Streptococcus suis
Encyclopedia
Streptococcus suis is a peanut-shaped, Gram-positive
bacterium, and an important pathogen
of pigs
. Endemic
in nearly all countries with an extensive pig industry, S. suis is also a zoonotic disease
, capable of transmission to humans from pigs. Humans can be infected with S. suis when they handle infected pig carcasses or meat, especially with exposed cuts and abrasions on their hands. Human infection can be severe, with meningitis
, septicaemia, endocarditis
, and deafness as possible outcomes of infection. Fatal cases of S. suis are uncommon, but not unknown.
Penicillin
is the most common antibiotic used in treatment of S. suis infection; in cases with cardiac involvement (endocarditis
), gentamicin
should also be given for synergistic effect.
, and signs may be severe, ranging from tremors to seizures and death. Joints may become infected and pigs may be lame or have swollen limbs. Skin disease is another presentation, and reproductive disease can also occur. Meningitis is the most common presentation in humans.
The bacterium can be isolated from various body fluids, and serological testing with an ELISA
can also be performed.
Control relies on good husbandry and biosecurity protocols and appropriate disinfection. Vaccines exist but are not reliable.
, China
, with higher than usual human morbidity and mortality; over 100 cases and more than 20 deaths were initially reported. Prior to this outbreak, less than 200 total human cases had been reported, and mortality was assumed to be less than 10%. Details of this outbreak and a similar earlier outbreak, also in Sichuan province, were published in 2006. A smaller outbreak occurred at the same time in Hong Kong, affecting 11 people.
A total of 204 human cases were documented during the Sichuan outbreak, with 38 fatalities. The human outbreak coincided with one in the local pig populations. There was no evidence of human-to-human transmission; all of the patients had been in direct contact with pigs. Many of the patients, and almost all of the fatal cases, had typical symptoms of Streptococcal toxic shock syndrome
(STSS). To date, STSS has only been documented in patients infected with S. pyogenes
, another member of the Streptococcus
family but very different from S. suis. However, the bacteria isolates from the human and pig samples were clearly S. suis, and those isolates were able cause typical S. suis disease in piglets. The genome
of S. suis isolates from the outbreak were examined to see whether its DNA sequence
could explain why these particular bacteria were able to cause STSS. However, none of the genes that are present in S. pyogenes and thought to cause STSS were detected in the S. suis isolates. Comparison with other S. suis isolates from around the world, including one from an earlier smaller S. suis outbreak in Sichuan province that killed 14 out of 25 reported human cases, revealed that the two Chinese isolates were more similar to each other than to any other strains.
Additional experiments are necessary to determine whether the size and high mortality of the recent outbreak is because the Chinese S. suis version is more virulent than other strains or due to the circumstances under which the Chinese patients got infected and treated. Studies are under way to characterize the bacterial isolates from the outbreak in detail. Physicians around the world should be aware of the possibility of S. suis-associated STSS when they see patients with unexplained sepsis who had been in contact with pigs.
Streptococcus suis has also been identified as the most common cause of meningitis in Vietnam.
After incubation with various amounts of the pathogen, magnetic concentration and ATP detection, bacterial levels down to 10^5 cfu could be detected.
Gram-positive
Gram-positive bacteria are those that are stained dark blue or violet by Gram staining. This is in contrast to Gram-negative bacteria, which cannot retain the crystal violet stain, instead taking up the counterstain and appearing red or pink...
bacterium, and an important pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
of pigs
PIGS
PIGS is a four letter acronym that can stand for:* PIGS , Phosphatidylinositol glycan anchor biosynthesis, class S, a human gene* PIGS , the economies of Portugal, Italy , Greece and Spain...
. Endemic
Endemic (epidemiology)
In epidemiology, an infection is said to be endemic in a population when that infection is maintained in the population without the need for external inputs. For example, chickenpox is endemic in the UK, but malaria is not...
in nearly all countries with an extensive pig industry, S. suis is also a zoonotic disease
Zoonosis
A zoonosis or zoonoseis any infectious disease that can be transmitted from non-human animals to humans or from humans to non-human animals . In a study of 1415 pathogens known to affect humans, 61% were zoonotic...
, capable of transmission to humans from pigs. Humans can be infected with S. suis when they handle infected pig carcasses or meat, especially with exposed cuts and abrasions on their hands. Human infection can be severe, with meningitis
Meningitis
Meningitis is inflammation of the protective membranes covering the brain and spinal cord, known collectively as the meninges. The inflammation may be caused by infection with viruses, bacteria, or other microorganisms, and less commonly by certain drugs...
, septicaemia, endocarditis
Endocarditis
Endocarditis is an inflammation of the inner layer of the heart, the endocardium. It usually involves the heart valves . Other structures that may be involved include the interventricular septum, the chordae tendineae, the mural endocardium, or even on intracardiac devices...
, and deafness as possible outcomes of infection. Fatal cases of S. suis are uncommon, but not unknown.
Penicillin
Penicillin
Penicillin is a group of antibiotics derived from Penicillium fungi. They include penicillin G, procaine penicillin, benzathine penicillin, and penicillin V....
is the most common antibiotic used in treatment of S. suis infection; in cases with cardiac involvement (endocarditis
Endocarditis
Endocarditis is an inflammation of the inner layer of the heart, the endocardium. It usually involves the heart valves . Other structures that may be involved include the interventricular septum, the chordae tendineae, the mural endocardium, or even on intracardiac devices...
), gentamicin
Gentamicin
Gentamicin is an aminoglycoside antibiotic, used to treat many types of bacterial infections, particularly those caused by Gram-negative organisms. However, gentamicin is not used for Neisseria gonorrhoeae, Neisseria meningitidis or Legionella pneumophila...
should also be given for synergistic effect.
Clinical signs and diagnosis
The first sign in pigs is usually pyrexia and there may be sudden deaths in the herd. Respiratory disease, with pneumonia, nasal discharge and respiratory difficulties, may also be present. Neurological signs result from meningitisMeningitis
Meningitis is inflammation of the protective membranes covering the brain and spinal cord, known collectively as the meninges. The inflammation may be caused by infection with viruses, bacteria, or other microorganisms, and less commonly by certain drugs...
, and signs may be severe, ranging from tremors to seizures and death. Joints may become infected and pigs may be lame or have swollen limbs. Skin disease is another presentation, and reproductive disease can also occur. Meningitis is the most common presentation in humans.
The bacterium can be isolated from various body fluids, and serological testing with an ELISA
ELISA
Enzyme-linked immunosorbent assay , is a popular format of a "wet-lab" type analytic biochemistry assay that uses one sub-type of heterogeneous, solid-phase enzyme immunoassay to detect the presence of a substance in a liquid sample."Wet lab" analytic biochemistry assays involves detection of an...
can also be performed.
Treatment and control
Most S. suis strains respond to treatment with ampicillin and amoxicillin. Anti-inflammatories should also be used.Control relies on good husbandry and biosecurity protocols and appropriate disinfection. Vaccines exist but are not reliable.
Zoonotic outbreaks
In July 2005, an outbreak of the disease in humans was reported in SichuanSichuan
' , known formerly in the West by its postal map spellings of Szechwan or Szechuan is a province in Southwest China with its capital in Chengdu...
, China
People's Republic of China
China , officially the People's Republic of China , is the most populous country in the world, with over 1.3 billion citizens. Located in East Asia, the country covers approximately 9.6 million square kilometres...
, with higher than usual human morbidity and mortality; over 100 cases and more than 20 deaths were initially reported. Prior to this outbreak, less than 200 total human cases had been reported, and mortality was assumed to be less than 10%. Details of this outbreak and a similar earlier outbreak, also in Sichuan province, were published in 2006. A smaller outbreak occurred at the same time in Hong Kong, affecting 11 people.
A total of 204 human cases were documented during the Sichuan outbreak, with 38 fatalities. The human outbreak coincided with one in the local pig populations. There was no evidence of human-to-human transmission; all of the patients had been in direct contact with pigs. Many of the patients, and almost all of the fatal cases, had typical symptoms of Streptococcal toxic shock syndrome
Toxic shock syndrome
Toxic shock syndrome is a potentially fatal illness caused by a bacterial toxin. Different bacterial toxins may cause toxic shock syndrome, depending on the situation. The causative bacteria include Staphylococcus aureus and Streptococcus pyogenes...
(STSS). To date, STSS has only been documented in patients infected with S. pyogenes
Streptococcus pyogenes
Streptococcus pyogenes is a spherical, Gram-positive bacterium that is the cause of group A streptococcal infections. S. pyogenes displays streptococcal group A antigen on its cell wall. S...
, another member of the Streptococcus
Streptococcus
Streptococcus is a genus of spherical Gram-positive bacteria belonging to the phylum Firmicutes and the lactic acid bacteria group. Cellular division occurs along a single axis in these bacteria, and thus they grow in chains or pairs, hence the name — from Greek στρεπτος streptos, meaning...
family but very different from S. suis. However, the bacteria isolates from the human and pig samples were clearly S. suis, and those isolates were able cause typical S. suis disease in piglets. The genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
of S. suis isolates from the outbreak were examined to see whether its DNA sequence
DNA sequence
The sequence or primary structure of a nucleic acid is the composition of atoms that make up the nucleic acid and the chemical bonds that bond those atoms. Because nucleic acids, such as DNA and RNA, are unbranched polymers, this specification is equivalent to specifying the sequence of...
could explain why these particular bacteria were able to cause STSS. However, none of the genes that are present in S. pyogenes and thought to cause STSS were detected in the S. suis isolates. Comparison with other S. suis isolates from around the world, including one from an earlier smaller S. suis outbreak in Sichuan province that killed 14 out of 25 reported human cases, revealed that the two Chinese isolates were more similar to each other than to any other strains.
Additional experiments are necessary to determine whether the size and high mortality of the recent outbreak is because the Chinese S. suis version is more virulent than other strains or due to the circumstances under which the Chinese patients got infected and treated. Studies are under way to characterize the bacterial isolates from the outbreak in detail. Physicians around the world should be aware of the possibility of S. suis-associated STSS when they see patients with unexplained sepsis who had been in contact with pigs.
Streptococcus suis has also been identified as the most common cause of meningitis in Vietnam.
Detection
Detection of the zoonotic bacterial pathogen Streptococcus suis was achieved using magnetic glycoparticles. The bacteria contain an adhesion protein for the carbohydrate sequence Gal-1,4Gal.After incubation with various amounts of the pathogen, magnetic concentration and ATP detection, bacterial levels down to 10^5 cfu could be detected.