B.C. equine disease surveillance and report


To communicate the status of reportable and notifiable equine diseases in B.C. To also communicate the status of equine non-reportable and non-notifiable diseases at the discretion of equine veterinarians. This information is intended for veterinarians, horse owners and other stakeholders in the provincial equine industry.

How the surveillance program works

The program is a cooperative information sharing partnership between the B.C. government's Animal Health Centre and veterinarians practicing in B.C. Verified diagnostic information regarding the occurrence of reportable, notifiable and non-reportable/notifiable diseases will be posted below in the B.C. Equine Disease Report. 

Diseases to be communicated in the report:

Non-reportable and non-notifiable diseases: To post a diagnosis of a non-reportable, non-notifiable disease on this site, the veterinarian will contact the page manager at 1-800-661-9903 with the clinical and diagnostic information for the case. The manager will upload the case to the Equine Disease Report and will follow the case with the veterinarian to resolution. Updates to the case will be added to the Equine Disease Report as warranted.

Reportable and notifiable diseases: These diseases prescribed under the Animal Health Act are mandatory to report to the Chief Veterinary Officer of B.C. upon diagnosis. After a reportable or notifiable disease is reported, the Chief Veterinary Officer will inform the page manager of the diagnosis for posting in the disease report below. To see a list of all equine reportable and notifiable diseases, please click the headings.

  • African Horse Sickness
  • Contagious Equine Metritis
  • Eastern, Western and Venezuelan Equine Encephalomyelitis
  • Equine Infectious Anemia
  • Equine Piroplasmosis caused by Babesia caballi or Theileria equi
  • Rabies
  • Vesicular Stomatitis
  • Anaplasmosis
  • Equine Herpes Myeloencephalopathy
  • Equine Rhinopneumonitis
  • Equine viral arteritis
  • Salmonella Dublin
  • Salmonella Enteritidis
  • Salmonella Heidelberg
  • Salmonella Typhymurium
  • West Nile Virus

The Reportable and Notifiable Diseases regulation requires that a report be made to the office of the Chief Veterinarian within 24 hours if you have reasonable grounds to suspect that a reportable or notifiable diseases has occurred:

Make a report to the office of the Chief Veterinarian Officer of B.C. 

Date: August 7, 2019

Disease: West Nile Virus

Location: Princeton area, BC

Status: New disease report

CFIA has confirmed that a horse resident in the Princeton area of BC meets the case definition for West Nile Virus disease (see below for CFIA case definition – copied from https://www.inspection.gc.ca/animals/terrestrial-animals/diseases/immediately-notifiable/west-nile-virus/surveillance/eng/1346131121021/1346131213336)

  • 9 year old Quarterhorse gelding
  • Clinical history: end of June horse became aggressive, restless, getting up and down, circling then became wobbly behind, lethargic, head down, muscle twitch in shoulder and flank
  • Vet exam July 3: depressed, ataxic at walk front and hind, proprioceptive deficits all round, T-39.9
  • Acute and convalescent serum samples – 4 fold increase in IgG titre demonstrated for WNV (SVN test)
  • IgM ELISA test was negative for WNV
  • Horse was not tested for EHV
  • Horse recovered by July 10 with supportive treatment (fluids, antibiotics, flunixin) and was in work again 2 weeks later
  • Vaccinated for WNV in April 2018 and April 2019
  • Horse travelled to multiple locations in eastern Washington, northeastern Oregon, BC and Alberta, mid to late June 
  • Unclear where the horse may have been exposed to WNV due to the travel history

CFIA Case Definition:

When reporting on West Nile Virus (WNV), the CFIA's Animal Disease Surveillance Unit will use the following criteria to classify the various results into categories:

Positive case

Compatible clinical signsFootnote 1 plus one or more of the following:

  • isolation of West Nile virus from tissuesFootnote 2;
  • an associated 4-fold or greater change in IgG ELISA testing or sero neutralization (SN) test antibody titre to WNV in appropriately-timedFootnote 3, paired sera;
  • detection of IgM antibody to WNV by ELISA testing in serum or cerebrospinal fluid (CSF) - see first assumption below;
  • a positive polymerase chain reaction (PCR) to WNV genomic sequences in tissues and appropriate histological changes;
  • a positive immuno-histochemistry (IHC) for WNV antigen in tissue and appropriate histological changes.

Possible case

Compatible clinical signs plus one of the following:

  • elevated titre to WNV antibody by SN test in serum or positive IgG ELISA test, but only one sample is available;
  • static IgG titres to WNV (SN test or ELISA) in appropriately-timedFootnote 3, paired sera.

A possible case will normally be retested to further determine its actual status.


An animal for which a single positive SN or IgG test is reported, if there is no information regarding the presence of clinical signs or if it is reported that the animal didn't show any clinical signs, will be classified as a reactor. Such animal will be deemed to have been tested for other reasons than clinical signs, such as for surveillance, export or for verification of post vaccination protection.

Other possible categories

Generally speaking and in practice, the most frequent categories will be Positive Case, Possible Case and Reactor.

Suspicious: Clinical signs only

A suspicious case will only be reported by a laboratory that does not perform any testing for WNV and would have eliminated other possibilities (rare). In this case, the owner or the practitioner would not have asked for or authorized further testing.

Non-case: A case that was classified as suspicious or was recorded in another category, but for which another cause (which is not an immediately notifiable disease (IND)) was found to explain the presence of the clinical signs.

The non-case category is only meant to take into account the possibility that a case that was classified as a suspicious was later found to have had been affected by another disease that is not another IND (see above). In cases where it is later found that the disease is another IND, the WNV suspect case will be reclassified in the IND database under this other IND and dropped from the total count of WNV records.


Assumptions on which case definitions are based:

  • ELISA testing may be slightly nonspecific; cross reactions to closely related flaviviruses (e.g. SLE virus) may occur, but in Canada, the possibility of exposure to a "closely related flavivirus" is small enough to not consider it unless in very specific circumstances.
  • IgM antibody in equine serum is relatively short-lived; a positive ELISA means exposure to WNV or a closely related flavivirus has occurred (see first assumption), very likely within the last three months.
  • IgG antibodies may not be present in equine serum until two weeks or more after exposure to WNV; it is possible that clinical signs may be present in an equine before a serum is positive.
  • IgG antibodies detected in serum indicate past exposure to WNV; equine exposed to WNV in previous years may test positive.


Footnote 1

Clinical signs must include ataxia (including stumbling, staggering, wobbly gait, or incoordination) or at least two of the following: circling, hind limb weakness, inability to stand, multiple limb paralysis, muscle fasciculation, proprioceptive deficits, blindness, lip droop/paralysis, teeth grinding, fever, acute death.

Footnote 2

Preferred diagnostic tissues from equine are brain or spinal cord; although tissues may include blood or CSF, the only known reports of WNV isolation or positive PCR from equine blood or CSF have been related to experimentally infected animals.

Footnote 3

The first serum should be drawn as soon as possible after onset of clinical signs and the second drawn at least seven days after the first.

Date: July 26, 2019

Disease: Potomac Horse Fever

Location: Vanderhoof area of BC

Status: New disease report

Confirmed report of a horse with Potomac Horse Fever in B.C.

  • This case is from the Vanderhoof area of B.C. where a 22 year old Warmblood mare was lethargic, anorexic and had diarrhea.
  • Samples submitted by the attending veterinarian to IDEXX were PCR positive for Neorickettsia risticii.
  • The mare had not travelled within the last year and had no access to creek beds or swampy areas, but a small creek was about 60m from the dry pasture.

Date: September 18, 2017    

Disease: West Nile Virus    

Location: Nelson, B.C.

Status: New disease report

Confirmed report of another West Nile Virus positive horse in B.C.

  • This case is from Nelson, B.C. where a 10 year old quarter horse mare, not vaccinated for 8 years, displayed neurological signs of mild ataxia and a facial twitch.
  • The attending veterinarian submitted serum samples for WNV testing which were positive at Cornell Veterinary Diagnostic Laboratory for IgM and IgG, Cornell has a 3.3 cut off, IgG was 32.55, IgM was 5.64

Date: January 3, 2017    

Disease: West Nile Virus    

Location: British Columbia

Status: Summary of WNV in B.C. for 2016:

B.C. had 10 confirmed equine cases of WNV in 2016. Nine of the cases were in the south Kootenays (1 in the southern half of Kootenay Lake, 4 in the Creston area and 3 around Cranbrook and 1 in the Castlegar area; one of these horses came from Alberta).  And one case was in the Fraser Valley (Langley – shortly after arriving from the US). All cases occurred on separate premises.

The cases varied in age from 4 to over 20 years old.

Onset of clinical signs for the 10 cases ranged from August 7 to Sept 5. Their clinical presentations varied and included lethargy, impaired mentation, ataxia, proprioceptive deficits, and muscle fasciculations. All cases had a positive IgM titre as determined at various labs including Cornell, IDEXX and Prairie Diagnostic Services.

One of Kootenays cases and the Fraser Valley case had arrived from the US and Alberta, respectively, within 10 days of the appearance of clinical signs. So WNV infection of these horses outside BC cannot be ruled out.

Date: Clinical signs commenced August 26, 2016. Diagnosis confirmed September 14, 2016.

Disease: West Nile Virus

Location: Fraser Valley

Status: New disease report

A 10 year old Warmblood transported to B.C. from USA 10 days prior to commencement of  clinical signs. Horse was transported from an area of the USA which currently has WNV activity. Initial signs included low grade fever and neurological deficits with hypermetria progressing to ataxia. Positive IgM test for WNV. Horse was vaccinated in April, 2016 (further details regarding vaccination are pending). Horse is recovering.

Date: August 13 to September 1, 2016

Disease: West Nile Virus

Location: Southern Kootenay Lake, Creston, Cranbrook area

Status: New disease report

Seven horses located on seven separate premises. Clinical presentation varied and included lethargy, impaired mentation, ataxia, proprioceptive deficits and muscle fasciculation. All seven had positive IgM titres. One of the seven cases arrived from outside B.C. within 10 days of exhibiting clinical signs so may have contracted the infection elsewhere. Follow-up is being undertaken to determine vaccination status of all horses and case outcome. Initial information indicates the horses are recovering and some of the cases were unvaccinated or not up to date on vaccination.

Date: Horse died August 17, 2016. Diagnosis made August 31, 2016.

Disease: Potomac Horse Fever

Location: Robson Valley between McBride and Tete Jaune Cache

Status: New disease report

Mature mixed breed mare with diarrhea of 4 days duration. Colitis diagnosed on post mortem, positive for Neorickettsia risticii on PCR test with confirmatory sequencing. No history of other horses affected.

Date: August 8 and 11, 2016

Disease: West Nile Virus

Location: Cranbrook

Status: New disease report

Two dead crows from Cranbrook area were collected and tested for WNV. PCR test was strongly positive on brain.

Date: Examined August 7, 2016. Confirmed Aug 18, 2016

Disease: West Nile Virus

Location: Castlegar

Status: New disease report

West Nile Virus in a 20 year old mare.  The horse was ataxic with proprioceptive deficits and muzzle asymmetry. The animal had a low grade inflammatory leukogram, a WNV IgM capture ELISA titre of 12.99 and IgG capture ELISA of 37.42. (Diagnostic testing was conducted at Cornell). The clinical signs and IgM tire of > 3.3 meet the B.C. equine WNV case definition. The season and location of the case further support a case of WNV. The horse is responding to symptomatic treatment. The premise has two other horses, both are normal. The horse has not received WNV vaccinations and there is no travel history.

Date: March 10, 2016.

Disease: Strangles

Location: Southlands area of Vancouver

Status: New disease report

Confirmed in a 5 year old mixed breed feral rescue horse noted to have a draining abscess under the jaw. Voluntary quarantine was enacted. Three adjacent in contact horses at the barn tested negative for Strangles in 3 tests done at weekly intervals. The affected horse has since recovered and been moved to a new home. No new cases have been reported as of April 12, 2016.