Vibriosis - Fish

Also known as: Cold-Water Vibriosis — Haemorrhagic Syndrome — Hitra Disease — Red Pest of Eels — Vibrio infections in fish

Introduction

Vibriosis is one of the most prevalent fish diseases and is caused by bacteria belonging to the genus Vibrio. One of the most important strain is Vibrio anguillarum which is of major importance to salmonid fish culture industry and is also known as Red pest of eels. V. anguillarum has been divided into two separate biotypes of which V. anguillarum biotype II has been renamed and classified as a new species Vibrio ordalii. It causes haemorrhagic septicaemia and leucopenia.

Other members of the genus Vibrio have been associated with vibriosis outbreaks in fish and shellfish (molluscs and crustacean) and these include: V. salmonicida, V. damsela, V. vulnificus biotype II, V. tubiashii, V. carchariae, V. splendidus and V. pelagius.

Signalment

Vibrio anguillarum is found in cultured and wild marine fish in shallow salt or brackish water during late summer. The pathogen was thought to be spread by contact with scavenging wild fish feeding around the farms but V. anguillarum, has been found in the food of cultured and wild healthy fish.

Outbreaks of vibriosis have been seen in Pacific and Atlantic salmon, Trout, Turbot, Striped bass, Winter flounder, Cod, Red sea-bream, European and Japanese eel, Saithe (Pollachius Virens), Gilthead sea-bream, Sea mullet, Seriola, Channel catfish, Milkfish, Ayu, and Tilapia. It can also affect molluscs and crustacean including European and Japanese oyster, clam, lobster and shrimp.

Disease outbreaks can be influenced by water quality and temperature, the strain and virulence of the Vibrio bacteria and the amount of stress imposed upon the fish.

Other species of Vibrio affect a wide range of species for example V. salmonicida mainly affects Alantic salmon and trout and causes cold water vibriosis, V. damsela affects Blacksmith species (Chromis punctipinnis), V. vulnificus also known as V. anguillicidacuases causes disease in eels.

Both V. vulnificus and V. damsela are zoonotic. It is thought that the infection is caused from eating contaminated raw or undercooked seafood, in particular raw oysters. Immunocompromised and people with liver diseases are at increased risk.

Clinical Signs

Clinical signs of vibriosis are haemorrhage to intestines, body cavity, spleen and muscle, distended mucoid and necrotic intestine and petechiation, erosion and darkended colouration to the skin and fins. Changes to the eyes include distension and cloudiness and periorbital swelling. White/grey lesions can be found on the intestines and spleen and in fry, splenomegaly can be seen.

V. damsela and V.vulnificus cause severe, progressive necrotizing infection in humans.

Distribution

Asia, North America and Europe including outbreaks in the UK.

Diagnosis

Presumptive diagnosis can be made from clinical signs especially characteristic red spots, swollen and dark lesions on the skin that bleed and ophthalmic changes; although some acute and severe cases die without clinical signs. With V.anguillarum more severe pathology is seen in the descending gastrointestinal tract as the conditions become more alkaline. Most tissues are septic with no evidence of phagocytosis.

Identification methods include a culture medium for presumptive identification, a sensitivity assay to filter discs impregnated with a saturated solution of the vibriostatic agent 0/129 (2,4-diamino-6,7-diisopropylteridine), nitrate reduction, presence of oxidase, catalase and arginine decarboxylase, reaction with monoclonal antibodies and antiflagellar antiserum, and hybridization with specific 16S ribosomal ribonucleic acid (rRNA) oligonucleotides . Vibrio species can be identified using monoclonal antibodies (MAbs).

V. vulnificus can be identified using an ELISA for the haemolysin and PCR. Pathology for V. ordalii tends to be more localised to the muscle and areas of the salmonid skin, but can also be found in loose connective tissue of the gills, throughout the GI tract and in the pyloric caeca.

V. salmonicida also known as haemorrhagic syndrome, show haemorrhaging in the integument surrounding the internal organs and the fish are anaemic and fry show splenamegaly, cataracts and cranial haemorrhage. Whereas V. damsela shows mainly ulcerations from 0.5-2cm in diameter and are characterised by muscle lysis and histiocytes within the dermis and skeletal muscle of Chromis punctipinnis.

Treatment

Fish can be treated with ampicillin, chloramphenicol, nalidixic acid derivatives, nitrofurans, sulphonamides and trimethoprim.

Control

A formalin-killed V. anguillarium vaccine is available and can be administered via intraperitoneal injection, immersion or oral administration.

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