Enzootic Nasal Adenocarcinoma in Sheep: Nasal Tumor Signs and Management
- Enzootic nasal adenocarcinoma, or ENA, is a contagious nasal tumor of sheep linked to enzootic nasal tumor virus type 1 (ENTV-1).
- Common signs include chronic one- or two-sided nasal discharge, noisy breathing, reduced exercise tolerance, weight loss, and sometimes facial distortion.
- This condition usually progresses over time because the tumor grows inside the nasal passages and blocks airflow.
- Diagnosis often involves a farm exam, nasal exam, imaging, and confirmation with biopsy, histopathology, PCR, or necropsy findings.
- There is no widely used field cure. Management may focus on isolation, humane culling or euthanasia, and flock-level biosecurity with your vet.
What Is Enzootic Nasal Adenocarcinoma in Sheep?
Enzootic nasal adenocarcinoma, often shortened to ENA, is a tumor that develops from the secretory glands lining the nasal passages of sheep. It is considered an enzootic, contagious cancer because it is associated with enzootic nasal tumor virus type 1 (ENTV-1), a betaretrovirus closely related to the virus involved in ovine pulmonary adenocarcinoma.
As the tumor enlarges, it takes up space inside the nasal cavity. That can make breathing harder and lead to persistent nasal discharge, noisy airflow, and gradual weight loss. Many affected sheep look like they have a chronic respiratory problem at first, which is one reason the disease can be missed early.
ENA has been reported in many sheep-raising regions worldwide. It is not known to be a common disease in every flock, but when it appears, it matters because affected animals usually decline over time and may continue to expose flockmates. Your vet can help sort ENA from other causes of chronic nasal signs, including bacterial infection, foreign material, nasal bots, abscesses, and other tumors.
Symptoms of Enzootic Nasal Adenocarcinoma in Sheep
- Chronic nasal discharge
- Noisy breathing or stertor
- Open-mouth breathing or breathing effort
- Reduced appetite or weight loss
- Exercise intolerance
- Facial asymmetry or swelling
- Nosebleeds
- Head shaking or reduced airflow from one nostril
Call your vet sooner rather than later if a sheep has persistent nasal discharge for more than a few days, noisy breathing, or progressive weight loss. These signs are not specific to ENA, but they do mean something important is going on in the upper airway.
See your vet immediately if you notice open-mouth breathing, marked breathing effort, collapse, severe weakness, or rapid decline. Advanced nasal tumors can obstruct airflow enough to become an urgent welfare problem.
What Causes Enzootic Nasal Adenocarcinoma in Sheep?
ENA is strongly associated with enzootic nasal tumor virus type 1 (ENTV-1). This virus infects sheep and is linked to the development of tumors in the ethmoid and nasal gland tissue. Research supports that ENTV-1 is involved in the disease process, and experimental transmission has produced ENA in sheep under study conditions.
The virus is thought to spread mainly through respiratory secretions and close contact, which is why flock-level exposure matters. Sheep with chronic nasal discharge may shed infectious material into the environment or directly onto nearby animals. As with other contagious respiratory diseases, crowding and repeated close contact can make control harder.
Not every sheep exposed to the virus will show obvious disease right away. ENA often develops gradually, and affected animals may be adults by the time signs become noticeable. Your vet may also consider other flock diseases at the same time, because sheep can have more than one respiratory condition in a group.
How Is Enzootic Nasal Adenocarcinoma in Sheep Diagnosed?
Diagnosis starts with a careful history and physical exam. Your vet will ask about how long the nasal discharge has been present, whether one or both nostrils are affected, whether other sheep are showing similar signs, and whether there has been weight loss or breathing effort. On exam, they may hear upper-airway noise, see reduced airflow, or find facial asymmetry.
Because many conditions can mimic ENA, your vet may recommend a stepwise workup. Depending on what is available, that can include a farm call exam, endoscopic evaluation of the nasal passages, skull radiographs, or CT imaging if referral is practical. Imaging helps show how much of the nasal cavity is occupied and whether nearby bone is involved.
Definitive diagnosis usually relies on histopathology of tumor tissue, often paired with PCR or immunohistochemistry to support the viral cause. In field settings, some cases are confirmed after euthanasia or culling through necropsy and laboratory testing. That information can still be very valuable because it helps your vet guide flock management and biosecurity decisions.
Treatment Options for Enzootic Nasal Adenocarcinoma in Sheep
Spectrum of Care means you have options. Here are treatment tiers at different price points.
Budget-Conscious Care
- Farm exam and breathing assessment
- Isolation from the main flock while your vet evaluates the case
- Supportive care focused on comfort and feed access
- Welfare monitoring for breathing effort, body condition, and ability to eat
- Humane culling or euthanasia discussion if quality of life is declining
Recommended Standard Treatment
- Farm or clinic exam plus targeted diagnostics
- Skull radiographs or limited upper-airway evaluation when available
- Biopsy or post-mortem tissue submission for histopathology
- PCR or other lab confirmation when available through a diagnostic lab
- Isolation, flock review, and humane culling or euthanasia planning for confirmed cases
Advanced / Critical Care
- Referral consultation with advanced imaging such as CT under sedation or anesthesia
- Endoscopic nasal evaluation and more detailed sampling
- Comprehensive pathology testing to distinguish ENA from other nasal masses
- Intensive short-term supportive care for severe breathing compromise
- Case-by-case discussion of surgical debulking or specialty intervention where available
Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.
Questions to Ask Your Vet About Enzootic Nasal Adenocarcinoma in Sheep
Bring these questions to your vet appointment to get the most out of your visit.
- What other conditions could cause these nasal signs besides ENA?
- Does this sheep need to be isolated from the rest of the flock right now?
- Which tests are most useful on-farm, and which require referral or a diagnostic lab?
- Would radiographs, endoscopy, or CT change the management plan in this case?
- Can we confirm the diagnosis with biopsy, PCR, or necropsy if needed?
- What signs would mean this sheep's breathing or quality of life is becoming an emergency?
- If this is confirmed ENA, what flock-level monitoring or biosecurity steps do you recommend?
- How should we handle breeding, replacement animals, and culling decisions if more cases appear?
How to Prevent Enzootic Nasal Adenocarcinoma in Sheep
There is no widely used commercial vaccine for ENA, so prevention focuses on biosecurity and early recognition. Work with your vet to investigate sheep that have chronic nasal discharge, noisy breathing, or unexplained weight loss instead of assuming the problem is a routine respiratory infection.
If ENA is suspected, separating the affected sheep from the flock while your vet evaluates the case is a reasonable step. Avoid sharing close airspace with vulnerable animals when possible, and be thoughtful about introducing new sheep whose health history is unclear. Closed-flock practices and careful sourcing can help reduce disease introduction.
For flocks with a confirmed case, your vet may recommend culling affected animals, submitting tissues for diagnosis, and monitoring flockmates for chronic upper-airway signs. Prevention is less about one product and more about a consistent plan: identify suspicious cases early, confirm what you can, and make practical management decisions that fit your flock.