2023.Vol39.Iss1.EquineInfectiousDiseases Flashcards
Streptococcus equi subsp equi
what is the key to controlling outbreaks?
-daily temperature checking
-isolation of febrile horses
Streptococcus equi subsp equi
what type of hypersensitivity is purpura hemorrhagica?
type III
**immune complex-mediated hyeprsensitivity– ag-ab complex deposition
Streptococcus equi subsp equi
what type of myopathies have been documented after exposure to S. equi?
-muscle infarctions
-rhabdomyolysis with acute myonecrosis
-rhabdomyolysis with progressive atrophy
Streptococcus equi subsp equi
In Quarter horses, what type of gene mutation results in a type of immune-mediated myositis?
missense mutation in MYH1
Streptococcus equi subsp equi
What are virulence factors that aid in Strep equi’s ability to evade phagocytosis?
hyaluronic acid capsule
antiphagocytic SeM protein
Mac protein
Streptococcus equi subsp equi
How long can horses be shedding the organism after purulent discharge have stopped?
~3-6 weeks
Streptococcus equi subsp equi
Do horses develop immunity after infection with strangles?
~75% of horses develop a waning immunity to strangles that lasts about 5 years after recovery from the disease
Streptococcus equi subsp equi
What is a potential risk of older horses with residual immunity?
**have limited susceptibilty & develop a mild form of strangles, but shed virulent S. equi that will produce severe disease in more susceptible, often younger hroses
Streptococcus equi subsp equi
Are foals protected from strangles infection?
foals that obtain maternal antibodies via colostrum and milk that coat the upper respiratory and oral mucosa
**usually resistant till weaning
Streptococcus equi subsp equi
Dsecribe the pros and cons of sampling for diagnosis for Strep equi subsp equi infection.
Streptococcus equi subsp equi
What are the purposes of performing SeM protein serology?
- Detection of recent infection evidenced by a 4-fold or greater increase in paired titers taken 10 days apart
- support a diagnosis of purpura hemorrhagic or metastatic abscessation (titer >1:12,800)
- Safety of vaccination: horses with a high serum SeM specific antibody titers (>1:3200) may be predisposed to developing purpura hemorrhagica when vaccinated against S. equi
Streptococcus equi subsp equi
What is also important to note in an outbreak of strangles, as far as human health?
Strep equi infection is zoonotic to people with immunosuppression
Eastern, Western and Venezuelan Equine Encephalitis and West Nile Viruses: clinical and public health considerations
WNV is a positive-sense-ss RNA flavivirus, that is transmitted by what vector?
mosquitoes
Eastern, Western and Venezuelan Equine Encephalitis and West Nile Viruses: clinical and public health considerations
what are the dead-end hosts of WNV?
horses
humans
**new world camelids & sheep
Eastern, Western and Venezuelan Equine Encephalitis and West Nile Viruses: clinical and public health considerations
What C/S are seen with WNV encphalomyelitis?
-assymetric motor deficits & multifocal
-primarily limb ataxia
-weakness
-obtundation
-recumbency
-hyperesthesia/hyperresposniveness
-muscle fasciculations
less common: dog-sitting postures, thoracic limb collapse, compulsive walking, muscle atrophy, seizure, circling, blindness or head pressing
Eastern, Western and Venezuelan Equine Encephalitis and West Nile Viruses: clinical and public health considerations
what C/S are similar between EEE and WNV?
muzzle twitching, progressing to recumbency and death
Eastern, Western and Venezuelan Equine Encephalitis and West Nile Viruses: clinical and public health considerations
What CSF abnormalities are seen on CSF with WNV encephalomyelitis?
mononuclear pleocytosis
high protein
Eastern, Western and Venezuelan Equine Encephalitis and West Nile Viruses: clinical and public health considerations
What ist he diagnostic test for WNV?
IgM antibody-capture ELISA
Eastern, Western and Venezuelan Equine Encephalitis and West Nile Viruses: clinical and public health considerations
EEE and WEE viruses are maintained in an enzootic cyle between….
passerine birds & ornithophilic mosquitoes
Eastern, Western and Venezuelan Equine Encephalitis and West Nile Viruses: clinical and public health considerations
Which mosquito vectors for WEE vs EEE
C tarsalis- WEEV
C. melanura– EEEV
Eastern, Western and Venezuelan Equine Encephalitis and West Nile Viruses: clinical and public health considerations
What are risk factors for equine and human infections with WEE/EEE?
high levels of rainfall
standing surface water
bush cover
proximity & size of tree plantations
immune status of hosts
Eastern, Western and Venezuelan Equine Encephalitis and West Nile Viruses: clinical and public health considerations
Venzuelan has what important differences from EEE/WEE?
-birds do not play a significant role in amplication & maintenance VEE
-VEE maintained in enzootic ccyle between rodents & mosquitoes
-epizootic cycle involves equids as amplifying and reservoir hosts
-important human pathogen
Eastern, Western and Venezuelan Equine Encephalitis and West Nile Viruses: clinical and public health considerations
What neurologic signs are seen with EEE/WEE?
diffuse or multifocal forebrain dz: recumbent, comatose, dead, initial sign obtundation, head pressing, odontoprisis, irritabilty, hyperesthesia, aggression, lack of menace
CN signs
Eastern, Western and Venezuelan Equine Encephalitis and West Nile Viruses: clinical and public health considerations
What are differentials for horses with encephalitic signs in horses?
EEE/WEE/VEE
WNV
EPM
EHV-1
Rabies
verminous or bact mengingoencephalomyelitis
hepatic encephalopathy
leukoencephalomalacia
Salmonella in Horses
What is the recommended number of testings for animals with salmonella?
3 to 5, using enriched culture methods to improve overall sensitivity of the testing strategy
**horses an shed low levels of organisms
Salmonella in Horses
What is one of the most commonly identified agents associated with epidemic dz in veterinary hospitals and freq associated with on-farm contamination?
Salmonella enterica
Salmonella in Horses
what increases the probability of salmonella shedding?
systemic illness, increases sheeding by estimated 70%
Salmonella in Horses
what are factors that increase the occurrence of endemic disease?
transportation distance (travel time >1 hour)
abnormal findings on NG intubation
diarrhea
leukopenia (<5000 WBC/uL)
previous antimicrobial therapy
abdominal surgery
duration of hospitalization
Equine Coronaviruses
what are the predominant C/S associated with:
anorexia
lethargy
fever
Equine Coronaviruses
Why can some horses with ECoV develop acute neurological signs?
hyperammonemia, secondary to disruption of the gastrointestinal barrier
Equine Coronaviruses
What neurologic signs are reported with Equine Coronavirus cases that develop hyperammonemia?
severe lethargy
head pressing
ataxia
proprioceptiv deficits
recumbency
nystagmus
seizures
Equine Coronaviruses
Coronaviruses are susceptible to which disinfectants?
heat
detergents
disinfectants: sodium hypochlorite, povidone iodine, 70% ethanol, glutaraldehyde, quaternary ammonium compounds, phenolic compounds, formaldehyde, peroxymonosulfate and accelerated hydrogen peroxide
Equine Coronaviruses
How is equine coronavirus detected?
molecular detection in feces
Equine Coronaviruses
What is significant about the treatment of ECoV?
usually self-limiting, requiring no medical treatment
Infectious causes of equine placentitis and abortion
What are routine tissue collection for diagnostic testing of cases of equine abortion or placentitis?
Infectious causes of equine placentitis and abortion
Identify the parts of fetal membranes.
Infectious causes of equine placentitis and abortion
What is the most common rout eof infection with equine herpresvirus ifnection?
inhalation of viral particles
**although direct contact w/ infected aborted fetuses & fetal membranes or contaminated fomites
Infectious causes of equine placentitis and abortion
Equine herpesvirus latency develops in what locations?
T lymphocytes
trigeminal ganglia
Infectious causes of equine placentitis and abortion
How is equine viral arteritis transmitted?
primarily via respiratory: aerosolization of secretions
venereal route: breeding to acute or chronically infected stallion
Infectious causes of equine placentitis and abortion
equine viral arteritis, natural infections mortality is more common in who?
foals that develop severe interstitial pneumonia
or
aborted fetuses
Infectious causes of equine placentitis and abortion
How is equine viral arteritis virus transmitted?
-aerosolization of respiratory particles & secretions (ie., urine)
-horizontal transmission via direct/cose contact between an infected & naive animal
-venereal transmission via semen from an cutely infected or carrier stallion during natural or AI
-transplacental transmission
-fomites for transmission
Infectious causes of equine placentitis and abortion
Can a pregnant mare be vaccinated for EVA?
NOt in the last 2 month sof gestation– can result in abortion
(unknown if can be vaccinated before then)
Infectious causes of equine placentitis and abortion
How is equine infectious anemia spread?
via bloodsucking insects (ie. horsefly)
iatrogenically throug hcontam blood products or instruments
Infectious causes of equine placentitis and abortion
EIA can result in abortion or birth of foals that may or may not be seropositive. What other routes may infect foals?
-transplacenta
-via colostrum/milk
-vectors
Infectious causes of equine placentitis and abortion
Control of EIA involves which factors
euthanasia or lifelong quarantine of positive animals
disinfection of various instruments after each use
prohibited repeated use of needle & syringes on multiple animals
fly control
up-to-date Coggins testing to confirm a negative EIA result for itnerstate travel
Infectious causes of equine placentitis and abortion
Wildlife reservoirs of leptospira
opossums
striped skunks
racoons
foxes
Infectious causes of equine placentitis and abortion
How are horses exposed to leptospira?
Direct contact with infected urine– contaminated water sources or reproductive tissues and fluids
Infectious causes of equine placentitis and abortion
How is the diagnosis of leptospirosis made?
flourescent antibody testing
PCR for leptospires on fetal kidney
microscopic findings
Infectious causes of equine placentitis and abortion
What is the causative organism of Potomac horse fever?
gram neg obligate bacterium Neorickettsia risticii
**N. findlayensis– novel spp
Infectious causes of equine placentitis and abortion
Describe how horses are infected with PHF?
bacteria infect trematodes that parasitize water snails
**snails release infected cercariae that progress to metacercariae in the second IH, aquatic insects
**acquatic insects that act as a vector: mayflies, caddis flies, dragon flies
Infectious causes of equine placentitis and abortion
What are the vectors of PHF?
mayflies
caddis flies
dragon flies
Infectious causes of equine placentitis and abortion
What is the cause of ascending placentitis?
bacterial or fungal infection of the chorioallantois via the cervix
Infectious causes of equine placentitis and abortion
what are the most common bacteria isolated in ascending palcentitis?
streptococcus sp
E. coli
Pseudomonas
Kelbsiella
Infectious causes of equine placentitis and abortion
Which bacteria is most commonly implicated where an accumulation of several thick, brown-tan mucoid material on the chorionic surface, located often at the bifurcation of the placental horns?
nocardioform placentitis
Infectious causes of equine placentitis and abortion
What increases the risk of developing mare reproductive loss syndrome?
-exposure to the eastern tent caterpillar, Malacosoma mericanum
-presence of choke cherry tress
-stocking density
Infectious causes of equine placentitis and abortion
Where are commonly associated infectious agents based on sites of placental pathology?
Equine Rotaviral Diarrhea
Diarrhea d/t equine rotavirus is because of what mechanisms?
malabsorption
temporary lactose intolerance
activation of the enteric nervous system
Equine Rotaviral Diarrhea
Rotavirus development and contribution of lactose intolerance to diarrhea , what is recommended in equine rotaviral diarrhea foals?
-restricted nursing
-short periods of intstinal rest
-lactase (120 U/kg PO q3-8 hours or before/with meal feeding)
Equine Rotaviral Diarrhea
Other than good farm management & biosecurity practices, what is the most widely used mechanism for the prevention of serious disease caused by equine rotaviral infection?
maternal vaccination
An overview of equine enteric clostridial diseases
How does Clostridioides difficile cause a pseudomembranous colitis?
via toxin mediated mucosal damage of the large bowel, by production of toxins A and B and binary toxin
An overview of equine enteric clostridial diseases
Paenoiclostridium sordelli (previously Clostridium sordelli), can cause pseudomembranous enteric disease of the the small and large intestine, mediated by which toxins?
lethal toxin (TcsL)
hemorrhagic toxin (TcsH)
An overview of equine enteric clostridial diseases
What is the causative agent of Tyzzers disease in foals of 6 weeks of age?
clostridium piliforme
An overview of equine enteric clostridial diseases
What is the infectious form of C. difficile?
the spore
**highly tolerant of oxygen, disinfectants & variety of other stressors & can persist outside the body for years
Potomac Horse Fever
What are the causative agents of PHF?
Neorickettsia risticii
less commonly N. findlayensis
Potomac Horse Fever
What is recommended in the treatmetn of PHF?
tetracycline antibiotic
– initiate immediately in euvolemic horses that are compatible C/S during summer months in endemic regions
Potomac Horse Fever
What are the most commonly reported clinical signs in horses with PHF?
diarrhea
fever
anorexia
lethargy
colic
Potomac Horse Fever
What is the diagnostic test of choice for PHF?
PCR of blood and feces
**PCR whole blood for approx 7-21 days
Potomac Horse Fever
What is the prognosis for survival in of PHF?
approx 70% survival rate with PHF that presented to a tertiary care facility
Equine Granulocytic Anaplasmosis
What is the best effective preventative strategy for Equine Granulocytic anaplasmosis?
No effective vaccine exists
Tick prevention strategies recommended– both equine & human health
Equine Granulocytic Anaplasmosis
What is the organism that transmits equine anaplasmosis?
Ixodid tick– Ixodes scapularis & ixodes pacificus
Equine Granulocytic Anaplasmosis
Anaplasma is maintained in reservoir hosts, such as
white-footed mouse- Peromyscus leucopus
and livestock spp
Equine Granulocytic Anaplasmosis
Anaplasma inavdes host neutrophils, where does replication occur?
vacuoles– fail to fuse with lysosomes or neutrophil-specific granules
- allows replication of organism and formation of microolonies– morulae
Equine Granulocytic Anaplasmosis
What clinical signs are seen with equine anaplasmosis?
fever (102-104F)
depression
tachycardia
icterus
anorexia
**Later in dz: petechiation, distal limb edema, gait stiffness, myalgia, +/- overt lameness or unwillingness to move forward
What organisms are within these neutrophils?
Anaplasma phagocytophylum
Equine Granulocytic Anaplasmosis
When should anaplasmosis be considered?
in cases of:
-neurologic disease, vasculitis, dysphagia, rhabdomyolysis or bicavitary effusion assoc with hypoproteinemia, which cannot be otherwise explained
Equine Granulocytic Anaplasmosis
The diagnosis of Equine anaplasmosis is best made by
paired serology
PCR
visualization of organism on blood smear
Rhodococcus equi– What is the new decade?
When are foals infected with R. equi?
shortly after birth
Rhodococcus equi– What is the new decade?
What is the most common cause of subacute or chronic granulomatous bronchopneumonia in foals less than 5 months of age?
Rhodococcus equi
Rhodococcus equi– What is the new decade?
Virulent and avirulent strains of R. equi exist and both are commonly isolated from horse manure, air and soil in equine farms. What do virulence strains carry?
-virulence plasmid– expresses a highly immunogenic surface protein called virulence assoc protein
a (Vap A)
Rhodococcus equi– What is the new decade?
Virulent R. equi initially infects what cells?
alveolar macrophages
**where organism replicates until macrophage necrosis occurs
Rhodococcus equi– What is the new decade?
Without treatment, what percentage of foals remain subclinical and will heal over time?
70-85%
Rhodococcus equi– What is the new decade?
What is the diagnostic specificity and sensitivity of radiographs in the diagnosis of R. equi?
sensitivity 71%
specificity 85%
Rhodococcus equi– What is the new decade?
what mixed bacterial populations are common with R equi infections?
Strep spp
Actinobacillus spp
Rhodococcus equi– What is the new decade?
which antibiotics are recommended in the treatment of R. equi pneumonia?
-macrolide: clarithromycin (7.5 mg/kg PO q12h) ; azithromycin 10 mg/kg PO q24h for 5 days, then q48 thereafter)
-rifampin (5 mg/kg PO q12h)
or doxy & azithromycin
Rhodococcus equi– What is the new decade?
What are potential complications of macrolide administration?
-diarrhea (usu self-limiting)
-drug-induced anhidrosis– hyperthermia
Rhodococcus equi– What is the new decade?
macrolide resistance in macrolide-resistant isolates of R. equi is due to what gene mutation?
erm (46), an erythromycin-resistant methylase gene
Vesticular Stomatitis Virus
How is the virus spread?
biting insects
direct contact w/ virus containing fluids
indirect contact with contaminated fomites– shared water, feed, feeders, lick tubs, tack or veterinary supplies, like oral drenching equipment or dental floats
Vesticular Stomatitis Virus
Which tests are reliable indicators of recent infection for the purposes of VS case definition during an outbreak?
CFT: complement fixation test
rRT-PCR: real-time reverse transcription polymerase chain reaction
and/or VI: virus isolation
Vesticular Stomatitis Virus
What occurs in a VSV outbreak?
-Diagnosis of case
-all confirmed positive & suspect VS premises are placed under state quarantine for a minimum of 14 days from onset of lesions in the last affect animal on the premises
-quarantine applies to all Vs-susceptible species on premises
-no movement of spp off-site are permitted w/o approval of state veterinarian
Vesticular Stomatitis Virus
What are the diagnostic samples to collect in suspect VS cases?
-a serum sample and swabs of the lesions in viral transport media.
-samples submitted to a US department of agriculture (USDA)- approved vesicular stomatitis virus (VSV) lab with the authorization of the state veterinarian or federal AVIC
