Lecture 19: Viral Diseases of Wildlife and Pocket Pets

what is the SE cooperative?

national service lab for diagnosing agents causing occurrences or outbreaks of diseases in wild animals

what is the most important viral disease of deer in the US?

epizootic hemorrhagic disease

what are the 2 diseases that deer can get?

• epizootic hemorrhagic disease virus (EHD)

• bluetongue virus

epizootic hemorrhagic disease virus and bluetongue virus are both

closely related orbiviruses that both cause hemorrhagic disease in deer and clinical signs are indistinguishable

EHD and bluetongue transmission

• Culicoides sonorensis is the vector

• transmitted July through November

• widely distributed in temperate and tropical climates

wildlife hosts of EHD and bluetongue

white-tailed deer, mule deer, pronghorn, bighorn sheep

clinical signs of EHD and bluetongue

• hemorrhagic disease

• damage to small blood vessels (replicate in lymphoreticular system) resulting in fluid loss, hemorrhage, and tissue damage

• signs range from sudden death to chronic disease

• reddening of periocular skin and nostrils

• swelling of head and neck

• sick and dead animals often found near water

diagnosis of EHD and bluetongue (gross pathology)

• petechial hemorrhages

• pulmonary edema

• swelling of tongue, mucosal surfaces, head, neck

• pericardial effusion

• splenomegaly

• hyperemia

vaccine for EHD and bluetongue

available for farm animals, but not approved for zoo animals or wildlife

chronic wasting disease is called

transmissible spongiform encephalopathy (TSE)

characteristics of TSE’s

• brain degeneration with vacuolation

• long incubation period

• cause is believed to be an infectious agent called a prion

• infectivity very hard to inactivate

• transmitted by meat products, indirect contact, and iatrogenic

transmission and diagnosis of chronic wasting disease

• spread to other states by deer farming and trophy hunting

• can be detected in lymph nodes and lymphoid tissues in rectum

• method of transmission is not known

• prion material has been detected in urine

what wildlife species can be affected by rabies and canine distemper?

racoon, skunk, gray fox, red fox, coyote

pathogenesis and transmission of rabies virus

• bite or scratch of a rabid animal

• aerosol transmission in bat caves

• contamination of mucus membranes

• incubation period is 1-3 months

• virus replicates in peripheral nerves or non-nervous tissue → moves to CNS via spinal cord to brain

clinical course of rabies virus

1. infection by bite

2. incubation <10 days to several months

3. prodromal period: 1-2 days

4. acute neurologic period: 1-10 days

5. death: paralysis leads to respiratory, cardiac failure

prodromal period of virus

• early symptoms and signs of an illness that precede the characteristic manifestations of the acute, fully developed illness

• viral shedding occurs despite lack of obvious clinical signs

acute neurologic period of virus

• obvious clinical signs: excitable, hyperesthesia, agitation, aggression, head tilt, head pressing, strange phonation, drooling

• active viral shedding

• paralytic phase may follow aggressive phase, or occur directly after prodromal period with no excitation

in what phase of the rabies virus does wildlife lose fear of humans and domestic animals?

acute neurologic period

rabies virus control

• raboral V-RG approved for raccoons and coyotes

• fish paste-based recombinant oral vaccine

• gene for rabies G-protein has been inserted into the vaccinia virus TK gene = recombinant

• vaccinia allows for replication in mammal cells (back of throat)

the most common source of human rabies in the US is from

bats

canine distemper virus distribution

• worldwide

• occurs in raccoons throughout the southeast, major disease problem in this species

• red foxes susceptible to CDV, but appear to be more resistant than the highly susceptible gray fox

canine distemper transmission

• direct contact, aerosol droplets

• virus shed from all excretions and secretions

• virus replicates in the lymphatic tissue associated with the respiratory tract mucosa

• subsequent viremia, widespread infection of epithelial tissue

• most lymphatic tissue becomes infected as well as CNS

clinical signs of canine distemper

• respiratory distress

• fever

• anorexia

• serous nasal discharge and mucopurulent ocular discharge

• weight loss and diarrhea

• hyperkeratosis of nasal planum and footpads

CNS signs of canine distemper

• localized twitching

• paresis/paralysis beginning in the hind limbs (ataxia)

• convulsions, salivation, and chewing movement of the jaws

• paddling movements of the legs, urination, and defecation

what are other species affected by canine distemper virus?

big cats, pandas, seals, ferrets, raccoons

what is the vaccine for black footed ferrets?

• canarypox fusion gene-based recombinant vaccine

• canarypox does not replicate in mammals, so no danger of replication of CDV viral particles

cowpox in cheetahs

• foreign animal disease

• seasonal recurrence of cowpox outbreaks in captive cheetahs

what was globally eradicated in 1980?

smallpox

how did the monkeypox outbreak occur?

through a chain of legal importation of small mammals, pet shops, and pet swaps

human monkeypox outbreak in US-2022

• to date, over 600 probably and confirmed cases have been estimated across 47 states

• indicates an actively spreading infection that is part of a worldwide outbreak

• current outbreak represents the first time that monkeypox is spreading through sexual activity networks

characteristics of rabbit hemorrhagic disease

• hemorrhages in lungs and liver

• killed ½ million rabbits in 6 months

• some of the spread is intentional to control wild rabbit populations

• fecal/oral transmission

• classified as foreign animal disease

clinical signs of rabbit hemorrhagic disease

• older than 2 months

• 24-72 hour incubation time

• depression, fever, serosanguinous or bloody nasal discharge, nervous signs such as incoordination and shaking

what shows up on necropsy for rabbit hemorrhagic disease?

nasal hemorrhages, pulmonary congestion, edema, zonal necrosis of the liver

control for rabbit hemorrhagic disease

• no licensed vaccines available for rabbits in the US

• easily spread and highly resistant

• good husbandry

myxomatosis in rabbits

• natural host is wild rabbits in NA → seen as localized benign fibromas

• domestic rabbits:

  • seen as severe generalized disease

  • blepharaconjunctivitis and swelling of the muzzle

  • become febrile and listless

  • often die within 48 hours of clinical signs

myxoma and RHD was used for

controlling rabbit overpopulation

lymphocytic choriomeningitis

• in rodents

• zoonotic

• keep rodent cages clean and free of soiled bedding

• wash hands after handling pet rodents

• do not kiss pet rodents or hold them close to your face

eastern equine encephalitis transmission

• multiple mosquito genera transmit virus to other animals

• transmission cycle between birds and vectors (mosquitoes)

• transmission by direct contact

• horse is dead end host

clinical signs of eastern equine encephalitis in birds

• clinical signs do not usually develop in most native species of wild birds infected with EEE

• several nonindigenous birds submitted to SCWDS died due to EEE

• clinical signs for nonindigenous birds, pen reared birds, and whooping cranes include → depression, tremors, paralysis of the legs, unnatural drowsiness, profuse diarrhea, voice changes, ataxia, death

control of eastern equine encephalitis

• killed-virus vaccine was used in captive whooping cranes to protect the rest of the breeding flock following an outbreak in 1984

• emu farmers also use the EEE vaccine for horses

• mosquito free flight cages recommended for rehab situations and bug zappers

west nile virus transmission

• mosquito vectors

• avian reservoirs

• horses are dead end hosts

clinical signs of west nile virus

depression, ataxia, weight loss, torticollis, difficulty flying, death

west nile in florida alligators

• large die-off of hatchling to 3 years

• neurological disease in 3 animals

• necropsy → necrotizing hepatitis and splenitis, pancreatic necrosis, myocardial degeneration, stomatitis and glossitis

west nile virus transmission in alligators

• fighting between alligators

• fecal/oral between alligators

• feeding infected meat, such as horse meat

• feeding opportunistically on infected wild birds

• not mosquito transmitted

what are the natural hosts and reservoir for avian influenza?

wild waterfowl, shorebirds, and gulls

HPAI H5N in swans and raptors

• various species of raptors, geese, and swans have died of H5 virus infections

• raptors probably become infected from eating infected waterfowl