Characterization of an avirulent FCV strain with a broad serum cross-neutralization profile and protection against challenge of a highly virulent vs feline calicivirus.

Highly virulent, systemic strains of Feline calicivirus (vs FCV) have been described in recent years. These vs FCV isolates cause severe edema, cutaneous ulcers, lameness and other upper respiratory and oral clinical signs typically associated with FCV infection in cats. Vs FCV isolates can cause high mortality even in cats vaccinated with currently available commercial vaccines. This study reports identification and characterization of an avirulent FCV strain (FCV 21). This strain offers a broader serum cross-neutralization profile in comparison with the commonly used vaccine strain (FCV F9), as tested with two separate viral panels of FCV isolates. The first viral panel consists of 45 FCV strains isolated around 1993. The second viral panel consists of 26 FCV strains with most isolated around 2003. The potential of using this strain as a vaccine, in a 3-way (FCV+FHV+FPV) or 4-way (FCV+FHV+FPV+FCp) format, was tested by using a highly virulent vs FCV strain (FCV-33585) as a challenge virus. The mortality induced by this vs FCV in unvaccinated control cats was 78% (7 out of 9 cats). The mortality decreased to 44% (4 out of 9 cats) in cats vaccinated with a 4-way vaccine containing FCV F9. However, when this novel FCV vaccine strain (FCV 21) was used, either in combination with FCV F9 or by itself, the mortality decreased to 0% (0 out of 10 cats). The 3-way vaccine (FCV+FHV+FPV) that contained both FCV 21 and FCV F9 also had mortality of 0% (0 out of 10 cats). The clinical scores, as calculated taking into consideration the frequency and severity of various clinical signs, correlated with mortality data. The results suggested this FCV vaccine has the potential to be broadly protective against newly emergent FCV isolates, including complete protection against challenge with a highly virulent vs FCV 33585.

Characterization of a highly virulent feline calicivirus and attenuation of this virus.

Feline calicivirus (FCV) is a common cause of upper respiratory and oral disease in cats. Highly virulent, systemic strains of FCV (vs FCV) have been recently described. These vs FCV isolates cause edema, cutaneous ulcers and high mortality in affected cats. This study reports a disease model with such a vs FCV isolate (FCV-33585). It also describes a full-length capsid gene sequence of this vs FCV isolate and the capsid sequence comparison of this strain with 35 other virulent and non-virulent FCV strains. In addition, sequence comparison of this strain with other 114 known sequences in the hyper-variable region of capsid gene was analyzed. Two amino acids were identified within the hyper-variable region as potentially unique signature for this vs FCV strain. This study also describes the attenuation of FCV-33585 by two methods: serial passaging at low temperature, and the generation of a temperature sensitive (ts) mutant by UV irridiation. Moreover, the potential use of attenuated vs FCV as vaccine was also explored. Monoclonal antibodies were also identified which could differentiate commonly used FCV vaccine strain from this vs strain (FCV-33585). And two monoclonal antibodies were found to react specifically the wild-type, not the attenuated FCV-33585.

The immunopathogenesis of flea allergy dermatitis in dogs, an experimental study.

In this study, we investigated the development of clinical disease and immune responses in the development of an experimental model of flea allergy dermatitis. Dogs were randomly divided into four treatment groups and were infested with fleas on two different feeding schedules (continuous and episodic). Group 1 consisted of four non-exposed dogs (negative controls) and Group 2 consisted of six dogs exposed to fleas continually. Groups 3 and 4 consisted of 14 dogs each that were exposed to fleas on an episodic schedule (two consecutive days every other week for 12 weeks). Group 4 also received intraperitoneal injections of a low dose of lectin (ricin) with immunomodulatory properties. The purpose of Group 4 was to investigate the effects of ricin on enhancing the development of clinical signs, flea antigen-specific IgE levels and altering the number of CD4+ and CD8+ T cell subsets in peripheral blood. Clinical signs developed in all flea exposed dogs, however, the dermatology lesion scores were less and shorter in duration for continuously exposed dogs compared to episodic exposed dogs, independent of ricin treatment. Lesion development was concentrated in the flea triangle and consisted principally of erythema, followed by alopecia, excoriation, papules, and crusts. CD4+ and CD8+ lymphocyte subsets or IgE levels were not altered by ricin treatment. Flea antigen-specific IgE values were highest in dogs exposed to fleas on a continuous basis compared to those episodically exposed. A greater percentage of clinical responder dogs with negative flea-specific IgE titers or negative intradermal test (IDT) were present in the episodic exposure groups than in the continuous exposure group. IgE titers corresponded slightly better with clinical responders than the IDT. The agreement between the IgE titers and IDT was good (weighted K = 0.67). Histopathology of skin samples were consistent with a Type I hypersensitivity. In conclusion, we were able to develop a model of flea allergy dermatitis by experimentally exposing dogs to fleas on an episodic and continuous feeding schedule. In this study, continuously exposed dogs did not develop immunotolerance, and ricin did not enhance the development of FAD.