Disease

1. DISEASES OF POULTRY

FOWL PEST OR NEWCASTLE DISEASE

This is an acute, highly infectious disease with a mortality rate of up to 100%. It causes a large drop in egg production in laying flocks, and delays maturity in broiler flocks. The disease spreads rapidly throughout a flock by birds coughing or sneezing infected droplets, and the virus can be spread through contaminated food, eggs or the clothing of workers.

The incubation period is 5 days and is followed by dullness, coughing, sneezing and gasping by the birds. All birds in a flock will contract the disease, and mortality is often 50% but higher in baby chicks. There is no treatment for the disease and some countries follow a policy of slaughtering all infected birds together with their contacts. Control can be achieved by a combination of good hygiene and immunity by vaccination. Laying flocks must be vaccinated at least twice a year, while broilers can be vaccinated once. Two types of vaccine are used, dead and live, the dead vaccine being easier to handle. Using the dead vaccine, young chicks are vaccinated at 10 – 14 days old and again 2 – 3 months later, and this should be done as a routine in all poultry units.

Young chicks hatched from eggs that have been laid by hens vaccinated against the disease have a natural immunity for 4 weeks; the chicks do not need to be vaccinated until they are 4 weeks old, but they must be done at this age.

Types of vaccine

There are several types of vaccines available, and the producer should consult his veterinarian to get the type most suited for his area. They can be administered as eye drops or by injection into the breast or wing.

The different types of the disease are listed below:

LENTOGENIC

Produces respiratory symptoms, loss of egg production but no mortality. Infection is 100% of the flock.

MESOGENIC

Produces respiratory and nervous symptoms with 30% mortality in the infected flock, and 100% infected birds.

VELOGENIC

Produces 95% mortality with no time to see any symptoms.

FOWL TYPHOID

With 80% mortality, this disease is caused by bacteria of the Salmonella group. Adult birds are most commonly affected, and infection is spread by droppings from infected birds, and those birds that have recovered can act as carriers for the disease. Incubation is 4 – 5 days, after which the birds become depressed, cease feeding and develop bright yellow diarrhoea; death can occur in 3 – 6 days. Treatment of the disease is to slaughter affected birds and treat the rest with the drug Furazolidone, at the rate of 0.04% in the mash for 10 days. The flock should be blood tested, any reactors slaughtered and their carcasses burnt as these are carriers of the infection. The flock should then be removed to a clean area of the farm, and the survivors can be vaccinated to prevent any further outbreaks.

Figure 1: Method of Vaccination

BACILLARY WHITE DIARRHOEA

(BWD) is a disease of baby chicks in which infection is transmitted via the hatching eggs. It is also caused by bacteria of the salmonella group. In the acute form, chicks die immediately after hatching and for a further 3 – 4 weeks with mortality being from 20 – 80%. If infection occurs after hatching, most deaths occur between 1 and 3 weeks of age. Birds which suffer from the disease and recover, become carriers. The white, chalky droppings which foul the vent feathers and which give the disease its name do not always occur. The disease can be treated with Furazolidone in the mash, but prevention can be by blood testing all birds over 5 months old every year in areas where the disease exists. All reactors should be slaughtered and burned. All incubators and other poultry equipment should be treated with a disinfectant as a routine measure.

FOWL CHOLERA

Is a highly infectious and fatal disease caused by Pasturella bacteria. Infection is from a carrier bird brought on to the farm, or it can be introduced by wild birds. The disease is spread by infected oral or nasal discharges contaminating food and water in the poultry house, and by contaminated droppings. In acute outbreaks there are no symptoms and birds are found lying dead. In less acute cases symptoms vary from depression, drowsiness, coughing, sneezing, diarrhoea (which can be green) purple wattles and combs, and a liquid discharge from the eyes. Treatment is not economical and affected birds should be slaughtered, burned and all houses and equipment disinfected. Prevention is by good management and hygiene, and any birds introduced onto the farm or poultry unit should be kept in isolation for a month. Birds can be vaccinated against the disease at 8 – 12 weeks old. Young birds and growing pullets should never be mixed with older laying stock.

FOWL POX

This is a virus disease which can affect birds of all ages and particularly those between 6 – 12 months old. The virus can be transmitted by ticks, lice, mosquitoes and other biting flies, and it is passed on by direct contact between birds. The virus enters the skin through small cuts and scratches, particularly on the head and wattles, and produces small, watery pustules on the head, comb and wattles and around the corners of the mouth. After a few days these pustules dry into a brown crust and run together to form large grey or brown wart-like growths. In another form of the disease, small white patches occur at the corners of the beak, on the sides of the tongue, on the roof of the mouth and the epiglottis. These patches spread and can cover the tongue and the sides of the mouth and throat. There is no treatment for the disease, but it can be prevented by vaccinating the growing birds at 4 – 5 months old, and at least 3 weeks before laying begins. In Southern Africa, the disease may appear at the start of the rainy season because of the increase in the activity of mosquitoes and midges.

MAREK’S DISEASE

This is caused by a virus, and occurs mostly in birds between 10 and 25 weeks old, and occasionally in older birds. Losses can be up to 40% in unvaccinated birds. Vaccinating day-old chicks gives good control.

INFECTIOUS BRONCHITIS

The viral disease causes a severe drop in egg production and quality. In layers, vaccination is with a live vaccine (H120), followed by inactivated oil-based vaccine. In broiders vaccination is by eye-drops to day old chicks.

INFECTIOUS LARYNGOTRACHEITIS

Caused by a virus, this disease gives breathing problems, a drop in egg production and up to 30% mortality. It occurs mainly in birds older than 6 weeks, but occasionally in young birds. Vaccination is by eye drops at 5 – 6 weeks of age, repeated at 16 weeks.

GUMBORO (INFECTIOUS BURSAL DISEASE)

Again, this is caused by a virus, at 3 – 6 weeks old. It results in up to 70% mortality in laying breeds and 25% in broilers. This disease is controlled by immunizing the breeder hens, which pass on immunity through the eggs to the chicks. In addition the chicks should be vaccinated at 14 days.

NECROTIC ENTERITIS

This is a bacterial disease that can lead to high mortality. It is controlled by the inclusion of antibiotics in the feed.

COCCIDIOSIS

This disease is caused by a protozoan parasite, a small parasite belonging to the same group of germs that cause malaria in man. The disease is spread by infected droppings which contain oocysts of the organism. These ripen in conditions of warmth and moisture within 48 hours. Birds eat the infected droppings and develop the disease. There are two types of the disease, the acute and chronic forms. The acute form, known as Caecal Coccidiosis usually occurs in young chicks during the first few weeks of life. The chronic form, Intestinal Coccidiosis, is more common in older birds. The two types are caused by different species of the parasite. Coccidia are found in a wide range of animals, but each type of coccidium is specific to a species. For example, the coccidium of the rabbit will not affect poultry.

Outbreaks of coccidiosis vary in severity from those in which only a few chicks are infected to those in which over 50% of the chicks die. In acute outbreaks, chicks may be found dead without any signs of illness. Generally, the first symptoms seen are the passing of dark-coloured or blood-stained droppings. The affected chicks appear to be listless, have a pale appearance about the head and comb, and ruffled feathers.

The disease can be prevented by not allowing chickens to have access to infected droppings. Battery rearing cages, houses with wire floors or range units prevent the disease occurring. In deep litter houses, the water and feed troughs should be raised above the floor to prevent the litter from becoming damp. Alternatively, there are a number of drugs available, called coccidiostats, which can be added to the drinking water. These can be used to prevent the disease, and, fed at higher levels, to treat infected birds. Good ventilation, good hygiene and thorough disinfecting of housing and equipment between batches of birds are also good preventative measures.

TABLE 1: VACCINATION PROGRAMME

PROPOSED VACCINATION PROGRAMME FOR LAYERS AND BROILERS

AGE	VACCINATION	TYPE OF VACCINE
Layers: Day old 19 days 14 days 5 weeks 8 weeks 10 weeks 12 weeks 14 weeks 16 weeks	Mareks Newcastle Gumboro vaccine ILT Newcastle Infectious Bronchitis Fowl cholera Fowl pox ILT Newcastle and IB	Turkey Herpes, FC 126 subcutaneously Close 30 eyedrop Mycofarm E-type ASL eyedrop La Sota spray H120 spray   Wing stab Spray Oil-based subcutaneously
Broilers: 12 days 24 days	Newcastle Newcastle	Hitchener B1 : Eyedrop La Sota : in water

PESTS OF POULTRY

The Fowl Tick or Tampan not only sucks the blood of fowls causing them to stop laying but also transmit a disease which causes diarrhea, paralysis and finally death. Poultry can build up certain immunity to ticks, but if clean birds are put into an infested house they will die within a few days. Ticks feed on the birds at night and during the day they sleep in cracks in the wood-work particularly the perches. All woodwork should be painted with carbolineum or creosote at frequent intervals. Good hygiene and thorough cleaning and disinfecting of houses between batches of birds should prevent ticks from becoming a problem and birds should be kept well away from older laying hens.

Creosote: a yellowish, brown oily substance with a characteristic smell, derived from wood tar and formerly used as a wood preservative.

Lice live on the birds and cause discomfort. When a bird cleans herself in a dust-bath she will throw off a lot of lice which die on the ground. However, birds infested with lice should be dusted with a proprietary powder which will kill off the lice and the perches and woodwork should be painted with creosote or carbolineum to kill any lice in the cracks.

Red Mite is a small grey organism which turns red when it fills with blood and which multiplies very rapidly. Treatment is the same as for fowl ticks.

Fleas breed very quickly particularly during wet weather or on damp floors, and infest the birds on the head and neck causing discomfort and reduced laying. Birds should be dusted with a suitable powder and the house cleaned and painted with creosote or carbolineum.

With all external parasites, prevention is better than cure. Houses must be cleaned out, disinfected and painted with lime wash on the walls and creosote on the woodwork. Houses that are enclosed can be sterilised by burning a suitable smoke ‘bomb’ in the house while it is empty. Once a house has been cleaned, it should be rested for as long as possible to kill off any parasites, which are left in the house without a host to feed on. Cleaning while birds are in the house is difficult, but all litter, straw from the nesting boxes etc. should be removed and burnt and replaced with fresh straw or shavings. If perches are painted with a 40% solution of nicotine sulphate, the fumes will rise during the night and kill any parasites on the birds. Sodium fluoride can be used to dust the birds, and if carbolineum is not available, paraffin oil can be painted on the perches and woodwork.

Poultry can suffer from a number of internal parasites, both round worms and tape worms. If hygiene and management are good they should not be a problem, but damp, dirty and poorly ventilated houses and malnutrition can lead to a rapid multiplication of parasites, causing the birds to become unthrifty causing a drop in egg production. Infested birds can suffer from diarrhea and anemia.

Prevention is by improved hygiene, frequent removal of droppings and soiled litter, using a separate rearing ground or house for young birds and always visiting the houses of young birds for feeding etc. before going to the houses of the older birds. Land that has become infested with parasites should be rested from poultry for at least 12 months.