Yersinia intermedia The organism has been associated with water and the

Yersinia intermedia the organism has been associated

This preview shows page 291 - 293 out of 594 pages.

Yersinia intermedia The organism has been associated with water and the intestines of apparently healthy fish (e.g. Kapperud, 1981; Shayegani et ai, 1986; Zamora and Enriquez, 1987), which are likely to be the source. Yersinia ruckeri In rainbow trout, ERM most commonly affects fish of approximately 7.5 cm in length. The disease is less severe but more chronic in larger fish, i.e. of 12.5 cm in length. Severity peaks with a water temperature of 15-18°C, and decreases when it drops to 10°C or below. Overly fat or debihtated (stressed) fish are thought to be more susceptible to severe epizootics (Rucker, 1966). Moreover, occurrence of ERM may be cyclic, suggesting the presence of asymptomatic carrier fish in the population (Busch and Lingg, 1975). Such fish would be capable of shedding the organism in the faeces. Alternatively, it may be argued that the pathogen is present normally in the water and/or sediment (Rucker, 1966). From the results of some fascinating experi- ments. Hunter et al. (1980) demonstrated that unstressed carrier fish did not transmit Y. ruckeri to recipient fish. In fact, it was necessary to stress these carriers, such as by heat (i.e. a water temperature of 25°C), in order to enable release and thus transmis- sion of the pathogen to other fish. Even under these conditions, colonisation of the lower intestine took place in the recipient fish without any mortalities. However, the handling of fish, which may appear to be extremely healthy, and crowded conditions causing excess ammonia and metabolic waste products in the water and, thus, a decrease in oxygen levels, may precipitate outbreaks of clinical disease (Bullock and Snieszko, 1975). Nevertheless, outbreaks generally occur only after the fish have been exposed to large numbers of the pathogen (Ross et al, 1966). Mortalities tend to start 5-19 days after exposure, depending on the size of the inoculum, and last for 30-60 days (Rucker, 1966; Busch, 1973). Cumulative losses due to ERM may account for as much as 30-35% of the rainbow trout population (Klontz and Huddleston, 1976). There is controversy over some aspects of the ecology of Y. ruckeri, insofar as the organism has been alternatively considered as well-adapted as a normal aquatic saprophyte (McDaniel, 1972) and, second, as not capable of free-living for any extended period in water (Klontz and Huddleston, 1976). Nevertheless, these authors conceded that survival for up to 2 months was possible in mud. Further experiments indicated that the pathogen could survive for 4 months in unsupplemented water at a saHnity of 0-20%o; survival being reduced in seawater (salinity = 35%o) (Thorsen et al, 1992). Romalde et al. (1994) reported survival for 3 months. Therefore, the implica- tion is that Y. ruckeri is capable of surviving in the (fresh) water column for a long
Image of page 291
272 Bacterial Fish Pathogens time after an outbreak of disease has occurred. Survival may be influenced by the abihty of virulent cultures to adhere to surfaces, a characteristic linked to the presence of flagella. Interestingly, oxoHnic acid was better able to inactivate planktonic rather than attached cells of the pathogen (Coquet et al, 2002). Perhaps, the organism is a
Image of page 292
Image of page 293

You've reached the end of your free preview.

Want to read all 594 pages?

  • Spring '20
  • Bacteria, representative, gram-negative bacteria

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Stuck? We have tutors online 24/7 who can help you get unstuck.
A+ icon
Ask Expert Tutors You can ask You can ask You can ask (will expire )
Answers in as fast as 15 minutes
A+ icon
Ask Expert Tutors