I recently got together with Dr Vicki Bowes, avian vet/pathologist to look at a number of ‘unsolved mysteries’ that I have collected. She diagnosed the first, then the second, case with Marek’s Disease and joked that it was going to be a day for Marek’s Disease. She wasn’t far wrong. We sifted through 42 cases and five of the six that included necropsy photos were Marek’s, or possibly Leukosis. There were some telltale signs of one or the other, but the definitive diagnosis usually requires an in-person exam and often microscopic lab work.
I asked Dr Bowes for a Cole’s Notes version of what the major differences are so that small flock keepers who are interesting in doing a DIY necropsy might be able to differentiate the two.
Marek’s vs Leukosis
- Marek’s Disease and Avian Leukosis are both neoplastic (tumour-causing) viruses that infect B cells (white blood cells) necessary to fight disease. They often present with similar symptoms.
- In Marek’s neurological symptoms/sciatic paralysis present around age 10-12 weeks; while tumours are common at point-of-lay (POL)/sexual maturity.
- Both pathogens can involve the following organs: liver, kidney, spleen, lung and intestines.
- Specific Marek’s tumour involvement includes the brain, sciatic nerve, skeletal muscles and heart.
- Microscopic work would reveal cellular differences: Marek’s involves mature cells while Leukosis cells are larger and immature.
- Marek’s tends to affect younger birds while Leukosis often presents in older birds already in egg production.
The following are cases I’ve collected that Dr Bowes looked at and diagnosed as Leukosis complex (Lymphoid Leukosis or Marek’s Disease).
Debra Watt, vet tech, sent me some DIY necropsy photos from her files. Unfortunately she didn’t make any notes and couldn’t remember details of the case.
Dr Bowes pointed out these details of interest:
- The presence of gelatinous, liquidy yellow fat and rapid deconditioning are indicative that the bird was using body fat from across the breast
- There was an intestinal impaction and massive dilation of the intestinal tract.
- Massive swelling in the kidney and spleen and serous atrophy (degenerative change in the fat cells).
- The tubular organ, either the oviduct or the intestine, is infected consistent with Marek’s.
- The virus has infiltrated and created a stricture in the intestine.
Cheri Lyon sent me a necropsy report of one of her hens that died in 2018. Xena was a two-year-old Ayam Cemani hen who was sick for three weeks before her death. Her symptoms included: lethargy, decreased appetite, weight loss, excessive head scratching, twisting her head and walking in circles. Several months before she died she had one toe on each foot amputated due to vasculitis (inflammation and narrowing of blood vessels) in her legs and feet.
The pathology report, done at the local state university, found potential hemorrhage of the cerebellum (part of the brain responsible for motor skills such as balance and coordination); nodular masses on the liver and kidney; atrophied ovary; local ulceration of the crop mucosa; lymphocytic (white blood cell) infiltration in the ovary, kidney and liver; and large bands of necrotic skeletal muscle bundles.
Histological changes were more suggestive of Lymphoid Leukosis than Marek’s Disease.
Dr Bowes felt that the neurological symptoms, the perivascular cuffs (white blood cells accumulated around blood vessels) in the brain, and compromised structure of the liver and kidney pointed to Marek’s Disease. Without access to Xena’s samples she agreed that this was a Leukosis-complex illness, but would need more information to make a definitive diagnosis.
“I had a chicken that displayed the typical symptoms of being egg bound. I decided to dissect and investigate. She wasn’t egg bound but the entire abdomen was tigh and filled with an enlarged liver. I am sure it was pressing on her lungs which caused laboured breathing.” – Ging Ging Points
- The nodular tumours in the liver are signs of Marek’s.
“We had this hen who was doing great then just died. When I opened her up her liver was huge and had marks all over it. The first picture is when I first cut her open. The second picture is the pile of her liver. “ – Rose McCurdy
- The pale discolouration is a sign of tumour infiltration.
- There are tumours on the lungs.
- It’s either Marek’s or Leukosis.
“I had two chickens die in similar ways: lethargic, puffed up and isolating from the flock. When I opened her up she smelled awful; there was green liquid inside and her skin and insides looked odd.” – Victoria L Cabaniss
- The keel is pronounced meaning the bird was thin and emaciated
- The ovary was inactive
- The margins of her liver are sharp which is a good sign
- I would suspect visceral Marek’s, but would need more information before making a diagnosis.
Well that wraps up another edition of Show & Tell With Bitchin’ Chickens and Dr Bowes. I hope that it’s been a learning experience for you.
If you’d like help with a case drop me a line using the ‘contact’ button on my home page. Remember to wear gloves, take good close up photos from several angles and supply us with plenty of information (e.g. timelines, symptoms, medications, general flock health, etc) so we’re able to more accurately pinpoint what’s going on.
Thanks again to Dr Vicki Bowes for her willingness to share her wealth of knowledge and experience to build capacity and skills in small flock keepers.