Influenzae Serotype Research Articles

Interspecies transmission of an H7N3 influenza virus from wild birds to intensively reared domestic poultry in Italy

Since the “bird flu” incident in Hong Kong SAR in 1997, several studies have highlighted the substantial role of domestic birds, such as turkeys and chickens, in the ecology of influenza A viruses. Even if recent evidence suggests that chickens can maintain several influenza serotypes, avian influenza viruses (AIVs) circulating in domestic species are believed to be introduced each time from the wild bird reservoir. However, so far the direct precursor of influenza viruses from domestic birds has never been identified. In this report, we describe the antigenic and genetic characterization of the surface proteins of H7N3 viruses isolated from wild ducks in Italy in 2001 in comparison to H7N3 strains that circulated in Italian turkeys in 2002–2003. The wild and domestic avian strains appeared strictly related at both phenotypic and genetic level: homology percentages in seven of their genes were comprised between 99.8% (for PB2) and 99.1% (for M), and their NA genes differed mainly because of a 23-aminoacid deletion in the NA stalk. Outside this region of the molecule, the NAs of the two virus groups showed 99% similarity. These findings indicate that turkey H7N3 viruses were derived “in toto” from avian influenza strains circulating in wild waterfowl 1 year earlier, and represent an important step towards the comprehension of the mechanisms leading to interspecies transmission and emergence of potentially pandemic influenza viruses.

Interspecies transmission of an H7N3 influenza virus from wild birds to intensively reared domestic poultry in Italy

Since the “bird flu” incident in Hong Kong SAR in 1997, several studies have highlighted the substantial role of domestic birds, such as turkeys and chickens, in the ecology of influenza A viruses. Even if recent evidence suggests that chickens can maintain several influenza serotypes, avian influenza viruses (AIVs) circulating in domestic species are believed to be introduced each time from the wild bird reservoir. However, so far the direct precursor of influenza viruses from domestic birds has never been identified. In this report, we describe the antigenic and genetic characterization of the surface proteins of H7N3 viruses isolated from wild ducks in Italy in 2001 in comparison to H7N3 strains that circulated in Italian turkeys in 2002–2003. The wild and domestic avian strains appeared strictly related at both phenotypic and genetic level: homology percentages in seven of their genes were comprised between 99.8% (for PB2) and 99.1% (for M), and their NA genes differed mainly because of a 23-aminoacid deletion in the NA stalk. Outside this region of the molecule, the NAs of the two virus groups showed 99% similarity. These findings indicate that turkey H7N3 viruses were derived “in toto” from avian influenza strains circulating in wild waterfowl 1 year earlier, and represent an important step towards the comprehension of the mechanisms leading to interspecies transmission and emergence of potentially pandemic influenza viruses.

Invasive Haemophilus influenzae disease in Alaskan residents aged 10 years and older before and after infant vaccination programs.

The introduction of Haemophilus influenzae type b (Hib) vaccination of children has led to a decline in incidence of Hib disease in young Alaskan children. However, the impact of vaccination on unimmunized Alaskan adolescents and adults has not been studied. To characterize trends in incidence of and mortality due to invasive H influenzae disease in Alaskan residents aged 10 years and older prior to and after the introduction of a statewide Hib infant vaccination program. Population-based, descriptive correlational study conducted 1980-1996 in Alaska. One hundred twenty-nine individuals (31 Alaska Natives and 98 nonnative Alaska residents) aged 10 years and older in whom H influenzae was cultured from a normally sterile site. Incidence of H influenzae infection before (1980-1990) vs after (1991-1996) vaccination program initiation; serotype, biotype, and beta-lactamase production of isolates. The overall annual incidence of invasive H influenzae in those aged 10 years and older declined 33%, from 2.1 per 100,000 persons per year to 1.4 per 100,000 persons per year (P=. 03) after initiation of statewide infant Hib vaccination programs in 1991. This reduction appeared to be the result of a decrease in serotype b disease (82%; P<.001). Infection with other H influenzae serotypes and nontypeable strains increased from 0.5 per 100,000 persons per year to 1.1 per 100,000 persons per year (P=.01). Incidence declined from 4.2 per 100,000 persons per year to 1.2 per 100,000 persons per year in Alaska Natives (P=.005) and from 1.7 per 100,000 persons per year to 1.4 per 100,000 persons per year in nonnative Alaska residents (P=.37). Pneumonia (43%), sepsis (26%), and meningitis (16%) were the most common clinical presentations. Alcohol/drug abuse was comorbid in 15% of patients, while 13% of patients were pregnant women. beta-Lactamase production occurred in 35% of isolates and was stable throughout the surveillance. The overall case-fatality rate was 15%. The overall statewide incidence of invasive H influenzae infections in unimmunized persons aged 10 years and older decreased after the initiation of an infant Hib vaccine program, perhaps by decreasing Hib carriage in child reservoirs. An increase in non-serotype b strains was observed. This trend justifies the need for continued surveillance of invasive disease caused by H influenzae. JAMA. 2000.

Evaluation of a Competitive ELISA for Detection of Antibodies against Avian Influenza Virus Nucleoprotein

A competitive enzyme-linked immunosorbent assay (C-ELISA) employing a baculovirus-expressed recombinant nucleoprotein and a monoclonal antibody was developed for the detection of antibodies to type A influenza virus nucleoprotein. The performance of the C-ELISA was evaluated by testing 756 chickens, 1123 turkeys, 707 emus, and 1261 ostriches, for a total of 3847 serum samples. Relative to the agar gel immunodiffusion (AGID) test, the C-ELISA had a sensitivity of 100% for all four species. The C-ELISA's sensitivity relative to the hemagglutination-inhibition (HI) test results was 100% for chicken, turkey, and emu and 96.2% for the ostrich serum samples. More than 90% of the AGID-negative/C-ELISA-positive serum samples were found positive by HI for at least one influenza serotype. The specificity of C-ELISA relative to AGID ranged from 85.5% to 99.8% for sera collected from these species. These results indicated that the C-ELISA was more sensitive and more specific than the AGID test and as sensitive and as specific as the HI test. The C-ELISA has the potential to replace the AGID test for screening sera from avian species, including ratites, for detection of antibodies to type A influenza virus.

Characterization of a monoclonal antibody to the capsule of Haemophilus influenzae type b, generated by in vitro immunization

Monoclonal antibodies to polyribosylribitolphosphare (PRP), the capsular polysaccharide of Haemophilus influenza type b ( Hib), are useful tools in the investigation of the molecular and cellular mechanisms causing Hib meningitis. A better understanding of these mechanisms may lead to improved therapeutic strategies. A number of different in vivo immunization techniques in BALB/c mice were used, which did not however reveal detectable serum levels of antibodies to PRP. Therefore a modified in vitro immunization technique, originally established for in vitro immunization of human B lymphocytes, was used for this weak immunogen in mice. After 5 days of in vitro stimulation with purified PRP the splenic lymphocytes of BALB/c mice were fused with the mouse myeloma line P3-X63-Ag8.653. One hybridoma produced an IgM antibody (12E7) which recognized the capsular polysaccharide in ELISA and specifically labelled all tested Hib strains in immune fluorescent microscopy. The blotted polysaccharide PRP was immunostained with monoclomal antibody 12E7. Preincubation of Hib with this antibody enhanced the oxygen radical metabolism of polymorphnuclear leucocytes in a chemiluminescence assay. There was no cross-reactivity with the supernatants of other Haemophilus influenzae serotypes and other bacterial species, as shown by counterimmunoelectrophoresis.

Update on mechanisms and prevalence of antimicrobial resistance in Haemophilus influenzae.

The prevalence of plasmid-mediated beta-lactamase production among clinical isolates of Haemophilus influenzae has increased globally since this characteristic was first recognized in 1972. Three nationwide surveillance studies conducted in the United States in the 1980s indicated that the rate of beta-lactamase production was approximately 30% among serotype b isolates and approximately 15% among nonencapsulated strains. The American studies also documented strains with resistance to chloramphenicol, tetracycline, trimethoprim-sulfamethoxazole, rifampin, erythromycin, and certain older cephalosporins. Surveillance studies performed at about the same time in Canada, Europe, the United Kingdom, and several developing countries have also documented the prevalence of beta-lactamase-producing isolates and resistance among them to alternative agents such as chloramphenicol and tetracycline. Perhaps of greatest concern has been the isolation of H. influenzae (both serotype b and nonencapsulated strains) in the United States, Europe, and Asia that possess multiple antimicrobial resistance mechanisms. At the present time, H. influenzae isolates have not been detected that are resistant to either third-generation cephalosporins or fluoroquinolones.

Limited genetic diversity of Haemophilus influenzae (type b)

170 strains of Haemophilus influenzae (serotype b), isolated largely from patients with invasive disease from differing temporal and geographic origins were characterized using the combined approaches of DNA hybridization and outer membrane protein classification. Hybridization of a DNA probe to a region of the chromosome involved in the expression of type b capsular polysaccharide revealed that 163 (96%) isolates had one of three distinct, but closely related, chromosomal restriction fragment length polymorphisms (RFLPs). Each polymorphism was associated with its own distinctive set of outer membrane protein subtypes, indicating that the majority of H. influenzae (type b) isolates have evolved from common ancestors, giving rise to globally distributed organisms that have clonal characteristics.

Interaction of bacteriophage T7 with Hind‐endonuclease‐producing Haemophilus influenzae Rd cells

In order to test the influence of the restriction endonucleases of Haemophilus species on in vivo DNA restriction of phage T7 and its close relative T3 as well as to determine whether the anti-DNA restriction effect of the T7 and T3 ocr+ gene is also expressed in Haemophilus cells, we studied the interaction of T7 and T3 with Haemophilus influenzae serotypes Rd and Rc and Haemophilus parainfluenzae. The results show that T7 and T3 are unable to infect these bacterial species because they do not absorb to the cells.

Genetic interaction between influenza A viruses of human and animal origin

The plaque-forming activity of ultraviolet-inactivated avian influenza A viruses (classical fowl plague and A/Turkey/England/63) was reactivated by a number of different serotypes of influenza A viruses of human, porcine, equine, and avian origins. Clones obtained after multiple cycles of UV inactivation and rescue of fowl plague virus (FPV) in cross-reactivation experiments carried out in chick embryo cell cultures with UV-FPV and living A2 virus maintained the plaque-forming ability of FPV, acquired the heat-labile haemagglutinin of the A2 parent and exhibited strain-specific antigens of both viruses. The phenotypic expression of both traits transferred from the A2 parent was gradual and increased in degree with each cycle of cross reactivation. The A2 haemagglutinin marker was unstable and was inherited independently of the antigenic marker, which was maintained through many plaque-purification cycles.