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Streptococcus suis is common and deadly on hog farms

S. suis infection in weaned pigs can result in heart valve infections that cause lesions, which vets often call “cauliflower heart,” seen here in the middle of the photo. Blood backs up into the lungs, resulting in congestive heart failure.  |  Western College of Veterinary Medicine/Dr. Ted Clark photo

Many health challenges come and go within pig populations. Recently we have had a lot of porcine epidemic diarrhea virus on Manitoba hog farms. Influenza virus and porcine reproductive and respiratory syndrome virus are also a frequent challenge on some farms. African swine fever gets a lot of attention around the world.

One disease that really plagues hog farms across Canada and around the world is caused by a bacteria called Streptococcus suis (S. suis or just simply referred to by farmers and vets alike as “Strep.”)

In fact, Strep is the main reason antibiotics are prescribed and used on hog farms. The increased focus on reduced and prudent use of antimicrobials in agriculture makes Strep a very important topic.

Despite many other Strep species on hog farms, Strep. suis is the dominant streptococcal species. Recently, there have been cases of the Strep. equi subspecies zooepidemicus in North America, but that is a disease for a future article.

S. suis is normally found on piglet tonsil and nasal cavities following passage through the sow’s birth canal at farrowing time. It can survive for weeks to months outside the pig in dust, water and manure. This makes exposure to the bacteria a certainty on most farms. To complicate health management programs, Strep is often found in the presence of other diseases, such as influenza and PRRS.

Health and welfare implications of Strep are massive. It often affects some of the best pigs in a group, and farmer and vet frustration with the disease is significant.

The economic impact of Strep is mainly through increased mortality and treatment costs. Mainly affecting young weaned pigs three to five weeks old, it can actually cause health challenges in all ages of farmed pigs.

Farms commonly find that one to two percent of weaned pigs deal with Strep-related health challenges, and on some farms, mortality can flare to five percent or higher in weaned groups of pigs.

The list of clinical signs is long, but this bacteria is able to escape the upper respiratory tract into the blood stream and then be carried to many organ systems.

A common condition observed in weaned pigs is Streptococcal meningitis, which is infection and inflammation on the surface of the brain causing neurologic symptoms such as inco-ordination, paddling/convulsions and eventually death if not treated early. Other health challenges related to Strep include arthritis and pneumonia.

A less common outcome of S. suis infection in weaned pigs is the development of heart valve infections leading to right-sided heart failure.

Clinical signs are typically severe, including laboured breathing with red-purple discolouration of the ears and extremities. It is clear these pigs are not getting enough oxygen.

On post-mortem examination, the heart valves have large chunks of inflammatory proteins (called fibrin) built up to the point of disrupting the ability of the valve to close properly, in effect ruining the forward pumping of blood through the circulatory system.

Essentially, blood backs up into the lungs, which is called congestive heart failure. Vets will refer to this heart lesion as “cauliflower heart” because the fibrin buildup appears like chunks of cauliflower on the heart valve. The actual lesion is called fibrinous valvular endocarditis.

Likely the most common observation related to Strep flare-ups on farms is the lack of clinical signs before a nice-looking pig in good body condition is suddenly found dead.

Strep challenges are unpredictable on most farms. They can remain low for months on end with a sudden and significant disease flare-up despite all other aspects of health and management seeming to be stable.

This makes it a very frustrating disease and one we will not eliminate from a farm. Instead, we need to control and minimize the impact through various management strategies.

Strep flare-ups are often thought to be stress induced. Areas of stress reduction that we focus on include ventilation (reducing drafts), chilling, over-crowding, reduction of weaning-related stress and the immune stress of fighting off other diseases.

It is common for many farms to use prophylactic (preventive) antibiotic therapy during stressful periods where historically farms have experienced Strep flare-ups. This includes the use of antibiotics delivered through feed or drinking water to prevent the opportunity for S. suis to flourish, causing disease.

Antibiotic susceptibility testing is commonly used by farm veterinarians to determine what therapy will optimally manage this disease on individual farms.

Like other diseases, the inflammatory response of the immune system dealing with an infection also needs to be managed. Pig caregivers commonly use anti-inflammatory medications at the same time as using antibiotics to address the pain and inflammation associated with S. suis disease.

Other management strategies being developed or researched include autogenous vaccines (S. suis isolated from individual farms is used to manufacture a vaccine specific to that farm’s bacterium).

The field of microbiome research (the population of “normal” microbes on, in and around us) could offer new tools for pig farmers and their veterinarians.

Blaine Tully is a veterinarian and owner of Swine Health Professionals Ltd. in Steinbach, Man. 

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