Prevention and Control Methods and Technical Key Points for Pasteurellosis in Guinea Pigs

Pathogen

Pasteurella multocida, a Gram-negative, short, small bacillus with bluntly rounded ends and an oval shape. When tissue lesions are smeared and stained by Giemsa or Wright's method, the two poles of the bacterial body stain more deeply.

Epidemiological Characteristics

30% to 75% of guinea pigs carry Pasteurella in the mucous membranes of the upper respiratory tract and tonsils, but show no symptoms. When various factors (sudden temperature changes, poor feeding and management, long-distance transport, etc.) reduce the resistance of guinea pigs, the Pasteurella in the body multiplies in large numbers, its virulence increases, and disease is thereby triggered. This disease can occur in all four seasons, but is more common in spring and autumn, presenting as sporadic or endemic outbreaks, and is mainly transmitted through the digestive tract or respiratory tract.

Symptoms and Pathological Changes

The symptoms and lesions vary depending on the virulence of the bacteria, the route of infection, and the course of the disease, and are often divided into the following types.

1. Septicemic type: Mostly acute in course, often resulting in death within 1 to 3 days. Depression, refusal to eat, body temperature above 40°C, rapid breathing, discharge of serous or purulent nasal fluid, sometimes diarrhea. Before death, body temperature drops, with generalized trembling and convulsions of the limbs. Some die suddenly without obvious symptoms. Necropsy findings: nasal mucosa congested with adherent viscous secretions; laryngeal and tracheal mucosa congested and hemorrhagic, with red foam in the lumen; lungs severely congested, hemorrhagic, and edematous; hemorrhagic spots on the endocardium and epicardium; liver enlarged, congested, degenerated, and often with many small necrotic foci; intestinal mucosa congested and hemorrhagic; relatively large amounts of pale yellow fluid in the thoracic and abdominal cavities. The subacute form often develops from the rhinitis type and pneumonia type, with a course of about 1 to 2 weeks, ultimately resulting in death from exhaustion. The main symptoms are mucopurulent nasal discharge, frequent sneezing, and difficulty breathing. Body temperature is slightly elevated, and appetite is reduced. Diarrhea, joint swelling, and inflammation of the conjunctiva are sometimes seen. Necropsy findings: the lungs show fibrinous pleuropneumonia changes, and even abscess formation; pleural effusion; nasal and tracheal mucosa congested and hemorrhagic, with adherent viscous secretions; lymph nodes red and enlarged.

2. Rhinitis type: Relatively common, with a course that can last several months or longer. The main symptom is discharge of serous, mucous, or mucopurulent nasal fluid. Affected guinea pigs often sneeze and cough, and scratch their noses with their front paws, causing the hair around the nostrils to become moist, matted, and even fall out, with inflammation, redness, and swelling of the skin around the upper lip and nostrils. Mucopurulent nasal fluid forms crusts around the nostrils and blocks them, causing difficulty breathing and snoring sounds. If the bacteria invade the eyes, ears, subcutaneous tissue, etc., it can cause conjunctivitis, keratitis, otitis media, subcutaneous abscesses, and mastitis. Necropsy findings: nasal mucosa flushed, swollen, or thickened, sometimes with erosion, and the mucosal surface covered with serous, mucous, or purulent secretions. The mucosa of the nasal sinuses and paranasal sinuses is also congested, red, and swollen, with secretions accumulating in the sinuses.

3. Pneumonia type: Often acute in course. Although pneumonia lesions occur, clinical signs of pneumonia are difficult to detect; some die quickly, while others show only poor appetite, elevated body temperature, and depression. The nature of the lung lesions is fibrinous purulent pleuropneumonia. Grossly, the lesions are mostly located in the apical lobe, cardiac lobe, and the anterior-lower part of the diaphragmatic lobe, including consolidation, atelectasis, abscesses, and grayish-white small nodular foci. The pulmonary pleura and pericardium often have fibrinous attachments. As shown in the figure

4. Otitis media type: The otitis media type is also called torticollis disease. Simple otitis media often has no obvious symptoms, but if the lesions spread to the inner ear and brain, the affected guinea pigs develop torticollis symptoms, and in severe cases roll toward the side to which the head and neck are tilted until they hit the enclosure. If the meninges and brain parenchyma are affected, ataxia and other neurological symptoms may appear. Necropsy findings include purulent tympanic cavity otitis media and tympanitis. There is white creamy exudate in one or both tympanic cavities; when the tympanic membrane ruptures, this exudate flows out through the external auditory canal. If the inflammation spreads from the middle ear and inner ear to the brain, purulent meningoencephalitis changes can be seen.

5. Other disease types: Guinea pig pasteurellosis can also present as purulent conjunctivitis, endometritis (in female guinea pigs), epididymitis and orchitis (in male guinea pigs), and purulent inflammation in various subcutaneous areas and organs. The conjunctiva and uterine mucosa show purulent catarrhal changes, with purulent secretions on the surface and accumulation of pus in the uterine cavity. Other tissues and organs mainly show abscess formation.

Differential Diagnosis

Because this disease presents with multiple disease types, it should be differentiated from the following diseases.

1. Differentiation from Bordetella bronchiseptica infection in guinea pigs: Although Bordetella bronchiseptica infection in guinea pigs causes catarrhal rhinitis or pulmonary abscesses, it does not cause otitis media, and the pathogen is the pleomorphic Bordetella bronchiseptica.

2. Differentiation from staphylococcosis: The main lesions of staphylococcosis are abscesses and pododermatitis; abscesses mostly occur in the subcutaneous tissue and muscles, and are rare in the lungs and other internal organs, with no purulent rhinitis, otitis media, or other such lesions.

Treatment Methods

1. Guinea pig colonies should be self-bred and self-raised, and the arbitrary introduction of breeding guinea pigs is prohibited; when introduction is necessary, quarantine and observation for 1 month should be carried out first, and only healthy animals may enter the facility.

2. Strengthen feeding management and sanitation and epidemic prevention work, and strictly prohibit the entry of livestock, poultry, and wild animals.

3. Guinea pig farms with this disease can use guinea pig Pasteurella vaccine or avian Pasteurella vaccine for preventive injection.

4. Once this disease is discovered, immediately adopt isolation, treatment, culling, and disinfection measures.

5. The following drugs can be used for treatment: streptomycin 50,000 to 100,000 units per kilogram of guinea pig body weight, penicillin 20,000 to 50,000 units, mixed for a single intramuscular injection, twice a day for 3 consecutive days; gentamicin 40,000 units per kilogram of guinea pig body weight, once intramuscularly, twice a day for 3 consecutive days; sulfadimidine (sm,) oral dose 0.1 g per kilogram of body weight, once daily, intramuscular injection dose 0.07 g per kilogram of body weight, twice daily for 4 consecutive days.

Preventive Measures

The prevention of this disease should rely on establishing good environmental sanitation conditions. Pasteurella-free guinea pig colonies can be established through cesarean section.