An 8-year-old neutered male domestic short hair cat.The cat presented to the referring veterinarian with fever, lethargy and excess salivation.
Another cat in the household with similar signs had died the previous night. Both cats had been ill the previous year but had recovered. Both were indoor-outdoor cats that killed and ate wildlife. A FeLV/FIV test on this cat was negative.
The referring veterinarian suspected tularemia due to positive cases in sheep in the same area the previous year.
The body was in good postmortem condition with good body condition.Â The spleen was enlarged and had pinpoint white foci throughout the parenchyma.Â The lungs had severe, diffuse, acute pulmonary edema; and the urinary bladder mucosa was reddened by multiple petechiae.Â Mesenteric lymph nodes were enlarged.Â The liver was slightly pale, but was considered to be grossly normal.
Sections of liver and spleen were disrupted by multiple random foci of necrosis (Figs.Â 2-1 and 2-2).Â Necrotic foci were composed of cellular debris admixed with moderate numbers of mononuclear cells and fewer neutrophils (Fig.Â 2-3).Â Some foci were associated with hemorrhage.Â Brown and Hopp's tissue gram stain revealed small, gram negative coccobacilli both extracellularly and within macrophages.Â
Other lesions include large necrotic foci in the mesenteric lymph node similar to those seen in the liver and spleen and smaller foci in the lung and bone marrow.
Acute multifocal necrotizing hepatitis and splenitis, compatible with tularemia.
PCR for Francisella tularensis was positive on fresh spleen.Â The diagnosis was confirmed by culture in a BL-3 facility.
Tularemia is an often fatal septicemic disease endemic in rodents primarily in the western US but distributed worldwide.(2) The disease is caused by infection with Francisella tularensis, originally named Pasteurella tularensis but later found to be unrelated genetically to other Pasteurella species.Â F.Â tularensis has 4 subspecies: tularensis, holartica, mediasciatica and novidia.Â It is the subspecies tularensis, present only in North America, which most often causes fatal zoonotic infections in other species, especially sheep and human beings.Â The subspecies holartica is distributed throughout the northern hemisphere and primarily causes disease in semi-aquatic rodents such as muskrats and beavers.
The organism is a small Gram negative rod that is a facultative intracellular bacterium.Â It not only lives but proliferates in macrophages.(2) Transmission is by ingestion, inhalation, direct contact with skin or mucous membranes, or by arthropods, especially ticks and deer flies.Â Cats and dogs are thought to be somewhat resistant; however, this cat may well have been infected by ingestion of an infected rodent.Â Humans may be infected by direct contact or aerosols.Â Sheep are infected primarily by tick infestation.(4)
Clinical signs vary depending upon route of transmission.Â In humans the most common route of transmission is by direct contact in susceptible segments of the population (hunters, butchers, farmers, etc).(3) In these patients, the most common form of the disease is ulcerglandular, characterized by systemic illness with a skin ulcer at the site of infection and swelling and drainage of local lymph nodes.Â The increasing concern over weaponized bacteria for biological attack has brought renewed interest in the study of forms of tularemia caused by inhalation.Â The typhoidal form of tularemia is characterized by fever, prostration, and absence of lymphadenopathy.Â The pneumonia resulting from typhoidal tularemia can be severe and fatalities may reach 35%.Â The disease in domestic animals may be subclinical or may manifest as fatal septicemia.(4) Clinical signs previously reported in cats with tularemia include vomiting, weight loss and anorexia.(3)
The characteristic gross lesion of miliary foci of hepatic necrosis in rodents is not always visible in other species.Â Multifocal splenic necrosis, as seen grossly in this case, has been previously reported in other feline cases.(3) Histologic lesions of multifocal necrosuppurative inflammation in the liver, lung, spleen, and lymph nodes is characteristic of Francisella tularensis, but overlaps with other septicemic organisms such as Yersinia pestis and Yersinia psuedotuberculosis.(4) If possible, animals dying with a high suspicion of tularemia (signs of septicemia in an animal from an endemic area) should be necropsied under BL-2 conditions and culture should only be attempted in BL-3 facilities due to risks to laboratory personnel.Â In this case, characteristic gross and histologic lesions along with positive PCR for F.Â tularensis allowed fresh tissues to be forwarded to an appropriate laboratory for confirmation of the diagnosis.Â
Splenitis, necrotizing, random, multifocal, moderate with lymphoid depletion.
Francisella tularensis is a highly infectious zoonotic disease that is commonly found in the western United States.Â It has been reported in over 125 species of mammals, birds, reptiles, and fish.Â Tularemia gains access to its host by ingestion, penetration of the skin or mucous membranes, or injection by arthropods.Â The organism is engulfed by and multiplies within host macrophages, where it travels throughout the host via lymphatics and causes damage to vascular endothelium leading to vasculitis and thrombosis with subsequent necrotic lesions in the liver, spleen, lymph nodes, lung, and bone marrow.Â Cellular immunity is thought to be vital in fighting off this facultative intracellular bacteria.(1,4)
Rodents and lagomorphs are often found dead, but if found alive, they display signs of weakness and fever with lymphadenopathy.Â Tularemia causes a multifocal necrotizing hepatitis in rodents.Â Possible differential diagnoses for this lesion in rodents include Tyzzers disease, (Clostridium piliforme), salmonellosis, Listeria monocytogenes, Toxoplasma gondii, Yersinia pseudotuberculosis, and Yersinia enterocolitica.(1,4)
1.Â Greene CE, DeBey BM: Tularemia.Â In: Infectious Diseases of the Dog and Cat, ed.Â Greene CE, 3rd ed., pp.Â 446-451.Â Saunders, St.Â Louis, MO, 2006
2.Â Sjdstedt A: Tularemia: epidemiology, physiology and clinical manifestations.Â Ann NY Acad Sci 1105: 1-29, 2007
3.Â Tularemia.Â Institute for International Cooperation in Animal Biologics, The Center for Food Security and Public Health, Iowa State University, Ames, IA.Â www.cfsph.iastate.edu
4.Â Yalli VEO: Hematopoietic system.Â In: Jubb, Kennedy and Palmers Pathology of Domestic Animals, ed.Â Maxie MG, 5th ed., pp.Â 297-298.Â Elsevier Limited, Edinburgh, UK, 2007