CLOSTRIDIUM TETANI (TETANUS)
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; Easy: Distinct clinical signs and/or existing test(s) available at local/regional laboratory(s); Minor: Low prevalence, typically non-lethal infection with recovery very likely; 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; Widely available: Effective commercial vaccines widely available in the US (or held in national response stockpile); Highly likely: Can be eradicated using existing tools and knowledge
OVERVIEW
Clostridium tetani is an anaerobic, gram-positive, slender rod that forms highly resistant terminal spores ("drumstick" appearance) and causes tetanus, characterized by uncontrollable spasms of voluntary muscles. The organism produces tetanospasmin (TeNT), a potent neurotoxin that passes by retrograde axonal transport to inhibitory neurons in the spinal cord, where it cleaves synaptobrevin and blocks neurotransmitter release, resulting in sustained muscle contraction (tetany). Swine of all ages may be affected, but most cases involve young pigs following castration, tail docking, or umbilical infection. Sows may be infected through contaminated uterine prolapses. Disease requires spore germination in a wound environment with reduced oxygen tension. Clinical signs include stiffened gait progressing to rigid limbs, erect ears, extended tail, and ultimately lateral recumbency with opisthotonus. Tetanic spasms are heightened by sensory stimuli and can become severe enough to cause bone fractures. Death typically results from respiratory failure. Prognosis is poor once clinical signs develop. Prevention through sanitary wound management and vaccination is preferred. Tetanus toxoid provides excellent protection, while antitoxin can provide passive immunity. The ubiquitous distribution of spores in soil makes environmental elimination impossible.
FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Highly unlikely: No controls necessary
Tetanus is not transmitted through food. The chapter states: "Neither disease [tetanus or botulism] is zoonotic; hence, there is no public health concern." Human tetanus occurs through wound contamination with environmental spores, not through consumption of animal products.
NON-FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Highly unlikely: No evidence of non-foodborne zoonotic transmission
Tetanus is not transmitted from animals to humans: "Neither disease is zoonotic; hence, there is no public health concern." Both humans and animals acquire tetanus from environmental spores entering wounds; there is no animal-to-human transmission.
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
Tetanus is an environmental infection controllable through wound management: (1) Wound-associated: "Spores usually gain entrance via a deep penetrating wound"; (2) No direct transmission: C. tetani "is not invasive and remains localized at the primary site of infection"; (3) Environmental source: Terminal spores are "ubiquitous in the environment"; (4) Latent spores: "Spores may remain latent in healed wounds for 10 years or more"; (5) Risk factors: "Spores often enter via traumatic wounds, including, but not limited to, those from tail docking and castration." Standard wound management and sanitation control disease.
DIFFICULTY OF DETECTING AND CONFIRMING INFECTION
Level: Easy: Distinct clinical signs and/or existing test(s) available at local/regional laboratory(s)
Diagnosis is primarily clinical: (1) Clinical diagnosis: "Diagnosis is based on typical clinical signs"—stiffened gait, erect ears, extended limbs, opisthotonus, heightened response to stimuli; (2) Wound identification: "An obvious area of infection (e.g. a castration wound or umbilical abscess) may be apparent"; (3) Microscopy: "Identification of typical rods with terminal spores on Gram-stained smears of a wound lends credibility to a diagnosis"; (4) Laboratory confirmation optional: "The organism may be isolated by bacteriologic culture or identified by immunofluorescence from suspect wounds, but this is usually not necessary if there is adequate antemortem clinical observation"; (5) No lesions: "Animals dying of tetanus do not show specific gross or microscopic lesions."
FINANCIAL IMPACT ON FARM'S COST OF PRODUCTION
Level: Minor: Low prevalence, typically non-lethal infection with recovery very likely
Tetanus causes sporadic rather than epidemic losses: (1) Sporadic occurrence: Cases typically involve individual animals or small groups; (2) High case fatality: "With even moderate clinical tetanus, prognosis is poor"; "shorter incubation periods are associated with a more acute and fulminating course and a higher fatality rate"; (3) Young pig association: "most cases involve young pigs" following routine procedures; (4) Variable incidence: Depends on sanitary practices and wound management; (5) Preventable: "Prevention through sanitary wound management and vaccination is preferred."
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: Tetanus is not a reportable or trade-restricted disease; (2) Sporadic occurrence: Individual animal losses do not affect market access; (3) No carcass issues: Affected animals die or are euthanized; no food safety concerns.
PATHOGEN'S ABILITY TO DEVELOP AND SPREAD RESISTANCE
Level: Minimal risk: Agent inherently unlikely to develop clinically important resistance to antibacterial or antiviral treatments
Minimal resistance concerns: (1) Prevention preferred: Vaccination is the primary control method; (2) Susceptibility maintained: Penicillins and tetracyclines effective; (3) Limited treatment opportunity: Rapid progression limits antimicrobial selection pressure; (4) Toxin-mediated disease: Disease is caused by toxin, not bacterial replication, so antimicrobials have limited role once toxin is produced.
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
Disease management relies on prevention, not treatment: (1) Vaccination primary: "Active immunity may be obtained from a single injection of alum-precipitated tetanus toxoid"; (2) Prophylaxis: "Prophylactic use of large doses of long-acting penicillin or tetracyclines may be superior to antitoxin in preventing experimental tetanus if treatment is instituted within a few hours after infection"; (3) Treatment rarely successful: "there is little evidence that treatment is of real benefit" once clinical signs develop.
AVAILABILITY OF EFFECTIVE TREATMENT OPTIONS
Level: Available but with uncertain efficacy: Limited treatments available in US or are only effective in some situations
Treatment options exist but are rarely successful: (1) Poor prognosis: "With even moderate clinical tetanus, prognosis is poor, and there is little evidence that treatment is of real benefit"; (2) Antitoxin: Available "to neutralize toxins not already fixed by nervous tissue" but limited efficacy once toxin is bound; (3) Supportive measures: "Various suggested treatments include reopening castration wounds and flushing them with hydrogen peroxide, administration of antitoxin...administration of antibiotics, and the use of tranquilizers or barbiturates as muscle relaxants"; (4) Timing critical: Treatment must be immediate; once clinical signs are established, recovery is unlikely.
AVAILABILITY OF EFFECTIVE VACCINES OR BACTERINS
Level: Widely available: Effective commercial vaccines widely available in the US (or held in national response stockpile)
Vaccination is highly effective for prevention: (1) Single dose effective: "Active immunity may be obtained from a single injection of alum-precipitated tetanus toxoid"; (2) Excellent protection: "excellent protection for 1 year or more can be expected if three doses are given several weeks apart"; (3) Lifelong immunity: Properly vaccinated animals have lasting protection; (4) Passive immunity: "Passive immunization with tetanus antitoxin" available for immediate protection in high-risk situations.
FEASIBILITY OF ERADICATING THE DISEASE FROM THE US
Level: Highly likely: Can be eradicated using existing tools and knowledge
Herd-level elimination achievable through prevention; true eradication impossible due to environmental spores: (1) Preventable: "Good sanitation in the farrowing house, treatment of umbilical cords with antiseptics soon after birth, sanitary practices for castration and other surgeries"; (2) Vaccination: Effective toxoid vaccines available; (3) Environmental persistence: "There is no practical way to eliminate spores from soil"—spores persist indefinitely in environment; (4) Control focus: "control is directed toward prevention of wound contamination by soil or feces."