🦠Poultry Diseases - Ranikhet, Marek's, Bird Flu, Coccidiosis and Nutritional Disorders

Disease management is a cornerstone of successful poultry farming. Diseases in poultry are broadly categorised into viral, bacterial, protozoan, fungal, parasitic, and nutritional disorders. Understanding the causative agents, symptoms, and control measures for each disease is essential for maintaining flock health and preventing economic losses.

Disease Classification Overview

---

Viral Diseases

Ranikhet Disease (Newcastle Disease)

• Most dangerous viral disease of chicken. Ranikhet disease is considered one of the most devastating poultry diseases worldwide due to its extremely high mortality rate.
• Ranikhet disease, also known in the West as New Castle disease is a contagious and highly fatal diseases of fowls. The disease is caused by Avian Paramyxovirus serotype 1 (APMV-1), genus Orthoavulavirus, family Paramyxoviridae and can spread rapidly through an entire flock.
• One of the most serious virus diseases of poultry with mortality as high as 100% in severe cases.
• The disease is also suspected to cause conjunctivitis among laboratory workers and persons handling infected birds. This virus has zoonotic effect and can cause human deaths in rare cases.

NDV Strains — Pathogenicity Spectrum:

The Mukteswar strain (mesogenic) was developed at IVRI Mukteswar (Uttarakhand) and is used as a booster vaccine in India. Doyle’s strain (velogenic viscerotropic) is the most virulent NDV strain known.

Causes / Transmission:

• Contamination of water
• Contact with infected chicken
• Airborne spread through respiratory secretions
• Fomites (contaminated equipment, clothing, vehicles)

Clinical Symptoms:

• Torticollis (twisting of neck) and paralysis of wings and legs — classic nervous sign
• Cyanosis of comb (bluish discolouration)
• Facial edema
• Green diarrhoea with offensive smell — characteristic colour due to bile
• Drop in egg production; eggs may have soft shells
• Sudden death
• Sneezing, gasping, droopiness in young birds
• Profuse salivation, ruffled feathers

Treatment & Prevention:

• There is no treatment for Ranikhet disease.
• LaSota is a naturally occurring lentogenic strain first isolated in LaSota, USA. IVRI, Izatnagar manufactures and supplies the LaSota vaccine in India. The Lasota (also written as La Sota) vaccine is a live attenuated vaccine that is administered through drinking water or eye drops and provides effective immunity against Newcastle disease.
• Vaccination with F1/Lasota strain (live) and R2B strain (killed) at scheduled intervals.
• Zoonotic note: Laboratory workers and persons handling infected birds can develop mild conjunctivitis (eye infection). Serious human illness is very rare.

---

Marek’s Disease

• Viral Disease found in poultry. Marek’s disease is caused by a Herpesvirus (Gallid herpesvirus 2) and is one of the most common viral diseases affecting chickens worldwide.
• It is a highly contagious viral disease characterised by enlargement of nerves and internal organs.
• Marek’s Disease will cause inflammation and tumors in the nerves, spinal column, and brain. In this form, birds will become paralyzed in the legs, or wings or may develop head tremors. The neural form causes characteristic one-leg-forward-one-leg-backward paralysis, which is a classic diagnostic sign.
• Birds under 16 weeks are most commonly affected.
• It has great economic significance.

Symptoms:

• Poor growth and paralysis of one leg (stretched backward) — classic “splits” posture
• Tumors in nerves, liver, spleen, kidneys, and ovaries
• Grey eye / Pearl eye — in the ocular form, the iris loses its normal pigmentation and turns grey, causing irregular pupil shape and eventual blindness
• Skin tumours (cutaneous form) — enlarged feather follicles

Treatment & Prevention:

• There is no treatment for Marek’s disease.
• Diseased birds should be promptly removed from the flock and humanely destroyed (Culling).
• Vaccination of day-old chicks at the hatchery with HVT (Herpesvirus of Turkey) strain is the primary method of prevention. In commercial farms, the bivalent HVT+SB1 vaccine is the gold standard offering better protection than HVT alone.
• Vaccination is given subcutaneously at 0-2 days of age.

---

Infectious Bursal Disease (IBD)

• Caused by Birnavirus (Avibirnavirus) — double-stranded RNA virus. Means Viral disease.
• Also called Gumboro disease or Infectious Bursitis or Avian Nephrosis. The name Gumboro comes from the town of Gumboro, Delaware, USA, where the disease was first identified.
• Highly contagious. Morbidity ~100%; mortality 0–20% in classical strains, up to 60% in severe cases; 80–90% only in very virulent (vvIBDV) strains.
• Bursa disease causes immuno suppresion and which affects humoral antibodies production. The virus specifically targets the Bursa of Fabricius, the organ responsible for B-lymphocyte (antibody-producing cell) development in birds. Destruction of this organ leads to severe immunosuppression, making affected birds vulnerable to other secondary infections.
• Usually chicks of 3–6 weeks old are most susceptible for clinical disease; infection before 3 weeks causes subclinical immunosuppression without visible signs.
• Symptoms: watery/whitish diarrhoea (not bloody), the feathers around the vent are usually stained with faeces containing plenty of urates. Huddling, depression, ruffled feathers, prostration, high mortality in 3–6 week chicks.
• Prevention: Vaccination at 12-15 days (1st dose) and 7th-8th week (booster) with live Gumboro vaccine. Early vaccination is critical because the Bursa of Fabricius is most active and vulnerable during the first few weeks of life.

---

Fowl Pox

• It is viral disease. Fowl pox is caused by the Avipoxvirus and is one of the oldest known poultry diseases.
• The dry form of fowl pox is characterized by raised, wart-like lesions on unfeathered areas (head, legs, vent, etc.). These nodular lesions scab over and eventually fall off, but can cause significant discomfort and reduced feed intake.
• Raised skin lesions appear at the corners of the beak, as well as at the comb and wattle.
• In laying hens, infection results in a transient decline in egg production.

Two Forms of Fowl Pox:

• The wet form (diphtheritic form) is more severe and produces yellowish, cheese-like deposits in the mouth, throat, and trachea.
• The wet form may cause respiratory distress by obstructing the upper air passages.
• No treatment is available. However, fowl pox is relatively slow-spreading. Thus, it is possible to vaccinate to stop an outbreak.
• Fowl pox outbreaks in poultry confined to houses can be controlled by spraying to kill mosquitoes. However, if fowl pox is endemic in the area, vaccination is recommended. Mosquitoes are the primary vector for fowl pox virus transmission, so vector control is an important component of disease prevention.
• Vaccination with Fowl pox vaccine (BM strain) at 4th-5th week and 14th-15th week via intramuscular route. The fowl pox vaccine uses a live attenuated pigeon pox virus (closely related Avipoxvirus) as the vaccine strain.

---

Avian Influenza (Bird Flu)

• Viral disease.
• Also known as Bird Flu. Avian influenza is caused by Influenza A virus; key subtypes include H5N1, H5N8, H9N2. All species of birds can be affected.
• Avian influenza is classified based on pathogenicity:
  • LPAI (Low Pathogenic Avian Influenza) — mild symptoms: listlessness, respiratory distress, drop in egg production.
  • HPAI (Highly Pathogenic Avian Influenza) — facial swelling, blue comb and wattles, blood-tinged discharge, near-100% mortality. An OIE List A notifiable disease.
• India outbreaks: H5N1 and H5N8 caused major outbreaks in 2021 across Kerala, Maharashtra, and Rajasthan. H5N1 clade 2.3.4.4b was detected in Kerala (June 2024).
• Zoonotic significance: H5N1 can infect humans with high mortality (approximately ~60% case fatality rate in humans). Virus transmits from infected birds or contaminated environments; strict biosafety measures required during culling operations.
• Control policy in India (DAHD protocol): Stamping out — culling all birds within 1 km radius of the outbreak; enhanced surveillance and movement ban in 10 km surveillance zone; government compensation to affected farmers.
• No licensed vaccine is available in India; surveillance and strict biosecurity are the primary tools of control.
• A vaccination programme used in conjunction with strict quarantine has been used in some countries to control mild (LPAI) forms.

---

Blue Comb Disease

• Disease primarily of young laying hens.
• It is also called pullet disease.
• Blue colour of combs. The bluish discolouration of the comb (called cyanosis) occurs due to impaired blood circulation and oxygen supply, giving the disease its characteristic name.
• Caused by a coronavirus.
• Symptoms include drop in egg production, watery diarrhoea, dehydration, and shrivelled comb.

---

Infectious Bronchitis (IB)

• IB is one of the most important viral diseases of poultry. It is caused by a Coronavirus (Infectious Bronchitis Virus, or IBV).
• It causes major economic losses to the poultry industry.
• IB is an acute, highly contagious, viral respiratory disease of chickens. characterized by tracheal rales, coughing, and sneezing.
• Symptoms: Nasal discharge, rales, coughing, sneezing, respiratory distress, and gurgling sounds.
• Spread by aerosol, ingestion of contaminated feed and water, contact with contaminated equipment and clothing. The virus can also be transmitted through airborne droplets over short distances, making it extremely difficult to contain in densely stocked poultry houses.
• Prevention: Vaccination with IB vaccine at 4th-5th week and 13th-15th week.

---

Turkey Rhinotracheitis

• Viral disease. This disease is caused by the Avian Metapneumovirus (AMPV), also known as Turkey Rhinotracheitis Virus (TRTV).
• Swollen head syndrome (SHS) is an acute, highly contagious upper respiratory tract infection of poultry.
• The typical clinical signs seen in chickens infected with the virus include swelling of the periorbital and infraorbital sinuses, particularly around the eye, coupled with mild conjunctivitis. The facial swelling is a distinctive feature that helps in field diagnosis.

---

Egg Drop Syndrome (EDS)

• A viral disease caused by an Adenovirus.
• Characterised by sudden and severe drop in egg production (10-40%) and production of thin-shelled, soft-shelled, or shell-less eggs.
• Affects layers at peak production (25-35 weeks).
• Prevention: Vaccination with EDS vaccine at 15th-18th week via intramuscular route.

---

Vaccination Schedule

“Prevention is better than Cure”. Many viral diseases cannot be treated but can be controlled only by preventive vaccination. A well-planned vaccination schedule, followed consistently from day one, is the most cost-effective disease prevention strategy in poultry farming.

Complete Vaccination Schedule for Layers

Routes of Vaccine Administration

---

Bacterial Diseases

Bacterial diseases in poultry are caused by pathogenic bacteria and can often be treated with antibiotics, unlike viral diseases. However, prevention through good hygiene and biosecurity remains the best approach.

Pullorum Disease (Bacillary White Diarrhoea)

• Caused by Salmonella pullorum.
• Primarily affects young chicks (under 3 weeks) with high mortality.
• Transmission: Vertical transmission (transovarial) — the bacteria pass from infected hen into the egg yolk before shell formation. This is the classic route: infected dam → infected egg → infected chick. Horizontal spread (direct contact, feed, water) can also occur.
• Symptoms: Huddling, pasting of vent (white pasty droppings block the vent), white pasty diarrhoea, lethargy, high mortality in chicks.
• Diagnosis: Pullorum Agglutination Test (PAT) — a rapid plate agglutination test used to identify carrier adult birds in breeding flocks. Blood or serum is mixed with S. pullorum antigen; clumping (agglutination) indicates a positive (carrier) bird.
• Eradication policy: Test and cull — all reactor (positive) birds identified by PAT are culled to break the cycle of vertical transmission.
• Treatment: Antibiotics (furazolidone, sulfonamides). Remove carrier birds.
• Prevention: Test breeding flocks and eliminate carriers. Maintain strict hatchery hygiene.

---

Fowl Cholera

• Caused by Pasteurella multocida.
• Fowl Cholera is a severe bacterial disease characterised by sudden death, high fever, swollen wattles, and greenish-yellow diarrhoea.
• Symptoms: Combs and wattles become swollen and bluish. Pin-point blood spots on the heart and duodenum. White spots on the liver are present.
• Treatment: Antibiotics (oxytetracycline, sulfonamides).
• Prevention: Vaccination, good sanitation, rodent control.

---

Fowl Typhoid

• Caused by Salmonella gallinarum.
• Affects birds of all ages (more prominent in adult birds) with symptoms similar to Pullorum disease.
• High mortality in adult birds with greenish-yellow diarrhoea, anaemia, enlarged spleen and liver.
• Transmission: Primarily horizontal (direct contact, contaminated feed/water). Unlike Pullorum disease, Fowl Typhoid is NOT egg-transmitted (no transovarial transmission).
• Treatment: Antibiotics, culling of carriers.

---

Colibacillosis

• Caused by pathogenic strains of Escherichia coli.
• Colibacillosis causes respiratory distress, swollen joints, and septicaemia, especially in young chicks with compromised immune systems.
• Often occurs as a secondary infection after viral diseases (especially IBD) that suppress immunity.
• Treatment: Antibiotics based on sensitivity testing.

---

Chronic Respiratory Disease (CRD)

• Caused by Mycoplasma gallisepticum.
• Symptoms: Respiratory distress, sound of rales, sneezing, poor weight gain, and nasal discharge.
• Chronic and slow-spreading; causes significant economic losses through reduced growth and egg production.
• Treatment: Tylosin, erythromycin, or other macrolide antibiotics.

---

Infectious Coryza

• Caused by Avibacterium paragallinarum (formerly Haemophilus paragallinarum). Bacterial disease.
• Acute respiratory disease primarily affecting laying hens and older growing birds.
• Symptoms: Swollen face (facial/infraorbital sinus swelling), nasal discharge with foul smell, conjunctivitis, laboured breathing, and significant drop in egg production (10–40%).
• Transmission: Direct contact with infected birds or contaminated water and equipment. Carrier birds are a major source.
• Treatment: Sulphonamides (sulphadimidine, sulphamethazine) and tetracyclines are effective; treatment controls the disease but does not eliminate carriers.
• Prevention: Bacterin (killed) vaccine available; all-in all-out management and strict biosecurity.

Bacterial Disease Summary Table

Disease	Causative Organism	Key Symptoms	Treatment
Pullorum	Salmonella pullorum	White diarrhoea, huddling, high chick mortality	Antibiotics, eliminate carriers
Fowl Cholera	Pasteurella multocida	Sudden death, swollen bluish comb, liver spots	Oxytetracycline, vaccination
Fowl Typhoid	Salmonella gallinarum	Similar to Pullorum, affects all ages	Antibiotics, culling
Colibacillosis	E. coli	Respiratory distress, septicaemia	Sensitivity-based antibiotics
CRD	Mycoplasma gallisepticum	Rales, sneezing, nasal discharge	Tylosin, erythromycin
Infectious Coryza	Avibacterium paragallinarum	Swollen face, foul nasal discharge, egg drop	Sulphonamides, tetracyclines

---

Protozoal Diseases

Coccidiosis

• Severe upto 10 weeks of age, due to poor litter management, bloody droppings, high mortality, production performance is hampered.
• Coccidiosis is caused by protozoan parasites of the genus Eimeria that invade the intestinal lining. There are multiple species of Eimeria, each targeting different parts of the gut.

Key Eimeria Species in Poultry:

E. tenella is the most important species for exams — causes caecal coccidiosis with bloody caecal cores (blood-filled caeca) as the pathognomonic (definitive) lesion.

• Symptoms: Reddish (bloody) diarrhoea, huddling, stunted growth, crouching, dehydration, high mortality in young birds.
• The disease is closely linked to wet litter conditions, which promote the survival and sporulation of oocysts (the infective stage of the parasite).
• Treatment: Anticoccidial drugs (amprolium, salinomycin, sulfonamides) in feed or water.
• Prevention: Maintaining dry, clean litter and using coccidiostats in feed are the primary control strategies. Coccidiosis vaccines are also available.
• Wire-floored cages prevent coccidiosis because birds have no contact with droppings on the floor — oocysts in faeces cannot be re-ingested to complete the lifecycle.

---

Fungal Diseases

Aspergillosis (Brooder Pneumonia)

• Caused by the fungus Aspergillus fumigatus.
• Primarily affects young chicks (hence called brooder pneumonia).
• Symptoms: Gasping, respiratory distress, plaques in lungs and air sacs.
• Transmission: Inhalation of fungal spores from mouldy litter, feed, or hatchery contamination.
• Treatment: No effective treatment. Remove mouldy litter and feed. Improve ventilation.
• Prevention: Use clean, dry litter. Avoid mouldy feed. Proper hatchery sanitation.

Moniliasis (Candidiasis / Thrush)

• Caused by the yeast Candida albicans.
• Affects the crop and upper digestive tract.
• Symptoms: White, curd-like patches in crop and mouth; poor growth.
• Treatment: Nystatin or copper sulphate in drinking water.

---

Parasitic Diseases

External Parasites

• Lice, Mites, Ticks, and Fleas suck blood from the bird causing irritation, blood loss, anaemia, and reduced productivity.
• Control: Regular delicing using approved insecticidal dusts or sprays. Maintain hygiene in poultry house.

Internal Parasites

• Roundworms and Tapeworms cause weight loss, poor feed conversion, and reduced egg production.
• Treatment: Deworming with piperazine compound at intervals of 45 days.
• Deworming against tapeworms is done only on absolute necessity.

---

Nutritional Disorders

Nutritional disorders arise when birds do not receive adequate amounts of essential vitamins and minerals in their diet. These are preventable through proper feed formulation and management.

Vitamin Deficiency Disorders

• Vitamin A Deficiency: Nutritional Roup / Xerophthalmia

  • Vitamin A is essential for maintaining epithelial integrity (mucous membranes of the respiratory and digestive tracts). Deficiency leads to white pustule-like deposits in the mouth and throat (resembling wet pox — important distinction), nasal discharge, watery eyes, and increased susceptibility to respiratory infections.
  • Xerophthalmia = dry eye condition from corneal damage. Night blindness also occurs.
  • Note: Do NOT confuse Vitamin A deficiency mouth lesions with Wet Fowl Pox — Vit A lesions are smaller, more diffuse, and lack the raised wart-like base.

• Vitamin E Deficiency: Encephalomalacia

  • Crazy chick disease. The name Crazy Chick Disease describes the neurological symptoms seen in affected birds.
  • It causes paralysis of leg, retraction of head, convulsions, death. Encephalomalacia literally means “softening of the brain” and occurs due to oxidative damage to brain tissue in the absence of Vitamin E, which serves as a powerful antioxidant.
  • Provide vegetable oils, synthetic Vit E etc to the birds.

• Vitamin B2 (Riboflavin) Deficiency: Curled toe paralysis
  • Tendency to walk on hocks, dermatitis on corners of mouth, vent and foot pads. Affected chicks walk on their hocks (ankle joints) with toes curled inward because the peripheral nerves degenerate without adequate riboflavin.
  • Provide fish products, Vit B2, rice bran.
• Vitamin D Deficiency: Rickets. Rickets causes softening and deformation of bones in growing chicks due to impaired calcium and phosphorus metabolism. In poultry, specifically Vitamin D₃ (cholecalciferol) is required — D₂ (ergocalciferol) is far less effective for birds. Birds kept indoors without exposure to sunlight are particularly at risk. Also causes rubbery beak, thin-shelled eggs.

Mineral Deficiency Disorders

• Manganese (Mn) Deficiency: Perosis (Slipped Tendon Disease). Perosis is caused by a deficiency of manganese (Mn). It results in the displacement of the gastrocnemius (Achilles) tendon from its condyles, causing the hock joint to become swollen, twisted, and bent at an abnormal angle — the bird cannot walk properly. Choline and biotin deficiency can also contribute. Perosis literally means “maimed” or “crippled”.
• Zinc (Zn) Deficiency: Parakeratosis. Parakeratosis is caused by zinc (Zn) deficiency and is characterised by thickening and crusting of the skin, especially on the feet and around the beak.

---

Summary Cheat Sheet

Poultry diseases span six categories: viral, bacterial, protozoal, fungal, parasitic, and nutritional. The most exam-critical diseases are Ranikhet (Newcastle disease) caused by APMV-1, Marek’s disease caused by Herpesvirus, IBD (Gumboro) targeting the Bursa of Fabricius, and Avian Influenza (Bird Flu) caused by Influenza A virus subtypes H5N1/H5N8/H9N2. Key vaccines include LaSota/F1 and R2B for Ranikhet, HVT or bivalent HVT+SB1 for Marek’s, and live Gumboro vaccine for IBD. HPAI is an OIE List A notifiable disease controlled by stamping out; no licensed vaccine exists in India. Nutritional disorders like Perosis (Mn deficiency) and Curled Toe Paralysis (Vit B2 deficiency) are frequently asked in IBPS AFO and NABARD exams.

Quick Revision: Disease vs Causative Organism

References & Sources

1

G.C. Banerjee: A Textbook of Animal HusbandryBook