Aquatic animal disease and human health

Introduction

There are some fish diseases and  infections that can be transmitted from fish, and the water in which they are  cultured, to humans. Although the infection of humans with fish pathogens is a  relatively unusual event, it is a health risk that needs to be recognised by  fish farmers and other people who handle and/or consume farmed seafood.

The incidence of transmission of disease  from fish to humans is dependant upon several factors including the type of  organism (viral, parasitic or bacterial), the susceptibility of the host  (immuno-compromised individuals, presence of open wounds) and environmental  factors (quality of the water, depth of penetration of fish spines).

Most disease causing agents which can  transmit from fish to humans are bacterial and their clinical effects and  treatments are listed in Table 1.

Optimum farm design, appropriate  husbandry and handling, water quality management and regular fish health  monitoring will reduce the risk of disease transfer from fish and their  environs to workers in the aquaculture industry.

Bacterial diseases

Table 1. Some common bacteria and their clinical effects following infection in humans. Some    species have been recorded in Australian fishes. Clostridium botulinum is also found occasionally in the    intestinal tract of fish.

Bacteria	Clinical Effects	Treatment
Aeromonas hydrophila	Serious infection uncommon Usually in immuno-compromised individuals;    cellulitis, muscle necrosis or septicaemia	Antibiotics Ampicillin resistant
Edwardsiella tarda	Soft tissue infections; arthritis;    septicaemia; gastroenteritis; meningitis; osteomyelitis	Antibiotics
Erysipelothrix rhusiopathiae	Skin infection (on hands), septicaemia,    endocarditis (rare); lymphangitis	Antibiotics; most strains resistant to    Vancomycin
Streptococcus iniae	Suppurating ulcers; cellulitis; Lymphadenitis; septacaemia; Endocarditis and arthritis	Antibiotics
Vibrio spp.	Lesions; gastroenteritis; septicaemia	Antibiotics
Mycobacterium marinum	Skin lesions (usually hands); ulceration and    inflammation of joints	Antibiotics
Salmonellosis	Septicaemia; abdominal pain; diarrhoea;    nausea; vomiting	Antibiotics

Non-bacterial fish  disease pathogens capable of infecting humans

Non-bacterial disease-causing agents  include:

⦁ Parasites and harmful algae

⦁ Viruses

⦁ Parasitic diseases and  harmful algae

Several parasites can infect humans as  non-traditional hosts. They enter humans by ingestion of raw or undercooked  infected fish. Trematodes and nematodes are known to cause infection in humans.  Harmful algae (dinoflagellates and diatoms) may also accumulate in shellfish  and can cause illness in humans. Clinical signs can include muscular aches,  gastrointestinal and neurological disorders.

Viral diseases

Shellfish, such as oysters, mussels and  clams can bio-accumulate viral pathogens from polluted waters. The consumption  of contaminated shellfish can cause gastroenteritis, respiratory illness, fever  and hepatitis. Commercial  shellfish are grown under a strict food safety program administered by the NSW  Food Authority.

Prevention and control

Fish should be anaesthetised during handling to avoid injury to  fish and fish handlers.

Gloves should be worn at all times when handling fish.

Minor wounds should be thoroughly washed with clean water and  antiseptic applied.

More serious injuries and illness should be treated by a medical  practitioner.

Doctors should be informed if "fish handling" is  involved.

Workers having an underlying disease or compromised immune  system (diabetes, impaired liver function, cancer or HIV) are more susceptible,  and should avoid handling fish.

Workers having open wounds, cuts or abrasions should not come  into contact with fish or fish rearing waters.

Codes of hygienic practice and good aquaculture practices are  essential to lower the risk to employees.

Educating workers about the prevalence of these risks will go a  long way to preventing these diseases.

Glossary

Cellulitis– inflammation of  cellular tissue.

Endocarditis– inflammation of the  membranes which line the heart and heart valves.

Lymphadenitis– chronic swelling of  lymph nodes

Meningitis– inflammation of the  brain and spinal chord membranes.

Osteomyelitis– inflammation of the  bone

Septicaemia– bacterial infection  of the blood

Suppurating- discharging pus from  a wound.