Amoebae Associated with Ulcerative Lesions of Fish from Tidal Freshwater of the James River, Virginia

Abstract

While surveying ichthyofaunal diversity in the tidal freshwater James River (near Richmond, Virginia) during March and September 1997, we observed that 40-50% of live fish collected had ulcerative lesions. Concomitant sampling upstream in nontidal reaches produced few fish with lesions (Յ2%). These observations were unprecedented based on similar surveys conducted annually since 1989 and subsequently through 2000. Affected taxa included cyprinids, catostomids, ictalurids, centrarchids, and moronids, representing both resident and migratory species. During this episode of tissue ulceration, free-living pathogenic amoebae, predominantly Acanthamoeba and Naegleria, were the primary organisms associated with lesions across all degrees of severity and across all host species. Based on the focal nature of the lesions, the lack of physical injury to surrounding tissues, the low numbers of fungi and pathogenic bacteria, the absence of Pfiesteria and related organisms, and the large numbers of free-living pathogenic amoebae isolated from all of the lesions, we suggest the epizootic event was an instance of ulcerative amebiasis. The 1997 event in the tidal James River was the first documented case of a fish epizootic from these amoebae in North America in over 20 years and is the first such event described for a mid-Atlantic coastal tributary.

Distribution of free-living amoebae in James River, Virginia, USA

“…These epizootic events were unprecedented in the tidal freshwater James River and were coincident with similar events in other Chesapeake Bay tributaries that were attributed, in part, to Pfiesteria-complex organisms, (Lewitus et al 1995). The organisms associated with lesions during the 1997 events in the James River were, however, identified as free-living amoebae (FLA) belonging to the genera Acanthamoeba, Naegleria, Vahlkampfia and Vannella (Webb et al 2002). The relative importance of FLA in causing lesions and mortality in fish populations or assemblages under natural conditions remains obscure, but their role in human disease is well established.…”

“…They can be isolated from air, sediment, and a variety of fresh and marine water sources but tend to cluster in the interfaces between these habitats. This is especially true for the water-sediment interface (Rodriguez-Zaragoza 1994) where many fish reside and feed, including the predominant species affected during the epizootic that led to this study (Webb et al 2002). FLA in this interface zone feed primarily on bacteria, although fungi, yeast, algae, and other protozoa may also serve as food sources.…”

“…The study presented here confirms that FLA are prevalent in the James River and that water temperature, pH, DO and suspended food are all acceptable to FLA, and at times they become ideal for populations of FLA to bloom. We will never know whether a bloom of FLA led to the fish epizootic of fish in 1997 (Webb et al 2002), but conditions in this urbanized stretch of the James River are suitable for a bloom of amphizoic amoebae.…”

“…Identification of amoebae was based on the morphological guidelines established by Page's taxonomic key (Page 1988) and the genetic techniques employed by Webb et al (2002). Flagellation tests (Page 1988) were used to differentiate isolates of Naegleria from Vahlkampfia.…”

Etiology of ulcerative lesions of Atlantic menhaden (Brevoortia tyrannus) from James River, Virginia

“…Fish kills and ulcers on fishes in Atlantic coastal rivers also have been attributed to other known pathogens such as Mycobacterium spp. in lesions of striped bass, Morone saxatilis, from Rappahannock River, Virginia (Rhodes et al 2001), oomycete fungi Aphanomyces and Saprolegnia in B. tyrannus (Noga et al 1988;Blazer et al 1999;Dykstra and Kane 2000;Kiryu et al 2003;Johnson et al 2004), and amphizoic amoebae (e.g., Acanthamoeba and Naegleria) in various tidal resident and migratory fishes (Webb et al 2002). However, the observation that a single fish species (B. tyrannus) has a high prevalence of stereotypical disease outbreaks is not entirely consistent with hypothesized effects of opportunistic pathogens such as those mentioned above nor is it necessarily consistent with a multiplicity of toxins, pathogens, and environmental and physiological factors (Law 2001).…”