask your veterinarian or State veterinarian about state rules

APHIS says reporting under the national list "does not supersede State requirements," so your state can ask for more. As an owner, you do not need a diagnosis to call:

Sick or dying birds: your State veterinarian, or USDA toll-free at 1-866-536-7593; you can also contact your APHIS Area Veterinarian in Charge (APHIS Defend the Flock). The AVMA gives the same hotline and says to contact your veterinarian immediately.
After hours and weekends: the same number, 866-536-7593, is APHIS's Foreign Animal Disease hotline.
Find your State veterinarian: the U.S. Animal Health Association's State Animal Health Officials page links a contact list. Examples from extension pages: Tennessee State Veterinarian 615-837-5120 (UT Extension); Pennsylvania Department of Agriculture 717-772-2852, option 1, for the emergency on-call veterinarian (Penn State). More state hotlines are on the flock biosecurity page.

APHIS says virulent Newcastle disease is not a food safety concern; people handling sick birds or vaccines can rarely get mild conjunctivitis (pinkeye). Avian influenza A viruses rarely infect people (APHIS); the CDC's advice for flock owners is linked from the biosecurity page.

Prevention checklist

Buy chicks from NPIP Mycoplasma certified-free breeder flocks (Minnesota); Merck calls MG-free stock the main control strategy.
Keep new birds apart before they join the flock; adding new chickens has APHIS's quarantine guidance.
Be careful with shows, swaps and live-bird sales, where Kentucky says coryza exposure happens.
Keep dedicated shoes and clothing for the coop; ILT travels on clothing, shoes and tires (Kentucky).
Remember that wild birds can carry avian influenza without appearing sick (APHIS); the biosecurity checklist covers keeping them out.
Reduce stress, cold, crowding and poor air quality, which Merck says make MG worse; see coop ventilation.
Report sick or dying birds and the warning signs above right away (APHIS), and keep birds that may be infected away from shows: Tennessee says the stress of a show can reactivate ILT in carriers.

Shell problems from IB and other causes are compared on the egg problems chart.

HenClass summarizes official guidance and does not give veterinary advice, treatment instructions or doses. Follow your veterinarian, your State veterinarian and the label on any product used on poultry.