Seroprevalence of Toxoplasma gondii infection in stray and household cats in Tehran

The prevalence of anti-Toxoplasma gondii specific IgG in stray and household cats in Tehran was determined by Indirect Fluorescent Antibody Test (IFAT) on serum samples from 100 cats (50 stray and 50 households). Overall infection rate was 63%. The infection rate in stray cats (90%) was significantly higher (p<0.001) than that of household cats (36%). Last serum positive dilutions varied from 1: 32 to 1: 512 titres in which the highest percentage (27%) was for 1:256 and the least (4.8%) was at 1:32. The rate of infection between male and female cats of both groups was not significantly different; 90.3% versus 89.5% for male and female in stray cats, respectively. Different sexes of household cats were seropositive at the same rate (36%). A high positive correlation (r(2)=0.97) between age and the rate of infection was observed. The prevalence of Toxoplasma gondii infection in cats in Tehran was high, especially in stray cats which are probably the main source of Toxoplasma infection in this area.

N-terminal atrial natriuretic peptide immunoreactivity in plasma of cats with hypertrophic cardiomyopathy

Atrial natriuretic peptide (ANP) is an important regulator of fluid homeostasis and vascular tone. We sought to compare N-terminal ANP immunoreactivity (ANP-IR) in plasma from cats with and without hypertrophic cardiomyopathy (HCM). Secondarily, we evaluated relationships between ANP-IR and echocardiographical variables in cats with HCM and healthy cats. Venous blood samples were obtained from 17 cats with HCM and from 19 healthy cats. Plasma ANP-IR concentration was determined by an enzyme-linked immunoassay. Two cats with HCM had clinical evidence of congestive heart failure; the remainder had subclinical disease. Plasma ANP-IR concentration was higher in cats with HCM (3,808 +/- 1,406 fmol/L, mean +/- SD) than in control cats (3,079 +/- 1,233 fmol/L), but this difference was not statistically significant (P = .11; 95% confidence interval [CI] = -166 to 1,622). There was a significant, but modest correlation between plasma ANP-IR concentration and left ventricular posterior wall thickness (r = 0.42; P = .01). Additionally, plasma ANP-IR concentration was weakly correlated with left atrial size (r = 0.35; P = .03). A linear regression model was developed to further explore these relationships. Atrial size and wall thickness were included in the model; the 2 explanatory variables had an interactive effect on plasma ANP-IR concentration (R2 = 0.27; P = .02). There was no appreciable correlation between plasma ANP-IR concentration and any other echocardiographical variable. In a population that included cats with subclinical disease, those with HCM did not have significantly higher plasma ANP-IR concentration than did healthy cats. An exploratory multivariable regression analysis suggested a linear relationship between ANP-IR concentration and atrial size, wall thickness, and their interaction.

Lessons from the cat: development of vaccines against lentiviruses

Feline immunodeficiency virus (FIV) is a natural infection of domestic cats, which produces a disease with many similarities to human immunodeficiency virus (HIV) infection in man. The virus is an important cause of morbidity and mortality in pet cats worldwide. As such an effective vaccine is desirable both for its use in veterinary medicine and also as a model for the development of an HIV vaccine. A large number of candidate vaccines have been tested against feline immunodeficiency virus. These include inactivated virus and infected cell vaccines, DNA and viral vectored vaccines, subunit and peptide vaccines and vaccines using bacterial vectors. Ultimately, the development of inactivated virus and infected cell vaccines led to the release of the first licensed vaccine against FIV, in 2002. This review highlights some of the difficulties associated with the development of lentiviral vaccines and some of the lessons that have been learned in the FIV model that are of particular relevance to the development of HIV vaccines.

Pulmonary arterial disease in cats seropositive for Dirofilaria immitis but lacking adult heartworms in the heart and lungs

OBJECTIVE

To determine the prevalence and severity of pulmonary arterial lesions in cats seropositive for heartworms (Dirofilaria immitis) but lacking adult heartworms in the heart and lungs during necropsy.

ANIMALS

630 adult cats from an animal control shelter in Florida.

PROCEDURE

Cats were tested for adult heartworms in the heart and pulmonary arteries and antibody against heartworms in the serum. Histologic examination was conducted on the right caudal lung lobe of 24 heartworm- and antibody-positive cats; 24 heartworm-negative and antibody-positive cats; and 24 heartworm-, antibody-, and antigen-negative cats. Wall areas of 10 small to medium-sized pulmonary arteries of each cat were measured and expressed as a proportion of total cross-sectional area.

RESULTS

Heartworm infection or seropositive status was significantly and strongly associated with seventy of medial hypertrophy of pulmonary arterial walls. Heartworm- and antibody-positive cats and heartworm-negative and antibody-positive cats had a significant increase in wall thickness, compared with wall thickness for heartworm- and antibody-negative cats. Heartworm- and antibody-positive cats had the most severe hypertrophy. The proportion with occlusive medial hypertrophy was significantly higher in heartworm- and antibody-positive cats (19/24 [79%]) and heartworm-negative and antibody-positive cats (12/24 [50%]), compared with heartworm- and antibody-negative cats (3/24 [13%]).

CONCLUSIONS AND CLINICAL RELEVANCE

Cats with serologic evidence of exposure to heartworms, including those without adult heartworms in the lungs and heart, have a greater prevalence of pulmonary arterial lesions than heartworm-negative cats without serologic evidence of exposure. Additional studies are needed to define the pathogenesis, specificity, and clinical importance of these lesions.

Physiological and haematological findings and clinical observations in a model of acute systemic anaphylaxis in Dirofilaria immitis-sensitised cats

OBJECTIVE

This study aims to understand the pathophysiology of anaphylaxis in Dirofilaria immitis-sensitised cats by analysing objective physiological and haematological measurements after challenge.

DESIGN

Nineteen healthy D immitis-naive cats were sensitised using weekly injections of aluminium hydroxide-adjuvanted D immitis antigen, administered subcutaneously over 6 weeks. After sensitisation, cats (n = 16) were anaesthetised and challenged with intravenous D immitis antigen. A control group (n = 3) was sham-challenged using intravenous sterile 0.9% saline. Systolic blood pressure (measured non-invasively/indirectly), respiratory rate, degree of dyspnoea, blood O2 saturation, expired CO2, and heart rate and were measured immediately before and at 10 to 15 min intervals after challenge until terminal apnoea occurred or euthanasia at 140 mins post-challenge. Blood was collected for complete blood count immediately before and at 10, 20 and 35 mins after challenge. Clinical observations were recorded as they occurred.

RESULTS

Antigen-challenged cats were divided into two groups: acute (apnoea occurred within 25 mins of challenge) and subacute (breathing at 25 mins after challenge). In both groups, the degree of dyspnoea increased and blood O2 saturation and blood pressure decreased. Respiratory rate increased in the subacute group. Expired CO2 decreased in both Ag-challenged and control groups. Haematocrit increased in the subacute group. Neutrophil count decreased in the acute group and platelet count decreased in the subacute group. Eosinophil count decreased in the subacute and control groups. Sustained dyspnoea and gastrointestinal signs were the most common clinical manifestations of anaphylaxis in the antigen-challenged cats.

CONCLUSIONS

Intravenous challenge with D immitis antigen in sensitised cats results in dyspnoea, hypoxaemia and systemic hypotension accompanied by haemoconcentration.

Vaccine use and disease prevalence in dogs and cats

A yearly revaccination of adult pets against distemper, the adenoviral and parvoviral diseases is scientifically unwarranted, professionally obsolete and ethically questionable; other vaccinal antigens, however, may need yearly or even more frequent injections. Base immunisation is redefined: it is complete only after the multivalent booster in the second year of life. A yearly revaccination interview, not necessarily an injection, should become the new standard. This interview is a professional service that must be taught, expertly performed and invoiced. Adult animals should be “vaccinated to measure”, taking age, breed, lifestyle, the epidemiologic situation, etc. into account. Post-vaccination serology should become a guide in revaccination decisions. For a solid herd immunity, more animals of the population must be vaccinated. The profession should issue regular updates of the ‘code of vaccination practice’. To counteract vaccination antagonism, a concerted action of academia, the veterinary profession and industry is required.

Duration of immunity for canine and feline vaccines: a review

In our studies aimed at assessing the minimum duration of vaccinal immunity (DOI), approximately 1000 dogs have been vaccinated with products from all the major US veterinary biological companies. The DOI for the various products is determined by antibody titers for all dogs and, by challenge studies in selected groups of dogs. Recently, all major companies that make canine vaccines for the U.S. market have completed their own studies; published data show a 3 years or longer minimum DOI for the canine core products, canine distemper virus (CDV), canine parvovirus type 2 (CPV-2), and canine adenovirus-2 (CAV-2). Studies with feline core vaccines - feline parvovirus (FPV), calicivirus (FCV) and herpes virus type I (FHV-1) have shown a minimum DOI of greater than 3 years. Based on these results, the current canine and feline guidelines (which recommend that the last dose of core vaccines be given to puppies and kittens > or =12 weeks of age or older, then revaccination again at 1 year, then not more often than every 3 years) should provide a level of protection equal to that achieved by annual revaccination. In contrast, the non-core canine and feline vaccines, perhaps with the exception of feline leukaemia vaccines, provide immunity for < or =1 year. In general the effectiveness of the non-core products is less than the core products. Thus, when required, non-core vaccines should be administered yearly, or even more frequently.

Platelet-bound antibodies detected by a flow cytometric assay in cats with thrombocytopenia

In cats, primary or secondary immune-mediated thrombocytopenia have rarely been described or characterised. The objective of this study was to determine platelet-bound antibodies (PBA) by a flow cytometric assay in both healthy and thrombocytopenic cats. Direct PBA testing was performed in 42 thrombocytopenic cats (platelet counts 6-179 x 10(9)/l, median 56 x 10(9)/l). Of these 42 cats, 19 had positive PBA test results, 17 of which were considered to have secondary immune-mediated thrombocytopenia (sITP). Underlying diseases included fat necroses (four cases), feline infectious peritonitis (three), feline leukaemia virus (two) or feline immunodeficiency virus (two) infections, lymphoma (two), leukaemia (one), hepatitis (one), pyelonephritis (one), or hyperthyroidism (one). In two cats, no underlying disease was found suggesting a primary immune-mediated thrombocytopenia (pITP). The PBA test was negative in 23 cats diagnosed with varying underlying diseases and in 47 healthy control cats with platelet values within the reference range. Only seven of the 42 cats with thrombocytopenia (platelet count 10-57 x 10(9)/l, median 34 x 10(9)/l) had spontaneous bleeding. This study suggests that immune-mediated destruction of platelets might be an important pathological mechanism for feline thrombocytopenia caused by various underlying diseases. In cats, pITP appears to be rarely diagnosed.

Primary immune-mediated hemolytic anemia in 19 cats: diagnosis, therapy, and outcome (1998-2004)

Immune-mediated hemolytic anemia (IMHA) occurs less frequently in cats than in dogs. The value of the Coombs' test (CT) has been questioned, but detailed surveys of its use are lacking. The objective of this study was to describe 19 cats with primary IMHA (pIMHA) and to examine the diagnostic value of the direct CT. The CT was performed in 92 cats; it was negative in 5 healthy, in 9 sick nonanemic, and in 55 cats with different types of anemia. The CT was positive in 18 anemic cats (2 feline leukemia virus (FeLV) positive, 1 with cholangiohepatitis, 15 with no underlying disease). Moreover, agglutination persisted after saline washing in 5 anemic cats (1 lymphoma, 4 pIMHA). Inclusion criteria for pIMHA were a positive CT (15) or persistent agglutination (4), and the exclusion of other diseases. The age of the 19 cats ranged from 0.5 to 9 years (median, 2 years); male cats were overrepresented. The PCV on admission was 6-22% (median, 12%). The anemia was nonregenerative in 11 cats. Additional abnormal laboratory results were leukocytosis (2), lymphocytosis (6), hyperbilirubinemia (13), hyperglobulimemia (10), and increased liver enzyme activities (10). Initial treatment consisted of blood transfusions (10), crystalloids (11), prednisolone (19), antibiotics (19), and H2-blockers (11). Four of 17 cats were euthanized 9, 63, 240 and 2,160 days after initial presentation (mortality rate, 23.5%). Relapses were reported in 5 of 16 cases (31%). Thus, pIMHA appears to occur more frequently than recognized previously, with a more favorable prognosis in cats than in dogs. The CT was useful in identifying immune-mediated pathogenesis.

Mucosal defence along the gastrointestinal tract of cats and dogs

Diseases that are associated with infections or allergic reactions in the gastrointestinal and respiratory tracts are major causes of morbidity in both cats and dogs. Future strategies for the control of these conditions require a greater understanding of the cellular and molecular mechanisms involved in the induction and regulation of responses at the mucosal surfaces. Historically, the majority of the fundamental studies have been carried out in rodents or with tissues obtained from man, but the expanding range of reagents available for the study of farm and companion animals provides opportunities for study in a wider range of animals including cats and dogs. To date, these studies have tended to be focussed on characterising the cellular distributions in healthy animals and in groups of cats and dogs identified as having an increased risk of mucosal disturbance. Where species comparisons of mucosal immune systems have been made, the results have tended to be divided between monogastric and ruminant animals. It is then not surprising that the mucosal immune systems of both cats and dogs bear greatest similarity to that documented for man and pigs. For example, IgA is the dominant immunoglobulin in mucosal secretions of cats and dogs and oral tolerance can be induced following the introduction of novel antigens into the diet. Also like several other species, cats become transiently hypersensitive to the newly introduced dietary antigen prior to the establishment of tolerance. In contrast, there are a number of potentially important differences. In particular, there are significant differences between cats and dogs in the expression MHC class II molecules on gut epithelial cells. Similarly, it has been reported that cats have elevated numbers of intraepithelial lymphocytes (IEL) and that a proportion of these express surface IgM. It remains to be determined if these differences reflect the way in which the animals are maintained and if they may have greater biological significance.

Adoptive immunotherapy of feline immunodeficiency virus with autologous ex vivo-stimulated lymphoid cells modulates virus and T-cell subsets in blood

The potential of immunotherapy with autologous virus-specific T cells to affect the course of feline immunodeficiency virus (FIV) infection was explored in a group of specific-pathogen-free cats infected with FIV a minimum of 10 months earlier. Popliteal lymph node cells were stimulated by cocultivation with UV-inactivated autologous fibroblasts infected with recombinant vaccinia viruses expressing either FIV gag or env gene products, followed by expansion in interleukin-2. One or two infusions of both Gag- and Env-stimulated cells resulted in a slow increase in FIV-specific gamma interferon-secreting T cells in the circulation of cats. In the same animals, viral set points fluctuated widely during the first 2 to 3 weeks after adoptive transfer and then returned to pretreatment levels. The preexisting viral quasispecies was also found to be modulated, whereas no novel viral variants were detected. Circulating CD4(+) counts underwent a dramatic decline early after treatment. CD4/CD8 ratios remained instead essentially unchanged and eventually improved in some animals. In contrast, a single infusion of Gag-stimulated cells alone produced no apparent modulations of infection.

Feline lentivirus evolution in cross-species infection reveals extensive G-to-A mutation and selection on key residues in the viral polymerase

Factors that restrict a virus from establishing productive infection in a new host species are important to understand because cross-species transmission events are often associated with emergent viral diseases. To determine the evolutionary pressures on viruses in new host species, we evaluated the molecular evolution of a feline immunodeficiency virus derived from a wild cougar, Puma concolor, during infection of domestic cats. Analyses were based on the coding portion of genome sequences recovered at intervals over 37 weeks of infection of six cats inoculated by either intravenous or oral-nasal routes. All cats inoculated intravenously, but only one inoculated orally-nasally, became persistently viremic. There were notable accumulations of lethal errors and predominance of G-to-A alterations throughout the genome, which were marked in the viral polymerase gene, pol. Viral structural (env and gag) and accessory (vif and orfA) genes evolved neutrally or were under purifying selection. However, sites under positive selection were identified in reverse transcriptase that involved residues in the nucleotide binding pocket or those contacting the RNA-DNA duplex. The findings of extensive G-to-A alterations in this cross-species infection are consistent with the recently described editing of host cytidine deaminase on lentivirus genomes. Additionally, we demonstrate that the primary site of hypermutation is the viral pol gene and the dominant selective force acting on this feline immunodeficiency virus as it replicates in a new host species is on key residues of the virus polymerase.

Detection of Feline calicivirus (FCV) from Vaccinated Cats and Phylogenetic Analysis of its Capsid Genes

We analysed genogroups of four feline calcivirus (FCV) isolates (FCV-S, H10, Ao198-1 and ML89) obtained from cats that experienced FCV infection after having been vaccinated against FCV. New PCR primer sets (8F/8R, Ao-S/Ao-A, cp-S/cp-A) were also designed, since the conventional Seal primer failed to amplify the target sequences in two samples. The genogroups of the four isolates as well as eight global and 17 domestic strains were determined by phylogenetic analysis of their amino acid sequences. One out of the four strains (25%) isolated in this study, H10, was grouped into genogroup I, along with the vaccine strains F9 and FCV-255. The other three isolates (75%) belonged to genogroup II. Thus, there were more isolates in genogroup II than in genogroup I. However, the antibody values of the four isolates against cat anti-F9 antisera were significantly decreased. There may be no relationship between the neutralizing antibody titre and genogroup. Amino acid sequence alignment of the four isolates showed that only a single amino acid in region C, which is involved in neutralization epitopes, was different in ML89 strain from that of F9. The other three strains, H10, Ao198-1 and FCV-B, shared the same amino acid sequence with F9. Alignment of amino acids for linear epitopes in the F9 strain, which are located at regions D and E, showed variations in 5' hypervariable region (HVR) of E, whereas D and conE had only synonymous substitutions i.e. no change in the amino acid sequence. This mutation in 5' HVR of region E suggested a vaccine breakdown, as the region is known to be essential for antigenicity. The genogroup II FCV is likely to be the cause of the FCV infection in this study, while the vaccine strains belong to genogroup I. Thus, the existing vaccine may need reevaluation for its effectiveness.

Antibodies against Gag are diagnostic markers for feline foamy virus infections while Env and Bet reactivity is undetectable in a substantial fraction of infected cats

Spumaretroviruses or foamy viruses constitute a distinct subfamily of retroviruses. The biology of foamy viruses within the authentic host, their mode of transmission, and disease potential in the authentic host or after zoonotic transmission into human or other species are almost unknown. Using feline foamy virus (FFV) as model system, we established modular enzyme-linked immunosorbent assays (ELISA) suited to determine feline IgG and IgM antibody responses against structural and non-structural FFV proteins. We validated the ELISAs with standard reference sera. In 99 cats admitted to a Swiss veterinary hospital, overall FFV Gag antibody prevalence was 36%, reactivity against Env and the non-structural protein Bet each was about 25%, and 19% of the sera were directed against all three FFV antigens. With one exception, all Bet- and/or Env-positive sera were also positive for Gag. In this small epidemiological pilot study, FFV antibodies were not significantly associated with clinical disease.

Effects of a single dose of an intranasal feline herpesvirus 1, calicivirus, and panleukopenia vaccine on clinical signs and virus shedding after challenge with virulent feline herpesvirus 1

The objective of this study was to determine whether intranasal administration of a commercially available FVRCP vaccine to kittens lessened clinical signs and feline herpesvirus 1 (FHV-1) viral shedding when compared to unvaccinated control kittens after FHV-1 challenge. Three groups of 10 unvaccinated kittens were administered one dose of vaccine 6 days (group 1), 4 days (group 2), or 2 days (group 3) before challenge, respectively. One group was maintained as unvaccinated controls (group 4). FHV-1 challenge was then induced and the kittens were observed for 14 days. When the grouped vaccinated kitten results (groups 1-3) were compared to group 4 results, clinical scores following challenge were significantly lower (P<0.05) and significantly lower body temperatures (P<0.05) were detected on days 0, 5 and 9 post-challenge. When evaluated by individual group, group 1 and group 2 kittens had significantly lower clinical scores (P<0.05) than group 4 kittens post-challenge. In addition, FHV-1 shedding was lower in group 1 kittens when compared to group 4 kittens on day 6 after challenge (P<0.05). Administration of this vaccine within several days prior to exposure lessened clinical signs of disease and FHV-1 shedding compared to unvaccinated kittens.

Seroprevalence of antibodies against Borrelia burgdorferi and Anaplasma phagocytophilum in cats

OBJECTIVE

To determine whether cats in the northeastern United States develop serum antibodies against antigens of Borrelia burgdorferi and Anaplasma phagocytophilum and whether coinfection with the 2 organisms occurs.

SAMPLE POPULATION

Serum samples from 84 healthy cats and 9 cats with lameness, fever, anorexia, or fatigue.

PROCEDURE

Serum antibodies against B. burgdorferi and A. phagocytophilum were measured with an ELISA incorporating a whole-cell preparation or purified recombinant antigens, by means of Western blot analysis, or indirect fluorescent antibody (IFA) staining.

RESULTS

ELISA results indicated that 44 of 93 (47%) sera contained antibodies against > or = 3 B. burgdorferi antigens, whereas 43 (46%) were reactive to whole-cell B. burgdorferi. Serum reactivity to protein 35, VlsE, and outer surface proteins A and F was most common. Seropositivity to > or = 3 antigens occurred at the same rate (5/9) in the 9 ill cats as in the 84 healthy cats (46% [39/84]). Of 13 sera reactive to recombinant antigens, 9 were seropositive as measured by Western blot testing with whole-cell antigen. Seropositivity rates of 30% and 38% were detected for antibodies against A phagocytophilum via IFA and ELISA testing, respectively. Fifteen (16%) sera had antibodies against both pathogens.

CONCLUSIONS AND CLINICAL RELEVANCE

Cats living in areas infested by Ixodes scapularis ticks are exposed to B. burgdorferi and A. phagocytophilum and, in some instances, may be coinfected. Most cats appeared healthy. An ELISA incorporating specific recombinant antigens may be used adjunctively with Western blot and other assays to confirm B. burgdorferi and A. phagocytophilum infection in cats.

Three-year duration of immunity in cats following vaccination against feline rhinotracheitis virus, feline calicivirus, and feline panleukopenia virus

Forty-two seronegative cats received an initial vaccination at 8 weeks of age and a booster vaccination at 12 weeks. All cats were kept in strict isolation for 3 years after the second vaccination and then were challenged with feline calicivirus (FCV) or sequentially challenged with feline rhinotracheitis virus (FRV) followed by feline panleukopenia virus (FPV). For each viral challenge, a separate group of 10 age-matched, nonvaccinated control cats was also challenged. Vaccinated cats showed a statistically significant reduction in virulent FRV-associated clinical signs (P = .015), 100% protection against oral ulcerations associated with FCV infection (P < .001), and 100% protection against disease associated with virulent FPV challenge (P < .005). These results demonstrated that the vaccine provided protection against virulent FRV, FCV, and FPV challenge in cats 8 weeks of age or older for a minimum of 3 years following second vaccination.

Rush immunotherapy in an experimental model of feline allergic asthma

Specific allergen immunotherapy represents the only curative treatment of allergy. No studies have evaluated its efficacy in feline allergic asthma. We hypothesized that an abbreviated course of immunotherapy (rush immunotherapy, RIT) would blunt eosinophilic airways inflammation in experimental feline asthma induced with Bermuda grass allergen (BGA). The 6-month study included asthmatic-RIT treated cats; asthmatic-no RIT treated cats; and non-asthmatic cats. RIT involved increasing parenteral doses (20-200 microg) of BGA over 2 days. Numbers of eosinophils in bronchoalveolar lavage fluid (BALF), serum and BALF immunoglobulins, lymphocyte blastogenesis assays, and cytokines in blood and BALF were evaluated. BALF eosinophils decreased (P=0.048) only in asthmatic-RIT treated cats (baseline 1.1 x 10(6); Month 6, 2.4 x 10(5)). Serum BGA-specific IgG was higher (P<0.001) at all time points after baseline within the asthmatic-RIT group, and was higher (P<0.001) than asthmatic-no RIT cats at Months 1 and 3. No differences (P=0.133) in BGA-specific IgE levels over time were noted among asthmatic-RIT cats, but this group had lower IgE levels (P<0.001) levels than asthmatic no-RIT cats at Months 3 and 6. Differences in BGA-specific IgA levels over time and between the two groups did not reach the traditional level of significance. The mean BGA stimulation index in the asthmatic-RIT cats was biologically insignificant at 6 months, reflecting BGA-specific lymphocyte hypoproliferation. Preliminary results of cytokine profiles were not significantly different; however, BAL cytokine profiles favoring a Th2 response prior to RIT shifted to increased IFN-g and IL-10 thereafter. RIT dampens eosinophilic airways inflammation in cats with experimental asthma. The mechanism of RIT may involve changes in allergen-specific immunoglobulins, induction of hyporesponsive lymphocytes, or alteration of cytokine profiles.

Feline immunodeficiency virus vaccine: Implications for diagnostic testing and disease management

Feline immunodeficiency virus (FIV) is a common feline pathogen, with an overall infection prevalence of approximately 11% in cats worldwide. Most infected cats eventually succumb due to direct viral effects or, more commonly, to secondary infections resulting from virus-induced immunosuppression. FIV infection is considered lifelong, and diagnosis most often relies on detection of virus-specific antibodies. A currently available whole virus, adjuvanted, inactivated FIV vaccine induces antibodies in vaccinates that is indistinguishable from those induced by infection. As a result, currently available diagnostic tests cannot reliably distinguish vaccinated cats from infected cats, or from cats that are both vaccinated and infected. From both an epidemiologic and an individual cat perspective, it is impossible to determine whether use of this vaccination is more beneficial than it is harmful.

Toll-like receptor expression in feline lymphoid tissues

Toll-like receptors (TLRs) are germline-encoded pattern recognition receptors (PRRs) that activate the innate immune system. While it is clear that TLRs are important in the immune response against pathogens, they may also be exploited by some pathogens. Our objective is to determine whether feline immunodeficiency virus (FIV) infection affects TLR expression or function thereby resulting in innate immune dysfunction. To this end, we cloned partial sequences for feline TLRs 1--3, 5--8, and developed real-time PCR assays to quantify feline TLRs 1--9. TLR expression was quantified in normal cat lymphoid tissues, purified lymphocyte subsets, and FIV-infected cell lines. Different expression patterns of TLRs were found in spleen, mesenteric lymph node, retropharyngeal lymph node, thymus, intestinal intraepithelial lymphocytes, and lamina propria lymphocytes. B lymphocytes, CD4+ T cells, and CD8+ T cells all expressed TLRs 2--5, 7--9; however, the relative levels of expression varied among lymphocyte phenotypes. Infection of cell lines with FIV resulted in altered TLR expression levels that differed depending on cell type. These results demonstrate that tissue distribution of TLRs is associated with the immunological role of a particular tissue, that lymphocytes may also express these 'innate immune' receptors, and that FIV infection can alter TLR expression.

Effects of drug treatment on inflammation and hyperreactivity of airways and on immune variables in cats with experimentally induced asthma

OBJECTIVE

To compare the effects of an orally administered corticosteroid (prednisone), an inhaled corticosteroid (flunisolide), a leukotriene-receptor antagonist (zafirlukast), an antiserotonergic drug (cyproheptadine), and a control substance on the asthmatic phenotype in cats with experimentally induced asthma.

ANIMALS

6 cats with asthma experimentally induced by the use of Bermuda grass allergen (BGA).

PROCEDURES

A randomized, crossover design was used to assess changes in the percentage of eosinophils in bronchoalveolar lavage fluid (BALF); airway hyperresponsiveness; blood lymphocyte phenotype determined by use of flow cytometry; and serum and BALF content of BGA-specific IgE, IgG, and IgA determined by use of ELISAs.

RESULTS

Mean +/- SE eosinophil percentages in BALF when cats were administered prednisone (5.0 +/- 2.3%) and flunisolide (2.5 +/- 1.7%) were significantly lower than for the control treatment (33.7 +/- 11.1%). We did not detect significant differences in airway hyperresponsiveness or lymphocyte surface markers among treatments. Content of BGA-specific IgE in serum was significantly lower when cats were treated with prednisone (25.5 +/- 5.4%), compared with values for the control treatment (63.6 +/- 12.9%); no other significant differences were observed in content of BGA-specific immunoglobulins among treatments.

CONCLUSIONS AND CLINICAL RELEVANCE

Orally administered and inhaled corticosteroids decreased eosinophilic inflammation in airways of cats with experimentally induced asthma. Only oral administration of prednisone decreased the content of BGA-specific IgE in serum; no other significant local or systemic immunologic effects were detected among treatments. Inhaled corticosteroids can be considered as an alternate method for decreasing airway inflammation in cats with asthma.

Evaluation of live feline immunodeficiency virus vaccines with modified antigenic properties

Live-attenuated viruses have typically been generated from pathogenic viruses by genetic modifications that modified their replicative capacity. The present study investigated whether modification of the antigenic properties of live-attenuated viruses might improve upon the protection that such vaccines afford against lentivirus infection. In a previous study, random amino acid substitutions were introduced into the transmembrane envelope glycoprotein of the feline immunodeficiency virus (FIV), within a highly conserved domain (principal immunodominant domain) bearing immunodominant B-cell epitopes. Amongst a wide set of mutants, mutations that modified antibody specificity without abolishing infectivity ex vivo were selected. In the present study, two such mutants, TN14 and TN92, were evaluated for their replicative capacities and pathogenic properties in vivo in comparison with the parental virus, FIV 34TF10. No significant differences in viral load were observed between mutant and parental viruses. After 1 year of infection, all animals were subjected to a heterologous intraclade superinfection with a primary strain of FIV. Whilst both parental and modified viruses protected cats from high viral loads after superinfection, the TN92 virus afforded a higher degree of protection (P=0·0079). Such improvement in protection might correlate with a decrease in the immunogenicity of a B-cell epitope potentially involved in antibody enhancement of infection.

Feline herpesvirus type-1 transcription is associated with increased nasal cytokine gene transcription in cats

The etiopathogenesis of chronic nasal discharge in the cat is poorly understood. The objective of this study was to investigate alterations in transcription of genes for cytokines and chemokines in association with feline herpesvirus-1 (FHV-1) mRNA transcription. Nasal samples from 21 cats were submitted for FHV-1 virus isolation (VI), traditional endpoint polymerase chain reaction (PCR) detection of FHV-1 DNA, and quantitative real-time TaqMan PCR analysis of cytokines and chemokines (interleukin [IL]-4, IL-5, IL-6, IL-10, IL-12p40, IL-16, IL-18, interferon [IFN]-gamma, tumor necrosis factor [TNF]-alpha, and regulated on activation normal T cell expressed and secreted protein [RANTES]) and of FHV-1 mRNA and DNA. Co-infection with feline calicivirus or Chlamydophila spp. was excluded in all cats. Gene transcription in nasal samples from four specific pathogen free (SPF) cats served as the calibrator for cytokines. FHV-1 was detected by VI in 14 of 21 samples, by traditional PCR in 18 of 21 samples, and by quantitative PCR in 13 (mRNA+) and 18 (DNA+) samples. Nasal samples from cats positive for FHV-1 mRNA displayed significantly increased transcription of IL-6, IL-10, IL-12p40, IL-18, IFN-gamma, TNF-alpha, and RANTES (P<0.05) in comparison to samples from cats negative for FHV-1 mRNA. The cycle threshold for FHV-1 DNA was significantly higher in cats with detectable FHV-1 mRNA (P<0.05). Increased transcription of cytokines/chemokines in cats with detectable mRNA for FHV-1 suggests a role for FHV-1 in nasal inflammation.