Lecture 20: Viral Diseases of Aquatic Mammals and Fish

poxviridae

• large DNA virus

• species are susceptible to infection

• virus strains → seal pox, dolphin pox, whale pox

• zoonotic

pinniped parapoxvirus

• seals and walrus

• manifest as proliferative lesions on the skin or the mucosal surface of the mouth and nasal passages

• pox lesions sometimes observed in free-ranging seals and sea lions, but they are common as a complication in the treatment of debilitated pinnipeds in rehab centers

pinniped parapoxvirus zoonotic effects

the seal and sea lion parapoxviruses are zoonotic agents → animal handlers have acquired proliferative lesions on their hands

cetacean poxviruses

• dolphins and whales

• hyperpigmented skin lesions described as ring, pinhole, and tattoo lesions = tattoo skin disease

• can be associated with stressful conditions like poor water quality, environmental contamination and underlying ill health

when do dolphin pox outbreaks occur?

in post weanling pinnipeds recently introduced into captivity

whale poxvirus

• disseminated skin lesions in young beluga whale

• appears to replicate in epidermis

• not known if cause of disease may lead to death

cetacean gamma herpesviruses is associated with

mucosal lesions in digestive, genital, and respiratory tract

genital herpesvirus in bottlenose dolphins

• plaques on penile mucosa and vulvar mucosa

• likely transmitted by sexual contact

• history of abortion and perinatal mortality

papillomavirus in dolphins

• highly prevalent viruses involved in the development of various tumor types in a wide range of animals

• so-called high-risk PVs contribute to malignant progression

papillomavirus in manatees

causes warts similar to humans

morbillivirus outbreaks in seals and dolphins

first documented in 1988 as the cause of death of 18,000 harbor seals and 300 gray seals along the northern european coast

phocine distemper

• related but distinct from CDV

• clinical signs noted in young seals include depression, anorexia, crusting conjunctivitis, nasal discharge, and dyspnea, pneumonia

• mortality is high in naive populations

• seals vaccinated with CDV vaccine develop antibodies

cetacean morbillivirus

• delphinoid distemper virus that is closely related to rinderpest and peste de petits ruminants

• targets the brain and lungs primarily

• skin lesions, pneumonia, brain infections, and other secondary infections due to a compromised immune system

how is phocine distemper virus affecting other pacific animals?

sea otters and other mammals are threatened by the introduction of the virus in migrating seals

what can be possible contributors to phocine and cetacean distemper?

• pollutants → interferes with the ability of animals to mount a defense against infection

• climate change

• overfishing

influenza virus in seals

• sequence analysis of postmortem samples revealed the presence of an avian H3N8 influenza A virus

• people whose eyes were contaminated during necropsies or by being sneezed on by affected seals, developed keratoconjunctivitis within 2-3 days

influenza virus in whales

• pilot whale on the New England coast → major strandings

• subtypes H13N2 and H13N9 isolated from the lung

• closely related to H13 influenza from gulls

san miguel sea lion virus calicivirus

• lesions in marine mammals → skin vesicles

• in pinnipeds → vesicles are most prevalent on the dorsal surfaces of the fore flippers

• erode and leave shallow, fast-healing ulcers

• supportive treatment only, skin lesions resolve without treatment

• can cause premature parturition → pups have interstitial pneumonitis and encephalitis and fail to thrive

• people develop antibodies when exposed

infectious pancreatic necrosis

• economically-important in saltwater farming industry

• severe viral diseases of salmonid fish, atlantic salmon in pacific NW, Maine, Norway, Denmark

• disease of young fish, fry, and fingerlings, of trout and salmon

• adults can carry virus without showing symptoms

transmission of infectious pancreatic necrosis

• spread via infected water, also vertically

• high mortality

• some survive

clinical signs of infectious pancreatic necrosis

• abdominal swelling, abnormal swimming

• not eating

• darkening of skin

• feces trailing from vent

necropsy of infectious pancreatic necrosis

• necrosis to pancreas

• thick mucus inside intestines

channel catfish virus disease

• economically important in freshwater farming

• very virulent in young naive populations of cultured channel catfish, fry, and fingerling

• mortality near 100%

• latent carriers

• no vaccine

clinical signs of channel catfish virus disease

• distended abdomen - pot-bellied

• convulsive swimming with a head-up posture

• lethargy

• exophthalmia

• hemorrhages at the base of the fins

necropsy of channel catfish disease

red or yellow tinged peritoneal fluid, enlarged spleen, petechial hemorrhages on kidney, liver, and visceral fat

koi herpesvirus disease (navle species)

• important in freshwater farming industry

• very contagious to common carp

• carp intestinal nephritis gill necrosis virus → can become widespread

• very virulent with deaths occurring within 1-2 days of clinical signs with younger fish affected → mortality 80-100%

• virus dependent on warmer water, dropping temp controls disease

• latent carriers

clinical signs and diagnosis of koi herpesvirus disease

• excessive mucus production on gills, gill necrosis, sloughing of scales, sunken eyes, refusal to eat

• hemorrhagic gill at necropsy

spring viremia of carp (navle species)

• important in freshwater farming industry

• considered a foreign animal disease

• very contagious to common carp including the ornamental variety of the koi carp and rainbow trout

• ovarian transmission possible

• blood sucking parasites, leeches and fish lice, spread disease

• longevity of virus in water and mud, survives freezing

clinical signs and diagnosis of spring viremia of carp

• often non-specific

• affects young fish

• lethargic, decreases respiration, loss of equilibrium, lie on bottom of tank or along bank

• darkening of skin, hemorrhages on body wall, exophthalmia, dropsy, pale gills, protruding vent

treatment of viral fish diseases

• avoidance and prevention major tools (biosecurity)

• water supply considerations, high water quality

• brood stock screening, no mixing batches, moving fish

• multiple rearing units, so don’t overstock

• equipment and egg disinfection

• culling