Reticuloendotheliosis in Chickens: Lymphoma and Runting Syndrome

Quick Answer
  • Reticuloendotheliosis is a retrovirus infection of chickens that can cause immunosuppression, poor growth, feathering problems, and lymphomas in organs such as the liver, spleen, intestine, heart, and bursa.
  • Signs are often vague at first. Affected birds may look stunted, weak, pale, thin, or less active before tumors or sudden decline become obvious.
  • There is no specific antiviral treatment or commercial vaccine. Care focuses on flock assessment, supportive care, and confirming the diagnosis so your vet can guide next steps.
  • Diagnosis usually requires more than a physical exam. Your vet may recommend necropsy, histopathology, and PCR or other virus testing because this disease can look like Marek's disease or avian leukosis.
  • If one chicken is losing weight, acting weak, or has a swollen abdomen or enlarged organs at necropsy, isolate sick birds and contact your vet promptly.
Estimated cost: $80–$350

What Is Reticuloendotheliosis in Chickens?

Reticuloendotheliosis is a viral disease caused by reticuloendotheliosis virus, or REV. In chickens, it is best known for two major patterns: a runting syndrome in younger birds and lymphoma formation in older or chronically affected birds. The virus belongs to the retrovirus family and is distinct from the viruses that cause Marek's disease and avian leukosis, even though the diseases can look very similar.

This infection can affect the immune system as well as growth. Some chickens stay infected without dramatic early signs, while others develop poor weight gain, abnormal feathering, weakness, or tumors in internal organs. Tumors may involve the liver, spleen, intestines, heart, or bursa, and both B-cell and T-cell lymphomas have been described.

For backyard flocks, the hardest part is that the signs are not very specific. A chicken may only seem smaller than flockmates, less thrifty, or chronically unwell. Because REV can mimic other poultry tumor diseases, your vet often needs lab testing to sort out what is really going on.

Symptoms of Reticuloendotheliosis in Chickens

  • Poor growth or runting
  • Weight loss or thin body condition
  • Depression or reduced activity
  • Pale comb or wattles
  • Poor feathering or abnormal feather development
  • Enlarged abdomen or internal organ enlargement
  • Weakness or progressive decline
  • Sudden death

Reticuloendotheliosis often starts with subtle signs, especially in backyard flocks where one bird may only look smaller, quieter, or thinner than the rest. That makes it easy to miss early.

See your vet promptly if a chicken has ongoing weight loss, poor growth, weakness, abdominal swelling, or repeated unexplained illness. If a bird dies unexpectedly, a diagnostic necropsy can be one of the most useful next steps for the flock.

What Causes Reticuloendotheliosis in Chickens?

Reticuloendotheliosis is caused by reticuloendotheliosis virus (REV), an avian retrovirus. The virus is not considered highly stable in the environment, and it is not thought to spread as efficiently as some other poultry viruses. Even so, it is more widely distributed than once believed, and surveys suggest exposure occurs in chicken and turkey flocks in the United States and other countries.

Transmission can be complicated. Horizontal spread between birds can occur, and vertical transmission through breeding stock is also a concern in some settings. Merck also notes that some cases have been linked to accidental contamination of live poultry vaccines, especially historically with fowlpox or Marek's disease virus products, although that is not the usual concern for a backyard flock using modern regulated products.

The virus can suppress immune function and, over time, contribute to tumor development. In chickens, REV has been associated with both B-cell lymphomas and T-cell lymphomas. That is one reason it can be difficult to distinguish from avian leukosis or Marek's disease without laboratory confirmation.

How Is Reticuloendotheliosis in Chickens Diagnosed?

Diagnosis usually starts with flock history, age of affected birds, growth pattern, and a hands-on exam. If a chicken has died or is euthanized, your vet may recommend a necropsy because REV often causes internal lesions that cannot be confirmed from outward signs alone. Enlarged liver, spleen, intestine, heart, or bursa may raise suspicion, but those findings are not specific enough to make a final diagnosis by themselves.

The next step is typically histopathology and virus detection. Merck notes that presumptive diagnosis can be based on history, clinical signs, gross lesions, and microscopic examination, but a stronger diagnosis requires demonstrating REV through tests such as PCR, immunohistochemistry, virus isolation, or serology. This matters because REV can closely resemble Marek's disease and avian leukosis.

For pet parents, that often means your vet may suggest one of two practical paths: testing a sick live bird with targeted samples if available, or submitting a recently deceased bird to a veterinary diagnostic lab. In many US labs, poultry necropsy with histopathology commonly falls around $150 to $220, while office exams for avian or exotic patients often start around $115 to $185. Additional molecular testing can increase the total cost range.

Treatment Options for Reticuloendotheliosis in Chickens

Spectrum of Care means you have options. Here are treatment tiers at different price points.

Budget-Conscious Care

$80–$220
Best for: Single sick birds, pet parents working within a tighter budget, or cases where the main goal is comfort and practical decision-making
  • Avian or farm animal exam if available
  • Isolation of affected bird from the flock
  • Supportive care such as warmth, easy feed access, hydration support, and reduced stress
  • Basic flock review of age groups, sourcing, and recent illness patterns
  • Discussion with your vet about whether humane euthanasia or necropsy is the most practical next step
Expected outcome: Guarded to poor if REV is strongly suspected, because there is no specific antiviral treatment and tumor disease often progresses.
Consider: This approach may help comfort and flock management, but it often does not confirm the diagnosis. Without lab testing, it can be hard to distinguish REV from Marek's disease, leukosis, or other chronic illnesses.
Most Common

Recommended Standard Treatment

$150–$350
Best for: Most backyard flock situations where pet parents want a practical diagnosis and a plan for the rest of the birds
  • Veterinary exam plus flock history review
  • Necropsy of a recently deceased or euthanized bird
  • Histopathology of affected tissues
  • Basic biosecurity recommendations for the rest of the flock
  • Guidance on monitoring exposed birds and whether to pause additions to the flock
Expected outcome: Guarded. Individual birds with tumor disease usually do poorly, but confirming the cause can help your vet guide flock-level decisions and reduce future losses.
Consider: This tier gives more useful answers than supportive care alone, but it still may not fully separate REV from other tumor viruses unless specific viral testing is added.

Advanced / Critical Care

$250–$600
Best for: Complex flock cases, valuable breeding birds, repeated unexplained tumor losses, or pet parents who want the most complete diagnostic picture
  • Everything in the standard tier
  • PCR testing for REV on blood or tissues
  • Immunohistochemistry or referral pathology for tumor typing
  • Additional testing to rule out Marek's disease, avian leukosis, or other flock problems
  • Breeder or flock-level consultation on sourcing, segregation, and long-term control
Expected outcome: Still guarded for affected birds, but advanced testing can improve confidence in the diagnosis and help shape better prevention choices for the flock.
Consider: Higher cost range and more logistics. Even with a confirmed diagnosis, there is still no specific cure, so the value is mainly in clarity, flock planning, and prevention.

Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.

Questions to Ask Your Vet About Reticuloendotheliosis in Chickens

Bring these questions to your vet appointment to get the most out of your visit.

  1. Do this bird's signs fit reticuloendotheliosis, Marek's disease, avian leukosis, or another condition?
  2. Would a necropsy give us the most useful answer for this chicken and the rest of the flock?
  3. Which tissues or samples should be submitted for histopathology or PCR?
  4. Should I isolate this bird, and for how long?
  5. What supportive care is reasonable at home while we wait for results?
  6. Are other birds in my flock at risk, and what signs should I watch for next?
  7. Should I stop adding new birds or hatching eggs until we know more?
  8. Based on this flock's goals, what is the most sensible conservative, standard, or advanced plan?

How to Prevent Reticuloendotheliosis in Chickens

Prevention focuses on biosecurity and flock sourcing, because there is no commercial vaccine and no specific treatment for reticuloendotheliosis. Buy birds or hatching eggs from reputable sources with strong health programs when possible. Avoid mixing birds of unknown background into an established flock without a quarantine period and careful observation.

If you have unexplained chronic illness, poor growth, or tumor-like disease in multiple birds, work with your vet before bringing in replacements. A diagnostic necropsy can help you avoid repeating the same problem. In breeding situations, your vet may discuss whether vertical transmission is a concern and whether certain lines or hens should be removed from breeding plans.

Good day-to-day flock management still matters. Reduce stress, keep housing clean and dry, limit unnecessary bird movement on and off the property, and separate age groups when practical. These steps cannot guarantee prevention, but they can lower infectious pressure and make it easier to spot a problem early.

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