Sheep are valuable assets due to their significant share in meat, milk, and wool production, as well as replicating and growing quickly.
So, maintenance of their economic value requires a rapid and perfect diagnosis of any disease.
Effective and early diagnosis of respiratory diseases including pneumonia in sheep is a challenge as the laboratory resources are limited especially in Africa, and Southeast Asian countries where respiratory diseases outbreaks are frequent.
What are the respiratory diseases in sheep?
They are the diseases that affect the respiratory system of the sheep, causing high losses.
Respiratory diseases in sheep can be classified into:
Upper respiratory tract disease
They are the respiratory diseases that affect the upper part of the respiratory tract, including:
Nasal myiasis.
Laryngeal chondritis.
Salmonella arizonae.
Nasal foreign bodies.
Nasal tumors.
Lower respiratory tract disease
Bacterial pneumonia
It's pneumonia caused by bacterial pathogens, mainly:
Mannheimia haemolytica.
Pasteurella multocida.
Mycoplasma species, especially Mycoplasma ovipneumoniae.
Streptococcus zooepidemicus.
Opportunistic bacteria.
Viral pneumonia
It's pneumonia caused by viral pathogens, mainly:
Parainfluenza virus, type 3.
Respiratory syncytial virus.
Ovine adenovirus.
Retrovirus types 1, 2, and 3.
Chronic viral respiratory diseases, including:
Maedi-visna.
Ovine pulmonary adenocarcinoma (jaagsiekte).
Mycotic pneumonia
Pneumonia that caused by Aspergillus species.
Lung abscesses
They are mainly caused by:
Arcanobacterium pyogenes.
Fusobacterium necrophorum.
Staphylococcus aureus.
Actinobacillus lignieresii.
Corynebacterium pseudotuberculosis.
Parasitic pneumonia
It's pneumonia caused by Lungworm.
There's a study that targeted the average annual diagnosis of respiratory diseases in sheep in England and Wales, from 2002 to 2005 based on VIDA data.
This study confirmed that Mannheimia species cause 47.4% of the respiratory diseases in sheep, then parasitic pneumonia by 8.9%.
Ovine pulmonary adenocarcinoma (jaagsiekte) was the third cause of respiratory diseases in sheep by 6%.
Pasteurella multocida shared with 1.15%, followed by Maedi-visna by 1.7%.
Then laryngeal chondritis contributed by 0.4% and followed by oestrus Ovis which shared with 0.15%.
The remaining 34.3% is caused by others including Parainfluenza type 3, Mycoplasma ovipneumoniae, lung abscess, and mycotic pneumonia.
How are the respiratory diseases in sheep diagnosed?
Case history
The history of the sheep flock should be known, including:
Diseases frequency in the area.
Age, sex, and the vaccination status of the affected sheep.
Pregnancy stage in pregnant ewes.
Clinical signs
The clinical signs are the first alert of the presence of respiratory diseases in a sheep flock.
The symptoms differ according to the type and severity of the respiratory diseases. But generally, they include:
Fever.
Cough and fast breathing.
Loss of appetite.
Nasal and ocular
discharges.
Painful chest.
Differential diagnosis
All mentioned symptoms are common in most respiratory diseases in sheep, including pneumonia.
So, the differential diagnosis of pneumonia is necessary.
Methods of diagnosis of the causative agents of pneumonia in sheep
There are various and numerous causative agents of pneumonia in sheep, either potential or secondary.
So, an accurate diagnosis for each causative agent is the key to get successful treatment and vaccination courses.
Viral neumonia
Diagnosis of viral pneumonia differs according to the causative agent, such as:
Parainfluenza type 3
It's mainly diagnosed through 3 methods, including:
FAT on BAL fluid or lung tissue (fluorescent antibody test on Bronchoalveolar lavage) during the first 6 days of infection.
ELISA.
Immunohistocytochemistry on the fixed lung.
Adenovirus
This virus is diagnosed by AGIDT (Agar gel immunodiffusion test).
Respiratory syncytial virus
It's diagnosed through;
FAT on lung tissue or BAL fluid.
Immunohistocytochemistry on fixed lung tissue.
Maedi-Visna
Diagnosis of this virus depends on:
AGIDT or ELISA
Postmortem lung examination and lung histopathology.
Ovine pulmonary adenocarcinoma
This serious virus is diagnosed through:
Wheelbarrow test.
Postmortem examination and lung histopathology.
Jaagsiekte retrovirus PCR.
Bacterial pneumonia
As well as viral pneumonia, the bacterial pneumonia diagnosis is determined according to the causative agent.
Pasteurella species
It's diagnosed by:
Bacterial culture of lung tissue.
Histopathology of the lung.
Mycoplasma species
Mycoplasma pneumonia is diagnosed through:
Mycoplasma culture of lung tissues.
PCR / denaturing gradient gel electrophoresis on tissue or tissue swab.
ELISA test.
Other bacteria are diagnosed by bacterial culture.
Histopathology of pneumonic sheep lung
Interstitial pneumonia
The gross examination of this type shows:
Enlargement of the lung, causing rib imprints.
Rubber consistency of the lung with a meaty appearance.
The lesions mainly appear in the caudal lobe.
The microscopic examination of this type shows:
The thickness of the interalveolar septa.
Fibroblasts and smooth muscle proliferation.
Infiltration of inflammatory cells (lymphocytes, macrophages, and neutrophils).
Follicle-like aggregation.
Acute Suppurative Bronchopneumonia (ASBp)
The color of the lung is red to gray.
The consistency of the lung is consolidated and may be caseous on the incision.
The lesions mainly appear in the lung cranioventral aspect.
Microscopically, this type of pneumonia shows:
Infiltration of neutrophils in the suppurative areas.
Little infiltration of mononuclear cells in alveoli, bronchi, bronchioles.
Acute Fibrinous Bronchopneumonia (AFBp)
Its gross examination shows:
Consolidated areas appear in the cranial, cardiac, and accessory lobes.
The lung tissue is hard to be cut and may have a marbling appearance.
The thickness of both pleura and interlobular septa.
By the microscopic examination of this type, the formation of exudates of fibrin and neutrophils in alveoli, bronchioles, and bronchi is observed.
Chronic Bronchopneumonia (CBp)
By gross examination of this type, the changes that can be observed are:
Pale to gray color of the affected part with a firm to hard consistency.
Adhesion of the pleura to the chest wall.
The lesions mainly appear in the cranial lobe
The microscopic examination of this type shows:
High Fibrinous thickening in the pleura.
Different degrees of mononuclear infiltration.
Bronchointerstitial pneumoni
Grossly, this type shows some changes, including:
The meaty appearance of the affected part.
Lesions slightly appear in both the anterior and caudal lobe, but generally aren't remarkable.
The microscopic examination of this type shows:
Thickening of the intra-alveolar septa.
Presence of exudate in the alveoli, bronchioles, and bronchi.
Aspiration pneumonia
The gross examination of the lung with aspiration pneumonia shows:
Congestion in the affected part with meaty consistency.
Presence of foul-smelling greenish-brown exudate.
The lesions mainly appear in the cranioventral lobes
The microscopic examination of this type of pneumonia shows the presence of aspirated foreign body granuloma.
Ovine Pulmonary Adenomatosis (OPA)
The gross examination of this type shows:
Enlarged lung with grayish-white granular masses.
Meaty to firm consistency of the lung tissue.
Presence of grayish exudate.
The microscopic examination of this type shows papillomatous proliferation of type II pneumocytes projected onto alveoli.