II. Streptococcal Pneumonia
III. Antibiotic-Induced Enterotoxemia / Hemorrhagic Typhlitis
IV. Cervical Lymphadenitis (Lumps)
V. Pododermatitis (Bumblefoot)
VI. Mastitis
VII. Dermatophytosis
VIII. Tyzzer's Disease
IX. Salmonellosis
A. Etiology: Bordetella bronchiseptica is a small, Gram-negative, non-lactose fermenting rod. There is a high correlation of Bordetella isolation with clinical disease, however, apparently nonvirulent isolates have been recovered from asymptomatic Guinea pigs. Incidence of disease is moderate, especially in group housing situations.
B. Transmission: The organism can be carried by rats, rabbits, dogs, cats, swine, and primates. There is limited epidemiologic evidence that some isolates or strains are specific for certain animal hosts. Transmission between animals is by direct contact, respiratory aerosol, and contaminated fomites. A carrier state occurs in the Guinea pig. Incubation periods in new infections range from five to seven days.
C. Clinical Signs: Carrier or subclinically infected animals may
have no signs. Acutely infected animals may exhibit sneezing, nasal
discharge, anorexia, weight loss, conjunctivitis (see photo), dyspnea,
and death. Stillbirths and abortions may occur in pregnant females.
Young animals are more severely affected; mortality can reach 100% in immunologically
naive juveniles.
D. Pathology: Lesions include mucopurulent rhinitis, tracheitis,
and pulmonary consolidation with a purulent bronchitis and bronchopneumonia
(see photo). Exudate can be present in the tympanic bullae.
E. Diagnosis: Radiography of the chest can confirm pneumonia.
Radiographs of the tympanic bullae may be helpful where otitis media is
suspected.
Culture of exudates and bacterial identification provides diagnostic
confirmation of the disease. Gram staining of impression smears at post-mortem
exams can provide a tentative diagnosis, since Bordetella is the
primary Gram-negative bacillus to cause respiratory disease in Guinea pigs.
E. Treatment: Suggested antibiotic regimens include chloramphenicol (10 to 30 mg/kg b.i.d. IM or PO for 7 to 10 days), enrofloxacin (2.5 mg/kg twice daily for 7 to10 days), and sulfamethazine (4 ml of a 12.5% solution/500 ml water for 1 to 2 weeks). Fluid and respiratory therapy, as in conventional small animal species, may also be appropriate.
G. Control: An autogenous bacterin can be made to help prevent clinical bordetellosis. The bacterin should be administered at six weeks of age and repeated every six months. The bacterin does not prevent the carrier state. Commercial porcine and intranasal canine bacterins have also been reported to be effective in prevention of overt bordetellosis, but do not prevent colonization of the upper airways. Guinea pigs can be raised by hand at birth, and this neonatal weaning has been used to raise Bordetella-free Guinea pigs.
A. Etiology: Streptococcus pneumoniae is an alpha-hemolytic, Gram-positive coccus. Incidence of infection can be high in previously unexposed animals. Predisposing factors include pregnancy, environmental temperature changes, shipping, subclinical vitamin C deficiency, negligent husbandry practices, and stressful experimental procedures. Animals may carry virulent pneumococci in the upper respiratory tract without clinical disease.
B. Transmission is by primarily by direct contact. Rats and humans can also serve as carriers.
C. Clinical Signs: Respiratory signs may include nasal discharge,
rhinitis, conjunctivitis, torticollis (see photo), dyspnea, and acute death.
Guinea pigs may be lethargic, anorexic, and have a ruffled hair coat.
Pregnant dams may abort. During epizootics, mortality rates are very high
in naive animals.
D. Pathology: Commonly a fibrinopurulent bronchopneumonia, with
or without fibrinous pleuritis and pericarditis, is seen on necropsy.
Lungs are often consolidated with a frothy, serosanguinous fluid in airways.
Other suppurative processes such as metritis, otitis media, peritonitis
(see photo), and meningitis are occasionally seen.
E. A tentative diagnosis can be made during the necropsy exam
because the fibrinopurulent exudate is characteristic of S. pneumoniae.
Culture of affected tissues on blood agar and incubation in a 10% CO2,
37o C environment allows for identification of alpha-hemolytic
cocci which are sensitive to the optochin reagent. Diagnosis is based
upon demonstration of paired, gram-positive cocci (diplococci) on impression
smears and culture.
F. Treatment and Control: Antibiotic therapy as for Bordetella pneumonia has been recommended for streptococcal pneumonias. Control should be directed toward good husbandry, early weaning and isolation of diplococcal-free Guinea pigs, and reduction of environmental stress.
III. Antibiotic-Induced Enterotoxemia / Hemorrhagic Typhlitis
A. Etiology: Guinea pigs normally have an anaerobic Gram-positive
intestinal flora, which can be upset and overcome by enterotoxin-producing
bacteria. This anaerobic bacterial overgrowth can rapidly produce
enterocolitis, septicemia, and death. Hence many things (such as
diet change, stress, prolonged antibiotic therapy) that alter the enteric
microflora can potentially initiate this syndrome. Antibiotics that
have been implicated include penicillin, erythromycin, lincomycin, chlortetracycline,
oxytetracycline, bacitracin, dihydrostreptomycin, cefazolin, cephalexin,
cephalothin, ampicillin, clindamycin & gentamycin. Specific organisms
implicated in the overgrowth and subsequent toxemic pathogenesis include
Clostridium
difficile, C. perfringens, C. spiroforme and several coliforms.
Diarrhea may or may not be present. Enterotoxemia may include anorexia,
rapid weight loss, dehydration, depression, and/or acute death. A
large, distended cecum containing blood and liquid contents with hemorrhagic
serosal and mucosal surfaces is characteristic (Photo A.). Microscopic
lesions include extensive vascular congestion, submucosal hemorrhage and
edema, and sloughing of the absorptive epithelium throughout the GI tract
(photo B). Diagnosis is based upon a history of antibiotic administration,
necropsy findings, and the isolation of an offending organism or toxin.
Treatment is heroic and includes fluids and supportive care. Control
of this syndrome relies on the careful and discriminate use of broad-spectrum
antibiotics in the guinea pig. Some safer antibiotics that have been
used in guinea pigs are chloramphenicol, enrofloxacin and trimethriprim
and sulfamerazine.
IV. Cervical Lymphadenitis (Lumps)
A. Etiology: Streptococcus zooepidemicus is a beta-hemolytic coccus that is commonly carried in the nasopharynx of Guinea pigs. Streptobacillus moniliformis is rarely implicated.
B. Transmission: Bite wounds or direct contact with oral secretions are the major vehicles for transmission. The bacterium is believed to colonize injured mucosal surfaces and the draining lymph nodes.
C. Clinical Signs: The bacterium initially infects cervical
lymph nodes, which become enlarged (see photo) and develop abscesses.
Abscesses may spontaneously rupture and heal with time. Affected
animals may show no other signs except nonspecific symptoms of pyrexia
or anorexia immediately prior to rupture. Other regional lymph nodes
or, rarely, the middle ear and respiratory passages may become involved.
D. Pathology: Enlarged lymph nodes progressing to development of well encapsulated abscesses filled with a thick, yellow to white purulent exudate is characteristic of this infection. Numerous suppurative processes may be seen in multiple organ systems and may include bronchopneumonia, otitis media, pleuritis, peritonitis, and pericarditis.
E. Diagnosis is based on clinical presentation and culture of the organism from lesions.
F. Treatment and Control: Infected animals should be isolated from the colony and be treated with surgical drainage and lavage of the abscesses, and/or antibiotic therapy for 7-10 days. Spread of the organism through a colony can be controlled by culling or isolating affected animals prior to lymph node rupture. Limiting the amount of coarse feed may aid in decreasing the incidence.
V. Pododermatitis (Bumblefoot)
This disease is seen most frequently in Guinea pigs housed on rough,
unsanitized wire floors. Lesions occur on the palmar and plantar
surfaces of the feet and consist of granulomatous cellulitis or chronic,
fibrous granulomas with or without an exudative crust, of the feet.
Staphylococci have often been isolated from these lesions, probably as
secondary invaders. The best treatment is to transfer the affected
animal to a solid floored cage with dry shredded paper bedding. Resolution
of advanced lesions despite local and parenteral therapies is uncommon.
Soaking the feet in astringents or tamed iodine solutions and bandaging
the feet may be beneficial in severe cases.
Mastitis is a fairly common problem in lactating Guinea pigs. The affected gland becomes diffusely or focally enlarged, hyperemic and warm, and later becomes cyanotic and cool. Depression ensues and the animal may die of septicemic complications. Mastitis may be caused by a variety of organisms, including Pasteurella sp., Klebsiella sp., coliforms, streptococci, and staphylococci. Treatment consists of hot packs, systemic antibiotics, surgical resection of the affected gland(s) and weaning the precocious young at birth.
Trichophyton mentagrophytes is the most common dermatophyte isolated from guinea pigs. Prevalence of arthrospore carriage is quite high, though clinical disease is rarely seen. Transmission of ringworm is by direct contact with the spores. Young, aged, pregnant, and otherwise stressed animals are most susceptible to the disease.
C. Clinical signs: Lesions consist of irregular alopecia with
occasional crusts and broken hair shafts. Progression of lesions
occurs from the nose to limbs and back. Severe lesions may become
secondarily infected with bacteria. 
D. Diagnosis and Treatment: Diagnosis is based upon clinical signs and identification of the fungus on KOH cleared preps from inoculated dermatophyte test medium (DTM). Treatment includes clipping the area and griseofulvin (15 mg/kg s.i.d. PO, 2 to 4 weeks) or a topical antifungal cream applied b.i.d. for at least 4 weeks are probably equally effective. Griseofulvin should be used cautiously since it is derived from penicillium cultures. The environment should be evaluated because of unsanitary conditions and high humidity can increase the incidence of dermatophyte infections.
Public Health Significance: T. mentagrophytes has been reported to spread by contact and fomites from animal to animal and from animal to man.
Clostridium piliforme, a spore-forming, obligate intracellular bacteria, has been shown to cause disease in immunocompromised guinea pigs. Clinical signs, pathologic effects, and diagnostic procedures applicable to this disease are the same as for other rodent species. Control of outbreaks is by strict sanitation, good husbandry, and reduction of environmental stress.
Salmonella enterica serovar Typhimurium has been shown to infect guinea pigs. Acute deaths are occasionally seen in very young, very old, or stressed animals; diarrhea is not characteristic of the clinical picture, but nonspecific depression, anorexia, weight loss and unthriftiness are commonly noted. Abortion storms have been reported. No lesions are apparent in acute cases, but carriers and chronically infected animals may have enlarged livers, spleens, and lymph nodes containing small white necrotic foci. Identification of both acute cases and carriers depends on isolation of a Salmonella sp. from feces or mesenteric lymph nodes. No treatment is recommended. Animals that are culture positive for Salmonella should be removed from the facility. Elimination of a colony is recommended if numerous carriers are identified.
Public Health Significance: Humans ingesting Salmonella -
contaminated food or water experience a transient diarrhea. Children
or immunosuppressed adults are susceptible to more serious clinical disease
from Salmonella infection. Exposed personnel must be advised
of any apparent risks.
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