Poultry diseases and treatment
Dr. Mujeeb Ather Asst. Director (Pathologist)
Reoviruses, which in the past were considered to be harmless, have emerged to induce various manifestations in chickens. Economic losses caused by reovirus infections are frequently the result of crippling (viral arthritis) and a general lack of performance including diminished weight gain, poor feed conversion and a reduced marketability of affected birds.
Syndromes which have been reproduced in avian reoviruses include tenosynovitis, infectious stunting and runting syndrome, respiratory disease and enteric disease.
Tenosynovitis is a common and widespread condition of broilers and broilers in many countries.
Viral arthritis is usually seen in young birds 4 to 7 weeks old but may be seen in much older chicken as well. Morbidity can be as high as 100% while mortality is generally less than 6%.
The incubation period differs depending upon virus pathotype, age of host and route of exposure. For inoculated 2 week old chickens the IP varied from 1 day (foot pad inoculation) to 11 days (intramuscular, intravenous, intrusions inoculation). The incubation period following intra tracheal inoculation and contact exposure was 9 and 13 days respectively. Often, infections are inapparent and demonstrable only by serology or virus isolations.
The symptoms of serious lameness in the birds coupled with poor growth rates and poor feed conversion efficiency. With chronic infection, lameness is more pronounced and in a small percentage of infected chickens the swollen giving the shanks a very larged appearance i.e. swelling of hock joints.
Swelling of digital flexor and metatarsal extensor tendons. The later lesion is evident by palpation just above the hock and may be readily observed when feathers are removed. The hock usually contains a small amount of straw coloured or blood tinted exudate, in a few cases there is a considerable amount of purulent exudate resembling that seen with infections synovitis.
Early in the infection there is marked odema of the tarsal and metatarsal tendon sheaths.
It was characterized by a small percentage of the flock (1 to 5%) becoming severely stunted and a variable proportion of the remainder (10 to 50%) growing poorly. The affected birds were not ill, they were active with voracious appetites. Financial loss was considerable due to excess cull rates, poor feed conversion, reduced weight for age and greater than expected variation in weight at slaughter.
The term stunting highlighted the poor growth of affected chickens where as severely stunted chickens which do not grow when given plenty of good feed often were described as "rented"
All breeds and strains of chickens are susceptible but growth rate suppression is most obvious in broilers because of their rapid growth rates. Some farms are more often and more severely affected than others and some broiler houses are more often affected than adjacent houses indicating a significant role for environmental and / or management factors.
Signs and pathology
The disease is characterized by severe stunting of chicks arising very soon after they go into the broiler house it is usually first noticeable at about ten days of age.
The syndrome may affect anything from 5%to 40% of the flock and by the killing age the affected birds will weight about half their normal weight, between 6and 8 days, the stunted chickens are 20to 40 gms lighter than normal birds in the same flock.
There is occasionally a short period of very subtle signs of illness in the first week such as ruffled feathers, reluctance to move, eating of faeces and mucoid diarrhoea with pasting of faces around the cloaca. After 1 week of age the stunted chickens are characterized by with pendulous abdomen. At this stage they eat well and are very active.
One of the features of ISS is the presence of severely stunted (runted) chickens, which remains small despite their voracious appetite.
These small chickens became more noticeable after 2 weeks when the unaffected chickens grow rapidly. The affected flocks have poor feed conversion, the small chicks are active development of primary feathers is delayed and irregular.
Intestines are pale and dilated and contain undigested feed, enlarged proventriculus, which may be haemorrhagic or necrotic and catarrhal enteritis.
In addition there may be an apparent lameness associated with arthritis and osteoporosis with femoral head disintegration.
Prevention and ControlReovirus vaccination of breeding stock can be done with viable or inactivated vaccines or combinations of both.