Blood cell markers

Cytochemistry and immunocytochemistry are important adjunctive technologies to the morphologic characterization of blood cells and hematopoietic neoplasms. Although cytochemistry is briefly discussed, the emphasis of this article is on the clinical application of flow cytometry and leukocyte monoclonal antibodies in veterinary medicine. Classification and significance of immunophenotyping in canine and feline lymphomas and immunodeficiencies such as feline immunodeficiency virus and feline leukemia virus are discussed.

Persistent papillomavirus infection in a cat

A seven-year-old, neutered male, crossbred Persian was diagnosed as having persistent, cutaneous papillomavirus infection. The skin lesions consisted of round, multifocal-to-confluent, raised, black plaques on the neck, thorax, shoulders, and forelegs. Papillomavirus virions were demonstrated in negative-stained, electron microscopic preparations of homogenized skin lesions and within the nuclei of cells from the stratum granulosum. Avidin-biotin immunoperoxidase stains were positive for papillomavirus in the same cells. The cat was euthanized due to a clinical diagnosis o concurrent, severe, chronic pancreatitis.

Evaluation of a saliva test kit for feline leukemia virus antigen

An enzyme-linked immunosorbent assay (ELISA) test kit for the detection of feline leukemia virus (FeLV) antigen in saliva was evaluated in 150 cats. Saliva and blood samples from all cats were tested for FeLV using the saliva ELISA kit and a plasma ELISA kit, respectively. These results were compared with indirect immunofluorescent antibody (IFA) testing of blood smears also obtained from each cat. The proportion of cats that tested positive were 10%, 7%, and 8% for each test, respectively. Using the IFA test as the gold standard, the saliva FeLV test had a sensitivity of 91.7% and specificity of 97.1%, while the plasma ELISA test had a sensitivity of 91.7% and specificity of 100%.

When viral serological testing is not enough: diagnosing disease in vaccinated animals

Serological testing can be a key factor in diagnosing viral diseases. However, the extensive use of vaccines in companion animals can severely limit the use antibody detection testing. Modified-live vaccines induce an immune response that is indistinguishable from street virus in the antibody pattern and time course. Alternative testing schemes may be needed to assist the practitioner in arriving at a valid diagnosis.

Feline toxoplasmosis: interpretation of diagnostic test results

Based on seroprevalence studies, approximately 30% of the cats in the United States have been infected by T gondii. Cats are the only species that pass the environmentally resistant oocyst in feces. Sporulated oocysts are infectious to humans and the organism can cause significant disease in immunocompromised people and transplacentally-infected babies. Clinical illness including liver disease, lung disease, central nervous system disease, fever, and uveitis occur in some infected cats. Veterinarians need to be able to identify T gondii infection in cats because of potential public health risks and during the workup of clinical diseased cats. Oocyst shedding by cats is of short duration, but can be detected by fecal examination. There are currently no serological tests that can accurately determine when a cat has shed oocysts in the past. The combination of serological test findings, clinical signs of disease, exclusion of other causes, and response to anti-Toxoplasma drugs is required to make the diagnosis of antemortem++ clinical toxoplasmosis in cats.

Susceptibility of cats to equine morbillivirus

OBJECTIVE

To assess the susceptibility of cats to equine morbillivirus (EMV) by direct administration of the virus by subcutaneous, intra-nasal or oral routes, and following exposure to infected cats.

DESIGN

A disease transmission study, with controls, using ten cats.

PROCEDURE

Groups of cats were given the virus by the designated methods and assessed for evidence of infection by clinical examination, plus pathological and virological tests.

RESULTS

All cats administered the virus by subcutaneous, intra-nasal or oral routes became infected and developed the disease within 4 to 8 days. One of two cats in contact with affected cats also developed the disease, but two cats kept near to affected cats did not become infected. The virus was isolated from a range of tissues collected from the infected cats, and the lesions observed in affected cats were similar to those previously observed in horses naturally and experimentally infected with the virus.

CONCLUSION

This is the first demonstration that animals can be infected with EMV by non-parenteral means, that the virus can transmit naturally between animals and confirms other reports of the similarity of EMV disease in horses and cats.

Local immune response in Helicobacter pylori-infected cats and identification of H. pylori in saliva, gastric fluid and faeces

Helicobacter pylori-infected cats were screened by culture and polymerase chain reaction (PCR) for the presence of H. pylori in salivary secretions, gastric juice, gastric tissue and faeces. H. pylori was cultured from salivary secretions in six of 12 (50%) cats and from gastric fluid samples in 11 of 12 (91%) cats. A 298 base pair polymerase chain reactions (PCR) product specific for an H. pylori 26000 MW surface protein was amplified from dental plaque samples from five of 12 (42%) cats and from the faeces of four of five (80%) cats studied. Analyses of serum and mucosal secretions by enzyme-linked immunosorbent assay (ELISA) revealed an H. pylori-specific immunoglobulin G (IgG) response, and elevated IgA anti-H. pylori antibody levels in salivary and local gastric secretions. Immunohistochemical analyses of gastric tissue revealed the presence of IgM+ B cells assembled into multiple lymphoid follicles surrounded by clusters of CD4+ and CD8+ T cells. The lamina propria also contained single cells or aggregates of IgA+ and IgM+ B cells. These observations show that H. pylori can be identified in feline mucosal secretions, and that a localized IgA immune response develops in gastric tissue of H. pylori-infected cats. The findings suggest a zoonotic risk from exposure to personnel handling H. pylori-infected cats in vivaria.

Bartonella henselae infection in cats: evaluation during primary infection, treatment, and rechallenge infection

Bartonella henselae infection was established in eight cats of various ages by experimental inoculation. All cats remained persistently bacteremic until they were treated 4 to 7 weeks after primary inoculation. Antibody titers increased and peaked between 4 and 12 weeks for all cats. Treatment with doxycycline for 1 week was effective in suppressing bacteremia in all cats but was effective in clearing infection from only four cats. Amoxicillin, given subsequently, was effective in clearing the infection from three of the remaining cats. One kitten that remained bacteremic was treated unsuccessfully with enrofloxacin, and its bacteremia was finally cleared when it was treated with a clavulanate-amoxicillin combination. After the bacteremia was cleared, with a corresponding reduction in serum antibody titers, all eight cats were rechallenged with B. henselae. None of the cats became bacteremic after secondary challenge, and all had higher and more rapid increases in serum antibody titers than after primary inoculation. The cats became resistant to reinfection following recovery from infection, indicating that immunoprophylaxis in cats might be beneficial in helping to reduce their public health risk.

Immunohistochemical identification of B and T lymphocytes in formalin-fixed, paraffin-embedded feline lymphosarcomas: relation to feline leukemia virus status, tumor site, and patient age

The lymphocyte phenotype of 70 formalin-fixed, paraffin-embedded feline lymphosarcomas (LSAs) was determined immunohistochemically using a T cell polyclonal antibody, and a B cell monoclonal antibody. Forty-seven of 70 (67%) tumors were T cell, 19/70 (27%) were B cell, and 4/70 (6%) did not stain with either marker. Thirty-eight of 70 (54%) tumors were positive for feline leukemia virus (FeLV) antigen by immunohistochemistry (IHC), and 52/70 (74%) tumors were positive for FeLV DNA using the polymerase chain reaction (PCR). B cell tumors were as frequently FeLV-positive as T cell tumors using either IHC or PCR. Intestinal tumors were more likely to be B cell than T. The incidence of B and T cell tumors was not different among young (< or = 3 y), middle-aged (> 3 y to < or = 8 y), and old (> 8 y) cats. Both B and T cell tumors from old cats were FeLV-positive more often by PCR than by IHC. Feline leukemia virus DNA but not antigen, was detected in B cell tumors and intestinal tumors from cats > 8 y as often as it was detected in B cell tumors and intestinal tumors from cats < or = 8 y. Previously, most B cell and intestinal tumors from old cats were considered to be negative for FeLV. Here, the results suggest involvement of latent or replication-defective forms of the virus in such tumors from old cats. This study supports a role for FeLV in feline B cell as well as T cell tumorigenesis.

Glycoproteins gl and gE of feline herpesvirus-1 are virulence genes: safety and efficacy of a gl-gE deletion mutant in the natural host

Feline rhinotracheitis virus (FRV) is an important upper respiratory tract pathogen of cats. FRV is a member of the subfamily Alphaherpesvirinae and is designated feline herpesvirus-1 (FHV-1). Besides upper respiratory clinical signs, FHV-1 may cause generalized infections in neonates or abortions in pregnant queens. Recently we described a recombinant FHV-1 strain with a deletion in the genes for glycoproteins gl and gE (FHB beta-galglgE delta) and reported that cats vaccinated subcutaneously with high doses of the recombinant FHV-1 strain responded with only mild clinical signs and developed strong immunity against subsequent virulent virus challenge. Here we compare the intranasal and subcutaneous routes of administration of this strain and assess its ability to induce protective immunity and prevent virus shedding after challenge. Cats vaccinated subcutaneously or intranasally with high doses of the recombinant FHV-1 strain responded with only mild clinical signs and developed strong immunity against subsequent virulent virus challenge. This was especially evident when the mutant vaccine was administered oronasally. In contrast, intranasal administration of two other FHV-1 isolates induced severe clinical signs in cats. We conclude from testing this FHV-1 mutant in the natural host that deletion of gE and a portion of gl genes strongly reduces viral virulence but that immunogenicity is maintained.

Raccoon poxvirus feline panleukopenia virus VP2 recombinant protects cats against FPV challenge

An infectious raccoon poxvirus (RCNV) was used to express the feline panleukopenia virus (FPV) open reading frame VP2. The recombinant, RCNV/FPV, was constructed by homologous recombination with a chimeric plasmid for inserting the expression cassette into the thymidine kinase (TK) locus of RCNV. Expression of the VP2 DNA was regulated by the vaccinia virus late promoter P11. Southern blot and polymerase chain reaction (PCR) analyses confirmed the cassette was in the TK gene of the RCNV genome. An immunofluorescent antibody assay using feline anti-FPV polyclonal serum showed the expressed viral antigen in the cytoplasm of infected cells. Radioimmunoprecipitation with the same antiserum detected a 67-kDa VP2 protein which exactly matched the migration of the authentic FPV VP2 protein by SDS-polyacrylamide gel electrophoresis. Nine five-month-old cats were vaccinated and 21 days later were boosted with the recombinant virus. Peroral FPV challenge 2 weeks after the booster showed that the cats were fully protected as measured by examining clinical signs and total white blood cell counts in peripheral blood. Cats not immunized developed low to very low leukocyte counts following peroral FPV challenge. The nine vaccinated cats showed high FPV neutralization antibody prior to challenge, whereas nonvaccinated cats formed anti-FPV antibodies only after challenge.

Brugia pahangi in cats: the passive transfer of anti-microfilarial immunity from immune to non-immune cats

Serum from cats (Felis catus) that were repeatedly infected with Brugia pahangi and had become amicrofilaraemic (mf-ve) was injected intravenously into microfilaraemic (mf+ve) cats. If more than 1 microliter of immune serum per 1000 mf was injected, microfilarial counts fell dramatically within minutes and, in some cats, mf completely disappeared. In most cases mf reappeared 21-44 days later. However, in two experiments mf never reappeared and circulating antigen (indicative of the presence of living adults) could not be detected. At autopsy no adult worms were found, but in one cat 6 mf/ml were detected by filtration of cardiac blood. Passive transfer of single Ig isotypes showed that IgG is the immunoglobulin responsible for the mf killing effect of immune serum, and that IgG1 is probably the most active isotype. Mf killing and destruction, occurred in the lungs in an antibody dependent cell mediated reaction involving neutrophils, eosinophils and mononuclear cells. Three of the 20 recipient cats died from what appeared to be anaphylactic shock while under anaesthesia probably due to the sudden release of inflammatory mediators in the lung.

Studies on natural transmission of Bordetella bronchiseptica in cats

Two pregnant specific-pathogen-free (SPF) cats, from a colony endemically infected with Bordetella bronchiseptica, were housed under barrier conditions in the latter stages of pregnancy in order to study the possible transmission of the organism to their kittens. Both queens had antibody titres to Bordetella bronchiseptica of 1 in 320 at the start of the experiment but did not shed Bordetella bronchiseptica until 9 days and 6 weeks after parturition, respectively. Five of the nine kittens had detectable maternally-derived-antibody to Bordetella bronchiseptica which declined to < or = 1 in 40 by two weeks of age. Kittens were weaned at 12 weeks of age. No Bordetella bronchiseptica was isolated from any of the kittens and none seroconverted over this time. At 15 1/2 weeks of age, half of each litter were housed separately and inoculated intra-nasally with 10(8) colony-forming-units B. bronchiseptica. Mild signs of upper respiratory tract disease were seen and the organism was isolated for 19 weeks following inoculation when the experiment ended. Seroconversion occurred at 4 weeks postinoculation. Oral treatment of two clinically-recovered kittens with doxycycline once a day did not eliminate shedding.

Relationship of lower urinary tract signs to seropositivity for feline immunodeficiency virus in cats

A group of 41 cats with signs of lower urinary tract disease was compared to a group of 41 cats without any history of disease for prevalence of seropositivity for feline immunodeficiency virus (FIV). The group of healthy cats was similar in age and gender to the group of cats with signs of lower urinary tract disease. Three of the cats with lower urinary tract disease and one control cat were seropositive for FIV. This difference was not statistically significant. The most common cause of lower urinary tract signs was idiopathic. Only 7 cats had urinary tract infection, most associated with perineal urethrostomy or catheterization. Six of the cats with bacterial urinary tract infections were FIV negative.

Demonstration of borna disease virus RNA in peripheral blood mononuclear cells derived from domestic cats in Japan

Borna disease virus (BDV) naturally infects horses, sheep, and several other species, including humans, and it is believed to be related to neurological disorders. BDV infection in domestic cats has also been demonstrated by serological assays. We demonstrated for the first time BDV RNA in peripheral blood mononuclear cells from 11 of 83 (13.3%) randomly selected domestic cats in Japan by nested reverse transcriptase-PCR. The BDVs from cats were similar to but slightly different from those from horses and humans, as shown by sequencing the reverse transcriptase-PCR products. None of the cats was positive for both BDV RNA and anti-BDV antibodies.

Mediation of immunity to Toxoplasma gondii oocyst shedding in cats

Immunity to Toxoplasma gondii, as measured by oocyst shedding, was studied in cats. In 3 trials, 12 3-mo-old T. gondii-free cats were fed tissue cysts of the ME-49 strain of T. gondii. All cats shed T. gondii oocysts for approximately 1 wk starting 3-5 days after ingesting tissue cysts. One cat became ill because of toxoplasmic pneumonia and was killed 17 days after inoculation. The remaining cats remained clinically normal. Approximately 3 mo after primary infection, these 11 cats (immune) and 11 age-matched or littermate uninfected cats (nonimmune) were challenged orally with tissue cysts of the ME-49 strain. In trials 1 and 3, 1 immune and 1 nonimmune cat were killed at 36 hr, 60 hr, 5 days, and 12 days after challenge and the development of T. gondii in intestines was studied histologically; in trial 2, cats were killed at 36 hr, 60 hr, and 5 days only. None of the "immune" cats shed oocysts after challenge. Asexual T. gondii types were found at 36 and 60 hr and at 5 days, indicating partial development of T. gondii in the intestine of immune cats. There were no significant differences in lymphocyte CD4+/CD8+ from spleen, popliteal, and mesenteric lymph nodes of immune cats compared to nonimmune cats.

Long-term antibody responses of cats fed toxoplasma gondii tissue cysts

As part of a long-term study on immunity to oocyst shedding, 12 4-6-mo-old cats were inoculated orally with tissue cysts of the ME-49 strain (6 cats) or the TS-2 strain (6 cats) of Toxoplasma gondii. Two cats fed the ME-49 strain died or were killed because of acute toxoplasmosis 12 and 13 days after inoculation (DAI), respectively. On day 39 after primary infection, 5 cats (2 infected with the ME-49 strain and 3 infected with the TS-2 strain) were challenged orally with tissue cysts of the ME-49 strain. One cat died following rechallenge infection due to causes unrelated to toxoplasmosis. Seventy-seven months after primary infection, the remaining 9 cats were challenged orally with tissue cysts of the P89 strain of T. gondii. Blood samples were obtained weekly or monthly and sera were analyzed for antibodies to T. gondii using the modified agglutination test (MAT), the Sabin-Feldman dye test (DT), and the enzyme-linked immunosorbent assay (ELISA) for IgM (IgM-ELISA) or IgG (IgG-ELISA). The MAT was performed using both formalin-fixed (FF) and acetone-fixed (AF) tachyzoites. The MAT (FF) was the most sensitive test; cats seroconverted within 14 DAI and high titers (> 10,000) persisted > 6 yr, although cats had no clinical signs. The MAT titers using the AF detected recent exposure and titers declined sharply after 2 mo postinoculation. DT and ELISA titers were lower and developed slower than MAT titers. Fluctuations in antibody titers were limited to 8-fold during the 6-yr observation period. Anamnestic serum antibody responses were seen in 2 cats after the final challenge, but not after first challenge.

A feline herpesvirus-1 recombinant with a deletion in the genes for glycoproteins gI and gE is effective as a vaccine for feline rhinotracheitis

Using a site-directed mutagenesis technique we constructed a new feline herpesvirus-1 recombinant strain containing a deletion in two genes encoding glycoproteins gI and gE. These proteins may have a role in virulence, the establishment of latency, and viral recurrence as shown in other herpesviruses of the varicella and simplex types. This recombinant was characterized and used to immunize juvenile cats against virulent virus challenge. Significant protection resulted from vaccination of cats by the subcutaneous route.

Tumor necrosis factor production in cats in response to lipopolysaccharide: an in vivo and in vitro study

Supernatants from feline peritoneal exudate cells (PECs) exposed to lipopolysaccharde (LPS) produced significantly (P < 0.05) more tumor necrosis factor (TNF) activity than supernatants from cells exposed to media. An in vitro LPS response was obtained following incubation of whole blood with 10 micrograms ml-1 LPS for 2 h. Intravenous infusion of LPS (750 micrograms kg-1 rapidly increased plasma TNF activity to a maximum at 60 min after initiation of LPS infusion. By 180 min, TNF activity returned to baseline. Cats produce TNF in response to LPS in a manner similar to other species. Measurement of TNF activity in plasma or in LPS-stimulated whole blood are methods to further characterize the inflammatory response in feline diseases.

Mechanisms for persistence of acute and chronic feline calicivirus infections in the face of vaccination

The study was concerned with possible reasons for the persistence of both acute and chronic feline calicivirus (FCV)-induced disease and sustained oral carriage in the field in the face of routine FCV immunization. It was concluded from this study that: 1) the original FCV-F9 strain, which is the basis of most live vaccines, still generates cross-reactive antibodies against almost all field strains in California, 2) vaccine strains derived from FCV-F9 may not be as broadly cross-protective as the parent strain, 3) whole inactivated FCV-2280 vaccine evokes high virus neutralizing antibody titers with an equally broad spectrum of cross-reactivity as FCV-F9, 4) all vaccine strains of FCV cause acute disease signs and protracted oral shedding when administered orally, 5) strains isolated from the mouth five to ten weeks following oral inoculation can differ from parental virus, usually appearing more vaccine resistant, 6) cats previously infected with field or vaccine strains develop much less severe acute illness when subsequently infected with heterologous FCV strains but are not protected against the chronic carrier state. Therefore, the persistence of FCV in the field cannot be explained solely by the emergence of vaccine resistant strains and vaccine virus itself may contribute to both acute and chronic infection and disease.

Prevalence of Bartonella henselae antibodies in pet cats throughout regions of North America

Cat exposure has been directly associated with the development of human Bartonella henselae infections, resulting in cat-scratch disease, bacillary angiomatosis, or bacteremia. The prevalence of serum antibody titers to B. henselae was determined for selected pet cats from 33 geographic locations throughout the United States and several areas in western Canada. Seroprevalences paralleled increasing climatic warmth (P < .02) and annual precipitation (P < .03). These warm, humid areas with the highest seroprevalence would also have the highest number of potential arthropod vectors. The southeastern United States, Hawaii, coastal California, the Pacific Northwest, and the south central plains had the highest average prevalences (54.6%, 47.4%, 40.0%, 34.3%, and 36.7%, respectively). Alaska, the Rocky Mountain-Great Plains region, and the Midwest had low average prevalences (5.0%, 3.7%, and 6.7%, respectively). Overall, 27.9% (175/628) of the cats tested were seropositive. The seroprevalence of B. henselae in cats varies throughout the United States and appears to be influenced by climate.

Analysis of feline dual lymphocyte populations observed by flow cytometry

Two discrete lymphocyte populations were observed commonly on flow cytometric analysis (FCM) of feline lymphocyte subsets. The identity of these populations as small and large lymphocytes was established by correlating data from FCM with that from peripheral blood films. Dual lymphocyte populations were more likely to be seen in feline immunodeficiency virus-positive (FIV(-)+ ve) cats but their occurrence was not affected by health status, age, gender or breed. FIV(-)+ ve cats had a significantly higher proportion of large lymphocytes than FIV-negative (FIV(-)- ve) cats. However, FIV(-)+ ve cats had significantly fewer small lymphocytes than FIV(-)- ve cats but similar numbers of large lymphocytes. Lymphocyte subset analysis revealed that small lymphocytes had a greater proportion of CD4+ cells than large lymphocytes, regardless of the FIV or health status of the cat. In FIV(-)- ve cats, small lymphocytes had a greater proportion of Pan T + lymphocytes than large lymphocytes, but the converse was seen in FIV(-)+ ve cats. The proportion of CD8 + cells was higher in small lymphocytes than large lymphocytes in well FIV(-)- ve cats but this distinction was not seen in sick FIV(-)- ve cats or FIV(-)+ ve cats of any health status. Regardless of health status, FIV(-)+ ve cats had a lower absolute count of small lymphocytes which were T cells (due to lower numbers of both CD4 + and CD8 + cells) than FIV(-)- ve cats. The numbers of small B cells were similar for both FIV(-)+ ve and FIV(-)- ve cats. However, there were no differences between FIV(-)+ ve and FIV(-)- ve cats in the absolute values of any subset of the large lymphocytes, which suggested that FIV may affect only small lymphocytes. Statistically, the inclusion or exclusion of the large lymphocyte population for routine lymphocyte subset analysis did not affect the overall results. However, because there were significant differences in subset distribution between small and large lymphocytes, analysis of both groups should be included in studies examining the role of lymphocytes in disease.