Erysipelothrix rhusiopathiae is a rod-shaped, gram-positive intracellular pathogen that can cause erysipelas in a variety of vertebrates, including humans, livestock, wild mammals (both marine and terrestrial), and birds. In wild mammals, the mode of infection by the organism is unclear; however, most of apparently healthy domesticated pigs carry the organism in their tonsils and other lymphoid tissues, and the organism can multiply and spread, and causes the disease when host defenses are compromised. I hereby would like to explain new findings revealed by genome analyses and the pathogenicity of E. rhusiopathiae and host defense mechanisms.
Swine erysipelas caused by Erysipelothrix rhusipathiae is an infectious disease of swine and Wild boar. E. rhusiopathiae infections are also reported in cattle, dogs, birds and cetaceans. In particular, the occurrence of swine erysipelas in dolphins has reported many cases of death due to acute septicemia. Penicillins are effective for the treatment of swine erysipelas. In addition, live vaccines and inactivated vaccines are applied for the prevention of E. rhusiopathiae infections. Furthermore, it is important for swine to be thorough daily hygiene managements in order to prevent for swine erysipelas. In this lecture, I would like to think about a more effective preventive measure against E. rhusiopathiae infection in dolphins by preventing contamination of feed fish, by vaccination with swine inactivated vaccine, and by examining the trend of the antibody titer against E. rhusiopathiae.
In Yokohama Hakkeijima Sea Paradise, we have experienced a few cases of swine erysipelas infection to our live collection of cetacean specimens since we established our facility in 1993. Because this infectious disease is known as a zoonosis and also we have lost some of our specimen by acute sepsis from this, we have been vaccinating our specimens with inactivated vaccine since 2003 （interrupted vaccination temporarily from 2004 to 2006）. As of September 2018, we have successfully vaccinated 25 specimens over 5 species out of 30, specimens over 5 species in our collection. We have been using inactivated vaccine contains alkali treated somatic antigen of swine erysipelas strain M2 （serotype 2） and tocopherol acetate adjuvant （PORCILIS® ERY, MSD Animal Health Co., Ltd.）. Every six months, each specimen received 2ml of vaccine injected into muscle around dorsal fin regardless of species or body weight. All specimens except for the youngest one born last year were trained to accept vaccination with voluntary behavior, so that we are able to give them shots without holding animals. Since we started vaccination program, we have not recorded swain erysipelas infection on our collection and scarcely developed any side reactions.
At Okinawa Marine Research Center, Motobu-genkimura, we have experienced one case of cutaneous form erysipelas by Erysipelothrix rhusiopathiae in 2004. Because of this, we have decided use of inactivated vaccine to test effectiveness of vaccination. Next year, we have experienced two cases of cutaneous erysipelas in unvaccinated animals, But, vaccinated animals kept elevated levels of antibody against Erysipelothrix and did not affected with disease. The antibody titers were 1:64 and over for well over a year. Therefore vaccination was terminated. In September 2017, we have experienced one cutaneous and two case of acute septicemic form erysipelas. One of septicemic form was post-mortem diagnosis. In January 2018, four bottlenose dolphins elevated serum GOT and GPT. All of these dolphins had elevated levels of antibody to Erysipelothrix, confirmed by growth agglutination（GA）titer. That indicated possibility of infection with Erysipelothrix. Infection from food was suspected as the reason for the frequent occurrence of disease. We feed 7 different species of frozen fish to our cetacean collection and gene fragments specific to E. rhusiopathiae were detected from 2 out of 7 species of feed fish. Therefore these contaminated feeding fish were considered to be the source of infection.
At the Adventure World, there were a few cases of erysipelas infections in three species of cetaceans, such as bottlenose dolphin, pacific white-sided dolphin, and false killer whale. One of them was occurred that all five cetaceans were suffered from cutaneous lesions of erysipelas between 1990 and 1998. After several years, second case was occurred from 2006 to 2008, 2 bottlenose dolphins and 2 pacific white-sided dolphins died at 3-4 days after onset of erysipelas infectious disease. As a countermeasure, we started vaccination for erysipelas infection from November 2007. After the vaccination, one pacific white-sided dolphin died from erysipelas infections in March 2008. Since then there has been no record of erysipelas infection therefore we are considering that vaccination has a certain effect on prevention of this infectious disease.
At Shimonoseki Marine Science Museum, there is no record except for one case as described in detail below of outbreak of Erysipelas infection about 18 years since establishment of our facility in 2001. The case out of 20 individuals of our Cetacean collection （12 Bottlenose Dolphin and 8 Finless Porpoise）, Erysipelothrix rhusiopathiae was isolated from one of Finless Porpoise blood sample. The antibody titers against E. rhusiopathiae of Growth Agglutination （GA） of 12 individuals in April 2018 were all less than 16 times. On the other hand, gene fragments specific to E. rhusiopathiae were detected from our frozen foods for marine mammals which was in use as of February 2018. We have been using Neutral PH Electrolyzed Water through storing these food items in refrigerator after thawing, and these results indicate the possibility of suppression for bacterial growth by Neutral PH Electrolyzed Water on E. rhusiopathiae.
At Enoshima Aquarium from 1957 to 2003, there have been several types of erysipelas infections in cetaceans were recorded. In 1960, these incidents caused mortality on three species of 21 individuals. Additionally, 9 out of 10 staff members who performed autopsy were infected by erysipelas. In 1980, one bottlenose dolphin died from endocarditis. In 1999, 20-year-old bottlenose dolphin also died from septicemia, and serotype 2 was isolated from its blood sample. Six-year-old bottlenose dolphin recovered from infection by administering oral dose of penicillins and tetracyclines combination. At new Enoshima Aquarium from 2004 to 2018, only one pacific white-sided dolphin died from septicemia. Also, serotype 2 and untypeable were isolated from blood samples of two bottlenose dolphins in poor health condition at time. The untypeable was isolated from blood sample of the same dolphin again 4 months later from initial record of this type. It has been more than 60 years since Enoshima Aquarium started its cetaceans display, however, even now erysipelas infections have occasionally been observed.
An oriental white stork (Ciconia boyciana), which had been rescued after hatching in a nest on an electric pole in Shimane Prefecture, was released after hand rearing at Hyogo Park of the Oriental White Stork. However, the bird was found dead after 27 days in Tottori Prefecture. Necropsy revealed three pieces of foam rubber (840 mm in total length) in the bird’s gizzard. This finding suggested that the bird was weakened and died because of the lack of digestion and absorption of food owing to the accidental ingestion of foam rubber. This is the first report of accidental ingestion of an artificial material causing death in the reintroduced population of oriental white storks in Japan.