Lecture 10: Viral Neurologic Diseases of Ruminants

rabies

lyssavirus genus, in the family rhabdoviridae

rabies clinical signs

• may be quite variable and inconsistent

• hindlimb ataxia, weakness, or paralysis

• constant straining to the point of having or almost having a rectal prolapse is red flag

• cattle signs in order of most common are salivation, bellowing, aggressiveness, paresis/paralysis, and straining

• bite wounds unlikely

• self-mutilation

cerebral or furious form of rabies

aggressive behavior, photophobia, hyperesthesia, straining, and convulsions

brainstem or dumb form of rabies

depression and dementia with ataxia, excessive drooling, and pharyngeal paralysis

spinal cord or paralytic form of rabies

progressive ascending paralysis

rabies diagnosis

• lab confirmation → may be state or public health lab

• if only spinal cord disease, virus and negri bodies may not be found in brain

• death within 10 days of clinical signs

rabies EEP

• all ages susceptible

• incubation period → few weeks up to 6 months

• passes along neurons within the nervous system

• may be hyperactivity of affected neurons with signs such as hyperesthesia, tremor, straining, and salivation

• eventually the neurons die and are followed by flaccid paralysis, dysphagia, and anesthesia

rabies treatment

• texas protocol

• immediate vaccination after exposure

• booster 3 to 8 weeks after

• 90 day quarantine

rabies control

• vaccines are available but consider economics

• administration may be limited to veterinarians

rabies prognosis

grave

dogs shed rabies about 10 days prior to clinical signs…what about cattle?

• shedding of the virus in the nasal secretions and saliva may precede the onset of clinical signs

• the virus may be present in the saliva for periods up to 5 days before signs are evident

• virus shed in low levels in the milk of infected animals and may occasionally infect the offspring that are nursing infected dams

rabies is transmitted only when

the virus is introduced into bite wounds, open cuts in skin, or onto mucus membranes

the rabies outbreak in southern mexico came from

vampire bats who feed on animals

if a cow had rabies, would her calf also get rabies by drinking her milk?

probably not from milk, but grooming

when do rabid animals shed the virus?

they don’t tend to shed until clinical signs are evident

one red flag that would you consider rabies?

unrelenting tenesmus, weak rear end, behavior change

rabies disinfection

• easier to inactivate than prions

• sodium hypochlorite

• 45-75% ethanol

• iodine

• quaternary ammonium compounds

• formaldehyde

• phenol

• ether

• trypsin

• beta-propiolactone

• detergents

pseudorabies (mad itch)

• defined as an acute viral encephalitic disease of ruminants primarily characterized by severe pruritis

• very rare currently in the US

aujeszky’s disease virus

• alphaherpesvirus → genus varicellovirus, single serotype

• highly contagious

• natural hosts → domestic and feral swine, most mammals are susceptible

clinical signs for pseudorabies

• multiple animals with severe pruritis

• or sudden death without obvious clinical signs

• dermal abrasions, swelling and alopecia virus inoculation site, fever, bellowing, bloat, stamping of feet, salivation, and tongue chewing

• progresses etc to death

pseudorabies post mortem lesions

• lesions often subtle or absent

• serous or fibrinonecrotic rhinitis

• pulmonary edema, congestion, consolidation

• congested and hemorrhagic lymph nodes

• necrotic foci in organs

pseudorabies diagnosis

• reportable → immediately contact appropriate regulatory officials

• clinical signs suggestive → virus isolation, detection of viral DNA or antigens, serology

pseudorabies treatment, EEP

• no effective treatment

• primary host → pig

• proximity to swine affects differentials, ingestion of raw meat in some species

• horses are resistant

• incubation period → 4-7 days

• duration of illness → 8 to 72 hours

• limit exposure between swine and cattle

how do you prevent feral swine and cattle contact in texas?

• doesn’t appear to be a concern, needs to be close contact and texas is large

• no cases reported in anything other than pigs

• feral swine pseudorabies does not prevent the free status

what are the gold areas showing?

areas where wild pigs are seropositive for pseudorabies in the US

hydrocephalus and hydrancephaly

• in utero exposure to multiple viral pathogens can lead to failure of cell growth or cellular necrosis in ruminant neonates

• examples → bluetongue, bovine viral diarrhea, akabane, cache valley virus, border disease