Experimental infections of Orchitophrya stellarum (Scuticociliata) in American blue crabs (Callinectes sapidus) and fiddler crabs (Uca minax) Terrence L. Miller a , Hamish J. Small b , Bhae-Jin Peemoeller c , David A. Gibbs d , Jeffrey D. Shields b,⇑ a School of Marine & Tropical Biology, James Cook University, Cairns, QLD 4870, Australia b Department of Environmental and Aquatic Animal Health, Virginia Institute of Marine Science, College of William and Mary, P.O. 1346, Gloucester Point, VA 23062, USA c University of Maryland Eastern Shore, Princess Anne, MD 21853, USA d Georgia Institute of Technology, North Ave., Atlanta, GA 30332, USA article info Article history: Available online xxxx Keywords: Facultative parasite Disease Portal of entry Injury Crustacea abstract Outbreaks of an unidentified ciliate have occurred on several occasions in blue crabs from Chesapeake Bay held during winter months in flow-through systems. The parasite was initially thought to be Mesanophrys chesapeakensis, but molecular analysis identified it as Orchitophyra stellarum, a facultative parasite of sea stars (Asteroidea). We investigated the host-parasite association of O. stellarum in the blue crab host. Crabs were inoculated with the ciliate, or they were held in bath exposures after experimen- tally induced autotomy of limbs in order to determine potential mechanisms for infection. Crabs inocu- lated with the ciliate, or exposed to it after experimental autotomy, rapidly developed fatal infections. Crabs that were not experimentally injured, but were exposed to the ciliate, rarely developed infections; thus, indicating that the parasite requires a wound or break in the cuticle as a portal of entry. For com- parative purposes, fiddler crabs, Uca minax, were inoculated with the ciliate in a dose-titration experi- ment. Low doses of the ciliate (10 per crab) were sometimes able to establish infections, but high intensity infections developed quickly at doses over 500 ciliates per crab. Chemotaxis studies were initi- ated to determine if the ciliate preferentially selected blue crab serum (BCS) over other nutrient sources. Cultures grown on medium with BCS or fetal bovine serum showed some conditioning in their selection for different media, but the outcome in choice experiments indicated that the ciliate was attracted to BCS and not seawater. Our findings indicate that O. stellarum is a facultative parasite of blue crabs. It can cause infections in exposed crabs at 10–15 °C, but it requires a portal of entry for successful host invasion, and it may find injured hosts using chemotaxis. Ó 2013 Elsevier Inc. All rights reserved. 1. Introduction Scuticociliate infections are known to cause significant pathol- ogy, mortality, and in some cases castration in a wide range of mar- ine organisms, including molluscs (Bower et al., 1994; Bradbury, 1994; Elston et al., 1999), echinoderms (Cepede, 1907), and teleost fishes (Dickerson, 2006; Smith et al., 2009). The first scuticociliate reported from a crustacean was found in the hemolymph of Carcinus maenas by Cattaneo (1888). Since then endoparasitic cili- ates, including scuticociliates, have been widely reported in crusta- ceans, including Anophryoides haemophilia in wild-caught and cultured American lobsters, Homarus americanus (Ragan et al., 1996; Lavallée et al., 2001; Greenwood et al., 2005), Collina oregonensis in euphausiids (Gomez-Gutierrez et al., 2003, 2006), Parauronema sp. in the hemocoel of penaeid shrimps (Couch, 1978), Tetrahymena pyriformis infections in the freshwater red-clawed crayfish, Cherax quadricarinatus (Edgerton et al., 1996) and Mesanophrys or Mesanophrys-like infections (syns. Anophrys and Paranophrys) in brachyuran crabs from the Atlantic and Pacific oceans (Bang et al., 1972; Armstrong et al., 1981; Messick and Small, 1996; Messick, 1998; Morado et al., 1999; Wiackowski et al., 1999; Cain and Morado, 2001; Morado, 2011), isopods (Hibbits and Sparks, 1983) and the Norway lobster, Nephrops norvegicus (Small et al., 2005a,b). During winter 2007, systemic ciliate infections caused mortali- ties in blue crabs, C. sapidus, held in large flow-through systems within our facilities at the Virginia Institute of Marine Science. Such mortalities had occurred earlier within our system but they were thought to be restricted to a few crabs injured from dredge operations. The pathogen was putatively identified based on sim- ple morphology and host distribution as Mesanophrys chesapeaken- sis, a parasitic ciliate described from C. sapidus by Messick and Small (1996). However, further study and molecular characteriza- tion revealed that the ciliate was O. stellarum (Small et al. in press). In a previous study, morphological analysis of a Mesanophrys-like scuticociliate from N. norvegicus indicated that the parasite was 0022-2011/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jip.2013.08.009 ⇑ Corresponding author. Fax: +1 804 684 7186. E-mail addresses: terry.miller1@jcu.edu.au (T.L. Miller), jeff@vims.edu (J.D. Shields). Journal of Invertebrate Pathology xxx (2013) xxx–xxx Contents lists available at ScienceDirect Journal of Invertebrate Pathology journal homepage: www.elsevier.com/locate/jip Please cite this article in press as: Miller, T.L., et al. Experimental infections of Orchitophrya stellarum (Scuticociliata) in American blue crabs (Callinectes sapidus) and fiddler crabs (Uca minax). J. Invertebr. Pathol. (2013), http://dx.doi.org/10.1016/j.jip.2013.08.009