Immunity of fleas (Order Siphonaptera).

The immune response of arthropod vectors plays a key role in the spread and transmission of vector-borne diseases. Although fleas transmit several human pathogens (e.g., Bartonella henselae, Rickettsia felis, R. typhi, and Yersinia pestis), few studies have examined how these vectors respond to infection. In hematophagous arthropods, imbibed pathogens must survive the hostile environment of blood meal digestion, which includes proteolytic digestive enzymes, protease inhibitors and expression of genes associated with protection of epithelial linings. Additionally, insect epithelial cells exhibit local immune defense against ingested pathogens by producing antimicrobial peptides and reactive oxygen species. This review details these and other aspects of insect immunity as it relates to fleas, with an emphasis on the gut immune response to two blood-borne pathogens, R. typhi and Y. pestis.

Impact of Sylvatic Plague Vaccine on Non-target Small Rodents in Grassland Ecosystems.

Oral vaccination is an emerging management strategy to reduce the prevalence of high impact infectious diseases within wild animal populations. Plague is a flea-borne zoonosis of rodents that often decimates prairie dog (Cynomys spp.) colonies in the western USA. Recently, an oral sylvatic plague vaccine (SPV) was developed to protect prairie dogs from plague and aid recovery of the endangered black-footed ferret (Mustela nigripes). Although oral vaccination programs are targeted toward specific species, field distribution of vaccine-laden baits can result in vaccine uptake by non-target animals and unintended indirect effects. We assessed the impact of SPV on non-target rodents at paired vaccine and placebo-treated prairie dog colonies in four US states from 2013 to 2015. Bait consumption by non-target rodents was high (70.8%, n = 3113), but anti-plague antibody development on vaccine plots was low (23.7%, n = 266). In addition, no significant differences were noted in combined deer mice (Peromyscus maniculatus) and western harvest mouse (Reithrodontomys megalotis) abundance or community evenness and richness of non-target rodents between vaccine-treated and placebo plots. In our 3-year field study, we could not detect a significant positive or negative effect of SPV application on non-target rodents.

The Cat Flea (Ctenocephalides felis) Immune Deficiency Signaling Pathway Regulates Rickettsia typhi Infection.

Rickettsia species are obligate intracellular bacteria with both conserved and lineage-specific strategies for invading and surviving within eukaryotic cells. One variable component of Rickettsia biology involves arthropod vectors: for instance, typhus group rickettsiae are principally vectored by insects (i.e., lice and fleas), whereas spotted fever group rickettsiae are exclusively vectored by ticks. For flea-borne Rickettsia typhi, the etiological agent of murine typhus, research on vertebrate host biology is facilitated using cell lines and animal models. However, due to the lack of any stable flea cell line or a published flea genome sequence, little is known regarding R. typhi biology in flea vectors that, importantly, do not suffer lethality due to R. typhi infection. To address if fleas combat rickettsial infection, we characterized the cat flea (Ctenocephalides felis) innate immune response to R. typhi Initially, we determined that R. typhi infects Drosophila cells and increases antimicrobial peptide (AMP) gene expression, indicating immune pathway activation. While bioinformatics analysis of the C. felis transcriptome identified homologs to all of the Drosophila immune deficiency (IMD) and Toll pathway components, an AMP gene expression profile in Drosophila cells indicated IMD pathway activation upon rickettsial infection. Accordingly, we assessed R. typhi-mediated flea IMD pathway activation in vivo using small interfering RNA (siRNA)-mediated knockdown. Knockdown of Relish and Imd increased R. typhi infection levels, implicating the IMD pathway as a critical regulator of R. typhi burden in C. felis These data suggest that targeting the IMD pathway could minimize the spread of R. typhi, and potentially other human pathogens, vectored by fleas.

Th1/Th2 immune responses and oxidative stress in caprine flea allergy dermatitis.

Flea allergy dermatitis (FAD) is the common, often neglected skin disease of goats caused mainly by Ctenocephalides felis. This study aimed to evaluate the immuno-oxidative pathobiology of FAD in goats. Twelve goats from the same herd were divided into two groups of six animals each. The group I (FAD) included animals with natural flea infestation and severe dermatitis lesions. The group II (Healthy control) animals were free from any parasitic infestation. To assess the pathological changes, the markers of oxidative stress (lipid peroxidation, reduced glutathione and total antioxidant capacity), and immune status (Tumour necrosis factor alpha, Interleukin 10, Transforming growth factor beta 1 and Th1/Th2 cytokine ratio) were evaluated from the blood and the serum samples. Remarkable oxidative stress and severe inflammatory response with Th2 cytokine dominance were observed in flea infested animals. Highly antigenic agents of fleas, either secretory or excretory or structural, induced severe inflammatory responses and significant oxidative stress in caprine FAD. Massive release of cytokines may be responsible for severe skin inflammation and lesions in FAD in contrast to other Th2 dominant ectoparasitic skin conditions of goats'.

Evaluation of the effect of host immune status on short-term Yersinia pestis infection in fleas with implications for the enzootic host model for maintenance of Y. pestis during interepizootic periods.

Plague, a primarily flea-borne disease caused by Yersinia pestis, is characterized by rapidly spreading epizootics separated by periods of quiescence. Little is known about how and where Y. pestis persists between epizootics. It is commonly proposed, however, that Y pestis is maintained during interepizootic periods in enzootic cycles involving flea vectors and relatively resistant host populations. According to this model, while susceptible individuals serve as infectious sources for feeding fleas and subsequently die of infection, resistant hosts survive infection, develop antibodies to the plague bacterium, and continue to provide bloodmeals to infected fleas. For Y. pestis to persist under this scenario, fleas must remain infected after feeding on hosts carrying antibodies to Y. pestis. Studies of other vector-borne pathogens suggest that host immunity may negatively impact pathogen survival in the vector. Here, we report infection rates and bacterial loads for fleas (both Xenopsylla cheopis (Rothschild) and Oropsylla montana (Baker)) that consumed an infectious bloodmeal and subsequently fed on an immunized or age-matched naive mouse. We demonstrate that neither the proportion of infected fleas nor the bacterial loads in infected fleas were significantly lower within 3 d of feeding on immunized versus naive mice. Our findings thus provide support for one assumption underlying the enzootic host model of interepizootic maintenance of Y. pestis.

An open, self-controlled study on the efficacy of topical indoxacarb for eliminating fleas and clinical signs of flea-allergy dermatitis in client-owned dogs in Queensland, Australia.

BACKGROUND: Canine flea-allergy dermatitis (FAD), a hypersensitivity response to antigenic material in the saliva of feeding fleas, occurs worldwide and remains a common presentation in companion animal veterinary practice despite widespread availability of effective systemic and topical flea-control products. HYPOTHESIS/OBJECTIVES: To evaluate the clinical response in dogs with FAD treated topically with indoxacarb, a novel oxadiazine insecticide. ANIMALS: Twenty-five client-owned dogs in Queensland, Australia diagnosed with pre-existing FAD on the basis of clinical signs, flea-antigen intradermal and serological tests. METHODS: An open-label, noncontrolled study, in which all dogs were treated with topical indoxacarb at 4 week intervals, three times over 12 weeks. RESULTS: Twenty-four dogs completed the study. Complete resolution of clinical signs of FAD was observed in 21 cases (87.5%), with nearly complete resolution or marked improvement in the remaining three cases. Mean clinical scores (Canine Atopic Dermatitis Extent and Severity Index-03) were reduced by 93.3% at week 12. Mean owner-assessed pruritus scores were reduced by 88% by week 12. Mean flea counts reduced by 98.7 and 100% in weeks 8 and 12, respectively. CONCLUSIONS AND CLINICAL IMPORTANCE: Topical indoxacarb treatment applied every 4 weeks for 12 weeks, without concomitant antipruritic or ectoparasiticide therapy, completely alleviated flea infestations in all dogs and associated clinical signs of FAD in a high proportion of this population of dogs in a challenging flea-infestation environment.

Differences in systemic and skin migrating-specific CD4 T cells in papular urticaria by flea bite.

BACKGROUND: Papular urticaria by flea bite is a chronic allergic condition in which clinical improvement may occur at the age of 7 years, thus representing a natural model of acquired immunologic tolerance in humans. The aim of this study was to characterize regulatory cells and specific responses to flea antigens of CD4(+) T lymphocytes expressing cutaneous migration markers in patients with papular urticaria caused by flea bite and with different disease evolution times. METHODS: Cell populations were characterized by flow cytometry in samples from patients and healthy controls. Specific cell stimulation was performed with a complete flea body extract. The Mann-Whitney U test was used for comparisons. RESULTS: Total dendritic cells were lower in patients than in healthy controls. No quantitative differences were found in CD4 regulatory T cells. CD4(+) T cells from patients produced more IL-4, lL-10, IL-17, and IFN-γ. Patients who experienced the onset of symptoms within the first 5 years of age showed a greater percentage of local (cutaneous lymphocyte antigen +) IL-4- and IL-17-producing cells, while patients who experienced the onset of symptoms after the age of 5 years had a higher percentage of systemic (cutaneous lymphocyte antigen -) IL-10-producing cells. CONCLUSION: Analysis of the cellular immune response against whole flea antigen in patients with papular urticaria by flea bites suggests a possible participation of inflammatory cytokines in the skin reaction (Th17) and a systemic control mechanism (IL-10). This pattern of cytokine production in patients could be a consequence of an impaired dendritic cell population.

Expression of the rubber-like protein, resilin, in developing and functional insect cuticle determined using a Drosophila anti-Rec 1 resilin antibody.

BACKGROUND: The natural elastomeric protein, insect resilin, is the most efficient elastic material known, used to store energy for jumping and flight in a variety of insects. Here, an antibody to recombinant Drosophila melanogaster pro-resilin is used to examine resilin expression in Drosophila and a wider range of insects. RESULTS: Immunostaining of Drosophila embryos reveals anti-resilin reactivity in epidermal patches that exhibit a dynamic spatial and temporal expression through late embryogenesis. Resilin is also detected in stretch receptors in the embryo. In developing adult Drosophila, resilin pads are described at the base of wings and at the base of flexible sensory hairs in pupae. Resilin is also detected in embryos of the tephritid fruitfly, Bactrocera tryoni, and two well-known concentrations of insect resilin: the flight muscle tendon of the dragonfly and the pleural arch of the flea. CONCLUSIONS: The anti-Rec1 antibody antibody developed using Drosophila pro-resilin as antigen is cross-reactive and is useful for detection of resilin in diverse insects. For the first time, resilin expression has been detected during embryogenesis, revealing segmental patches of resilin in the developing epidermis of Drosophila.

Successful immunotherapy of canine flea allergy with injected Actinomycetales preparations.

AIMS: Can heat-killed, borate-buffered suspensions of Gordonia bronchialis, Rhodococcus coprophilus or Tsukamurella inchonensis be used to treat canine flea allergy? MATERIALS & METHODS: Organisms cultured on Sauton's medium into stationary phase were autoclaved in borate-buffered saline and stored at 10 mg wet weight/ml. Intradermal injections of 0.1 ml containing 1 mg of bacilli were administered on the first and 20th days of the study. G. bronchialis and R. coprophilus were most effective in a pilot study of a small number of dogs with flea allergy. A larger number of affected dogs were then randomized to receive placebo or either of the two selected reagents. The extent and severity of allergic signs and symptoms were scored and blood samples were collected just before the first injection and 28 days after the second. RESULTS: Both selected reagents reduced the extent and severity of lesions (p < 0.001) and reduced scratching. Eosinophil numbers were reduced (p < 0.0001) between the first and second assessment. CONCLUSIONS: Injections of G. bronchialis or R. coprophilus effectively reduce the signs and symptoms of flea allergy in dogs.

Efficient induction of CD25- iTreg by co-immunization requires strongly antigenic epitopes for T cells.

BACKGROUND: We previously showed that co-immunization with a protein antigen and a DNA vaccine coding for the same antigen induces CD40 low IL-10 high tolerogenic DCs, which in turn stimulates the expansion of antigen-specific CD4+CD25-Foxp3+ regulatory T cells (CD25- iTreg). However, it was unclear how to choose the antigen sequence to maximize tolerogenic antigen presentation and, consequently, CD25- iTreg induction. RESULTS: In the present study, we demonstrated the requirement of highly antigenic epitopes for CD25- iTreg induction. Firstly, we showed that the induction of CD25- iTreg by tolerogenic DC can be blocked by anti-MHC-II antibody. Next, both the number and the suppressive activity of CD25- iTreg correlated positively with the overt antigenicity of an epitope to activate T cells. Finally, in a mouse model of dermatitis, highly antigenic epitopes derived from a flea allergen not only induced more CD25- iTreg, but also more effectively prevented allergenic reaction to the allergen than did weakly antigenic epitopes. CONCLUSIONS: Our data thus indicate that efficient induction of CD25- iTreg requires highly antigenic peptide epitopes. This finding suggests that highly antigenic epitopes should be used for efficient induction of CD25- iTreg for clinical applications such as flea allergic dermatitis.

The effects of skin disease on the penetration kinetics of hydrocortisone through canine skin in vitro.

This study investigated the effects of allergic skin disease on the penetration kinetics of hydrocortisone through canine skin in vitro. Full-thickness lesional and nonlesional (normal) skin was removed from the dorsal lumbosacral and dorsocaudal thoracic regions, respectively, of five canine cadavers. The dogs were suspected of having flea allergy dermatitis based on their distribution and types of skin lesions. Nonlesional skin was confirmed to be histologically normal, and the histopathology of the lesional skin was consistent with allergic dermatitis. Excised skin was clipped, mounted in Franz-type diffusion cells, and the transdermal penetration of a saturated, radiolabelled hydrocortisone solution was measured over 30 h. When the penetration data for all five dogs were pooled, a restricted (or residual) maximal likelihood mixed model predicted that the permeability coefficient and pseudosteady-state flux of hydrocortisone was more than twice as great (95% confidence interval 1.55-2.71 times as great; P < 0.0001) through lesional compared with nonlesional skin. There was no significant difference in the lag time for hydrocortisone penetration through lesional compared with nonlesional skin of the dogs. This study has confirmed that the transdermal penetration of hydrocortisone may be altered, typically increased twofold, but could be as high as 10-fold, through lesional compared with nonlesional skin of dogs with suspected flea allergy dermatitis. This is likely to be affected by variables such as disease severity, concurrent infections and interindividual differences in skin characteristics.

An immunotherapeutic treatment against flea allergy dermatitis in cats by co-immunization of DNA and protein vaccines.

Flea allergy dermatitis (FAD) is considered a harmful and persistent allergic disease in cats, dogs and humans. Effective and safe antigen-specific treatments are lacking. Previously we reported that the simultaneous co-immunization with a DNA vaccine and its cognate coded protein antigen could induce antigen-specific iTreg cells (inducible Treg cells); demonstrating its potential to protect animals from FAD in a murine model. Its clinical efficacy however, remains to be demonstrated. In this report, we clinically tested this protocol to treat established FAD in cats following flea infestations. We present data showing a profound therapeutic improvement of dermatitis in these FAD cats following two co-immunizations, not only in relieving clinical symptoms, but also the amelioration of the allergic responses, including antigen-induced wheal formation, elevated T cell proliferation, infiltration of lymphocytes and migration of mast cells to the sites. This study demonstrates that a co-immunization approach as described can be used to treat flea-induced allergic disease in animals, thus implicating its potential for a practical clinical application.

Prevalence of flea infestation in dogs and cats in Hungary combined with a survey of owner awareness.

A survey was conducted in order to gain current information on flea species (Siphonaptera: Pulicidae) infesting dogs and cats living in urban and rural areas of Hungary, along with data on the factors that affect the presence, distribution and seasonality of infestation. In addition, owner awareness of flea infestation was evaluated. Practitioners in 13 veterinary clinics were asked to examine all dogs and cats attending the clinic and to collect fleas, when present, on 2 days in each month from December 2005 to November 2006. They also completed a questionnaire for each animal examined. A total of 319 dogs (14.1%) were found to be infested; the highest prevalence (27.1%) of infestation on dogs occurred in August and the lowest (5.4%) in May. Prevalence of fleas on cats was higher (22.9%); the highest (35.0%) and lowest (8.1%) prevalences occurred in July and April, respectively. Fleas were more prevalent in rural (387/1924 animals, 20.2%) than in urban (161/1343 animals, 12.0%) areas. Three species, Ctenocephalides felis (Bouché), Ctenocephalides canis (Curtis) and Pulex irritans L., were found. On dogs, the prevalence of C. canis alone was 53.0%, whereas that of C. felis alone was 36.0%. Only 19 specimens of P. irritans were found on 14 dogs from rural habitats only. Prevalence of C. felis only on cats was 94.3%; the remaining cats were infested with either C. canis or with mixed infestations of C. felis and C. canis. More than half (51.4%) of the owners of infested dogs and cats had not used flea control products in the past year or more, and five times as many owners in rural than urban areas had not used flea control products in the same period. Very few owners reported having attempted to kill fleas in their animals' environment; instead, they believed that fleas were acquired from other cats or dogs.

Therapeutic efficacy of topical hydrocortisone aceponate in experimental flea-allergy dermatitis in dogs.

OBJECTIVE: To evaluate the treatment efficacy of a topical spray containing hydrocortisone aceponate (HCA) on dogs with flea-allergy dermatitis (FAD). DESIGN: A controlled clinical study was conducted on dogs with experimentally induced FAD. Sixteen laboratory beagles with mild to moderate clinical signs were divided into two groups. The test group received HCA by topical spray once daily for 7 days, while the control group did not. Pruritic events (time and frequency) were videotaped and then scored. Clinical signs (erythema, papules, excoriation and alopecia) present on four anatomical regions were monitored and their severity directly assessed. RESULTS: After 2 days, pruritus was reduced by 94% in the treatment group and by 24% in the control group (P = 0.014) in cumulative time, and by 86% versus 34% (P = 0.034) in frequency. The HCA spray also resulted in significant improvements in overall clinical signs: 23% versus 0% in the control group (P = 0.0006) on day 3 and 43% versus 15% in the control group (P = 0.0006) on day 7. During the 7-day trial, no drug-related adverse effects were observed. CONCLUSIONS: Topical treatment with HCA showed a rapid and potent antipruritic effect on dogs with FAD. HCA also demonstrated significant overall therapeutic effects on FAD-associated skin lesions.

Differential Th1/Th2 balance in peripheral blood lymphocytes from patients suffering from flea bite-induced papular urticaria.

BACKGROUND: The Th1/Th2 balance has not been characterized in patients suffering from flea bite-induced papular urticaria (FBPU). Our aim was to improve understanding of the immunopathogenesis of CD4+ and CD8+ T-cells in humans suffering from flea bite-induced papular urticaria. METHODS: Peripheral blood mononuclear cells were obtained from 18 pediatric patients and 10 age-matched healthy controls. Cellular phenotypes, intracellular production of interferon gamma (IFNgamma) and interleukin-4 (IL-4) in T-cells stimulated with polyclonal stimuli was determined by flow cytometry following short-term in vitro stimulation. RESULTS: The results revealed lower frequencies of IFNgamma-secreting (p = 0.02) and higher frequencies of IL-4-secreting (p = 0.03) CD4+ T-cells in patient lymphocyte cultures compared to healthy control cultures in the presence of polyclonal stimuli. This is the first description of differential cytokine patterns in papular urticaria patients. CONCLUSION: Patients suffering from papular urticaria have an atopic status compared to healthy children.

Monitoring of basophil sensitization to antigens of the cat flea (Ctenocephalides felis felis): a new tool for the diagnosis of feline flea bite hypersensitivity?

Suitability of blood basophils for in vitro diagnosis of flea allergy dermatitis (FAD) or flea bite hypersensitivity was studied in cats. A functional in vitro test (FIT) for sensitized type I allergic effector cells was used to evaluate the degree and kinetics of in vivo basophil sensitization against flea antigens in cats under long-term flea exposure. FIT results were compared with intradermal (IDT) and serological testing. Before, during, and after weekly repeated exposure to Ctenocephalides felis; 14 cats were repetitively FIT-assessed for general and flea-specific sensitization. In three cats, flea-specific sensitization was seen before and throughout flea exposure. Five cats, although generally sensitized, never developed a flea-specific sensitization. Six cats initially FIT-negative became sensitized for flea antigen during flea infestation. Induction, upregulation, and binding of C. felis-specific sensitizing antibodies to basophils during flea challenge may explain the developing sensitization in these cats. Strong discrepancies between the levels of flea-specific circulating IgE and basophil sensitization contrasted comparable results for basophil and mast cell sensitization using FIT and IDT, respectively. Hence, the FIT might provide an immunological supplement to the clinical diagnosis of FAD in cats by elucidating the state of basophil-sensitization to flea antigens. And it may be a comfortable alternative to IDT.

Induction of adaptive T regulatory cells that suppress the allergic response by coimmunization of DNA and protein vaccines.

Allergen-induced immediate hypersensitivity (AIH) is a health issue of significant concern. This robust inflammatory reaction is initiated by the allergen-specific T cell responsiveness. Severe lesion reactions on skin are consequential problem requiring medical treatment. Effective Ag-specific treatments or preventions are lacking. Using a rodent model of AIH induced by flea allergens, we first report that coimmunization of DNA and protein vaccines encoding the flea salivary specific Ag-1 ameliorated experimental AIH, including Ag-induced wheal formation, elevated T cell proliferation, and infiltration of lymphocytes and mast cells to the site of allergen challenge. The amelioration of AIH was directly related to the induction of a specific population of flea antigenic specific T cells exhibiting a CD4(+)CD25(-)FoxP3(+) phenotype, a characteristic of regulatory T (T(REG)) cells. These T(REG) cells expressing IL-10, IFN-gamma, and the transcriptional factor T-bet after Ag stimulation were driven by a tolerogenic MHC class II(+)/CD40(low) dendritic cell population that was induced by the coimmunization of DNA and protein vaccines. The tolerogenic dendritic cell could educate the naive T cells into CD4(+)CD25(-)FoxP3(+) T(REG) cells both in vitro and in vivo. The study identified phenomenon to induce an Ag-specific tolerance via a defined Ag vaccinations and lead to the control of AIH. Exploitation of these cellular regulators and understanding their induction provides a basis for the possible development of novel therapies against allergic and related disorders in humans and animals.

Temporal dynamics of a T-cell mediated immune response in desert rodents.

Immunocompetence, the general capacity of an individual host to mount an immune response against pathogens, is commonly assessed by the response to a challenge of the immune system by injection of phytohaemagglutinin (PHA). The response to PHA is commonly considered a reliable estimate of the T-cell mediated immune response. We investigated the temporal pattern of the PHA response in 10 rodent species from the Negev desert, Israel. We hypothesized that the temporal dynamics of the PHA response would differ among species with different natural patterns of flea parasitism. We injected PHA subcutaneously in the footpad of each rodent and measured its PHA response 6, 24 and 48 h after injection. Rodent species showed two types of PHA response. One type was rapid and characteristic of rodents that had either species-poor flea assemblages, or that are rarely attacked by fleas. This response peaked approximately 6 h after PHA injection. The second type of response was delayed and was typical of rodents that have either species-rich flea assemblages or high abundance and prevalence of fleas or both. Their response to PHA peaked 24 h after injection. Furthermore, rodents that responded promptly had a lower maximum response than rodents with a delayed response. Our results suggest the occurrence of a trade-off between intensity and latency of the PHA response and, therefore, the necessity to account for the relationship between maximum PHA response and time after injection when making interspecific comparisons of immunocompetence.

A rodent model for allergic dermatitis induced by flea antigens.

There have been very few reports of experimentally induced animal models of allergic dermatitis, an immunologic disorder. This report describes the induction of histopathology confirmed allergic dermatitis in C57BL/6 mice along with the consistent clinical sign of alopecia following the administration of flea antigens emulsified in complete Freund's adjuvant (CFA). By comparing different strains of mice, routes of injection, types of adjuvants and different dosages of flea antigens, C57BL/6 mice were found to be most susceptible to flea antigens administered intramuscularly (i.m.) and subsequently developed dermatologic excoriations and local alopecia. The level of specific IgE reactive to flea antigens in C57BL/6 mice after the onset of clinical signs was significantly higher than such levels in mice without clinical signs, suggesting that flea antigen-specific IgE level can be correlated to the severity of allergic hyper-reaction. CD4(+) T lymphocytes and IL-4 rather than IL-10, or IFN-gamma were found to be the predominant cytokines associated with the clinical onset of allergic symptoms in C57BL/6 mice. Further, histopathologic analysis indicated that not only mast cells had infiltrated into the area of the skin lesion, but the damage was found to be at a stage where mast cells were degranulating causing considerable exacerbation of the local injury. In conclusion, this murine allergic dermatitis model induced by flea antigens may provide a useful means to evaluate vaccines or immunodulatory drugs; thus providing researchers with a tool to study allergy-related disorders and other parameters needed in the area of allergic investigations.

Serological, intradermal and live flea challenge tests in the assessment of hypersensitivity to flea antigens in cats (Felis domesticus).

The results of intradermal testing with three commercial flea antigens and a serological test for IgE antibodies to flea antigens were compared with live flea challenge in cats. Eight control cats with no prior flea exposure had negative serological test and flea challenge results. By contrast, 17 out of 27 cats with previous flea exposure showed immediate reactivity to flea challenge; reactivity at 6, 24 and 48 h after flea exposure was noted in 12, 16 and 21 cats, respectively. Seventeen of these cats had positive serological test results. Seven cats showed immediate intradermal test reactions to the ARTU allergen, six reacted to the Biophady allergen, and six reacted to the Greer allergen. Intradermal test reactivity was less frequent at the other time points. Using the results of the flea challenge as the 'gold standard' for the presence or absence of sensitisation to fleas, the sensitivity and specificity of the serological test was 0.88 and 0.77, respectively. Sensitivities of the intradermal tests at the four time points ranged from 0 to 0.33, whereas the specificities ranged from 0.78 to 1.0. Live flea challenge is better able to detect cats with hypersensitivity to fleas than either intradermal or serological testing.