Infectious

Question 1

Is EHV-1 an enveloped or non-enveloped virus?
What environmental conditions are unfavorable for the virus?

Answer 1

EHV-1 has a viral envelope which must remain intact for its environmental survival, transmission and infection. It is susceptible to many commonly used disinfectants as well as environmental conditions such as air temperature, desiccation and UV light.
Potentially infectious EHV-1 persists in the environment
for at least 48 hours (wood shavings ++) and for up to 14 days in water.

Environmental persistence of equid herpesvirus type-1
evj 2021
Updated ACVIM consensus statement on equine herpesvirus-1
jvim 2024

Question 2

Are horses genetically predisposed to equine herpesvirus myeloencephalopathy?

Answer 2

The results exclude the involvement of a recessive genetic factor in the susceptibility to develop clinically apparent EHM.

Genome-wide association study for host genetic factors associated with equine herpesvirus type-1 induced myeloencephalopathy
evj 2020

Question 3

Which assertion is true concerning the detection of EHV-1 in urine samples of EHM horses?
A- DNA presence in urine for longer duration and with higher concentration than buffy coat
B- DNA presence in urine for longer duration and with higher concentration than nasal swab
C- DNA presence in urine was similar in duration and concentration than nasal swab
D- DNA presence in urine was similar in duration and concentration than buffy coat

Answer 3

Answer A
Urine vs buffy coat → DNA presence was detected in urine samples for longer duration and with slightly higher concentration.
Urine vs nasal swab → detection of EHV-1 in urine was similar in duration with lower DNA concentrations.

Detection of equine herpesvirus-1 (EHV-1) in urine samples during outbreaks of equine herpesvirus myeloencephalopathy
evj 2024

Question 4

What is the best sampling technique to detect EHV-1 infection? (depending on the outbreaks)

Answer 4

• When possible, it is advisable to test both nasal secretions and blood for the presence of EHV-1 but when resources are limited or large numbers of horses have to be tested then only nasal secretions should be tested.
• The exception is in mares after abortion when blood samples are more sensitive than nasal secretions.

Viremia and nasal shedding for the diagnosis of equine herpesvirus-1 infection in domesticated horses
jvim 2024
Updated ACVIM consensus statement on equine herpesvirus-1
jvim 2024

Question 5

What are the negative prognostic factors for a return to sport in horses with EHM? (several answer)
- Urinary complications
- Vascular complications (vasculitis)
- Ataxia grade ≧ 4/5
- Ataxia grade ≧ 3/5
- Lymphopenia
- Neutrophilia
- Neuropathogenic genotype

Answer 5

• Horses with an ataxia grade at admission ≥4/5 had an increased fatality rate and 10% chance of reaching their preoutbreak performance level.
• None of the horses with both vascular and urinary complications returned to their previous performance level.
• Overall, horses affected by EHM had 68% chance of returning to exercise.

Long-term performance of show-jumping horses and relationship with severity of ataxia and complications associated with myeloencephalopathy caused by equine herpes virus-1
jvim 2024

Question 6

A group of healthy horses received a combined equine influenza virus (EIV) and equine herpesvirus (EHV-1) vaccine. One subgroup was treated with a single intravenous dose of dexamethasone, while another subgroup received three doses over 72 hours. What is the likely outcome regarding their antibody response to EIV and EHV-1?

A) Both groups will have significantly lower antibody titers against EIV and EHV-1 compared to the control group.
B) Only the group receiving multiple dexamethasone doses will have reduced antibody titers against EIV.
C) Both groups will show no change in antibody titers against EIV but a decrease in EHV-1 titers.
D) Antibody titers will not be affected by dexamethasone in any of the groups.

Answer 6

Correct answer: B

Justification: The study found that horses receiving multiple doses of dexamethasone did not show a significant increase in EIV antibody titers, while horses receiving a single dose did show an increased response. Dexamethasone did not significantly affect antibody titers against EHV-1.
Dexamethasone appeared to decrease the postvaccine inflammatory response in the study.

Effect of dexamethasone on antibody response of horses to vaccination with a combined equine influenza virus and equine herpesvirus-1 vaccine.
JVIM 2024

Question 7

A 14-year-old Quarter Horse presents with fever, lethargy, limb edema, and severe muscle pain. Laboratory findings show significantly elevated CK and AST levels. Neurologic examination reveals diffuse proprioceptive ataxia. What is the most likely diagnosis and initial management strategy?

A) Anaplasma phagocytophilum infection; treat with tetracyclines and corticosteroids.
B) Equine herpesvirus myeloencephalopathy; administer antivirals and supportive care.
C) Polysaccharide storage myopathy; initiate dietary management and vitamin E supplementation.
D) Hyperkalemic periodic paralysis; administer potassium-free fluids and manage with diet.

Answer 7

Correct answer: A

Justification: The combination of fever, muscle disease with elevated CK/AST, and neurologic symptoms (ataxia) in a Quarter Horse suggests Anaplasma phagocytophilum infection, especially given the MYHM association with severe muscle disease in QH breeds. Treatment with tetracyclines is recommended, along with corticosteroids for immune-mediated myositis​.

2023 Common and atypical presentations of Anaplasma phagocytophilum infection in equids with emphasis on neurologic and muscle disease

Question 8

What is one of the key limitations of the currently available African horse sickness (AHS) vaccines?

A) They are too expensive to produce.
B) They do not prevent the spread of the virus.
C) They may cause disease through reversion to virulence.
D) They are not available in endemic regions.

Answer 8

C) They may cause disease through reversion to virulence: live attenuated viruses, can revert to virulence or cause reassortment, posing a risk​.

JUSTIFICTION:

A) They are too expensive to produce: NO. The study does not mention high production costs as a key limitation of current AHS vaccines​. (US$3.5 million: represents the estimated investment needed to bring a new AHS vaccine to market VS US$95 million: the annual economic impact of AHS affecting endemic regions​​.)

B) They do not prevent the spread of the virus: NO. The vaccines do help prevent the spread, but concerns revolve around their safety and effectiveness in global trade​.

D) They are not available in endemic regions: NO. The vaccines are available in endemic regions such as South Africa, Ethiopia, and Senegal, though they have technical limitations​.

Economic assessment of African horse sickness vaccine impact
2021 EVJ

Question 9

What is the main challenge associated with using live attenuated vaccines (LAV) for controlling African horse sickness (AHS), and how could DIVA vaccines address this issue?

A) The high cost of producing LAV
B) The inability to differentiate vaccinated horses from naturally infected ones, which DIVA vaccines could resolve
C) The low efficacy of LAV in preventing AHS, whereas DIVA vaccines offer better protection
D) LAV vaccines are not available in Southeast Asia, but DIVA vaccines are widely used

Answer 9

B) correct. The main limitation of LAV vaccines is that they induce an immune response to all virus antigens, making it hard to differentiate between vaccinated and naturally infected horses. DIVA (Differentiation of Infected from Vaccinated Animals) vaccines can address this issue by using a selected suite of viral antigens, enabling diagnostic tests to distinguish between vaccinated and infected horses.

A) no

C) no. The text does not claim that LAV vaccines are ineffective, but rather that they complicate monitoring the disease. DIVA vaccines, while promising, are not discussed as offering superior protection in efficacy terms​​.

D) no. LAV vaccines are currently being used in Thailand to control the outbreak, but DIVA vaccines are still in development

African horse sickness in Thailand: Challenges of controlling an outbreak by vaccination, 2020, EVJ

Question 10

What is the Strep equi survival duration in the environment ?

Answer 10

Rapid death on fencing (1-3 days) but 4-6 weeks in water (according to the Consensus).

Recent studies : bacterial viability was shown to be enhanced by a wet environment and colder weather.
Summer : S equi survived up to 9 days in wet sites and 2 days in dry sites in the summer.
Winter : survived up to 34 days in wet sites and 13 days in dry sites in the winter.

ACVIM Strep equi consensus
VetClinics 2023

Question 11

According to ACVIM consensus, what is the best diagnostic method of strangles ?

Answer 11

GP lavage > NP wash > NP swab → false negative in early stage
Best option : aspiration of mature abscessed lymph nodes.
Culture : no longer valid as the gold standard.
qPCR : sensitivity x3 than culture, false negative if dead bacteria

ACVIM Strep equi consensus

Question 12

What are the SeM serology dosages associated with :
- purpura hemorrhagica ?
- Bastard strangles ?
- Contraindication to vaccination ?
- Myopathies ?

Answer 12

• Purpura hemorrhagica : ≧ 1:12.800
• Bastard strangles : ≧ 1:12.800
• Do not vaccinate if ≧ 1:3.200 because of the increased risk of purpura hemorrhagica
• Immune-mediated myopathies : ≧ 1:6.400

Cross-reactivity with Strep. equi zooepidemicus
SeM serology → peak at 5 weeks after infection and can remain high for at least 6 months.

ACVIM Strep equi consensus

Question 13

What is the gold standard for the identification of Strep equi carriers ?

Answer 13

Carriers : horses that are S equi positive for greater than 6 weeks
One GP lavage → qPCR testing

ACVIM Strep equi consensus

Question 14

When should ATBs be used to treat strangles?

Answer 14

• High fever
• Respiratory distress
• Metastatic abscess
• Purpura hemorrhagica

ACVIM Strep equi consensus

Question 15

What are the myopathies associated with Strep equi ?

Answer 15

• Muscle infarctions
• Rhabdomyolysis with acute myonecrosis
• Rhabdomyolysis with progressive atrophy (QH with MYH1 mutation)

VetClinics 2023

Question 16

What to think of a PCR-positive and culture-negative S equi horse?

Answer 16

There has been much controversy over whether a qPCR-positive, culture-negative animal is still infectious.

Two studies provide evidence that suggest that these animals should be considered a threat to naïve populations. Pringle and colleagues showed that S equi PCR–positive, culture-negative horses can become culture positive again.

VetClinics 2023

Question 17

Why use combined Antigen A and Antigen C serology?

Answer 17

It has similar sensitivity but greater specificity when compared
with the whole SeM antibody titer.

This iELISA is recommended :
1. To identify horses with strangles exposure as recent as 2 weeks previously
2. To identify animals without clinical signs that may be carrying S equi for the purposes of isolation and further evaluation through endoscopic guttural pouch examination (new entrant).

VetClinics 2023

Question 18

What is the minimum quarantine period for new arrivals?

Answer 18

Quanrantine new arrivals for 3 weeks : corresponds to the potential duration of bacterial excretion after resolution of clinical signs.

VetClinics 2023

Question 19

Which of the following is true regarding silent carriers of Streptococcus equi in horses, as concluded in the study?

A) Clinical examination and serology can reliably differentiate silent carriers from non-carriers.

B) Most horses that tested positive for S. equi on culture or qPCR were also seropositive for S. equi.

C) Silent carriers of S. equi did not show significant differences in clinical markers or inflammation compared to non-carrier herd-mates.

D) Weanlings from outbreak A showed a significant association between clinical markers and carrier status.

Answer 19

Answer:
C) Silent carriers of Streptococcus equi did not show significant differences in clinical markers or inflammation compared to non-carrier herd-mates.

Explanation:
The study concluded that silent carriers of S. equi did not differ clinically or in terms of inflammation markers compared to non-carrier horses. Additionally, serology alone could not distinguish carriers from non-carriers, and there was no significant association between clinical markers or serology and carrier status.
Moreover, 3/12 culture positive carriers were seronegative to S. equi.

Markers of long term silent carriers of Streptococcus equi ssp. equi in horses
jvim 2020

Question 20

Which of the following conclusions can be drawn from the study on disinfection methods for Streptococcus equi on endoscopes and twitches?

A) All disinfection protocols completely eliminated both viable S. equi bacteria and bacterial DNA from endoscopes and twitches.

B) Sodium hypochlorite was the most effective disinfectant for eliminating both viable S. equi bacteria and bacterial DNA from twitches.

C) Field disinfection of endoscopes following carrier sampling yielded several culture-positive results.

D) While most disinfection methods eliminated cultivable S. equi, some residual DNA remained on both endoscopes and twitches.

Answer 20

Answer:
D) While most disinfection methods eliminated cultivable S. equi, some residual DNA remained on both endoscopes and twitches.

Explanation:
The study found that while most disinfection methods effectively eliminated S. equi bacteria from both endoscopes and twitches (i.e., making cultures negative), residual S. equi DNA was still detectable on both types of equipment after disinfection.
Sodium hypochlorite was the only disinfectant that completely eliminated S. equi DNA from twitches.

Potential for residual contamination by Streptococcus equi subspp equi of endoscopes and twitches used in diagnosis of carriers of strangles
evj 2020

Question 21

When evaluating disinfection methods to remove Streptococcus equi from endoscopes and twitches in an equine clinic, which of the following statements is TRUE according to this study?

A. All tested disinfection protocols eliminated both viable bacteria and DNA of S. equi from endoscopes and twitches.
B. Disinfection with sodium hypochlorite was the only method to remove S. equi DNA from twitches, though this disinfectant poses ecological risks.
C. Complete elimination of S. equi DNA on endoscopes was only achieved using an Automated Endoscope Reprocessor (AER).
D. Field disinfection protocols for endoscopes were insufficient for removing viable bacteria in all cases.

Answer 21

Correct Answer: B. Disinfection with sodium hypochlorite was the only method to remove S. equi DNA from twitches, though this disinfectant poses ecological risks.

Justification:

Option A is false: None of the protocols completely removed S. equi DNA from all samples.

Option B is correct: Sodium hypochlorite was the only disinfectant that eliminated bacterial DNA from twitches, though it is toxic to aquatic organisms.

Option C is incorrect: Although AER showed effectiveness (Results: No viable S. equi was found in bacterial cultures (0 out of 6 samples), and only 1 out of 6 samples remained PCR-positive, showing the highest efficacy in DNA removal among all methods tested), it did not completely remove all bacterial DNA from samples.

Option D is incorrect: Field-disinfected endoscopes showed no viable bacteria post-cleaning, though one sample remained culture-positive (ethanol)

Cl= DNA remains detectable, which could cause false positives in PCR.

Potential for residual contamination by Streptococcus equi
subspp equi of endoscopes and twitches used in diagnosis of
carriers of strangles
evj 2020

Question 22

What is the main conclusion regarding the use of serology for detecting guttural pouch carriers of Streptococcus equi in horses?

A) Serological testing for antibodies against S. equi antigens A and C is highly sensitive and can reliably detect guttural pouch carriers.

B) There was a significant association between serological status and guttural pouch carriage of S. equi in the horses studied.

C) Only a small percentage of guttural pouch carriers were seropositive, indicating that serology alone is not reliable for identifying chronic carriers.

D) The study confirmed that a higher OD cut-off increases the sensitivity of serological testing for identifying S. equi carriers.

Answer 22

Answer:
C) Only a small percentage of guttural pouch carriers were seropositive, indicating that serology alone is not reliable for identifying chronic carriers.

Explanation:
The study found no significant association between serological status and the presence of guttural pouch carriage. Only a small proportion of the guttural pouch carriers were seropositive, suggesting that serology is not a highly sensitive method for detecting chronic carriers of S. equi.

Failure of serological testing for antigens A and C of Streptococcus equi subspecies equi to identify guttural pouch carriers
evj 2021

Question 23

In the context of screening for Streptococcus equi guttural pouch carriers in horses, which of the following statements is TRUE based on the study findings?

A. Serological testing for antigens A and C is highly sensitive for detecting guttural pouch carriers.
B. A positive serological result for antigens A and C reliably indicates guttural pouch carriage of S. equi.
C. Microbiological sampling is more reliable than serology in identifying S. equi carriers.
D. Horses testing seronegative for antigens A and C are unlikely to be carriers of S. equi.

Answer 23

Correct Answer: C. Microbiological sampling is more reliable than serology in identifying S. equi carriers.

Option A is incorrect: The study demonstrated that serological testing has low sensitivity, missing many guttural pouch carriers.
Option B is incorrect: A positive serology result does not reliably indicate carrier status due to low positive predictive value.
Option C is correct: Microbiological sampling (PCR and culture) directly detects S. equi, making it more reliable than serology.
Option D is incorrect: Seronegative results do not exclude carrier status, as many carriers were seronegative in this study.

Failure of serological testing for antigens A and C of Streptococcus equi subspecies equi to identify guttural pouch carriers
evj 2021

Question 24

What did the study conclude about the use of repeated nasopharyngeal lavage (NPL) in detecting Streptococcus equi carriers in horses?

A) Serial NPL testing is not useful in predicting carrier status for S. equi in horses after recovery from a strangles outbreak.

B) Horses with at least three consecutive negative NPL samples were more likely to be free of S. equi at week 45.

C) The study showed that a single NPL test is sufficient to predict long-term carrier status for S. equi.

D) Only horses that were negative on all NPL samples were confirmed to be free of S. equi at week 45.

Answer 24

Answer:
B) Horses with at least three consecutive negative NPL samples were more likely to be free of S. equi at week 45.

Explanation:
The study concluded that repeated NPL testing on at least three separate occasions (weeks 18, 28, 29, and 30) could predict whether a horse would be S. equi-free at week 45. Specifically, horses that had at least three negative NPL tests from these time points were more likely to be free of S. equi at the final assessment, demonstrating that serial NPL testing is useful for predicting carrier-free status after recovery from a strangles outbreak.

Repeated nasopharyngeal lavage predicts freedom from silent carriage of Streptococcus equi after a strangles outbreak
jvim 2022

Question 25

Which of the following statements is TRUE regarding the use of the dual antigen iELISA test in horses vaccinated with the Pinnacle® IN vaccine?

A. The iELISA test can reliably distinguish between vaccinated horses and those naturally exposed to S. equi.

B. Horses vaccinated with Pinnacle® IN are unlikely to show seroconversion to Antigens A and C in the iELISA test.

C. Pinnacle® IN vaccination causes high seroconversion rates to Antigens A and C, affecting the iELISA test’s ability to indicate infection.

D. Only horses with natural S. equi infection show seroconversion in the dual antigen iELISA test.

Answer 25

Correct Answer: C. Pinnacle IN vaccination causes high seroconversion rates to Antigens A and C, affecting the iELISA test’s ability to indicate infection.

Option A is incorrect: The study indicates that the iELISA test does not reliably distinguish between antibodies from vaccination and those from natural infection.
Option B is incorrect: The majority of vaccinated horses in the study seroconverted to Antigen C and a significant portion to both antigens.
Option C is correct: The study found that Pinnacle IN vaccination leads to high seroconversion rates to both Antigens A and C, impacting the iELISA test’s diagnostic accuracy in vaccinated horses.
Option D is incorrect: Vaccinated horses, not only those with natural infection, can show seroconversion in the dual antigen iELISA.

Horses vaccinated with live attenuated intranasal strangles vaccine seroconvert to SEQ2190 and SeM
evj 2022

Question 26

What is the clinical efficacy of transpharyngeal fenestration to treat GP infection ?

Answer 26

This surgical technique for transpharyngeal diode laser fenestration of the guttural pouch was uncomplicated to perform and well tolerated in sedated horses and attributed to resolution of clinical signs associated with guttural pouch infection, and owners reported a high satisfaction with the clinical outcome.

Clinical outcome of horses with guttural pouch infection following transpharyngeal fenestration
javma 2022

Question 27

Which disinfectant showed the best results in terms of cleaning time, culture outcomes, and qPCR results after disinfection of endoscopes contaminated with Streptococcus equi?

A) Ortho-phthalaldehyde (OPA), requiring 12 minutes of cleaning, with no positive culture results but a 73% qPCR-positive rate

B) Accelerated Hydrogen Peroxide (AHP), requiring 8 minutes of cleaning, with no positive culture results and a 33% qPCR-positive rate

C) Water (control), requiring 12 minutes of cleaning, with no positive culture results but a 71% qPCR-positive rate

D) Both OPA and AHP, showing the same efficacy in terms of culture and qPCR results

Answer 27

ANSWER B)

Accelerated Hydrogen Peroxide (AHP) was significantly more effective than OPA in reducing qPCR-positive results, despite both disinfectants eliminating live bacteria as indicated by culture tests..

Efficacy of high-level disinfection of endoscopes contaminated with Streptococcus equi subspecies equi with 2 different disinfectants
jvim 2023

Question 28

What are the myopathies associated with Streptoccus equi equi infection ?

Answer 28

• Infarctive PH : serum CK activity is markedly elevated (>35,000 U/L) and horses are painful with firm swollen areas in pectoral, abdominal and crus muscles, muscles that are compressed when horses are lying down. Aggressive and prolonged corticosteroid treatment is essential in cases of infarctive PH to prevent fatal infarction of the gastrointestinal tract, lungs and other tissues.
• Myosin Heavy Chain Myopathy (MYHM) : Quarter Horse-related breeds are particularly susceptible to compli-
  cations from S. equi infection because of a genetic proclivity for myosin heavy chain myopathy (MYHM) caused by an E321G mutation in the myosin heavy chain 1 gene (MYH1) encoding type 2X myosin. In approximately 40% of cases of MYHM, a history of exposure to S. equi, other infectious diseases or vaccination with S. equi or influenza / rhinopneumonitis precedes clinical signs. Both horses heterozygous and homozygous for the MYH1 mutation develop MYHM with clinical signs being more severe and difficult to manage in homozygotes.
  Horses with MYHM may present with : immune-mediated myositis (IMM), calciphylaxis, nonexertional rhabdomyolysis (nER).
• IMM : Immune-mediated myositis usually develops in horses < 8 years of age or >16 years of age and is characterised by rapid profound atrophy of gluteal and epaxial muscle initially concurrent with moderate serum CK and AST elevations (often < 20,000 U/L). The aetiology of IMM has been proposed to be a loss of self-tolerance to type 2X myosin. The amino acid sequence of SEM overlaps that of type 2X myosin creating the possibility that antigenic mimicry is an instigator of disease.
  In the early phase of gluteal and epaxial muscle atrophy, lymphocytes infiltrate type 2X muscle fibres and cuff small blood vessels.
• Calciphylaxis : Systemic calcinosis or calciphylaxis is a rare sequelae to IMM in young (less than 9 years of age) horses with the MYH1 mutation. Severe atrophy is followed by diverse organ failure due to systemic dystrophic calcification.
  A high product of serum calcium multiplied by serum phosphorus (>65 mg/dL) is common in calciphylaxis.
• Nonexertional rhabdomyolysis : 67% of nER cases in Quarter Horse-related breeds were associated with the MYH1 mutation of which 75% were homozygotes and 25% heterozygotes. Severe, generalised muscle degeneration occurs with serum CK and AST in the hundreds of thousands. Triggering factors include infection with S. equi, Anaplasma phagocytophilum, Corynebacterium pseudotuberculosis and other infectious agents but often the trigger is unknown.
  Muscle biopsies of gluteal or epaxial muscles show acute muscle degeneration, glycogen depletion in large muscle fibres and, unlike IMM, < 18% of horses have lymphocytic infiltrates in muscle fibres. This suggests an alternate aetiology to immune-mediated muscle fibre destruction. The MYH1 mutation appears to enhance the calcium sensitivity of muscle fibres which could result in a hyper-contractile state where muscles are more likely to contract and fail to relax triggering myodegeneration.

Myopathies associated with Streptococcus equi equi infection
eve 2024

Question 29

What is the best frequency of EIV booster vaccination in young horses ?

Answer 29

Vaccine breakdown was observed primarily but not exclusively among young horses which had not received a booster vaccination within the previous 6 months.
Time since last vaccination was identified as an important factor during previous EI outbreaks. The findings of this study suggest that increasing the frequency of booster vaccinations particularly in young horses may be beneficial.

Annual booster vaccination and the risk of equine influenza to Thoroughbred racehorses
evj 2020

Question 30

What are the main contributing factors to EIV outbreaks according to studies ? (3)

Answer 30

Mechanism of disease spread in studies:
- vaccine breakdown (or unvaccination), reinforcing the necessity of keeping vaccine strains updated according to OIE recommendations,
- mixing of racing and other TB populations (breeding / pretraining) with inadequate vaccination,
- failure of appropriate biosecurity measures following the intro of new arrivals and restriction of horse movement in the face of disease.

Annual booster vaccination and the risk of equine influenza to Thoroughbred racehorses
evj 2020
Multifocal outbreak of equine influenza in vaccinated horses in Argentina in 2018: Epidemiological aspects and molecular characterisation of the involved virus strains
evj 2020
An epidemiological overview of the equine influenza epidemic in Great Britain during 2019
evj 2023

Question 31

What are the most common adverse reactions following EIV vaccination ?

Answer 31

Adverse events following vaccination in the previous year were encountered by 66% of respondents.
Most common reactions were transient, including stiffness, localised swelling, lethargy and pyrexia.

Equine influenza vaccination in the UK: Current practices may leave horses with suboptimal immunity
evj 2021

Question 32

What is the clinical presentation of EIV in donkeys ? What is the prognosis ?

Answer 32

Clinical signs of equine influenza virus infection in donkeys are similar to those observed in horses.
Prognosis for survival generally is good, but deaths have been observed especially in young donkeys < 1 year old, born to seronegative dams.
This finding emphasizes the importance of prenatal vaccination protocols in all equids, including donkeys.

Disease progression, pathologic, and virologic findings of an equine influenza outbreak in rescue donkeys
jvim 2022

Question 33

What is the way of transmission of EVA ?

Answer 33

2 ways :
- Respiratory : aerosolization from acutely infected horses, urine, aborted fetuses
- Venereal : semen of stallions acutely or chronically infected, embryo transfer, fomites.

Transplacental transmission possible in mares infected in late gestation (vertical).
Asymptomatic carrier stallion → fundamental natural reservoir of EAV.

Question 34

What are the clinical presentations of EVA ?

Answer 34

Majority of EAV infection → inapparent
Very young, old, or immunocompromised → predisposed to severe EVA
- Abortion of pregnant mares (autolyzed fetus)
- Fatal infection in neonatal foals (congenitally infected or not) → interstitial pneumonia and fibronectic enteritis
- Systemic illness in adult horses → fever and leukopenia, respiratory signs with nasal and ocular discharge, peripheral edema (supraorbital, limbs, ventral, scrotum, mammary glands), urticaria, mucosal petechiation.

Question 35

DDX of flu-like syndrome

Answer 35

• EHV-1, 4
• EIV
• EVA
• Equine rhinitis A and B
• Adenovirus
• Getah virus

Question 36

What precautions should I take before / after vaccination against EVA?

Answer 36

Modified live-virus attenuated vaccine → mild febrile reaction, and the virus may be sporadically isolated from the NP and buffy coat.

• Isolate stallions after vaccination for approximately 21 days (do not use semen)
• Recommend not to use in pregnant mares, especially during the last 2 months of gestation
• Recommend not to use in foals < 6 weeks of age
• Recommend to vaccinate prepubertal colts at 6 months of age → prevent the persistently infected carrier state after exposure.

In Europe → killed-virus vaccine

Question 37

Equine rhinitis viruses (ERAV and ERBV): which types of infection? Clinical signs? Diagnostic modalities?

Answer 37

Picornavirus :
- ERAV (Aphthovirus), formerly known as equine rhinovirus 1,
- ERBV (Erbovirus), formerly known as equine rhinovirus 2, are capable of affecting both the lower and upper airways.

In young performance horses, ERAV has been associated with the development of inflammatory airway disease.
Both natural and experimental infections of seronegative horses with ERVs have been considered to be a cause of fever, anorexia, seromucoid nasal discharge, coughing, lymphadenopathy and occasionally lower limb swelling

Difficulties in virus isolation

very short shedding time following the development of clinical signs

Serology, using acute and convalescent serum samples, has remained a diagnostic pillar when ERAV is suspected but detection via qPCR has yielded negative results

Challenges in navigating molecular diagnostics for common equine respiratory viruses 2021

Question 38

What is the significance of determining EIV clade affiliation?

Answer 38

Determining EIV clade affiliation is important for epidemiological monitoring, understanding outbreaks, and updating vaccine strains to improve protection against clinical disease.
H3N8 Florida sublineage, clade 1 in North America, Africa, Japan;
clade 2 in Europe, China, India

Challenges in navigating molecular diagnostics for common equine respiratory viruses 2021

Question 39

What are the primary immunodeficiencies in horses ? (4)

Answer 39

• Severe combined immunodeficiency (SCID) : in Arabian foals, failure to produce functional B- and T-lymphocytes → absolute lymphopenia
• Foal immunodeficiency syndrome in Fell and Dales ponies → anemia, B-cell lymphopenia
• Common variable immunodeficiency (CVID) in adult horses → failure of B-cell development in bone marrow
• Selective IgM deficiency in Arabian and QH (foals an adults)

Question 40

What are the secondary immunodeficiencies in horses ? (5)

Answer 40

• Failure of transfer of passive immunity (FTPI)
• Strenous exercise
• Age (young and old)
• Leukoproliferative diseases (lymphoma)
• Drug-induced (corticosteroids)