• Neoplasm or tumour is defined as growth of abnormal tisssue formed
due to excessive, autonomous, and uncoordinated cell proliferation.
• The term neoplasm means new growth and process is called neoplasia.
• The branch of biology dealing with neoplasm its development,
diagnosis and treatmeant is called oncology(gr. Oncos= tumour and
3. Origin of tumour or cancer
• Generally in normal cell, balance is maintained between cell renewal and cell
apoptosis(programmed cell death).
• There is particular life span for all the matured cell which die, and the new cell
replace the old ones by proliferation on differentiation mechanism.
• The entire process is regulated such that the number specific type of cells remains
constant without altering other process
• Occasionally due to carcinogens one of the cell gets mutated and doesnot respond
to normal cell growth mechanism.
• This mutated cell undergoes further mutations and transforms i.e. to converts into
tumour cells which starts proliferating vigorously. This in turn results in mass of
abnormal cells called tumour or neoplasm.
1 Bening tumour
Noncancerous. If the cells are not cancerous, the tumour is benign. It won't invade
nearby tissues or spread to other areas of the body.
Examples: Fibroma (from fibrous tissues , Chondroma(cartilage), Osteoma(bone)
2. Malignant tumour
These are cancerous. Invades large no. of tissues.
Examples: Sarcomas(connective) , carcinomas, lymphomas (blood cancer)
8. Neoplastic diseases of poultry
• 3 most economically important virus induced neoplastic diseases of poultry
• Marek’s disease, caused by a herpesvirus,
• The Avian leukosis and Reticuloendotheliosis, caused by retroviruses.
9. Marek’s disease
• Marek’s disease (MD) is a common lymphoproliferative disease of chickens,
usually characterized by mononuclear cellular infiltrates in peripheral nerves and
various other organs and tissues including iris and skin.
• It is malignant lymphoma.
• First time described by Joseph Marek’s, Hungarian scientist in 1907.
• In the absence of control measures, MD can cause devastating losses in
commercial layer and broiler flocks.
• MD is caused by DNA herpes virus belonging to group B.
• It is highly cell associated virus due to which it escapes effect of antibodies once
entered into the body.
• MD is principally disease of poultry and rarely seen in turkeys ,pheasants,red
jungle fowl and Japanese quail.
• Hens more susceptible than males.
• The chicks may get infected at any age,being most susceptible in 4th week of age.
• The disease appears in a clinical form at about 6th to 8th week of age in acute form
(AMD) and between 3 to 5 months in classical form (CMD)
• Females more susceptible than males.
12. Mode of infection
• MDV is transmitted readily by direct or indirect contact between chickens,
apparently by the airborne route (Inhalation of infective particles)
• The MD virus matures and reaches fully infectious stage in the skin epithelium
and is shed alongside with dander and feathers.
• Contaminated poultry house dust remains infectious for at least
several months at 20—25°C and for years at 4°C .
• MD has not been found to be transmitted through eggs.
Note: MDV has tropism for feather follicle epithelium, from which MDV is shedded into the environment.
After MDV enters through the respiratory tract, an early cytolytic infection is
T cells are activated, and latent infection is established in these activated T
MDV transforms a few latently infected cells, which develop into
• In AMD mortality varies from 25 to 50 to 60 percent.
• In CMD around 10 to 30 percent.
• Recovery is rarely seen.
16. Clinical Signs and Symptoms
• In AMD birds may die suddenly or after showing signs of dullness or respiratory
• In CMD, incoordination, lameness and paralysis of one or both legs or of wings
,shown by hanging or droopings wings is seen.
• A characteristic clinical presentation is a bird with one leg stretched forward and
the other back as a result of unilateral paresis or paralysis of the leg.
• If cervical nerves are affected, torticollis is seen.
• Ocular lesions may also seen.
• In CMD, Lesions may seen in following nerves affecting respective organs:
Sciatic nerves of leg leading leg paralysis.
Brachial nerves of wing leading wing drooping.
Vagus nerves along neck.
Mesentric nerves of abdomen.
• How nerve looks like?
Slightly thickened than normal. Nerves becomes rounded instead of normally flat and slightly
• Histopathologically , infiltration of lymphocytes is most characteristic lesion.
• The lesions consist of a mixed population of small, medium, and large lymphoid cells plus
plasma cells and large anaplastic lymphoblasts.
• These lesions have been classified in to types I,II and III.
• In Type I, there is diffuse infiltration of lymphocytes and cells looking plasma cells.
• In Type II, the nerves show oedema and little lymphocytic infiltration.
• In Type III, there is infiltration of lymphoblastic cells, forming tumerous follicles
• In AMD , tumours are found in gonads, liver, spleen, lungs, muscles, heart,
kidney, proventriculus, and intestine in decreasing order of frequency.
• Signs and symptoms
• Post mortem lesions
• Virus isolation
• Demonstration of viral antigens by agar gel precipitation test
• Differential stain for MD vs ALC: Pyronin
29. Avian Leukosis
• There is a group of virus causing “Avian Leukosis/Sarcoma viruses”.
• These virus produces a number of conditions in poultry k/a “leucosis/sarcoma
group of diseases” with cancerous nature.
• These disease include:
Myeloid leucosis (Myleblastosis)
Of these only lymphoid is common to be economic
30. Lymphoid leucosis
• Avian leucosis is a common worldwide cancerous disease of poultry.
• It is a tumour producing viral diseases ,and is characterized by
marked enlargement of liver.
• Lymphoid leucosis occurs any time after 14weeks of age(Incidence is
higher at sexual maturity)
• Usually a problem of breeders and laying hens.
• Caused by avian leucosis or sarcoma virus.
• Enveloped, single stranded RNA viruss(Alpharetro virus)
• Most birds are exposed by sexual maturity
• Chickens are the natural hosts for all viruses of the leukosis/sarcoma group.
• Transmitted both vertically and horizontally.
• Vertical infection occurs by shed of virus by the hen into the albumen or yolk, or
both; infection probably occurs after the onset of incubation.
• Congenitally infected chickens fail to produce neutralizing antibodies and usually
remain viremic for life.
• Horizontally, Virus is present in the saliva ,faeces, and feather debris of infected
• However its survival outside the body is relatively short.Thus lymphoid leucosis is
not very contagious.
• Chick infected horizontally have virus in their blood for only short time and then
develop virus neutralizing antibodies.Such birds usually remains as carriers.
• Lymphoid leukosis is a clonal malignancy of the bursal-dependent lymphoid
• Transformation invariably occurs in the intact bursa, often as early as 4–8 wk after
• The cells from Bursa of Fabricus transforms itself into cancerous type and then
spreads into different organs.The transformed cells are called Lymphoblasts.
• Lymphoblast proliferate and give rise to nodular growth into bursa which are
visible after 14weeks.
• Inappetence, weakness, diarrhea, dehydration, and emaciation. Infected chickens
become depressed before death.
• The comb may be pale shriveled and sometimes cyanotic.
• The abdomen is usually enlarged because of massive liver.
• Palpation often reveals an enlarged bursa and sometimes an enlarged liver.
38. Postmortem findings
• The liver is greatly enlarged.
• The spleen, bursa of fabricus, kidneys and ovary are also usually enlarged.
• Grossly, diffused or nodular lymphoid tumors are common in the liver, spleen, and
bursa and are found occasionally in the kidneys, gonads, and mesentery.
• Tumours are soft,smooth anf glistening.
• Signs and symptoms
• Post mortem findings
• virus detection tests including PCR, virus isolation.
• . Tumors can be differentiated from those of Marek’s disease by gross and
microscopic pathology and by molecular techniques that demonstrate the
characteristic clonal integration of proviral DNA into the tumor cell genome with
the associated disruption of the c-myc oncogene.
• Includes 3 disease conditions,caused by retrovirus of reticuloendotheliosis group
of single stranded RNA.
• The disease condition are:
• These disease are not common,although infection appears to be widespread.
• Direct contact with infected chickens(Horizonal)
• The viruses are present in faeces
• Infected hens to their progeny(Vertical) although usually at low frequency than
45. Forms of disease
1. Acute Neoplasia
• Affected birds have enlarged liver and spleen. Pancreas,ovary,testes ,heart and kidney
may also be enlarged.
• Infection of hatched chickens results in high morbidity from acute neoplastic diseases.
2. Runting disease syndrome
• Characterized by poor growth
• Affected birds are stunned and pale, abnormal feather development particularly of
• Virus can cause immune suppression.