No abstract

Lineages of hypervirulent Aeromonas hydrophila (vAh) are the cause of persistent outbreaks of motile Aeromonas septicemia in warm-water fishes worldwide. Over the last decade, this virulent lineage of A. hydrophila has resulted in annual losses of millions of tons of farmed carp and catfish in the People's Republic of China and the United States (US). Multiple lines of evidence indicate US catfish and Asian carp isolates of A. hydrophila affiliated with sequence type 251 (ST251) share a recent common ancestor. To address the genomic context for the putative intercontinental transfer and subsequent geographic spread of this pathogen, we conducted a core genome phylogenetic analysis on 61 Aeromonas spp. genomes, of which 40 were affiliated with A. hydrophila, with 26 identified as epidemic strains. Phylogenetic analyses indicate all ST251 strains form a coherent lineage affiliated with A. hydrophila. Within this lineage, conserved genetic loci unique to A. hydrophila were identified, with some genes present in consistently higher copy numbers than in non-epidemic A. hydrophila isolates. In addition, results from analyses of representative ST251 isolates support the conclusion that multiple lineages are present within US vAh isolated from Mississippi, whereas vAh isolated from Alabama appear clonal. This is the first report of genomic heterogeneity within US vAh isolates, with some Mississippi isolates showing closer affiliation with the Asian grass carp isolate ZC1 than other vAh isolated in the US. To evaluate the biological significance of the identified heterogeneity, comparative disease challenges were conducted with representatives of different vAh genotypes. These studies revealed that isolate ZC1 yielded significantly lower mortality in channel catfish, relative to Alabama and Mississippi vAh isolates. Like other Asian vAh isolates, the ZC1 lineage contains all core genes for a complete type VI secretion system (T6SS). In contrast, more virulent US isolates retain only remnants of the T6SS (clpB, hcp, vgrG, and vasH) which may have functional implications. Collectively, these results characterize a hypervirulent A. hydrophila pathotype that affects farmed fish on multiple continents.

No abstract

No pattern of adverse events that would be of concern was observed after the administration of influenza A (H1N1) vaccine, nor was there evidence of an increased risk of the Guillain-Barré syndrome.

The humoral immune responses and host protection of channel catfish, Ictalurus punctatus (Rafinesque), against Ichthyophthirius multifiliis (Ich) were determined after immunization with live theronts and sonicated trophonts. Immunizations with live theronts or sonicated trophonts were carried out by both bath immersion and intraperitoneal (i.p.) injection. Cutaneous and serum immunoglobulin (Ig) levels and anti-Ich antibodies were measured 12 and 21 days post-immunization. The level of Ich infection and survival of catfish were determined after theront challenge. Cutaneous and serum anti-Ich antibodies were significantly higher (P < 0.05) in fish immunized with live theronts by immersion or i.p. injection, or with sonicated trophonts administered by i.p. injection, than in fish immunized with sonicated trophonts by immersion, with bovine serum albumin by i.p. injection, or non-immunized controls. Host protection was noted only in fish immunized with live theronts by immersion or i.p. injection or with sonicated trophonts by i.p. injection. There was a positive correlation between higher levels of anti-Ich antibodies and host survival in the immunized fish.

This study determined whether cutaneous antibodies were present in the excised skin of channel cat®sh, Ictalurus punctatus Ra®nesque, immune to Ichthyophthirius multi®liis Fouquet (Ich). Theronts were immobilized on or near the excised skin from immune ®sh. The survival of immobilized theronts was signi®cantly reduced after exposure for 8 h to the culture of excised skin from immune ®sh. Culture¯uids from excised skin of immune ®sh immobilized theronts with a peak in the immobilization titre at 24 h post-exposure. Immobility of theronts in the culture¯uid from immune skin was removed after immunoabsorption with theronts. Indirect immuno¯uorescent staining of theronts treated with culture¯uid from excised skin of immune ®sh revealed strong and uniform uorescence on the cilia and cell surface of theronts. Western blot analysis of the culture¯uid from immune ®sh revealed a 70-kDa band which corresponded to the molecular weight of cat®sh immunoglobulin heavy chain. The results of this study show that cutaneous antibodies to Ich theronts were present in and released from the excised skin from ®sh immune to Ich. Immobilization and killing of the theronts are two characteristics of the antibody response that appear to prevent the successful invasion of theronts into excised skin.* Fifty theronts per well were counted for four wells for survival and invasion in the excised skin at each interval. Values are mean standard deviation. Within a row for survival or invasion (%), means followed by the same lowercase letter are not signi®cantly different (P > 0.05).

Ichthyophthirius multifiliis (Ich), a fish ectoparasite, comprises an important challenge in the aquaculture industry. In this study, a steroidal glycoside, cynatratoside-C, isolated from Cynanchum atratum roots by bioassay-guided fractionation was used to treat I. multifiliis. The cynatratoside-C at 0.25 mg/L demonstrated a 100% mortality of I. multifiliis in vitro after 5 h exposure. The 5 h median effective concentration (EC50) of cynatratoside-C to nonencysted tomonts was 0.083 mg/L. In addition, cynatratoside-C at concentrations of 0.125 and 0.06 mg/L could completely terminate the reproduction of encysted tomonts. The cynatratoside-C at 2 mg/L could cure the infected grass carp within 48 h. The exact mechanism of cynatratoside-C for killing I. multifiliis is unknown, but it manifests itself microscopically through loss of membrane integrity of nonencysted tomonts or through releasing immature theronts from encysted tomonts. The immature theronts finally died before infecting fish. On the basis of these results, cynatratoside-C could be used as a natural anti-I. multifiliis agent.

The HBV vaccine event resulted in the suspension of a safe vaccine, which was associated with a decline of parental confidence, and refusal of vaccination. Suspension of a vaccine can lead to loss of confidence that is difficult to recover. Timely and credible investigation, accompanied by proactive outreach to stakeholders and the media, may help mitigate negative impact of future coincidental adverse events following immunization.