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Mycobacterial infections in laboratory zebrafish Danio rerio are common and widespread in research colonies. Mycobacteria within free-living amoebae have been shown to be transmission vectors for mycobacteriosis. Paramecium caudatum are commonly used as a first food for zebrafish, and we investigated this ciliate's potential to serve as a vector of Mycobacterium marinum and M. chelonae. The ability of live P. caudatum to transmit these mycobacteria to larval, juvenile and adult zebrafish was evaluated. Infections were defined by histologic observation of granulomas containing acid-fast bacteria in extraintestinal locations. In both experiments, fish fed paramecia containing mycobacteria became infected at a higher incidence than controls. Larvae (exposed at 4 d post hatch) fed paramecia with M. marinum exhibited an incidence of 30% (24/80) and juveniles (exposed at 21 d post hatch) showed 31% incidence (14/45). Adult fish fed a gelatin food matrix containing mycobacteria within paramecia or mycobacteria alone for 2 wk resulted in infections when examined 8 wk after exposure as follows: M. marinum OSU 214 47% (21/45), M. marinum CH 47% (9/19), and M. chelonae 38% (5/13). In contrast, fish feed mycobacteria alone in this diet did not become infected, except for 2 fish (5%) in the M. marinum OSU 214 low-dose group. These results demonstrate that P. caudatum can act as a vector for mycobacteria. This provides a useful animal model for evaluation of natural mycobacterial infections and demonstrates the possibility of mycobacterial transmission in zebrafish facilities via contaminated paramecia cultures.

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The effect of Ichthyophthirius multifiliis (Ich) parasitism on survival, hematology and bacterial load in channel catfish, Ictalurus punctatus, previously exposed to Edwardsiella ictaluri was studied. Fish were exposed to E. ictaluri 1 day prior to Ich in the following treatments: (1) infected by E. ictaluri and Ich at 2,500 theronts/fish; (2) infected by E. ictaluri only; (3) infected by Ich at 2,500 theronts/fish only; and (4) non infected control. Mortality was significantly higher in fish previously exposed to E. ictaluri and then infected by Ich (71.1 %). Mortalities were 26.7 %, 28.9 % and 0 % for fish infected by E. ictaluri only, by Ich only and non-infected control, respectively. Quantitative polymerase chain reaction demonstrated the presence of E. ictaluri in the brain, gill, kidney and liver of fish infected with E. ictaluri regardless of Ich parasitism. At day 8, E. ictaluri parasitized fish had significantly more bacteria present in the brain, gill and liver, with no bacteria detected in these organs in the E. ictaluri-only treatment, suggesting that the bacteria persisted longer in parasitized fish. Decreased red blood cells count and hematocrit in fish at days 8 and 19 after co-infection suggests chronic anemia. Lymphocyte numbers significantly decreased in all infected treatments versus the non-infected controls at days 2, 8 and 19. Lymphopenia suggests that lymphocytes were actively involved in the immune response. Bacterial clearance was probably influenced by the stress of parasitism and/or the mucosal response induced by ectoparasitic Ich that resulted in the higher mortality seen in the co-infected treatment.

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Ichthyophthirius multifiliis Fouquet (Ich) and Streptococcus iniae are 2 major pathogens of cultured Nile tilapia Oreochromis niloticus (L). Currently there is no information available for the effect of coinfection by Ich and S. iniae on fish. The objective of this study was to determine the effects of parasite load and Ich development size on fish mortality following S. iniae infection. Low mortality (< or =20%) was observed in tilapia exposed to Ich or S. iniae alone. Mortalities increased from 38% in tilapia exposed to Ich at 10,000 theronts fish(-1) to 88% in fish at 20,000 theronts fish(-1) following S. iniae exposure. The median days to death were significantly fewer (7 d) in fish exposed to Ich at 20,000 theronts fish(-1) than fish exposed to 10,000 theronts fish(-1) (10 d). A positive correlation (correlation coefficient = 0.83) was noted between tilapia mortality and size of Ich trophonts at the time of S. iniae challenge. Fish parasitized with well-developed trophonts (Day 4, 2 x 10(7) microm3 in volume) suffered higher mortality (47.5%) than fish (10.0%) infested by young trophonts (Hour 4, 1.3 x 10(4) microm3 in volume) after S. iniae challenge. The results of this study demonstrated that both parasite load and trophont size increased susceptibility and mortality of tilapia to S. iniae infection.

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Dermatitis with intradermal cilated protozoa was identified in 18 of 95 (19%) Atlantic Bottlenose Dolphins (Tursiops truncatus) that died during the 1987-1988 Atlantic-dolphin morbillivirus epizootic. The lesions were characterized by focally extensive suppurative and histiocytic dermatitis and cellulitis with ulceration and variable numbers of dermal and hypodermal ciliates. Vasculitis, thrombosis, and/or intravascular ciliates were rarely present. In one dolphin, there was an associated lymphadenitis with ciliates, and in another, bronchopneumonia with rare intrabronchiolar ciliates. Ten of the dolphins were female, and eight were male. The animals ranged in length from 148 to 260 cm. Eleven were from Virginia, four were from New Jersey, and three were from Florida. In 13 dolphins, results of immunohistochemical and/or polymerase chain reaction (PCR) tests were positive for morbillivirus infection. Results of immunohistochemical tests were negative in four dolphins that were not also tested with PCR. Results were also negative in one dolphin tested using both methods. Nine dolphins had concomitant bacterial, fungal, and/or other protozoal infections. Fourteen other dolphins with ciliate-associated dermatitis were identified from 414 Atlantic bottlenose dolphin cases (3%) archived at the Armed Forces Institute of Pathology. The incidence of dermatitis with invasive ciliates is much greater in dolphins that died during the 1987-1988 epizootic.

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