Cerebral toxoplasmosis in a cat with feline leukemia and feline infectious peritonitis viral infections

Abstract

A diarrheic young cat died after neurological involvement. Biochemistry pointed to feline infectious peritonitis (FIP). The final diagnosis was severe multifocal meningoencephalitis due to Toxoplasma gondii. The presence of the parasite in the brain was confirmed using immunohistochemical staining. Concomitant feline leukemia virus (FeLV) and FIP were possible contributors to the clinical, fatal outcome.

Cats are definitive hosts in the life cycle of Toxoplasma gondii (1) and can shed the parasite in the environment. Chronic, apparently subclinical infection is common in cats; for example, seroepidemiological studies in Finland and the Netherlands suggest widespread infection in feline populations (2,3) with 3% proportional mortality rate (2,4). Prevention of T. gondii infection is a public health priority (5–7). Although direct contact with cats is not thought to be a risk factor for humans to acquire toxoplasmosis (5), preventing feline T. gondii infection is important to reduce the overall contamination of the environment with oocysts (7–9). Reports of clinical feline toxoplasmosis (1,9) highlight that diagnosing clinical toxoplasmosis in cats can be challenging and the disease is confirmed when the parasite is demonstrated in body fluids or tissues. A tentative diagnosis can be based on rising IgM titers, after excluding other causes for the clinical signs and a positive clinical response to anti-T. gondii drugs (1,9). The case reported here is of interest, as limited information is available on the clinical signs of feline toxoplasmosis.

Case description

In January 2017, a 6-month-old female cat, born in a feline colony but later adopted, was taken to a veterinary hospital because of sudden watery diarrhea. Clinical examination showed poor body development, monolateral cataract, and dehydration. The ophthalmologist suggested that the cataract was of nutritional origin. The body temperature was within the normal range. The cat was initially treated with dietary modification consisting of commercial food for gastrointestinal disorders and antibiotic for presumed bacterial diarrhea (spiramycin-metronidazole, Stomorgyl; Merial Italia, Milan, Italy), 10 mg/kg body weight (BW), PO, q12h for 10 d. Fluid replacement therapy was not provided. Fecal examination with a flotation method at 100× magnification for parasite eggs and oocysts was negative. A commercially available enzyme-linked immunosorbent assay (ELISA) test for Giardia spp. (SNAP Giardia; IDEXX Laboratories, Westbrook, Maine, USA) was negative. There was no clinical response to the dietary modification and antimicrobial therapy.

Fifteen days after the onset of diarrhea the patient displayed neurological signs such as body tremors and nystagmus. A blood sample was collected for a hemogram and serum biochemical tests to investigate the causes of the neurological signs. Treatment with clindamycin (Antirobe; Zoetis Italia, Rome, Italy), 10 mg/kg BW, PO, q12h, was initiated after tentative diagnosis of neurological toxoplasmosis or septicaemia with brain involvement. The following day the cat was blind, and had head tremors and convulsion. The cat died on the 17th day after presentation.

The laboratory report was available after the cat died. The hemogram detected leucocytosis [12.09 × 10⁶/L; reference range (RR): 5.0 to 11.0 × 10⁶/L] with neutrophilia and monocytosis. Erythrocyte count was within the reference range (red blood cell count 6.76 × 10¹²/L; RR: 6.35 to 9.0 × 10¹²/L); estimated platelet concentration was adequate. Biochemical blood tests showed evidence of systemic inflammation (serum amyloid, 122.5 mg/L; RR: 0.1 to 0.5 mg/L), hyper-bilirubinemia (11.9 μmol/L; RR: 2.4 to 4.4 μmol/L) with liver enzymes within the reference range, decrease in serum cholinesterase (848 IU/L; RR: 1955 to 3950 IU/L), decrease in serum creatinine (37.1 μmol/L; RR: 84.0 to 163.5 μmol/L), and hyponatremia (133 mmol/L; RR: 145 to 152 mmol/L). The serum protein concentration was 78 g/L (RR: 63 to 78 g/L) with hypoalbuminemia (18 g/L; RR: 30 to 40 g/L), and hyperglobulinemia (62 g/L; RR: 30 to 45 g/L). Serum protein electrophoresis showed polyclonal hyperglobulinemia and an increase in the alfa-2 globulin component. Serological and biomolecular screening for viruses causing infection in cats and for anti-Toxoplasma gondii antibodies (IgG-IgM) was not performed.

At necropsy examination, the patient was in poor body condition, with opacity of the lens due to monolateral cataract. The gut was affected by catarrhal enteritis with edematous mucosa and pale intestinal wall. The liver appeared mottled with multiple tiny white circular lesions disseminated throughout the entire parenchymal tissue. The kidneys had multifocal white circular lesions of various sizes. The frontal sinus was full of green exudate. The brain had edema of the cerebral cortex.

The kidney, liver, spinal cord, and brain were fixed in formalin and routinely processed for histological examination. The kidney showed chronic severe multifocal pyogranulomatous nephritis (Figure 1a) with multifocal tubular necrosis and mineralization. The liver showed multifocal moderate chronic hepatitis with perivascular lymphoplasmacellular infiltration and multifocal biliary stasis. The spinal cord and brain samples showed severe multifocal necrosis associated with severe lymphoplasmacytic infiltration and numerous macrophages, lymphoplasmacellular perivascular cuffing and vasculitis. Many hypereosinophilic oval protozoan cysts having a thin wall and containing basophilic parasites were seen near to vascular structures (Figure 1b). The meninges were moderately infiltrated by lymphocytes, plasma cells, and macrophages.

Figure 1.

Histological lesions and immunohistochemistry (IHC) of the brain and kidney of a 6-month-old cat that was diagnosed with cerebral toxoplasmosis following postmortem examination. a — Kidney showing chronic pyogranulomatous nephritis. Hematoxylin and eosin (H&E), 40×. b — Brain showing perivascular cuffing of lymphocytes and plasma cells with multifocal vasculitis. Many oval protozoan cysts having a thin wall and containing basophilic bradyzoites were seen near to the vascular structures. H&E, 20×. c — Kidney stained by IHC with feline coronavirus antibodies showing multifocal positive reaction in the cytoplasm of macrophages, 40×. d — Brain stained by IHC with anti-Toxoplasma gondii antibodies and showing several positively stained protozoan cysts and tachyzoites, 20×.

Immunohistochemistry (IHC) was done on 3-μm sections of the liver, kidney and brain which were all stained with antibodies against feline coronavirus (FIPV3-70 clone; BIO-RAD Segrate, Milan, Italy) and T. gondii (210-70-TOXO, VMRD, PO Box 502, Pullman, Washington, USA). Positive controls consisted of a lymph node from a coronavirus-positive cat and liver from a T. gondii-positive hare; negative controls were obtained by omitting the primary antibody during the labelling steps. The kidney showed multifocal positive reaction against feline coronavirus in the cytoplasm of macrophages (Figure 1c), while no viral particles were detected in the brain. Several protozoan cysts and tachyzoites that stained with the T. gondii antibody (Figure 1d) were seen in the brain but not in the liver or kidney.

Bacterial culture detected Clostridium perfringens and hemolytic Escherichia coli carrying the gene for cytotoxic necrotizing factor in specimens from the intestine. Hemolytic E. coli was isolated from the exudate of the frontal sinus. Biomolecular examination (RT-PCR) detected feline leukemia virus (FeLV) in the spleen, but did not detect feline immunodeficiency virus (FIV) RNA.

Discussion

The cat plays a central role in the lifecycle of T. gondii and prevention of feline infection is a measure for reducing the overall oocyst shedding in the environment (5–9). The case we report here is of interest because a neurological FIP was strongly suggested by the clinical signs and biochemical tests. Although it is usually included in differential diagnoses of neurologic diseases in cats, clinically manifested toxoplasmosis, especially with neurological clinical signs, is uncommon or underdiagnosed. In this case we linked the neurological clinical signs to toxoplasmosis only after the parasite was detected in the brain. The parasite was not detected in the liver, in contrast to the observations in other cases of fatal toxoplasmosis in cats (1,2). Furthermore, coronavirus viral particles were found only in the kidney and not in the brain. It is reported that an immunosuppressed cat may develop systemic toxoplasmosis with extraintestinal spread of tachyzoites following initial exposure or reactivation of tissue cysts (1). However, clinical and fatal toxoplasmosis, including toxoplasmosis with cerebral involvement, has been described in apparently immunocompetent cats (2,10). In the case we describe here FeLV and FIP co-infection may have facilitated the neurologic outcome of toxoplasmosis.

The brain is a common site of replication and chronic persistence of T. gondii infection. Neurological or ocular involvement, in the absence of other clinical signs, are perhaps more common after reactivated toxoplasmosis (1). Ocular localization of T. gondii appears common in cats infected during gestation (11). Regrettably in our case the eye lesions were not examined histologically.

Few reports in the literature describe clinically manifested cerebral toxoplasmosis. A Finnish study describes 6 clinical cases of cats that died because of generalized toxoplasmosis. All patients had a history of acute illness lasting approximatively 1 wk with nonspecific clinical signs (apathy, inappetence, dehydration, fever). None of the patients had received immunosuppressive drugs, but the presence of other immunosuppressive factors remained unclear. Incoordination was the only neurological sign observed in 3 of the 6 cats. Gross pathological lesions were not seen in the brain but 5 cats had histological brain lesions (glial granuloma) associated with T. gondii detected by IHC investigation (2). In an Austrian study on feline meningoencephalitis, cerebral toxoplasmosis was described in 14 of 89 samples, protozoan cysts were identified in the histological sections of the brain, and T. gondii infection was confirmed by immunohistochemistry (12). In both studies IHC was the confirmatory test after detection of histological lesions. In the Finnish study, the parasite strains were isolated in cell culture and genotyped from brain samples of 2 cats.

Fatal systemic toxoplasmosis was described in an apparently immunocompetent cat in Switzerland (10). Necrotic lesions were described in lung, liver, and lymph nodes; multiple and small foci of gliosis were present in the brain and protozoan cysts were occasionally observed in these foci (10). Diagnosis was confirmed by specific real-time polymerase chain reaction (RT-PCR) on fresh sample of intestine, lung, liver, spleen, bone marrow, and mesenteric lymph nodes (10).

Co-infection of FeLV and FIP occurs rarely (13) and we believe the immune imbalance due to virus co-infection may have facilitated the occurrence of clinically manifested fatal toxoplasmosis. This case underlines that toxoplasmosis in cats should always to be taken into account in differential diagnosis when neurological signs are displayed.