Chicken diseases caused by viruses include New Castle Disease (NCD), Bird flu, Marek’s disease, Gumboro, and fowl pox. It is critical to ensure you vaccinate your flock against viral diseases that are endemic in your area. Bacterial diseases can be treated with antibiotics and some can be prevented with vaccination. Examples are fowl cholera, infectious coryza, mycoplasmosis, and fowl typhoid.
1. Infectious Coryza
This is one of the most common chicken diseases encountered by farmers as well as vets on the ground. The farmer will report signs of swollen face/eyes — one or both eyes. Sticky discharge from the eyes and nostrils is also noted. Other clinical signs that may be observed are diarrhoea and respiratory signs – rales (snoring) and nasal discharge. Spread of the disease is perpetuated by multiple-age flocks.
Caution should be observed when introducing a new flock of chickens to the farm. Birds that recover usually act as carriers and easily spread the disease to uninfected chickens. The “All-in/all-out” system is the ideal technique for preventing the disease. Birds of different ages should not be mixed together. Transmission is normally by direct bird-to-bird contact as well as contamination of feed and water. Proper hygiene and biosecurity should be implemented on the poultry farm. Treatment with water-soluble antibacterials can be used mainly erythromycin, tetracycline and sulfa drugs.
2. Marek’s disease
This is one of the most ubiquitous poultry viral diseases; occurring worldwide. It is a type of cancer that affects the nervous system of the chicken. Pheasants, quail and turkeys may occasionally be infected. The disease mostly affects birds older than three weeks with the highest cases reported in birds between 12 to 25 weeks of age. Symptoms include lameness and paralysis, unthriftiness and weight loss. Greenish diarrhoea may be observed in the terminal stages. Mortality usually exceeds 60 per cent if the flock is unvaccinated. The virus is shed through the feather dander and may survive for months in the poultry house litter or dust. Birds with clinical signs should be culled. Marek’s has no treatment. Chicks need to be vaccinated at the hatchery level. To be on the safe side, it is paramount to source chicks from reputable hatcheries that vaccinate day-old chicks against Marek’s disease.
Coccidiosis is caused by a protozoa that is universally present in poultry-raising establishments. The clinical disease occurs only after ingestion of large numbers of the infective organism by susceptible birds. Contaminated feeds, water and soil act as the routes of transmission to other chickens. Mechanical carriers such as equipment, human clothing and footwear help in the spread of the protozoa. Severe diarrhoea and high mortality are reported in grave cases of coccidiosis. Bloody droppings/diarrhoea is a common observation. Depression, decreased weight gain and dehydration may be witnessed in long-standing cases. It is worth noting that feed companies normally include anticoccidials when formulating poultry feeds. These are chemicals that are generally included in feeds and help prevent the acute disease as well as reduce losses associated with the infection. Once clinical signs are observed, water medication with drugs such as amprolium, sulfadimethoxine and trimethoprim can be used. Vitamin A and K should also be included to improve the rate of recovery as well as prevent secondary infections.
Cases of misdiagnosis usually occur when farmers or animal caregivers miss out on vital clinical signs when reporting a disease to a veterinary officer. With that reality, it is crucial for farmers to be as detailed as possible when reporting a disease occurrence on their farm. It is always advisable for the farmer to sacrifice one sick bird for postmortem purposes and in return save the rest of the birds with the correct diagnosis and consequent correct medication.