Streptococcosis are diseases varying from mild to fatal side effects of the infection which originate from the bacterial group streptococcus.[1] Some of the areas of infection include wounds, body tissue, and respiratory areas.[1] Research within horses, dogs, cats, wound injuries and swine infections have been done to document specific side effects from streptococcosis.[1] Streptococcosis can occur to both humans and animals, the most common including horses, guinea pigs, dogs, cats and fish; while uncommon animals infected include monkeys, cattle, sheep, goats, ferrets and poultry.[1] The wide range of diseases is due to the variability of streptococcus strains which thus creates multiple species for the diseases to occur.[1]
Pathogenesis and classification
Pathogenesis
Occurring in pairs or chains, streptococcus are found to be Gram-positive (although older cultures may lose this characteristic), non-mobile, non-spore forming, and catalase-negative.[2] Bacteriophages, also known as phages, of streptococcus within different parameters of temperature, pH, and salinity maintain successfully stable and are lytic.[3] Integrase, transposase, and recombinase coding genes are found to be absent within phages.[3] Streptococcosis can start occurring due to a weak immune system, or by having bacteria enter wounds.[1] Spreading of streptococcus is often sporadic,[4] and can be done through direct contact (may be done through materials that are likely to carry infection), air transport or (rarely) ingestion.[1]
Classification
Multiple species of streptococcus exist. Differentiation of species is mainly determined by antibody detection, however morphology, biochemical reactions, and hemolysis can also be used for classification.[2] Antibody detection, also known as serologic grouping, categorizes with the labeling of Group A to Group V; it uses differences with cell wall carbohydrates and pili-associated protein.[2] With the use of hemolysis, species are divided within three different categories: incomplete (α hemolytic), complete (β-hemolytic), and no (γ hemolytic) hemolysis detected.[2] Two common species seen are S. agalactiae which has been associated with fish and (more significant) S. suis which has been associated with pigs.[4]
Clinical identification
The clinical manifestations of streptococcus infections differ greatly depending on both the host species and group and strain of the bacteria.[2]
Alpha-hemolytic streptococci (S. pneumoniae and viridians)
The first group of streptococci is alpha-hemolytic which comprises primarily S.pneumoniae and viridans streptococci. This group is referred to as alpha-hemolysis because the cell membrane of red blood cells is left intact.[2] When cultured, alpha-hemolysis can be deemed present when the agar gel appears greenish.[2]
Identifying and diagnosing alpha-hemolytic streptococcus is done with a sputum gram stain and culture test.[5] Further identification can be done serologically to test for the presence of capsular antigen, which is the dominant structure on the surface of S. pneumoniae.[2][5] Bile solubility can be used to further distinguish S. pneumoniae from viridans streptococci as S. pneumoniae are bile soluble and viridans streptococci are not.[6]
S. pneumoniae are the most significant alpha-hemolytic streptococci and are responsible for several infections including:
The identification and diagnosis of these conditions often require a combination of bacteriologic methods with other clinical identification characteristics that are condition-specific.
Beta-hemolytic streptococci (Group A, B, C, D, F, G, and H)
In contrast, the beta-hemolytic group of streptococci includes those capable of complete lysis of red blood cells.[5] Beta-hemolytic streptococci are further divided into additional subgroups consisting of: Group A, Group B, Group C, Group D, Group F, Group G, and Group H. Beta-hemolysis is identified by its yellow and transparent appearance on the cultured media.[5]
Clinical identification of beta-hemolytic streptococci relies on culturing the bacteria with agar media that has been supplemented with blood.[2] This method allows for beta-hemolysis to be easily identified, which is a critical step in further identification tactics.[2] Identification into subgroups can be done by the Lancefield antigen-determination test which uses antibodies to distinguish B-hemolytic streptococci into different species.[2][7] An additional method used to identify B-hemolytic streptococci is the PYR test, which is primarily used in distinguishing S. pyogenes from other B-hemolytic strains by testing for the presence of pyrrolidonyl aminopeptidase.[2] Both the Lancefield antigen grouping sera and PYR test are widely available for commercial usage. Each method presents its limitations and studies suggest that a combination of the two protocols be used to achieve the most reliable results.[2]
Group A
Group A streptococcal infections are predominantly caused by S. pyogenes. Human pathologies are mostly associated with Group A streptococci and arise most often as respiratory or skin infections.[8]
Group A streptococcal infections include:
- Pharyngitis
- Impetigo
- Necrotizing fasciitis
- Cellulitis
- Streptococcal toxic shock syndrome
- Rheumatic fever
- Post-streptococcal glomerulonephritis
The identification and diagnosis of these conditions often require a combination of bacteriologic methods with other clinical identification characteristics that are condition-specific.[8]
Group B
Group B streptococcal infections, most commonly associated with S. agalactiae, are extremely prevalent among pregnant women, newborns, and the elderly. Cattle have also been shown to be important reservoir hosts for S. agalactiae. Reports of S. agalactiae have also been identified in several other mammals, fish, and reptiles.[4]
Economic impacts and considerations
Streptococcosis has been shown to have serious consequences on Aquaculture industries around the world as a result of various streptococcal-based infections in marine and freshwater organisms.[9] Streptococosis in fish specifically has proven to be a public health concern due to the zoonotic capabilities of streptococcal infections and diseases.[9] Mitigating streptococcosis in marine and freshwater organisms, has the potential to improve the economics of the aquaculture sector and decrease the risks of human illness.
Traditionally, antibiotics and other chemotherapeutic drugs have been used to combat streptococcosis infections in aquaculture settings.[9] However, re-infection rates, drugs accumulating in aquatic ecosystems, demand for chemical-free aquaculture products, and the diversity of species and strains within the Streptococcus genus has proven to be a major challenge.[9] Since re-infection rates among fish populations are high, multiple treatments are often needed which introduces an additional problem of increased antibiotic resistance.[9] In search of alternative solutions, current research is investigating the possibility of using dietary supplements or medicinal herbs and other plants as alternatives to antibiotics, and recent findings have generated promising results.[9]
The existing literature has placed a strong emphasis on the economic impacts of streptococcosis in tilapia cultures.[10] Tilapia have rapid growth rates, exhibit tolerance to numerous environmental conditions, and are available globally which causes the species to be of major importance in the global aquaculture sector.[10] Tilapia production is often conducted by large-scale producers in intensive systems, which increases their susceptibility to disease and infection due to the density of cultures and subsequent water quality issues.[10] Streptococcosis has been identified as the most important pathogen affecting these systems and has caused considerable economic losses to the industry.[11] In general, preventing disease and infection should be a priority compared to simply controlling and mitigating outbreaks.[10] Research acknowledges that disease prevention may be possible by utilizing effective biosecurity measures at both global and local levels.[10] In addition, recent studies have found several benefits of using medicinal herbs to treat streptococcosis in aquaculture. Studies suggest that a combination of vaccines, antibiotics, and phytotherapy may be the most viable solution to improve both the economics of the industry and mitigate public health concerns.[9] Considerations and adjustments will have to made depending on national regulations, the countries economic status, and the farms production capacity.[10]
Epidemiology
Different organisms it affects/host range
Streptococcosis encompasses a spectrum of diseases caused by bacteria from the genera Streptococcus and Lactococcus.[12]Various species within these genera can cause infections in both wild and cultured animals, including fish and terrestrial species.
Commonly affected organisms include:
Fish species: Streptococcus iniae, Streptococcus agalactiae, Streptococcus dysgalactiae, Lactococcus garvieae, Lactococccus piscium, and Streptococcus parauberis have a significant impact in aquaculture, impacting freshwater, marine, and brackish water species.[13] Among these L. garvieae, S. iniae, and S. parauberis are considered the primary causative agents responsible for diseases in marine aquaculture among the streptococcal bacteria affecting fish.[13][12]
Terrestrial animals: Streptococcus agalactiae, commonly found in cattle and dromedary camels, has been detected in numerous species, including small ruminants, llamas, horses, and marine mammals, often associated with human sources.[14] Streptococcus dysgalactiae primarily infects cattle but also affects small ruminants, pigs, dogs, horses, and vampire bats. Streptococcus equi subsp. zooepidemicus, prevalent in horses, is also present in guinea pigs, pigs, monkeys, and various other animals, including dogs, cats, ferrets, and birds.[15] Additionally, Streptococcus suis mainly affects suids but can be found in other animals like cattle, sheep, goats, and chickens, with different genotypes found in rabbits and chickens compared to pigs.[14][15]
Humans: Streptococcal infections in humans are primarily caused by Streptococcus pyogenes, the most common beta-hemolytic group A streptococcus, often referred to simply as group A streptococcus.[14] Similarly, group B streptococcus typically denotes Streptococcus agalactiae, although minor beta-hemolytic group B streptococci like S. troglodytidis exist.[15] While most streptococcal illnesses in humans originate from species adapted to humans, such as S. pneumoniae or S. pyogenes, there are zoonotic species capable of causing infections.[15] These include S. canis, S. dysgalactiae subsp. dysgalactiae, S. equi subsp. zooepidemicus, S. halichoeri, S. iniae, and S. suis, along with some animal-associated genotypes of S. agalactiae.[16][17] Notably, some streptococci found in animals may infect humans under certain circumstances. Fish-associated S. agalactiae, primarily affecting farmed freshwater and marine fish, have also been implicated in human illnesses, particularly the ST283 genotype.[17] The prevalence of specific S. suis serotypes varies by region, impacting disease incidence in both pigs and humans.
Transmission routes
Members of the Streptococcus genus are frequently found as part of the normal microbial community in both animals and humans, commonly inhabiting sites such as the upper respiratory tract, urogenital tract, mucous membranes, mammary glands, or skin.[18] While these organisms can occasionally cause infections as primary pathogens, they more commonly act as opportunistic pathogens, particularly in carriers.[19] However, their transmission between hosts does not always lead to disease manifestation.[19] Streptococci are typically transmitted through close contact, though aerosols may sometimes play a role. Some species, such as S. suis, S. equi subsp. zooepidemicus, and S. agalactiae ST283, can be acquired through the consumption of undercooked pork, horsemeat, or fish, respectively, or via unpasteurized dairy products. S. iniae infections in humans often occur through skin abrasions during fish cleaning. The mode of transmission among fish is not fully elucidated but can occur orally or through exposure to contaminated water baths, particularly in laboratory settings. Streptococci can also be transmitted through fomites and can persist in the environment for varying durations, especially in organic material under moist, cool conditions. For instance, S. suis can remain viable for approximately a week in pig feces at 25°C (77°F) and up to six weeks in carcasses at 4°C (39°F).[19]
Geographic distribution
The strains of Streptococcus, including S. canis, S. dysgalactiae subsp. dysgalactiae, S. equi subsp. zooepidemicus, S. suis, and mammalian S. agalactiae, maintained in domestic animals are widely distributed and their presence follows the hosts that they reside in.[20] Regional variations in the predominant serotypes of S. suis may impact disease prevalence in both pigs and humans. S. iniae infections have predominantly been documented in regions such as North America, the Caribbean, parts of Asia (such as Japan, China, Singapore, and Taiwan), Australia, and the Middle East. Meanwhile, occurrences of S. halichoeri have been reported in certain parts of Europe and South Korea, with potential wider distribution.[20][21] Notably, S. agalactiae ST283 appears to be primarily found in Asia but has recently been identified in farmed fish in South America.[20][21]
Symptoms
Fish affected by streptococcosis exhibit various symptoms indicative of the disease. These symptoms can manifest in different forms, ranging from external visual changes, to internal and behavioral changes, as well as histopathological alterations.[22]
External visual changes
Visually, fish may display darkening of the skin, although acutely infected individuals may succumb to septicemia with minimal observable clinical signs.[24] Affected fish may exhibit raised, hemorrhagic, and inflamed areas on the skin, including around the mouth, operculum, fins' bases, and along the dorsolateral portions of the body. Unilateral or bilateral exophthalmos (pop eye) with or without hemorrhage, distended abdomen due to fluid accumulation, ventral reddening, and fecal casts or strings are indicative of streptococcal infection. Fish, whether deceased or surviving recent infections, may present with jaw and caudal pustules.[25]
Internal changes
The peritoneal cavity may contain fluid ranging from straw to bloody in color. The liver may appear pale, while the spleen typically exhibits a dark red hue, often enlarged in S. agalactiae infections. Although posterior kidneys are not frequently targeted by clinical pathology, bacterial recovery is possible upon culture. Hemorrhagic enteritis with bloody fluid in the intestinal lumen may also be observed.[24]
Behavioral changes
Among the initial signs of disease, fish may exhibit lethargy and loss of appetite. In cases where the central nervous system is affected, additional behavioral changes may manifest, such as tail-chasing and spiral swimming due to spinal curvature. Buccal paralysis is also observed in infections caused by S. agalactiae.[25]
Histopathological changes
Histopathological findings vary depending on the pathogen and host species involved. Recent reviews detail the pathological changes observed.[25] Infections of the head and brain often lead to granulomatous encephalitis and meningitis. In the eye, infections may result in granulomatous or lymphohistiocytic choroiditis. Streptococcus sp. infections in tilapia may lead to polyserositis, granulomatous splenitis, ovaritis, granulomatous or lymphohistiocytic epicarditis, pericarditis, and myocarditis.[24]
Treatment
Streptococcal infections are commonly managed with antibiotics, particularly beta-lactams, macrolides, and quinolones. In some cases, additional interventions like surgical removal of necrotic tissues may be required.[26] Prompt administration of supportive therapy is crucial, particularly in cases of streptococcal toxic shock-like syndrome.[22] Treatment typically involves a combination of antibiotics and supportive measures. While most cases are treated with antibiotics commonly used in veterinary medicine, occasionally, medications typically reserved for humans, like vancomycin, may be employed.[26] Prompt administration of supportive therapy is crucial, particularly in cases of streptococcal toxic shock-like syndrome.
Disease control
Research indicates that preventing fish diseases is more effective and economically advantageous than treating outbreaks after they occur.[27]
Vaccination
The utilization of vaccines in aquaculture to combat pathogenic diseases is widely acknowledged as a preventive measure.[10] In recent years, vaccines have gained prominence in preventing streptococcosis in tilapia by enhancing the fish host's resistance to infection, making it a common practice in disease prevention.[10]
Utilization of probiotics and synthetic compounds
There is growing interest in using probiotics and synthetic compounds to bolster immune response and increase fish resilience to diseases.[10] Probiotics, containing live microorganisms that positively impact the host's intestinal microbiota by inhibiting the growth of harmful bacteria while promoting beneficial bacteria development, have garnered attention for their potential benefits.[28]
Preventing pathogens from entering the farm
Streptococcal diseases in fish primarily affect external organs like the skin, fins, and gills. Therefore, it is crucial to rigorously monitor water sources and implement filtration and treatment measures to prevent pathogen entry into culture systems.[10] While liquid disinfecting agents like copper sulfate and formalin can control external infections effectively, they also pose environmental risks.[29]
Aquatic environmental management
Establishing effective control systems requires comprehensive understanding and coordination across various domains, including fishery industry dynamics, fish biology, environmental factors, and management practices.[29] Given the limitations of vaccines and antibiotics for fish diseases, environmental protective measures emerge as cost-effective, easily monitored strategies without associated side effects.
Control measures during an outbreak
During streptococcosis outbreaks, a range of measures is deployed to contain the infection spread. While traditional approaches involve antimicrobial use and culture condition adjustments, their efficacy may be limited due to factors such as antibiotic resistance.[29] Alternative strategies like herbal remedies, along with practices such as adjusting feeding rates and prompt removal of dead fish, are recognized as essential preventive measures. Employing a combination of these strategies enables effective control of streptococcosis outbreaks in fish populations.
References
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- ^ a b c McCormick, A.W. (2003). "Geographic diversity and temporal trends of antimicrobial resistance in Streptococcus pneumoniae in the United States". Nature Medicine. 9 (4): 424–430. doi:10.1038/nm839. PMID 12627227.
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- ^ a b Mishra, Anshuman; Nam, Gyu-Hwi; Gim, Jeong-An; Lee, Hee-Eun; Jo, Ara; Kim, Heui-Soo (June 2018). "Current Challenges of Streptococcus Infection and Effective Molecular, Cellular, and Environmental Control Methods in Aquaculture". Molecules and Cells. 41 (6): 495–505. doi:10.14348/molcells.2018.2154. PMC 6030242. PMID 29754470.
- ^ Anshary, Hilal; Kurniawan, Rio A; Sriwulan, Sriwulan; Ramli, Ramli; Baxa, Dolores V (December 2014). "Isolation and molecular identification of the etiological agents of streptococcosis in Nile tilapia (Oreochromis niloticus) cultured in net cages in Lake Sentani, Papua, Indonesia". SpringerPlus. 3 (1): 627. doi:10.1186/2193-1801-3-627. PMC 4216822. PMID 25392797.
- ^ a b c "BLUE BOOK | AFS Fish Health Section". units.fisheries.org. Retrieved 2024-04-09.
- ^ a b c LaFrentz, Benjamin R.; Lozano, Carlos A.; Shoemaker, Craig A.; García, Julio C.; Xu, De-Hai; Løvoll, Marie; Rye, Morten (May 2016). "Controlled challenge experiment demonstrates substantial additive genetic variation in resistance of Nile tilapia (Oreochromis niloticus) to Streptococcus iniae". Aquaculture. 458: 134–139. Bibcode:2016Aquac.458..134L. doi:10.1016/j.aquaculture.2016.02.034.
- ^ a b Bridy-Pappas, Angela E.; Margolis, Marya B.; Center, Kimberly J.; Isaacman, Daniel J. (September 2005). "Streptococcus pneumoniae : Description of the Pathogen, Disease Epidemiology, Treatment, and Prevention". Pharmacotherapy: The Journal of Human Pharmacology and Drug Therapy. 25 (9): 1193–1212. doi:10.1592/phco.2005.25.9.1193. PMID 16164394.
- ^ Yanong, Roy PE; Francis-Floyd, Ruth (2002). Streptococcal infections of fish (PDF) (Report). Florida Cooperative Extension Service. IFAS, University of Florida. Circular 57.
- ^ Buruiana, Cristian-Teodor; Profir, Alina Georgiana; Vizireanu, Camelia (2014). "Effects of probiotic Bacillus species in aquaculture–an overview". The Annals of the University of Dunarea de Jos of Galati. 38 (2): 9–17. ProQuest 1684189662.
- ^ a b c Mishra, Anshuman; Nam, Gyu-Hwi; Gim, Jeong-An; Lee, Hee-Eun; Jo, Ara; Kim, Heui-Soo (2018-05-10). "Current Challenges of Streptococcus Infection and Effective Molecular, Cellular, and Environmental Control Methods in Aquaculture". Molecules and Cells. 41 (6): 495–505. doi:10.14348/molcells.2018.2154. PMC 6030242. PMID 29754470.
Further reading
- Yoshida, Kio; Chambers, James K; Uchida, Kazuyuki (2022). "Systemic Streptococcus agalactiae infection with meningo-ventriculitis in a Linnaeus's two-toed sloth (Choloepus didactylus)". Journal of Veterinary Medical Science. 84 (10): 1417–1421. doi:10.1292/jvms.22-0317. PMC 9586031. PMID 36058878.