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Specific Diseases of Sheep and Goats

By goGreen | November 13, 2011
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Diseases caused by viruses

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Rift valley fever (RVF)

RVF is an acute viral disease of sheep, cattle, goats and humans. It is manifested with hepatitis and high mortality in young lambs and calves, and abortion in adult animals. Rift valley fever resembles influenza in humans. The disease is of significant importance in Africa.

Transmission : Biting insects and mosquitoes. Possible direct contact via cornea. Human infection occur by handling diseased tissues, and strict precautions should be instituted to prevent infection with this virus, such as wearing goggles and gloves.

Antemortem findings :

Sheep

  1. Incubation 12 – 48 hours in young animals
  2. High morbidity and mortality in lambs and calves
  3. Fever
  4. Lambs refuse to eat, have abdominal pain and are recumbent.
  5. Animals seek a shaded area because of photophobia (squinting and blinking)
  6. Photosensitization characterized with a thickened head and ears.
  7. Encrustation around the muzzle (Fig. 149)
  8. Vomiting in adult animals
  9. Congenital malformation of the brain and muscles
  10. Abortion in ewes during the illness or convalescence

Cattle

  1. Edematous unpigmented skin showing cracking and sloughing due to photosensitization
  2. Salivation and inflammation in the mouth
  3. Abdominal pain
  4. Diarrhoea associated with haemorrhagic inflammation of stomachs and intestine
  5. Lameness
  6. Cessation of milk production
  7. Abortion

Postmortem findings :

  1. Cyanotic visible mucosae
  2. Necrosis of the liver in lambs (liver may be mottled grey, or reddish-brown to bright yellow in colour)
  3. Edematous and haemorrhagic gall bladder
  4. Haemorrhage of the gastrointestinal tract, serosae, internal organs and lymph nodes
  5. Partial erosions may be seen in the ileum, caecum and colon
  6. Udder is purple but inflammation is not observed
  7. Haemorrhages in the fetus and haemothorax (Fig. 150)

Judgement : Carcass of an animal showing clinical signs of Rift Valley fever is condemned. Reactors and recovered animals areapproved. Affected parts of the carcass, liver and the blood must be condemned.

Differential diagnosis : Defect in porphyrin metabolism, fungal conditions, acute viremias/toxaemias including enterotoxaemia, bluetongue, bovine ephemeral fever, Wesselbron disease, rinderpest, heartwater, East Coast fever; abortions caused by Brucella, Vibrio, Trichomonas, Nairobi sheep disease and ovine enzootic abortion

fig 149

Fig. 149: RVE. Encrustation around the muzzle.

fig 150

Fig. 150: RVF. Haemorrhages in the fetus and haemothorax.

Contagious ecthyma (contagious pustular dermatitis, orf)

A highly infectious pox virus disease of sheep and goats manifested by the occurrence of the pustular and scabby lesions on the lips, muzzle and udder.

Transmission : Direct contact between animals. Indirect contact with dry scabs in pens. The virus is resistant to drying and may be viable in scabs for months and years in empty feedlots and pens. Farm workers may disseminate the virus among animals of different pens with contaminated equipment, feed and farm vehicles.

Antemortem findings :

  1. Incubation: 2 – 3 days
  2. Pustular and scabby lesions on the muzzle (Fig. 151), lips and eyes.
  3. Lesions on the udder and teats and the coronary band
  4. The invasion of lesions by larvae of the screw worm fly and secondary bacterial ection with Fusobacterium necrophorum
  5. Lambs and kids are unable to suckle or graze due to lip lesions.
  6. Uncomplicated cases may heal within one month.
  7. Emaciation
  8. Pneumonia in feeder lambs

Postmortem findings :

  1. Pustular and scabby lesions on the head, udder and feet
  2. Ulcerative lesions in the nasal cavity and erosions in the mucosa of the oesophagus and upper respiratory tract.
  3. Inflammation of the reticulum, omasum and intestine
  4. Necrotic lesions in the lungs, pleura and liver

Judgement : The carcass is condemned if the disease is accompanied with inflammation of the stomachs and intestines, and with bronchopneumonia. Otherwise, it is approved.

Differential diagnosis : Bluetongue, sheep and goat pox, ulcerative dermatosis, cutaneous anthrax and vesicular diseases

fig 151

Fig. 151: Contagious ecthyma. Close up view of a proliferative muzzle lesion.

Bluetongue (BT, catarrhal fever of sheep, “soremuzzle disease”)

Bluetongue is a highly contagious viral disease of sheep, manifested by fever, oral lesions, lameness and emaciation. The disease occurs mostly in the African region, but also in Asia and the Pacific and in the Western hemisphere, but can be well controlled by vaccination.

Transmission : Biting insects, especially Culicoides gnats and mosquitoes. Vertical transmission occurs in utero. Semen of infected bulls and mechanical transfer of infected blood by needles.

Antemortem findings :

In sheep:

  1. Incubation 6 – 8 days
  2. Fever
  3. Difficult breathing
  4. Excessive salivation
  5. Loss of appetite, weakness and emaciation
  6. Reluctance to move
  7. Mucopurulent to bloody nasal discharge (Fig. 152)
  8. Edema of the face, lips and jaw
  9. Cyanosis of the tongue and mucous membranes (bluetongue) with erosion and sloughing of the oral mucosa (Fig. 153)
  10. Lameness associated with sore feet caused by the inflammation of the coronary band (Fig. 154)
  11. Abortion and deformed lambs

In cattle, the disease resembles the infection in sheep and the clinical signs are from unapparent to mild.

Postmortem findings :

  1. Vesicles or ulcers in the mouth
  2. Generalized edema and haemorrhage of subcutaneous tissue and musculature
  3. Excessive mucus in the trachea
  4. Congestion of lungs
  5. Generalized lymphadenitis
  6. Enlarged spleen
  7. Necrosis of the heart and skeletal muscles

Judgement : Carcass of an animal affected with bluetongue is condemned when the clinical signs of an acute disease are associated with generalized postmortem lesions. The reactor animals are approved.

Differential diagnosis :

Sheep: Photosensitization, contagious ecthyma, sheep pox, polyarthritis, footrot, foot abscesses, laminitis, vesicular stomatitis, white muscle disease, muscular dystrophy in lambs, lungworm infestation and pneumonia.

Bovine: Bovine viral diarrhoea, malignant catarrhal fever, infectious bovine rhinotracheitis, stomatitis, laminitis and Ibaraki disease, FMD.

fig 152

Fig. 152 : Blue tongue. Mucopurulent to bloody nasal discharge.

fig 153

Fig. 153 : Blue tongue. Intense congestion and swelling of lips and gums and sloughing of the dental pad mucosa.

fig 154

Fig. 154 : Blue tongue. Close-up view of a lesion on the coronary band of a sheep.

Sheep and goat pox

Sheep and goat pox is a contagious viral disease of sheep and goats manifested by papular and pustular eruptions on the skin and in generalized conditions with haemorrhagic inflammation of the respiratory tract.

Transmission : Direct contact with infected animals, aerosols of nasal secretions and saliva and dried scabs. Indirectly by fomites and transportation vehicles.

Antemortem findings :

  1. Incubation 6 – 8 days
  2. Fever
  3. Laboured breathing
  4. Depression
  5. Lacrimation and salivation
  6. Lesions on the muzzle and lips (Fig. 155)
  7. Skin lesions may vary from macules, papules, vesicles, pustules to pocks and scabs.
  8. Necrosis and coalescing of the lesions and loss of wool (Fig. 156)
  9. Clinical signs of goat pox are less severe than in sheep pox. The benign form of sheep pox is commonly found in adult sheep and the malignant form in lambs.

Postmortem findings :

  1. Reddish to whitish firm nodules in the mucosa of the pharynx and trachea
  2. Reddish to whitish nodules in the lungs (Fig. 157). Rarely pneumonia
  3. In malignant form: inflammation of the respiratory and digestive tract

Judgement : Carcass of an animal showing the clinical disease without secondary complications is conditionally approvedpending heat treatment. The recovered animals are approved. The carcass is condemned if the acute febrile or pustular stage of the disease is associated with secondary bacterial infections or if the carcass is inadequately bled. If bacteriological examination showed negative results, this carcass may be conditionally approved pending heat treatment.

Differential diagnosis : Contagious ecthyma, scabies, eczema. ulcerative dermatitis and peste des petits ruminants.

fig 155

Fig. 155: Sheep pox. Lesions on the muzzle and lips.

fig 156

Fig. 156: Sheep pox. Necrosis and coalescing of the lesions and loss of wool.

fig 157

Fig. 157: Sheep pox. Reddish to whitish nodules in the lungs.

Scrapie

Scrapie is a chronic disease of the central nervous system in sheep and occasionally goats characterized by itching, nervous signs and a long incubation period. It is caused by a viral agent called “viroid” or “prion”, which has some of the characteristics of the virus, a “slow” virus like BSE and Maedi.

Transmission : Most likely, the organism enters through breaks in the skin and mucous membranes of susceptible sheep. The agent is present in the lymph nodes, spleen, spinal cord and brain of infected sheep. It is transmitted from sick animals to healthy animals through pasture, where it may be infective for over 3 years. Vertical transmission from the dam and possibly the sire in sheep may also occur. The disease may be transmitted by inoculation of infective material. The agent is resistant to rapid freezing, thawing, boiling for 30 minutes and even to a 20 % formalin solution. At temperatures of 0 – 4°C, the prion is still active after two years. Oscillation of the temperature from 37– 70°C does not affect its infectivity. At temperatures of 94–98°C, the prion is still resistant for 24 hours.

Antemortem findings :

  1. Dry wool and rough skin
  2. Loss of wool from the head down over the side of the face, rump, thigh, tail base and abdomen
  3. Changes of behaviour. Charging of fences, dogs etc.
  4. Biting of legs, flanks and belly because of severe itchiness (pruritus)
  5. Smacking and rarely curling of the lips and wagging of the tail during rubbing of the skin over the back and sacrum
  6. Grinding the teeth
  7. Twitching of muscles, excitability and wild expression of the eyes
  8. Restless animal, continuously laying down and getting up
  9. Incoordinated gait, tendency to run and fall down.
  10. Convulsions

Postmortem findings :

  1. No gross lesions observed
  2. Microscopy reveals the presence of large vacuoles in the cytoplasm of neurons; this is considered a diagnostic lesion.

Judgement : Carcass and viscera affected with the clinical disease are condemned. Carcass of contact animals, offspring and ancestors may have a limited distribution or it may be condemned if economically feasible.

Differential diagnosis : Pseudorabies, scabies, thallium poisoning, cobalt deficiency, louping ill, pregnancy toxaemia, external parasitism and photosensitive dermatitis

fig 158

Fig. 158: Scrapie. Incoordinated gait, twitching of muscles and wild expression in the eyes.

Pulmonary adenomatosis (Jaagsiekte, Driving sickness)

Pulmonary adenomatosis is a chronic progressive pneumonia of sheep with the development of a primary lung neoplasm. This neoplasm is carcinomatous and infrequently metastatic to regional lymph nodes. A retrovirus causes the disease and a herpesvirus acts in a secondary role. This is a disease of old ewes, more then 4 years of age. Lambs and yearling are rarely affected.

Transmission : The disease is experimentally transmitted by inhalation of infected droplets by sheep that are kept in close contact. Vertical transmission from pregnant ewes to fetus has also been demonstrated.

Antemortem findings :

  1. Incubation 2 months to 2 years
  2. Difficult breathing and lacrimation
  3. Loss of weight and emaciation
  4. When the rear of a sheep is lifted, excess fluid will run from the nose (wheel barrow test).
  5. Emaciation and lacrimation

Postmortem findings :

  1. The lungs are increased in size and weight (as much as triple their normal size) and do not collapse when the thoracic cavity is opened (Fig. 159).
  2. Bluish grey consolidation of the ventral part of the lung
  3. Secondary bacterial infections in the lungs
  4. Focal lung lesions are interspersed with areas of emphysema.
  5. Metastasis of the neoplasm into the bronchial and mediastinal lymph nodes may occur infrequently.

Judgement : Carcass judgement depends on the extent of lung involvement, condition of the carcass and secondary bacterial infection. Extensive lung lesions with metastasis and loss of musculature would necessitate the condemnation of the carcass.

Differential diagnosis : Verminous pneumonia, Maedi/Visna, caseous lymphadenitis and other debilitating diseases

fig 159

Fig. 159: Pulmonary adenomatosis. Lung lesions showing light grey, enlarged apical and cardiac lobes consisting of numerous greyish coalescing nodules (1 mm to 1 cm in diameter).

Ovine progressive interstitial pneumonia (Maedi, Maedi-visna)

Maedi/visna is a highly fatal viral disease of sheep and goats caused by a lentivirus.

Transmission : Through colostrum to newborn lambs and less often by contact with respiratory route.

Antemortem findings :

  1. Listlessness
  2. Difficult breathing and frequent coughing
  3. Nasal discharge
  4. Emaciation
  5. Lameness
  6. In chronic cases, anaemia and secondary bacterial infections

Postmortem findings :

  1. Enlarged grey-yellow non collapsible lungs of rubbery consistency (Fig. 160)
  2. Cross section of lung parenchyma showing a meaty appearance
  3. Enlarged and firm mediastinal lymph nodes

Judgement : Carcass in good flesh with slight to moderate pulmonary involvement is approved. An emaciated carcass with extensive pulmonary lesions or secondary bacterial infection is condemned.

Differential diagnosis : Parasitic pneumonia, pulmonary adenomatosis (Jaagsiekte) and pseudoglanders (Melioidosis)

fig 160

Fig. 160: Ovine progressive interstitial pneumonia. Cross section of the lung parenchyma. The lungs are enlarged, non collapsible and have a meaty appearance.

Nairobi sheep disease

Nairobi sheep disease is a non contagious, tick borne viral disease in sheep manifested by acute haemorrhagic inflammation of the stomach and intestine and by respiratory signs.

Transmission : Adult forms of a tick Rhipicephalus appendiculatus which attach themselves inside the ear of an animal. Unfed adult ticks are infective for one year. Faeces does not contain the virus.

Antemortem findings :

  1. Incubation 4 – 15 days
  2. Fever; during fever the blood, urine and tissue are infective
  3. Rapid painful breathing
  4. Dullness and depression
  5. Mucopurulent nasal discharge
  6. Pain and grunting with defecation
  7. Acute haemorrhagic gastroenteritis
  8. Bright to dark green faeces (is important in the differential diagnosis.)
  9. Abortion in pregnant ewes
  10. Swollen vulva and external genitalia
  11. Collapse and death

Postmortem findings :

  1. Excess fluid in the pericardium
  2. Ecchymotic and petechial haemorrhage in the heart muscle
  3. Acute haemorrhagic inflammation of the stomachs (Fig. 161) and intestine
  4. Distended gall bladder contains thick syrupy bile
  5. Enlarged and edematous lymph nodes
  6. Hyperaemic genital tract

Judgement : Carcass of an animal affected with the acute disease accompanied with fever and acute gastrointestinal lesions iscondemned. Carcass of recovered animals and of animals with non systemic or generalized lesions is approved. The affected organs are condemned.

Differential diagnosis : Rift Valley fever in sheep. Diarrhoea in RVF may show blood tinged watery faeces, but is not green in colour as in NSD. In rinderpest ulcerative lesions are noted with bloody (and not green) faeces. Heartwater, anthrax and plant poisoning should also be considered in differential diagnosis.

fig 161

Fig. 161: Nairobi sheep disease. Acute haemorrhagic inflammation of the stomachs.

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