Ветеринарно-санитарная экспертиза английский язык. Учебное пособие

Transmission: It is spread by airborne infection involving follicle cells called chicken dander. Transmission of the virus is horizontal. At room temperature the virus of Marek's disease remains viable for 16 weeks and in litter for 6 weeks. Birds are most susceptible to the infection during the first few weeks of life. Infected birds will start to shed the virus in the second or third week after infection and will continue to do so throughout their life, although they do develop antibodies against the virus.

Marek's disease is commonly associated with coccidiosis in the field. This is probably due to lack of immunity against coccidiosis in birds affected with Marek's. There are 6 types of Marek's disease.

1.Peracute in 3–5 weeks old chicks; manifested with sudden

death

2.Anaemia in 3–6 weeks old chicken

3.Classical Marek's disease (range paralysis) showing paralysis of two wings and legs due to peripheral nerve involvement. The nerves are 2–3 times their normal size. Central nerve involvement may also occur.

4.Acute Marek's disease occurs mainly in 6–12 weeks old birds. It is manifested with tumours in the liver, spleen, kidneys, brain, spinal cord and dorsal root ganglia and with sudden death. The heart, lungs, gonads and muscles may also be involved.

5.Skin leucosis. Noted in broiler chicken on postmortem examination in abattoirs as enlargement of feather follicles and associated lymphoid infiltrations.

6.Transient paralysis in 12–18 weeks old pullets become paralysed and may recover with 24 hours if moved to a quiet place.

Postmortem findings:

1.Skin neoplasia

2.Enlarged spleen

3.Diffuse proliferation of white pulp

Judgement: Carcass of a chicken affected with Marek's disease is condemned in the extensive cutaneous form and in the visceral form. Localized skin lesions require the condemnation of the affected portions, the rest of the carcass may be approved. The condemned material may be used for animal food.

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Differential diagnosis (for skin lesions): Lymphoid leucosis, erythema, dermatitis, pigmentation and normal large follicles. If the central nervous system is affected the lesions of Marek's disease should be distinguished from those of Newcastle disease and of avian encephalomyelitis. In immunized birds for Marek's disease, the inflammation of the feather follicles (folliculitis) may be caused by the Marek's disease virus. In both cases follicular enlargement is noted; however, the lesion may differ in colour. In immunized birds the lesions of folliculitis are yellowish-white, whereas with the Marek's virus, lesions are blue-grey in colour with a pinkish appearance due to petechial haemorrhage.

Ornithosis (Psittacosis, Avian chlamydiosis)

Ornithosis is an acute or chronic disease of turkeys, ducks, chicken, pheasants and pigeons. It is caused by Chlamydia psittaci. In psittacine birds such as parrots, parakeets, cockatoos, macaws etc. and humans, this disease is called psittacosis.

Transmission: Wild carrier birds and cage birds transmit Chlamydia to their nestling which may survive and become carriers. Carrier birds shed Chlamydia in their secretions and excretions. Chlamydia present in faecal dust may be inhaled or ingested. Pigeons are suspected of being disseminators of infection.

Antemortem findings:

1.Mild cases may be unobserved or show mild respiratory signs and diarrhoea

In turkeys

2.Depression and weakness

3.Reduced weight

4.Nasal discharge

5.Green yellow diarrhoea

6.Watery diarrhoea in ducks, geese

In pigeons

7.Unilateral or bilateral conjunctivitis

8.Depression and loss of appetite

9.Abnormal respiratory sounds (rales) and watery diarrhoea

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Postmortem findings:

1.Inflammation of the lungs, airsacs, liver, heart, spleen, kidneys and peritoneum

In turkeys

2.Wasting

3.Vascular congestion

4.Fibrinous inflammation of pericardium, airsacs, lungs

5.Congestion of the lungs and an enlarged congested spleen

In pigeons

6.Swollen eyelids and conjunctivitis

7.In cage birds enlarged spleen and liver, inflammation of the airsacs and pericardium and intestinal congestion.

Judgement: If the disease is suspected on antemortem, birds are treated as suspects and samples should be shipped to the Laboratory. All reasonable precautions should be taken to avoid risk of human contact. If the disease is suspected on postmortem, delayed slaughter of the birds from the same source should be required. Samples are also forwarded to the diagnostic laboratory. Positive laboratory finding necessitate condemnation of the bird or carcass. If the disease is not confirmed the carcass may be approved if otherwise wholesome.

Differential diagnosis: Mycoplasma gallisepticum infection, pasteurellosis, salmonellosis (pullorum disease; bacillary white diarrhoea(BWD)).

III. Text 3

SPECIFIC DISEASES OF POULTRY

DISEASES CAUSED BY BACTERIA

Salmonellosis

Salmonellosis is responsible for significant losses to the poultry industry. Salmonella infections in this Manual include pullorum disease, fowl typhoid, arizona infection and paratyphoid. Pullorum

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disease occurs in chicken and turkeys and is caused by Salmonella pullorum. The greatest losses are in chicken less than 4 weeks old.

Antemortem findings (in young chicks):

1.Anorexia

2.Diarrhoea

3.Pasting of vent

4.Stunted, unthrifty

5.Poor feathering

6.Pale shrunken comb and wattles

Postmortem findings:

1.Multiple grey nodules in the heart, lungs, liver, spleen,

peritoneum, the gizzard, intestine and pancreas of a poult

2. Abnormal ovary showing discoloured follicles in an adult

bird

3.Rarely peritonitis, ascites or oviduct impaction

4.Swelling of the tibiotarsal joint

Judgement: Carcass and viscera affected with pullorum disease are condemned.

Differential diagnosis: Liver and heart lesions should be differentiated from infections due to other salmonellae and from campylobacteriosis, colibacillosis and omphalitis. Nervous lesions should be distinguished from nervous signs observed in Newcastle disease. Respiratory tract lesions should be differentiated from aspergillosis and joint lesions with synovitis and bursitis caused by other bacteria or viruses.

Fowl typhoid

Fowl typhoid is an infectious disease in chicken and turkeys and rarely in other poultry, game birds and wild birds. The causative agent is Salmonella gallinarum. It is seen more often in adult birds. Antemortem signs of fowl typhoid and pullorum disease are similar in birds.

Postmortem findings:

1.Enlarged, bronzed liver and enlarged spleen in a turkey

2.Enlarged kidneys

3.Pale cadaver

4.Inflammation of the anterior part of the intestine

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Judgement: Carcass and viscera affected with fowl typhoid are condemned.

Differential diagnosis: see pullorum disease

Paratyphoid infection

Paratyphoid infection is an acute and chronic infection of poultry and mammals. Ten to twelve species of Salmonella are associated with most outbreaks in poults. The most commonly involved is S. typhimurium in birds less than one month old.

Antemortem findings:

1.Drooping wings

2.Shivering and huddling near a heat source

3.Muscular incoordination and trembling

Postmortem findings:

1.Nodular lesions in the pancreas

2.Button type lesion in the intestine

3.Enteritis

4.Dehydration

5.Unabsorbed yolk material and omphalitis

6.Less frequent are joint infections

7.Blindness

8.Swollen eyelids

Judgement: Carcass and viscera affected with paratyphoid infection are condemned.

Differential diagnosis: see pullorum disease

Arizona infection (Arizoonosis, Paracolon infection)

Arizoonosis occurs in young turkey poults. It is caused by Arizona hinshawii (Syn. Salmonella arizona). Arizona infection is egg transmitted.

Antemortem findings:

1.Listlessness and trembling

2.Pasting of vent area with faeces

3.Huddling near a light source

4.Twisted head and neck

5.Cloudiness and enlargement of the eye causing blindness Antemortem findings: Antemortem findings in young birds

are similar to those of paratyphoid.

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Postmortem findings:

1.Enlarged yellow liver

2.Congestion of the duodenum

3.Unabsorbed yolk material

4.Cheesy plugs in the intestine or caecum

5.Inflammation of the oviduct and peritoneum

6.Eye lesions

7.Purulent exudate in the brain

Judgement: Carcass and viscera affected with arizoonosis are condemned.

Differential diagnosis: The causative organism must be isolated and identified for differentiation from salmonellosis.

Fowl cholera (Pasteurellosis)

Fowl cholera is an infectious disease affecting almost all classes of fowl and other poultry. The disease is more prevalent in turkeys than in chicken. It occurs more frequently in stressed birds associated with parasitism, malnutrition, poor sanitation and other conditions. Fowl cholera is caused by Pasteurella multocida. This organism is easily destroyed by sunlight, heat, drying and most of the disinfectants. However, it will survive several days of storage or transportation in a humid environment. It persists for months in decaying carcasses and in moist soil. The agent is frequently carried in the oral cavity of wild and domestic animals.

Transmission: If birds are bitten by infected animals such as rodents and carnivores, the disease could be disseminated in the flock. Contaminated feed, water, soil and equipment are also considered as potential factors in the spreading of the disease.

Antemortem findings: Acute septicemic form

1.High morbidity and mortality and sudden death

2.Dead birds may be found on dropping boards or in nests.

3.Depressed, cyanotic and loss of appetite

4.Nasal and oral discharge

5.Greenish diarrhoea

6.The comb may be swollen and discoloured.

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7.Emaciated Chronic fowl cholera

8.Swelling of wattles, sinuses, joints, foot pad and tendon

sheaths

9.Cheesy exudate in the conjunctival sac

10.Twisting of the head and neck may be observed in some

birds.

11.Middle ear infection is rare but occurs when the bacterial agent reaches the middle ear through the nasal cavity.

12.The bird may lose its sense of balance with the head and neck twisted to one side.

13.If both ears are infected, the bird's head and neck are pulled back over the body and between the legs.

Postmortem findings: In the very acute stages, lesions may be lacking.

1. Caseous exudate in wattles, sinuses, the nasal turbinates, middle ear, joints or tendon sheaths.

2. Petechial and ecchymotic haemorrhages on the heart, serous and mucous membranes, on the gizzard and abdominal fat.

3. The liver is swollen and is streaked with white areas and associated small grey areas of necrosis (corn meal liver).

4. Free yolk in the peritoneal cavity in breeder hens and layers. 5. Acute oophoritis and peritonitis are often seen.

6. The lining of the upper intestine is reddened and gut content is slimy.

In chronic cases

7. Darkened breast muscle is frequently noted and haemorrhagic lesions are often missing.

Judgement: Localized lesions of pasteurellosis such as infection of wattles, joints or tendon sheaths require the condemnation of the affected parts; the rest of the carcass is approved. Septicemic carcasses should be condemned.

Differential diagnosis: Acute colibacillosis and erysipelas in turkeys, salmonellosis, tuberculosis, listeriosis. Pasteurellosis is differentiated from septicemic and viremic diseases by culture of P. multocida. Closely related bacteria such as S. gallinarum, P.

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haemolytica and others may cause a cholera like disease or they may complicate other diseases.

Public health significance: Fowl cholera, although known for 200 years is still a poorly controlled disease in birds. Humans may become infected with this disease, and then they may also infect poultry with exudates from the nose and mouth.

Tuberculosis

Tuberculosis is a chronic granulomatous disease of poultry caused by Mycobacterium avium. It is usually found in older chicken which are kept beyond the laying season. Other poultry are also affected.

Antemortem findings:

1.Depressed and progressive loss of weight leading to emaciation

2.Pale skin of the face, wattles and comb

3.Dull, ruffled feathers

4.Diarrhoea

5.Unilateral lameness

Postmortem findings:

1.Irregular greyish yellow or greyish white nodules of different sizes in the liver, spleen, and intestine

2.In advanced cases, TB nodules are found in the bone marrow.

3.Lesions are rarely found in the heart, ovaries, testes and

skin.

4.TB lesions on organ surfaces are easy enucleated from the surrounding tissue. Mineralization is not present in the lesions.

Judgement: A carcass affected with tuberculosis is condemned.

Differential diagnosis (on postmortem): Aspergillosis, typhoid and paratyphoid, salmonellosis, fowl cholera, campylobacter, colibacillosis, chlamydiosis, histomoniasis and neoplasm. In neoplasm, the cut surface of the lesion is uniform and without necrosis.

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“Air sac disease” and Chronic Respiratory Disease (CRD)

The term “Air sac disease” usually refers to a respiratory syndrome characterized by airsacculitis, perihepatitis and pericarditis in broiler chickens between 4 – 8 weeks of age. Pneumonia is also frequently present. Primary factors associated with the etiology of air sac disease are poor air quality and dust, associated with either viral or mycoplasmal agents. E. coli is usually a secondary invader.

Chronic respiratory disease (CRD) refers to respiratory infection of the upper respiratory tract of chicken caused by Mycoplasma gallisepticum. This agent affects turkeys more severely and causes infectious sinusitis.

Postmortem findings: Postmortem examination of affected chicken reveals inflammation of trachea and frothy exudate in the air sacs. With presence of secondary invaders, inflamed airsacs have a opaque appearance in the early stages of infection. In the later stages airsacs are thickened and caseous yellow exudate is usually present. Yellow fibrinous deposits on the pericardium (pericarditis) and liver (perihepatitis) are also observed.

Judgement: In poultry inspection, it is of great importance to differentiate between the inflammation of the air sacs (airsacculitis) and peritonitis, as well as pathologic changes in the air sacs and bones. The communication of some air sacs and bones has to be observed during the judgement of carcasses with airsacculitis and bone diseases. Birds affected with airsacculitis are treated as suspects on antemortem examination. On postmortem examination affected parts with localized lesions are condemned and the rest of the carcass is approved if in good condition and no spread of infection into bones is noted. The rational for approving a carcass in good condition with localized lesions of airsacculitis may be supported with frequent negative findings of microorganisms in these lesions. Since an accumulation of the fluid in the airsacs and associated opacity may be early signs of infection, the other birds in the flock must also be examined. Sufficient evidence must be obtained in that these lesions would remain localized. Otherwise the carcass must be condemned. Generalized and extensive lesions of

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airsacculitis require total condemnation of the carcass. If pericarditis or perihepatitis are the only lesions present on postmortem the carcass may be approved if otherwise wholesome.

IV. Text 4

SPECIFIC DISEASES OF POULTRY

PARASITIC DISEASES

Diseases caused by protozoa

Histomoniasis (Enterohepatitis or Blackhead)

Histomoniasis is a protozoal disease of turkeys, chicken and game birds. It often occurs in turkeys run with or after chicken. It is caused by Histomonas meleagridis which is transmitted in the ova of caecal worms (Heterakis gallinarum) and by earth worms. Well developed hepatic and caecal lesions are pathognomonic for histomoniasis.

Antemortem findings:

1.In young turkeys, mortality and morbidity may reach 100 %.

2.Indifference and loss of appetite

3.Depression, drooping wings and closed eyes

4.Cyanotic (black) head

5.Yellow sulphur coloured faeces

6.Blood in faeces

7.Emaciation in older birds

Postmortem findings:

1.The ceca are characterized with a thickened wall, ulcerated mucosa and caseous exudate.

2.If the caecal wall becomes perforated, inflammation of the peritoneum is observed.

3.The liver lesions consist of circular yellow necrotic tissue surrounded with white rings.

On microscopy, histomonas are found in the caecal wall or in the liver lesion.

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