Swine streptococcosis can occur throughout the year, but it is most prevalent from 5 to 11; outbreaks are generally localized. It can easily spread on intensive pig farms where animals are raised at high density. In addition, excessive stocking density, poor hygiene, inadequate ventilation, sudden changes in weather, regrouping, long-distance transportation, and other stress factors can all trigger the occurrence and spread of swine streptococcosis.
Pigs of all ages can be infected, but piglets, growing pigs, and pregnant sows have the highest incidence rates. Sick pigs and carrier pigs are the main sources of infection. The weather is currently hot and humid in 6, a peak period for swine streptococcosis. Pig farmers should stay alert and guard against the disease.
Of course, preventing the disease and containing outbreaks requires a clear understanding of it and familiarity with relevant measures. Next, the author will discuss four aspects of swine streptococcosis: routes of infection, symptoms, treatment methods, and preventive measures.
I. Routes of Streptococcus suis infection
Streptococcus suis is a capsulated Gram-positive coccus. Based on its cell wall antigen composition, it can be broadly classified as a Lancefield group D streptococcus. According to differences in its capsular polysaccharide (CPS) antigens, Streptococcus suis is divided into 35 (1~34 serotypes, 1/2 serotypes), among which serotype 1，2，7，9 is pathogenic in pigs. Streptococcus suis colonizes the upper respiratory tract of pigs, especially the tonsils and nasal cavity. Some serotypes of Streptococcus suis are pathogenic and are mainly transmitted through wound infection. It can cause diseases in pigs such as acute septicemia, meningitis, arthritis, endocarditis, and pneumonia. Some strains can cause human infection, resulting in bacterial encephalitis or toxic shock-like syndrome.
Streptococcus bacteria comprise many species and are widely distributed in nature. They can cause infections in various animals, including humans, pigs, cattle, horses, sheep, and poultry. Streptococcosis in pigs mainly presents as septicemic disease and focal suppurative lymphadenitis. The natural sites of Streptococcus infection in pigs are the upper respiratory tract (especially the tonsils and nasal cavity), reproductive tract, and digestive tract. Among various animals, pigs are highly susceptible. Pigs of all ages can develop the disease, but the septicemic and meningoencephalitic forms are more common in piglets, while the suppurative lymphadenitis form is more common in growing pigs. Sick pigs, pigs that have clinically recovered, and healthy pigs can all carry the bacteria. When carrier pigs are introduced into a healthy herd, the bacteria can spread through mutual contact via the mouth, nose, or skin wounds.
II. Symptoms of Streptococcosis in Pigs
The incubation period of the disease is 1–3 days, and in the longest cases it exceeds 1 months.
Pigs with the most acute form often die suddenly without showing any obvious symptoms.
Acute cases generally show symptoms of septicemia and meningitis. They suddenly stop eating, have a temperature above 41℃ and a sustained fever, and appear depressed. They breathe rapidly, have a serous nasal discharge, conjunctival congestion and hemorrhage, and tearing, and may have constipation or diarrhea. They often die within 2 days. Symptoms of meningitis include shrill cries and convulsions, ataxia or circling, wandering aimlessly or suddenly collapsing, frothing at the mouth, swimming motions of the limbs, and eventual death from exhaustion or paralysis.
Chronic cases commonly develop arthritis, endocarditis, suppurative lymphadenitis, localized abscesses, uteritis, and mastitis and dermatitis. The disease course lasts from one to several weeks.
Three. Treatment of swine streptococcosis
1, strengthen management
Severely ill pigs with no prospect of recovery should be culled decisively. Sick pigs with a prospect of recovery should be isolated and treated, and pigs that die should be disposed of harmlessly to prevent the disease from spreading. Remove waste from the pig pens and disinfect them daily with disinfectant for at least 1 weeks. 0.5 hours after disinfection, open the windows for ventilation.
2, local treatment method
Remove the locally ulcerated tissue from the affected pig. After draining the pus, clean and disinfect the wound. Apply antibiotics or sulfonamides to the affected area as a powder or ointment, and bandage it if appropriate. For abscesses, make an incision, flush with 0.1% potassium permanganate, and then apply iodine tincture.
3, Medical treatment of affected pigs
For pigs with septicemic disease, administer penicillin 4×3U and sulfonamides 30mg per 104g of body weight, 2 times/d for 4d. Severely ill pigs may be given intravenous glucose, physiological saline, An Na Jia, vitamin C, etc., 1 times/d for 3d. For pigs with the arthritic form, penicillin, gentamicin, and an appropriate amount of aminopyrine may be mixed for injection, 2 times/d; lincomycin and dexamethasone may also be used. If a pig has a high body temperature, metamizole may be administered by intramuscular injection, or compound sulfadiazine-5-methoxypyrimidine may be administered by intramuscular injection. For the first administration, the dose may be doubled; after symptoms improve, the dosage may be reduced. For pigs with the meningitic form, sulfonamides may be selected, along with fluid replacement and cardiac stimulation. Weaned pigs may be given chlorpromazine by intramuscular injection, or a mixture of enrofloxacin and Bupleurum by intramuscular injection; piglets with neurological symptoms may be given intramuscular sodium sulfonamide potentiator diluted with isotonic saline at 1:1.
Four. Prevention of swine streptococcosis
1, Routine preventive measures. Prevention of this disease mainly requires strengthening feeding management and maintaining good environmental hygiene and disinfection. Strict disinfection should be carried out during tail docking, teeth clipping, and castration. Any injuries in pigs should be treated surgically in a timely manner. Adhere to the practices of breeding pigs on the farm and all-in/all-out production. Strictly implement quarantine and isolation procedures when introducing breeding pigs. Measures such as culling carrier sows are important for preventing the occurrence of this disease. Pig farms where this disease is frequently prevalent and occurs may add an appropriate amount of antibacterial drugs, such as sulfadiazine, to the feed; this can provide some preventive effect.
2, vaccination. Farms and regions where this disease is prevalent can use vaccines for prevention. Streptococcal vaccines for pigs include live attenuated vaccines and inactivated vaccines. The former are prepared from Group C streptococci and are not very effective at preventing disease caused by Streptococcus suis type 2. Inactivated vaccines are prepared from Streptococcus suis type 2 strains and provide good immunity against diseases caused by that type of strain. Pregnant sows can be vaccinated 4 weeks before farrowing; piglets are each vaccinated 1 times, at 30 days of age and 45 days of age, respectively. Replacement gilts are vaccinated 1 times before breeding, and the immunity can last up to half a year. Inactivated vaccines can also be prepared from strains isolated on the farm for vaccination, with better results.
3, public health. When handling sick pigs, farm workers, veterinarians, slaughterhouse workers, and quarantine personnel should prevent injuries, strictly disinfect, and take personal protective measures. Do not cull, slaughter, perform post-mortem examinations on, process, or sell sick pigs, to prevent human infection. Bury pigs that have died of disease deep underground and ensure they are disposed of harmlessly.
Five. Summary
Streptococcosis is a disease that poses a serious threat to the pig industry. Infected pigs can show a wide range of clinical signs, many of which resemble those of other pig diseases. If treatment is not given promptly, the mortality rate among affected pigs may increase. Pig farmers, especially veterinarians working at pig farms, should take preventive measures during these months. Sick pigs should be diagnosed promptly and treated according to their symptoms.