Virulence of Serovar C-1 Strains of Avibacterium paragallinarum.

The bacterium Avibacterium paragallinarum is the etiologic agent of infectious coryza of chickens. There are nine serovars of A. paragallinarum , and serovar C-1 has emerged in outbreaks of infectious coryza in layer hens in the Americas, with all isolates having been obtained from infectious coryza-vaccinated chickens. In the current study, the clinical and histopathologic outcomes of experimental infections in chickens with A. paragallinarum of serovar C-1 were investigated. The Japanese serovar reference strain, H-18, and a Mexican isolate, ESV-135, were included in the study. No differences in clinical sign scores or morbidity were observed between the two strains. The two bacterial strains caused microscopic lesions of lymphoplasmacytic inflammation in the mucosa of the nasal cavity, infraorbital sinus, and trachea. Similar severe lesions were observed in birds inoculated with both H-18 and ESV-135 strains. The lesions were present 48 hr after inoculation and persisted until day 10 after inoculation. Slight to severe, extensive hemorrhages were observed in the lumen, mucous membranes, and lamina propria of the nasal cavity and infraorbital sinus in most of the chickens inoculated with either the reference strain H-18 or the ESV-135 isolate. Hemorrhages in the upper respiratory tract of chickens experimentally infected with A. paragallinarum are reported here for the first time. The results have confirmed the high virulence of the reference strain H-18 as previously reported and have shown that the Mexican isolate was as virulent as the reference strain. The virulence of A. paragallinarum isolates may play a role in explaining why severe infectious coryza outbreaks are being seen in both vaccinated and nonvaccinated chicken flocks.

Genotyping, pathogenicity, and immunogenicity of Avibacterium paragallinarum serovar B-1 isolates from the Americas.

The bacterium Avibacterium paragallinarum is the etiologic agent of infectious coryza of chickens. Among the nine Kume serovars currently recognized in this bacterium, serovar B-1 is a common serovar in the Americas. In the current study, serovar B-1 isolates from Ecuador (seven isolates), Mexico (seven isolates) and Panama (two isolates) were genotyped. In addition one Panamanian, one Ecuadorian, and two Mexican isolates were used in a vaccination-challenge trial in which the vaccine was based on the 2671 serovar B-1 reference strain. Genotyping by enterobacterial repetitive intergenic consensus-based PCR (ERIC-PCR) resulted in ten distinguishable ERIC patterns for the 16 isolates and the two reference strains of Av. paragallinarum included in the study. No ERIC patterns were shared among isolates of the three different countries. In the vaccination-challenge trial, one isolate from Panama showed a significantly lower virulence than did the three other isolates. In terms of cross-protection, chickens vaccinated with reference strain 2671 and challenged with an Ecuadorian strain showed 40% protection, a significantly lower protection than the homologous protection level. The other three field isolates gave a similar protection level to the homologous challenge.

Prevalence of Cryptosporidium spp. in asymptomatic sheep in family flocks from Mexico State.

To determine Cryptosporidium spp. prevalence in faeces from asymptomatic sheep, 37 family flocks in Mexico State were sampled. Data were collected by the interview method and Ziehl-Neelsen stain of faecal samples for Cryptosporidium identification. The independent group proportion hypothesis test was used for differences in prevalences between sheep farms. A 34.3% general prevalence was found, and prevalence in herds with >100 animals was significantly higher (40.6%). Correlation was found between flock size and Cryptosporidium spp. presence (odds ratio, OR, 2.57; confidence interval, IC(95%), 1.84-3.60).

Virulence of the nine serovar reference strains of Haemophilus paragallinarum.

The virulence of the reference strains of the nine currently recognized Kume serovars of Haemophilus paragallinarum was investigated. The capacity of the H. paragallinarum strains to cause the typical clinical signs of upper respiratory tract disease associated with infectious coryza in unvaccinated, nasal-challenged chickens was assessed. Differences in virulence were assessed by means of a standardized scoring system for clinical signs. All nine strains were pathogenic to chickens, producing typical clinical signs of infectious coryza. The highest clinical signs score was obtained for serovar C-1 (1.72), while the lowest clinical signs score was obtained for serovar C-4 (0.32). Our results indicate that virulence differences exist among the serovars of H. paragallinarum.