MYCOPLASMA SUIS (INFECTIOUS ANEMIA)
LEVELS: Highly unlikely: No controls necessary; Highly unlikely: No evidence of non-foodborne zoonotic transmission; Highly effective: Routine on-farm biosecurity measures are effective in preventing farm-to-farm transmission; Moderate: Clinical signs not unique but existing tests available at local/regional laboratory(s); Moderate: Manageable losses related to endemic (population) or chronic (individual) occurrence; Negligible: Little or no market disruption when disease occurs on one or more farms; Minimal risk: Agent inherently unlikely to develop clinically important resistance to antibacterial or antiviral treatments; Minimal risk: Antibacterial or antiviral treatments rarely occur, or are typically limited to short-course individual animal therapy; Available but with uncertain efficacy: Limited treatments available in US or are only effective in some situations; No availability: Effective vaccines not currently available in the US (or have not been developed); Not feasible: Eradication extremely unlikely
OVERVIEW
Mycoplasma suis (formerly Eperythrozoon suis) is a hemotrophic mycoplasma that causes infectious anemia in pigs. Unlike other swine mycoplasmas, M. suis attaches to, invades, and replicates on and in red blood cells (RBCs). It cannot be cultured in cell-free media. A hallmark of infection is long-term persistence in subclinically infected carrier pigs, which serve as the main reservoirs. Reactivation can be triggered by immunosuppression. Transmission routes include iatrogenic (needles, surgical instruments), vertical (intrauterine), venereal (contaminated semen), and possibly blood-sucking arthropods. Acute disease causes hemolytic anemia with pallor, fever, icterus, and cyanosis; chronic infection causes unthriftiness and poor growth. In sows, infection may cause fever, anorexia, dysgalactia, and poor maternal behavior within days of farrowing. Diagnosis relies on PCR (more sensitive than blood smears) and ELISA-based serology. Treatment with oxytetracycline is effective but does not eliminate intracellular organisms. No commercial vaccine is available. Prevention focuses on changing needles between litters and minimizing iatrogenic blood transfer.
FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Highly unlikely: No controls necessary
M. suis is not a foodborne pathogen. It is a blood-borne hemotrophic organism with no documented foodborne transmission.
NON-FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Highly unlikely: No evidence of non-foodborne zoonotic transmission
M. suis infects pigs and wild boars but is not zoonotic. No human infections have been documented.
EFFECTIVENESS OF ON-FARM BIOSECURITY IN PREVENTING FARM-TO-FARM TRANSMISSION
Level: Highly effective: Routine on-farm biosecurity measures are effective in preventing farm-to-farm transmission
Transmission is primarily iatrogenic and controllable: (1) Iatrogenic transmission: Via needles, surgical instruments contaminated with blood; (2) Vertical transmission: "vertical (intrauterine) transmission" documented; (3) Arthropod vectors possible: "The presence of mosquitoes and flies (odds ratio 5.99) was associated with a higher prevalence"; (4) Prevention effective: "Transmission by needles and surgical instruments must be minimized by changing needles between sows and litters"; (5) Frequency of disinfection protective: "(odds ratio 0.23) were associated with a lower prevalence."
DIFFICULTY OF DETECTING AND CONFIRMING INFECTION
Level: Moderate: Clinical signs not unique but existing tests available at local/regional laboratory(s)
Diagnosis requires specialized testing: (1) Cannot culture: "Since isolation is not possible, pathogen detection relies on PCR assays or blood smears"; (2) PCR more sensitive: "there are several PCR and quantitative polymerase chain reaction (qPCR) assays available that are more sensitive for the detection of M. suis than blood smears"; (3) Serology available: "ELISAs based on recombinant antigens...are commonly used"; (4) Antibody persistence limited: "antibody titers may persist only 2–3 months resulting in frequent false negative results."
FINANCIAL IMPACT ON FARM'S COST OF PRODUCTION
Level: Moderate: Manageable losses related to endemic (population) or chronic (individual) occurrence
Impact is variable and often subclinical: (1) Subclinical carriers: "A hallmark of M. suis infection is the long-term persistence in subclinically infected pigs"; (2) Variable clinical expression: "Infected animals can remain normal for months prior to exhibiting clinical disease, which is often related to stress"; (3) Sow productivity: "Chronic infection in sows has been associated with reproductive problems (increased stillbirth rate); however, these findings deserve further investigation."
EFFECT ON DOMESTIC OR EXPORT MARKETS
Level: Negligible: Little or no market disruption when disease occurs on one or more farms
No trade implications: (1) Not regulated: M. suis is not a reportable disease; (2) Endemic worldwide: Reported in many countries.
PATHOGEN'S ABILITY TO DEVELOP AND SPREAD RESISTANCE
Level: Minimal risk: Agent inherently unlikely to develop clinically important resistance to antibacterial or antiviral treatments
No antimicrobial resistance documented. M. suis remains susceptible to tetracyclines, the primary treatment option.
AMR DEVELOPMENT DRIVEN BY DISEASE MANAGEMENT
Level: Minimal risk: Antibacterial or antiviral treatments rarely occur, or are typically limited to short-course individual animal therapy
Prevention and management are primary: (1) Prevention focus: Needle hygiene, vector control; (2) Treatment when needed: "The treatment of choice for infection is oxytetracycline administered parenterally"; (3) Strategic use: "Administration of oxytetracycline at times of stress or treatment in infected herds may help to prevent acute disease."
AVAILABILITY OF EFFECTIVE TREATMENT OPTIONS
Level: Available but with uncertain efficacy: Limited treatments available in US or are only effective in some situations
Tetracyclines are effective: (1) Treatment of choice: "The treatment of choice for infection is oxytetracycline administered parenterally"; (2) Does not eliminate: "treatment does not necessarily eliminate the organism from the pig, as M. suis may reside intracellularly in RBCs"; (3) Feed medication for sows: "Chlortetracycline fed to the entire sow herd at 22 mg/kg daily for 2 weeks resulted in a nearly complete disappearance of dysgalactia"; (4) Supportive care: "Supportive therapy and iron injections (200 mg iron dextran/pig) will help recovery."
AVAILABILITY OF EFFECTIVE VACCINES OR BACTERINS
Level: No availability: Effective vaccines not currently available in the US (or have not been developed)
No commercial vaccine exists: (1) Cannot culture: "vaccine development is complicated by the inability to culture M. suis and the lack of knowledge of the virulence factors"; (2) Experimental vaccines failed: "An attempt to produce a vaccine from a recombinant protein...failed to protect against challenge"; "An experimental subunit vaccine...provided limited clinical protection."
FEASIBILITY OF ERADICATING THE DISEASE FROM THE US
Level: Not feasible: Eradication extremely unlikely
Eradication is not feasible: (1) Persistent carriers: "A hallmark of M. suis infection is the long-term persistence in subclinically infected pigs"; (2) Intracellular survival: Organisms reside within RBCs, evading treatment; (3) No elimination strategy: "Strategies for the elimination of M. suis from infected herds are not available"; (4) Wild boar reservoir: "M. suis has also been detected by PCR in wild boars in Germany (10%) and in Brazil (50%)."