Bacterial and Mycotic Diseases

Nitric oxide is a noxious stable free radical gas that is released by activated neutrophils and macrophages during the inflammatory response. It reacts with superoxide anions to produce peroxynitrite (ONOO^-), an oxidating molecule believed to kill intracellular bacteria. Inducible nitric oxide synthase (iNOS) is one form of the enzyme responsible for producing nitric oxide in inflammatory cells, and when detected immunohistochemically can be used as a marker of nitric oxide production.{4083}

Gram negative organisms

Aeromonas

Motile aeromonad septicemia in fish and amphibians is a result of stress from overcrowding, temperature changes, reproduction or poor water quality. Signs include hemorrhage at the base of the fins and in the skin, skin ulcers, swollen abdomen, exophthalmia and red-colored ascites. A pathognomonic sign is bristling of the scales to resemble a pine cone. The causative organism is Aeromonas hydrophila. Furunculosis is caused by A. salmonicida, and is a deep necrotic lesion of the muscle.{3779}{4178}

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Bartonella henselae{4023}

Regional lymphadenitis has been associated with animal contact, especially with cats, for over 100 years.  Beginning in 1983, small argyrophilic, gram-negative bacteria were seen in blood vessel walls and macrophages in lymph nodes of people with "cat-scratch disease." A bacterium was associated with the disease in 1988; although it was last known as Rochalimaea, its current name is Bartonella. There are several species including B. quintana (cause of trench fever), B. vinsonii, B. henselae and B. elizabethae. They were formerly all considered in the family Rickettsiaceae, but the fact that they can be cultured on agar, as well as DNA studies, removed them from this family and placed them in the their own family, Bartonellaceae.

Several human diseases are associated with Bartonella, including bacillary angiomatosis (blood-filled cystic tumors), bacillary peliosis hepatis (same thing in visceral organs), relapsing fever, cat-scratch disease, endocarditis, granulomatous hepatosplenic syndrome, retinitis, osteolytic lesions and pulmonary granulomas. The disease is a problem in both immunocompetent and immunocompromised people. The exact role of Bartonella in contributing to these disease conditions is poorly understood. People can experience prolonged illness with persistent bacteremia. Diagnosis is achieved through use of PCR or by culture (although the organism takes 10-56 days to grow). Seroconversion (IFA or ELISA) can be useful, but in cats it is variable. Humans have a poor response to antimicrobial therapy for cat-scratch disease, but respond better to treatment for the other diseases listed above. Treatment (usually doxycycline, erythromycin and rifampin) must be continued for 2-6 weeks depending on the patient's immune status.

Cat-scratch disease in humans is usually considered a benign self-limiting disease, but 10% of cases may have other manifestations. B. henselae is apparently the predominant, but not the only cause of CSD. Signs in humans include an erythematous papule at the site, followed by regional lymphadenopathy which usually regresses in 6 weeks. Diagnostic criteria are: (1) positive serology for B. henselae, (2) history of cat contact, (3) characteristic histopathologic changes on lymph node biopsy, (4) absence of other disease, and (5) growth of the organism on rabbit blood agar in 5% CO₂. Transmission from environmental sources or other animals is possible, including fleas and ticks.{4780}

There are many chronically bacteremic healthy cats in the US, perhaps 25-41% of the population. Whether Bartonella is pathogenic for them is as yet unknown. Serologic response is variable, ranging from 4-60%, and bacteremic cats do not always have demonstrable titers. Antimicrobial therapy has not been established for eliminating B. henselae in cats.

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Branhamella catarrhalis

"Bloody nose syndrome" in cynos is caused by this Gram-negative diplococcus. Affected animals have epistaxis and periorbital edema. The disease responds to penicillin (as opposed to viral hemorrhagic diseases) and may be associated with low humidity.{3770}

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Bordetella bronchiseptica

It is not clear in what ways Bordetella itself causes disease, as it is a normal inhabitant of the respiratory tract of many healthy rabbits, guinea pigs, rats, mice, dogs, swine, cats, turkeys and primates. After aerosol transmission it may impair airway clearance to facilitate growth of Pasteurella. Lesions in the rabbit are chronic interstitial pneumonia and bronchiolitis.{3768} NHPs may be asymptomatic carriers or show mucopurulent nasal discharge, dyspnea and death from fibrinopurulent hemorrhagic bronchopneumonia.{3770}

Bordetellosis is an important disease of guinea pigs, particularly the young. The disease is usually subclinical, but epizootics may happen with high mortality in a few days. Clinical signs are ADR and pneumonia, i.e. inappetance, depression, upper respiratory discharges, dyspnea, cyanois, and death. It may also affect the genitals causing infertility, stillbirths and abortions. The hallmark of infection is mucopurulent exudate present in the nasal passages and trachea. Grossly the lungs are consolidated and have purulent bronchitis, tracheitis and otitis media. The morphologic diagnosis is fibrinous or fibrinopurulent bronchopneumonia. The organism has an affinity for ciliated respiratory epithelium and is also found in the female genital tract. Affected animals should be culled as they will likely become carriers. However, treatment with fluoroquinolones or trimethoprim-sulfas plus supportive fluids are effective. Borderline vitamin C deficiency and stress are thought to contribute to clinical disease.{3775}{4652} 

Bordetella can also cause pneumonia in chinchillas.{3560}

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Brucella

B. canis is the most likely zoonotic agent in lab animal facilities. Humans are relatively resistant to infection; there have been more than 35 cases since 1967 but it is not a reportable disease. In many cases it's probably subclinical, given the lack of disease in seropositive military recruits. Contact with aborting bitches is a risk factor. Bacteremia causes painful generalized lymphadenopathy, headache, fever, chills, and other signs. Antibiotics don't work well because the bacteria are intracellular; but CDC recommends 3 weeks of doxycycline and rifampin. Dogs are identified by a rapid slide agglutination test.{4780}

See the livestock page for information on brucellosis in livestock.

Campylobacter

Authors disagree on the terminology for the Campylobacter species of animals. Carter{3953} describes C. fetus fetus and C. fetus venerealis in cattle, sheep and humans, and C. jejuni and C. coli as separate species. However, Baskin{3770} describes the disease occurring in NHPs as caused by "Campylobacter fetus subsp. jejuni, coli". He may have meant that C. jejuni and C. coli are different species. In any event the organisms are Gram-negative, vigorously motile curved rods. They grow under microaerophilic conditions on special media; C. jejuni requires high temperatures (42°C). The two subspecies are differentiated with the hippuric acid test; C. jejuni is positive and C. coli is negative.{4487} They are ABSL-2 pathogens that are highly infectious for humans; ingestion of 500 organisms caused infection in one person.{3950}

Hamsters do not develop disease typically, but they can shed the organism for months creating a zoonotic hazard.{3991}

In NHPs, campylobacteriosis causes fluid, maybe bloody diarrhea and dehydration, although asymptomatic carriers are common too. The small intestine and colon are affected, being red, rough and edematous. The histologic lesions are less severe than those of Shigella. On sections, bacteria are identified by silver stains.{3770} Campylobacter infection is endemic in cotton-top tamarins (Saguinus oedipus) and other primates. One study determined the epidemiology of C. jejuni and C. coli infections in infant tamarins hand reared under two housing and management regimens. Infection with C. coli is more prevalent than with C. jejuni. Infections and re-infections with multiple strains are common among laboratory-housed primates, and were most prevalent between 3 and 9 months of age. Season of the year is an important factor since C. jejuni infection most frequently occurred between April and June whereas C. coli infections occurred between October and December. No association between the infections and diet or idiopathic colitis was observed.{4487}

C. fetus subsp. intestinalis is the most important cause of late abortion in ewes in the US. C. fetus subsp. venerealis is the main cause of bovine campylobacterial abortions. {4776}

C. jejuni and C. coli are a leading cause of diarrhea in humans. Laboratory-animal-associated infections have been reported. The disease is usually self-limiting without treatment.{4780}

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Cilia-associated Respiratory (CAR) Bacillus

CAR bacillus is an unclassified Gram negative motile bacterium that causes respiratory tract disease in rodents, particularly rats. It can also infect rabbits but the significance is unknown.{3768} It apparently colonizes the nasal passages first where it may be for weeks to months before clinical signs develop. Eventually it appears to move to the trachea and then to the lungs, at which point it causes weight loss, rough haircoat, wheezing and cyanosis. Antemortem diagnosis is probably best achieved with PCR of nasal swabs collected on calcium alginate swabs under light anesthesia. The swabs can be kept in sterile PBS at room temperature for up to 48 hours. ELISA is sensitive but there is cross-reaction to other bacteria; culture is labor-intensive as it has been achieved only in embryonated eggs and mammalian cell lines. On histology, the organisms are seen with Steiner silver stain as argyrophilic filamentous bacteria colonizing the ciliated respiratory tract epithelium. Tracheal lesions include hyperplasia of mucosa and submucosal inflammation as shown by mononuclear cell infiltrates. In the lung it causes hyperplasia of bronchiolar epithelium and hyperplasia of lymphoid tissue. In rats with advanced lesions there is mucopurulent bronchiolar exudate.{3952}

Gerbils experimentally infected with CAR bacillus showed no clinical signs, but had similar histologic lesions as in mice, rats and hamsters, i.e. tracheobronchitis and bronchopneumonia as diagnosed by the above-described lesions. This is in contrast to guinea pigs, which get only mild histologic lesions.{4043}

Mice are more susceptible to CAR bacillus than rats, but natural infection is much more common in rats. Rabbits and humans can also be infected.{3763}

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Transmissible Murine Colonic Hyperplasia (Citrobacter rodentium)

Citrobacter is a motile, Gram-negative rod that ferments lactose and uses citrate as a carbon source. It used to be called C. freundii, but the new name is C. rodentium and only strain 4280 is pathogenic for mice. It is relatively easy to culture and can be incorporated into routine colony surveillance. The organism is not part of the normal flora; rather, it is usually introduced to the colony via contaminated feed or bedding.{2738}Virulence of the organism is enhanced when it can attach to and efface the brush border prior to development of colonic hyperplasia. Strains of Citrobacter that can do this cause inflammation, erosion and necrosis.{4044} Affected mice are usually young (suckling or weanling) and show ruffled fur, retarded growth, soft or sticky feces, rectal prolapse and some mortality. The pathognomonic finding is a thickened descending colon, caused by hyperplasia of the mucosa. Mice can be treated with antibiotics in the water, and husbandry practices should be improved.{3551}

A valuable colony of mice transgenic for the T cell receptor were found to be infected with C. rodentium, Helicobacter and MHV.  Transgenic mice of all ages were affected by debilitation, loss of reproductive efficiency, rectal prolapse, and acute death. Several alterations in immunologic parameters were observed, including outgrowth of an unusual population of cells in the spleen and blood, reduction in ascites production, loss of the capacity of peritoneal exudate cells to serve as feeders for the cloning of long-term T-cell lines, and inhibition of antigen-specific cytotoxic T-cell activity. These altered immune functions also were apparent in commercially-derived nontransgenic mice housed with the infected colony, as well as in overtly healthy transgenic and nontransgenic littermates. After rederivation, the mice were given enrofloxacin at 170mg/l in their drinking water. This kept them from dying, and they were even able to reproduce.{4044}

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Clostridium piliforme (Tyzzer’s disease)

Members of the genus Clostridium are long, anaerobic, Gram positive spore-forming rods{3953}. However, most authors{3551, 3953, 3768, 4208} place the causative agent of Tyzzer’s disease in the Gram negative category. The agent was once called Bacillus piliformis but was reclassified in 1993 to Clostridium piliforme. Tyzzer’s disease affects many species, but it was first described in mice by Ernst Tyzzer in 1917. Isolates from outbreaks tend to be somewhat host-specific with minimal antigenic cross-reactivity.{4208} It is of rare prevalence in the rat{3763} and other species (mice, hamsters, guine pigs, dogs, cats, birds, pandas, deer, horses, cattle and both Old and New World NHPs). One case has been reported in a human, an HIV-1 positive man with crusted verrucous lesions of the skin.{4740} The bacteria cannot be grown on artificial media, but can be grown in hens’ eggs. Spores can survive for a year.

The disease in rabbits either occurs as explosive outbreaks (most often) or as subclinical infection. It should be suspected in outbreaks of diarrhea at weaning time. Important predisposing factors in rabbits are poor sanitation, stress and treatment with sulfonamides. Animals develop anorexia and profuse watery diarrhea, and die quickly.  Grossly there are hemorrhages on the serosal surface of the cecum, and thick, edematous bowel wall, and foci of necrosis in the mucosa. The liver has numerous pinpoint white foci, which are also seen in the myocardium.{4731}

Signs in mice are sudden death, colitis and occasional spread to the myocardium and liver. Gerbils are also affected.{3763} Guinea pigs have ileitis and typhlitis.{3775}{3768} Hamsters develop hunched posture, rough haircoat and pale watery diarrhea.{3991} In rats, it usually occurs during the post-weaning period.

Grossly, there is a "classic triad" of lesions: segmental necrosis of the intestine, multifocal pale gray-red necrotic foci in the liver, and gray-tan streaks in the myocardium. The lesions are detectable mainly in the ileum and colon, with hematogenous spread to the liver.  As shown in the images, the organism stains poorly with H&E, but shows up with Warthin-Starry silver stain, Giemsa, or PAS. Organisms are seen at the periphery of necrotic lesions, with intracellular bacteria found in hepatocytes, enterocytes and myocardial fibers in a classic "pick-up sticks" configuration.{4208}{4740} It is presumed{3551} that disease spreads by the spore forms, through fecal-contaminated feed or bedding. Control is by eradication of the colony.{3551}{3768}

MFIA testing is generally used, but cross-reaction with the whole-cell or bacterial extracts used often results in false positives. IFA is usually done to investigate positive results. Definitive diagnosis is by histopathology or PCR on cecal contents. Additionally, disease can be confirmed by provoking it in weanlings or immunosuppressed animals, although this isn't very practical. If seropositive results are obtained during screening, it is advisable to follow up with PCR and histopathology, and/or to wait and retest several weeks later.{4740}

Lesions in the mouse must be differentiated from mousepox, coronavirus, reovirus, and salmonellosis. Mice do not usually develop the "classic triad" as do rabbits and rats.{3551}

A brief synopsis of other clostridial diseases in livestock is on the livestock biology page.

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Edwardsiella ictaluri

This is the most common pathogen of farm-raised channel catfish. It has a multifocal distribution; if it affects the head it is known as "hole in the head disease". Otherwise it affects the liver, spleen, kidney, and gut. It is seen within a relatively narrow water temperature range of 22-28° C. The bacteria grow very slowly, requiring from 3-4 days to form visible colonies.{3779}

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Escherichia coli

This is a Level 2 pathogen, as enterohemorrhagic strains cause hemolytic uremic syndrome, especially in children. Enterobacteria can be speciated to some degree by using TSI slants and lysine decarboxylase broth. Miniature systems such as API or Minitek are also available. However, as there are now >100 species of Enterobacteriaceae, the laboratory must decide how hard to pursue species identification. Definitive diagnosis may require serotyping. On TSI slants, E. coli produce an acid slant, acid butt, no H₂S and gas. Other species that do the same are Enterobacter and Klebsiella, and all three species are lysine positive. In contrast, Salmonella spp. produce an alkaline slant and the other reactions are the same.{3953}

There are four groups of infections:{4776}

• Enterotoxigenic (ETEC) infections attach to enterocytes, produce enterotoxins, and are the primary cause of colibacillosis in humans and animals.
• Enterohemorrhagic (EHEC) infections attach and efface the microvillus, produce verotoxins, and occasionally cause disease in humans and animals.
• Enteropathogenic (EPEC) infections colonize and efface the microvillus but do not produce verotoxins; they cause secretory diarrhea in humans and rabbits.
• Enteroinvasive (EIEC) infections cause a shigella-like disease in humans.

E. coli is a common inhabitant of the intestine, and whether or not it causes disease is variable. In immunodeficient mice (SCID and multiple deficient, but not nudes which are only T cell deficient), it may cause hyperplastic typhlocolitis. It is a common secondary pathogen in viral disease.{3763}

Colibacillosis in rabbits is a major cause of enteritis in commercial rabbitries. The "attaching and effacing enteropathogenic" strains are not usually present in young rabbits. Serotype O15:H is one of the more virulent strains (formerly called RDEC-1).{4731} However, with predisposing factors (such as coccidiosis or a diet change which lowers the intestinal pH), the organisms proliferate. They colonize and attach to the Peyer’s patch dome epithelium, and later do the same to enterocytes. At necropsy, the small intestine looks normal, but the cecum and colon are distended with watery yellow to gray contents. Histologic lesions are most severe in weanling rabbits. The villi of the ileum are blunted and there is edema of the lamina propria with heterophils. The enterocytes at the tips of the villi are swollen and have bacilli attached. The disease must be differentiated from acute coccidiosis, clostridiosis, Tyzzer’s disease, mucoid enteropathy, and viral enteropathies.{3768}

Isolation of E. coli from birds with air sacculitis, arthritis, navel infection, foot pad infections or bone marrow must be considered a primary disease rather than one secondary to another pathogen. Hens may contaminate their eggshells with E. coli, leading to chicks with infected yolk sacs. Strains considered pathogenic for birds include 01:K1 (L), 02:K1 (L), and 078:K80 (B). Onset of disease is rapid and includes air sacculitis, fibrinous pericarditis, and fibrinous perihepatitis. Intestinal lesions of coligranuloma (Hjarre's disease) must be differentiated from avian tuberculosis by means of an acid-fast stain.{3568}

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Flavobacterium

Fish are affected by two species of Flavobacterium, F. branchiophilum and F. columnare. Both are ubiquitous bacteria that cause disease in stressed fish. F. branchiophilum causes gill epithelium to proliferate, and the fish congregate at the water inlet. F. columnare is necrotic, causing skin erosions, frayed fins and eroded gills. Wet mounts are very characteristic, as most fish pathogens are short Gram negative rods, but these are long rods that form a haystack appearance.{3779}

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Francisella tularensis

This small coccobacillus is widespread in the Northern Hemisphere. There are two biotypes: type A is more virulent and exists in a rabbit and tick reservoir system; type B is less virulent and less common in the US, having a water cycle with rat and aquatic hosts. Tularemia is transmitted by fly bites, ticks, abrasions, ingestion or inhalation. There are four disease syndromes: ulceroglandular/oculoglandular, oropharyngeal, pneumonic, and typhoidal. Signs in animals depend on whether the disease is rapidly fatal or causes a longer course with DIC and anemia. Histopathology includes multifocal necrosis of spleen, liver and lymph nodes, with neutrophils present in the lesions. Bronchial pneumonia may occur. A case of tularemia was reported in a squirrel monkey at Stanford in 1997{4001}. It is a Level 2 pathogen for clinical materials, but cultures and animal studies must be conducted at ABSL3. The human infectious dose is only a few organisms; there is a vaccine available.

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Fusobacterium necrophorum

This is a filamentous anaerobic organism that infects many animals, including man. The spectrum of clinical disease varies widely. In ruminants it causes necrotic stomatitis, gastroenteritis, hepatitis and foot rot. Carnivores appear to be more resistant. It produces both exotoxins and endotoxin which may facilitate invasion into deeper tissues including blood vessels and bone.

Lemierre's Syndrome of man was very common in the pre-antibiotic era. It is an acute clinical condition caused by oropharyngeal infection that leads to septic thrombophlebitis of the internal jugular vein. There are pulmonary embolic abscesses in over 95% of cases. Mortality in untreated patients was >90%. In teenagers and young adults, it usually occurs after an episode of sore throat and is known as postanginal sepsis. Signs are fever and acute illness that progress rapidly to death if not treated. Lemierre's syndrome occurred in a New Zealand White rabbit with acute onset of anorexia, lethargy and depression and a swelling around the left mandible. In humans, treatment may consist of antibiotics with beta-lactamase anaerobic bacterial activity. In animals, metronidazole, penicillin, cephalosporins, chloramphenicol and tetracyclines have been used.{4127}

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Haemophilus

H. parasuis is the causative organism of Glasser's disease in swine, a syndrome of polyserositis and polyarthritis. It causes suppurative bronchopneumonia that is fatal in severe cases. The organism is normally carried in the nasopharynx and requires stress such as weather changes, weaning, or concurrent viral infection (i.e. swine influenza) to cause disease. SPF pigs seem to be particularly susceptible to Glasser's disease.{2737}

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Helicobacter

This organism was the subject of a Special Topic Overview in 1997{3845}. Helicobacter was first cultured from diseased human gastric tissue in 1982 although spiral organisms had been seen long before that. The key to the new finding was that the organisms grow in microaerophilic conditions on special agar (Brucella agar with 10% horse blood, vancomycin, polymyxin B and trimethoprim{3763}). They resemble water stains, not forming the usual colonies, and so might be overlooked. Helicobacter was originally placed in the genus Campylobacter, but it has several sheathed polar flagella and some strains are strongly urease-positive, a feature that can be used for rapid presumptive diagnostic testing.{3845} All Helicobacters are Gram negative, and are urease, catalase and oxidase positive{4170} (except see H. typhlonicus).

H. pylori is the type species and infects humans, macaques and cats. It is a Level 2 organism. In humans it causes chronic persistent active gastritis and peptic ulcers. It has been linked to gastric adenocarcinoma and gastric mucosa-associated lymphoma. Although originally isolated from two human volunteers, later it was found that H. pylori could also colonize pigs, puppies and cats. Natural infections seem to occur in macaques. Known species grow in the stomach, the intestine, or the liver of various animals. {4780}

©1999, Janet Becker Rodgers, DVM, MS

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Comments? Send an email to rodgers@uky.edu