United States Department of Agriculture

Animal and Plant Health Inspection Service

July 25, 2019

Key Points

• Starting on September 28, 2019 a high mortality 

event occurred in a cull sow slaughter plant in 

Tennessee. A chiller malfunction caused the hold of 

22 loads of cull sows. On September 30, 2019, Food 

Safety and Inspection Service (FSIS) reported over 

40 percent of the 2,222 sows in holding pens, dead

or euthanized when condemned on antemortem 

inspection. Samples from the affected sows in 

Tennessee showed Streptococcus equi subspecies

zooepidemicus (S. zooepidemicus).

• Preliminary information suggests that similar events 

may have occurred at other locations in the United 

States. This includes a continuous-flow swine 

aggregating and buying station in Ohio

epidemiologically linked to the event in Tennessee. 

Reports from knowledgeable individuals describe 

both feeder swine and cull sows as being affected.

• The finding of high mortality rates in cull swine at 

holding facilities is unusual. The cause of this and 

similar recent events identified in the United States 

are under investigation to understand if S. 

zooepidemicus is the single cause or if the deaths 

are due to multiple factors.

• The Canada West Swine Health Intelligence Network 

(CWSHIN) 2019 Second Quarter Swine Disease 

Report described detections of S. zooepidemicus in 

sows and gilts that occurred in Manitoba in the 

beginning of May 2019. In April 2019 and May 2019, 

Canada noted other similar swine die-offs. Although 

the Canadian Network watched for additional high 

mortality events linked to S. zooepidemicus, they 

had not noted any previous trends in swine.

• China has reported significant detections of S. 

zooepidemicus in swine. The reports emphasize

large economic losses to the swine industry 

affecting sows and replacement gilts and has 

become a threat to human health.

1-4

• S. zooepidemicus is a zoonotic organism. 

Although rare, it can cause severe illness in 

humans exposed to infected horses or other 

infected species. This includes exposure through 

consumption of associated unpasteurized milk 

products.

Concerns for U.S. Animal Health

• There is a need to investigate and understand 

the exposure and the epidemiology of S. 

zooepidemicus in swine to avoid potential 

negative economic impacts to the swine industry. 

• Identification of effective measures are needed

to prevent negative impacts due to S. 

zooepidemicus infection in swine. Further 

investigation of this pathogen is required to 

determine the role, if any, of S. zooepidemicus in 

high mortality events in swine.

• Current recommended controls to decrease the 

impact of S. zooepidemicus infection in swine 

include reducing transportation-related stressors.

These include trauma, extreme temperatures, 

inclement weather, malnutrition, and extended 

holding times prior to slaughter.

Emerging Risk Notice

November 2019

Streptococcus equi subspecies 

zooepidemicus

Figure 1: S. zooepidemicus colonies on a blood agar plate
United States Department of Agriculture

Animal and Plant Health Inspection Service

Epidemiology

• S. zooepidemicus is an emerging zoonosis. It is a

ubiquitous opportunistic commensal organism in the 

respiratory and reproductive tracts of horses. 

Although rare, there are reports of infection in other 

species, including: humans, cattle, sheep, pigs, 

camels, alpacas, foxes, birds, rabbits, guinea pigs, 

dogs, cats, and monkeys, often with severe disease.

Many of these infections are associated with 

exposure to infected horses.

5,6

• In the recent swine mortality events in the United 

States, the clinical picture observed in swine 

included: lethargy, weakness, high fever, swift 

spread among pigs from highly varied sources 

within the affected premises, and rapidly escalating 

mortality levels approaching 30 to 50 percent. There 

were also reports of: bacterial septicemia, 

inflammation, and necrosis of submandibular lymph 

nodes. Noted pathology included: fibrinosuppurative 

peritonitis, hepatitis and vasculitis, fibrinous pleuritis 

and polyserositis in thoracic and abdominal cavities,

and suppurative lymphadenitis and cutaneous 

hyperemia. Aerobic cultures from liver and lung 

samples were positive for S. zooepidemicus. 

• Studies from China suggest severity of disease in 

swine is possibly related to a particular strain of S. 

zooepidemicus.

7,8 Studies using genetic analysis 

suggest it is an invasive and virulent strain.

3, 4

• An intracellular phase may be one way S. 

zooepidemicus survives in the host, and could in 

part explain recurrent/persistent infections.9

• Human infection with S. zooepidemicus is rare but is 

often related to contact with infected horses. Human 

infection is also linked to contact with other infected 

animals including: dogs, monkeys, domestic 

ruminants, pigs, and with ingestion of unpasteurized 

dairy products.

• Human infection is of particular concern for 

immunocompromised individuals, such as those 

undergoing chemotherapy, treatment with steroids, 

or who have an immunosuppressive condition, such 

as diabetes.

• In reported human cases, the organism causes

severe and potentially fatal disease, including: 

bacteremia, endocarditis, arthritis, 

glomerulonephritis, necrotizing myositis, and 

meningitis.

10-16

Transmission

• Transmission routes to humans, pigs and other 

animals include direct exposure to infective 

respiratory droplets, uterine exudates, and 

consumption of unpasteurized milk and cheese 

from animals with mastitis due to infection with S. 

zooepidemicus.

5-6,10-16,19-20

Diagnostic Testing in Swine

• The USDA-APHIS National Veterinary Services 

Laboratories performs testing with MatrixAssisted Laser Desorption/Ionization-Time of 

Flight Mass Spectrometer (MALDI-TOF), which 

produces a spectrum that is matched to a 

database to identify the organism. Results are 

supplemented by biochemical tests.

• Whole genome sequencing is used to compare 

strains and assist with identifying the possible 

source of the infection. The organism identified 

from the Tennessee mortality event shared the 

same genotype and is remarkably similar to the 

published strain causing mortality events in China

and the detection in Manitoba in May 2019.

Samples to collect include: fixed and fresh 

tissues, including lymph node, lung, liver, kidney, 

spleen, and fresh tonsil.

• S. zooepidemicus was isolated from multiple 

organs collected from the affected swine in 

Tennessee with high growth from kidney and 

spleen and lower growth from the lung.

Treatment

• S. zooepidemicus bacteria are largely susceptible 

to β-lactam antibiotics, like penicillins, amoxicillin, 

ampicillin, and cephalosporins. Susceptibility to 

tetracyclines, macrolides, clindamycin, and 

fluoroquinolones is variable.

18-20

• Common cleaning and disinfecting procedures 

can inactivate this bacterium. Quaternary 

ammonium compounds, phenol-based agents, or 

oxidizing agents are all effective against S.

zooepidemicus.20 Because this bacterium has the 

potential to form biofilms, appropriate mechanical 

cleaning with disinfection should be incorporated 

into any cleaning procedure.

21
United States Department of Agriculture

Animal and Plant Health Inspection Service

Prevention in Swine

• Decrease stress related to transport. Stress is a 

common factor noted in the recent investigations 

related to the swine deaths at holding facilities in 

Ohio, Tennessee, and Canada. Additionally, 

stress was also observed in a recent report of S. 

zooepidemicus in dogs in Georgia. 

• Avoid holding animals in pens overnight to several 

days.20 Proper cleaning and disinfection of pens 

and equipment before introducing new animals

decreases the risk of pathogen transmission.

19

• Avoid commingling groups of transported swine, 

as direct contact occurs along with other stress 

factors.

• Minimize or mitigate conditions for swine that

present risks for trauma, including exposure to 

extreme temperatures, overcrowding, inclement 

weather, malnutrition, inadequate water supply, or 

loud noises. 

• Early identification of S. zooepidemicus can

facilitate appropriate medical intervention and 

timely epidemiologic surveillance, preventing the 

spread of a potentially life-threatening pathogen.11

• There is currently no commercial vaccine 

available for S. zooepidemicus for any species,

though autogenous vaccines may have limited 

use.

22

Prepared by: Sherrilyn Wainwright, DVM, MPH

USDA APHIS VS CEAH Risk Identification Team

For further information contact: Dana Cole, DVM, PhD 

Risk Identification & Risk Assessment Director.

USDA APHIS VS CEAH 

E-mail: Dana.J.Cole@usda.gov

The USDA is an equal opportunity provider, employer, and lender.

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