Effect of Exposure Dose on Ichthyophonus Prevalence and Infection Intensity in Experimentally Infected Rainbow Trout, Oncorhynchus mykiss.

This study describes the effect of increasing exposure dose on Ichthyophonus prevalence and infection intensity in experimentally infected rainbow trout, Oncorhynchus mykiss. Specific-pathogen free trout were exposed per os to increasing numbers of Ichthyophonus schizonts obtained from naturally infected donor fish, then sampled after 30 and 60 days post-exposure. Both in vitro explant culture and histology revealed that as the number of schizonts per dose increased there was a proportionate increase in the number of infected fish, as well as an increase in the number of infected organs; parasite density in individual infected organs also increased with dose.

Viability and infectivity of Ichthyophonus sp. in post-mortem Pacific herring, Clupea pallasii.

Ichthyophonus-infected Pacific herring, Clupea pallasii , were allowed to decompose in ambient seawater then serially sampled for 29 days to evaluate parasite viability and infectivity for Pacific staghorn sculpin, Leptocottus armatus . Ichthyophonus sp. was viable in decomposing herring tissues for at least 29 days post-mortem and could be transmitted via ingestion to sculpin for up to 5 days.

Evidence for an amoeba-like infectious stage of Ichthyophonus sp. and description of a circulating blood stage: a probable mechanism for dispersal within the fish host.

Small amoeboid cells, believed to be the infectious stage of Ichthyophonus sp., were observed in the bolus (stomach contents) and tunica propria (stomach wall) of Pacific staghorn sculpins and rainbow trout shortly after they ingested Ichthyophonus sp.-infected tissues.

Diagnostic methodology is critical for accurately determining the prevalence of Ichthyophonus infections in wild fish populations.

Several different techniques have been employed to detect and identify Ichthyophonus spp. in infected fish hosts; these include macroscopic observation, microscopic examination of tissue squashes, histological evaluation, in vitro culture, and molecular techniques. Examination of the peer-reviewed literature revealed that when more than 1 diagnostic method is used, they often result in significantly different results; for example, when in vitro culture was used to identify infected trout in an experimentally exposed population, 98.

Release of infectious cells from epidermal ulcers in Ichthyophonus sp.-infected Pacific herring (Clupea pallasii): evidence for multiple mechanisms of transmission.

A common clinical sign of ichthyophoniasis in herring and trout is "sandpaper" skin, a roughening of the epidermis characterized by the appearance of small papules, followed by ulceration and sloughing of the epithelium; early investigators hypothesized that these ulcers might be a means of transmitting the parasite, Ichthyophonus sp., without the necessity of ingesting an infected host. We examined the cells associated with the epidermal lesions and confirmed that they were viable Ichthyophonus sp.

Prevalence and spatial distribution of intraerythrocytic parasite(s) in Puget Sound rockfish (Sebastes emphaeus) from the San Juan Archipelago, Washington (USA).

Two morphologically distinct forms of an intraerythrocytic parasite(s) were detected by microscopic observation of Giemsa-stained blood films in 45.7% of 119 rockfish (Sebastes emphaeus) from the San Juan Archipelago (Washington State, U.S.

Isolation and characterization of a rhabdovirus from starry flounder (Platichthys stellatus) collected from the northern portion of Puget Sound, Washington, USA.

The initial characterization of a rhabdovirus isolated from a single, asymptomatic starry flounder (Platichthys stellatus) collected during a viral survey of marine fishes from the northern portion of Puget Sound, Washington, USA, is reported. Virions were bullet-shaped and approximately 100 nm long and 50 nm wide, contained a lipid envelope, remained stable for at least 14 days at temperatures ranging from -80 to 5 degrees C and grew optimally at 15 degrees C in cultures of epithelioma papulosum cyprini (EPC) cells. The cytopathic effect on EPC cell monolayers was characterized by raised foci containing rounded masses of cells.