Enzootic Nasal Adenocarcinoma in Sheep: Nasal Tumor Signs and Care

Enzootic nasal adenocarcinoma, often shortened to ENA, is a tumor that develops from the secretory lining of the nasal passages in sheep. It most often arises around the ethmoid turbinates deep in the nose and can grow on one or both sides. As the mass enlarges, it blocks airflow and increases mucus production, which is why affected sheep often develop a long-standing nasal discharge and louder breathing.

ENA is considered an infectious tumor disease because it is associated with enzootic nasal tumor virus type 1 (ENTV-1), a betaretrovirus of sheep. Research has shown that ENTV-1 can be transmitted experimentally and is strongly linked to naturally occurring cases. In practical flock terms, that means this is not a routine nasal infection that clears with a short course of medication.

Most affected sheep are adults, but younger animals can be infected. The disease tends to progress over time rather than appearing overnight. Many pet parents and producers first notice a sheep that seems to have a "stuffy nose" for weeks or months, then later develops weight loss, exercise intolerance, or open-mouth breathing.

Although ENA is locally destructive, it is mainly a problem because it occupies space in the nasal cavity and interferes with normal breathing. Your vet can help separate it from other causes of chronic nasal signs, including bacterial infection, nasal parasites, foreign material, trauma, and other tumors.

ENA is linked to enzootic nasal tumor virus type 1 (ENTV-1), an ovine betaretrovirus. This virus infects cells in the nasal lining and is associated with tumor formation in the ethmoid region of the nasal cavity. Experimental work has supported a causal role, and ENTV-1 genetic material can be detected in affected tumors and nasal secretions.

Transmission is thought to occur mainly through close contact with respiratory and nasal secretions from infected sheep. That means flock density, prolonged nose-to-nose contact, and introduction of infected animals may all increase risk. Cases can appear after apparently healthy carrier animals join a flock.

Not every sheep exposed to the virus will show obvious disease right away. ENA often has a long incubation period, so infected animals may look normal for months before signs become clear. This delay makes flock control challenging.

ENA is not caused by poor care. It is also not the same disease as ovine pulmonary adenocarcinoma, which affects the lungs and is linked to a related but different retrovirus. Because several upper respiratory conditions can overlap clinically, your vet may recommend testing and flock-level review before concluding ENA is the cause.

Diagnosis usually starts with a history and physical exam. Your vet will look at how long the nasal discharge has been present, whether one or both nostrils are involved, how the sheep is breathing, and whether there is weight loss or facial distortion. Because ENA can mimic chronic rhinitis, sinus infection, nasal bots, or other masses, the first step is often ruling out more common problems.

Further workup may include endoscopy, imaging, or both. Skull radiographs can sometimes show a mass, but advanced imaging such as CT gives a much clearer picture of how much of the nasal cavity is involved and whether nearby bone has been affected. In referral settings, rhinoscopy can help visualize the lesion and collect samples.

Definitive diagnosis is usually based on pathology and/or detection of ENTV-1. Tissue collected by biopsy or after necropsy can confirm adenocarcinoma. Some laboratories and research groups have also described RT-PCR testing for ENTV-1 from nasal material or tumor tissue, which can support an antemortem diagnosis.

In many farm settings, the practical diagnosis is a combination of chronic compatible signs, poor response to routine treatment, and confirmation after culling or necropsy. If one sheep is affected, your vet may also discuss whether other flockmates with chronic nasal signs should be examined.

Prevention focuses on flock biosecurity and early removal of suspect animals. Because ENA is linked to a contagious retrovirus spread through close contact and nasal secretions, the safest approach is to avoid introducing sheep with chronic unexplained nasal discharge, noisy breathing, or poor thrift. Quarantine new arrivals and have your vet examine any animal with persistent upper respiratory signs before mixing.

If a sheep is diagnosed or strongly suspected to have ENA, your vet may recommend segregation followed by culling or euthanasia rather than prolonged group housing. This is especially important in closed flocks, breeding groups, and situations where multiple animals have similar signs.

Necropsy can be very helpful for prevention. Confirming the diagnosis in one sheep gives your vet better information for monitoring flockmates and refining biosecurity plans. Without confirmation, ENA may be mistaken for chronic infection and continue to spread unnoticed.

There is no widely used commercial vaccine for ENA in sheep. Good records, careful sourcing of replacement animals, prompt evaluation of chronic nasal disease, and minimizing prolonged contact with affected sheep are the most practical prevention tools available today.