Leptospirosis
LEVELS: Sometimes occurs; Moderate; Routine biosecurity keeps it out; Laboratory-dependent; Minor; Negligible; Some; Available but inconsistent
| Register id | leptospira_species |
| Type | bacteria |
| Scientific name | Leptospira |
| NCBI taxid | 171 |
| Evidence | 2 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
Leptospires are thin, spiral bacteria that settle in the kidneys and genital tract of carrier pigs and are shed in urine and genital fluids. In pigs the disease is essentially a reproductive one: infertility, abortion, stillbirths and weak piglets. Acute illness — brief fever and inappetence, rarely jaundice — is usually mild and easily missed. Pigs are the maintenance host for a small number of serovars, notably Pomona and Bratislava, meaning the infection can circulate in a herd indefinitely; other serovars come from wildlife and rodents as incidental infections. Where infection is endemic there may be little visible disease, but introducing it to a susceptible herd, or a lapse in immunity, can cause substantial reproductive loss. Because Bratislava is spread venereally, artificial insemination removes an important route. Vaccines exist but protection is short-lived, around three months, so control also relies on rodent control, clean water and treatment with streptomycin or tetracyclines. It is an important occupational zoonosis: farmers, veterinarians and abattoir workers can develop a febrile illness that occasionally progresses to the severe form with jaundice, kidney failure and haemorrhage.
C1 Zoonotic potential
Likelihood of transmission from pigs to humans
Sometimes occurs: Known risk of transmission to humans (foodborne or occupational), but requires failure of one or more control points for transmission to humans
Basis. ch52 52.3, a Public Health section that names the exposed occupations and the route: "LEPTOSPIROSIS IS A POTENTIAL OCCUPATIONAL ZOONOSIS OF THOSE WHO WORK WITH PIGS in regions in which infection in swine is common, ESPECIALLY FARMERS, VETERINARIANS, AND ABATTOIR WORKERS. INFECTION IS BY DIRECT OR INDIRECT CONTACT OF MUCOUS MEMBRANES OR SKIN WOUNDS WITH THE URINE OF AN INFECTED PIG." 52.1: "Leptospires PERSIST IN THE KIDNEYS and female and male genital tracts of carrier swine AND ARE EXCRETED IN URINE and genital fluids. SURVIVAL OUTSIDE THE HOST IS FAVORED BY WARM, MOIST CONDITIONS."
How this level was decided
Level 3. Both halves of the label are stated by the chapter: a known occupational risk to the named trades, and a control point that has to fail -- gloves, mucous-membrane protection and wound cover between a person and pig urine. NOTE THE SCOPE QUALIFIER THE CHAPTER ATTACHES, because it matters for the US reading and is the argument for level 2: the risk applies "in regions IN WHICH INFECTION IN SWINE IS COMMON", and 52.1 records that in the intensive pig industries of the northern hemisphere "ITS IMPORTANCE HAS APPARENTLY DECLINED". Level 3 is scored on the route being real and unprotected where the infection is present, not on how often it is present.
C2 Zoonotic impact
Severity of human illness caused by the agent
Moderate: Clinically important illness is common and may require medical treatment or hospitalization, but death or permanent disability is uncommon
Basis. ch52 52.3: "MOST CASES ARE ASYMPTOMATIC or present as sudden onset of an approximately WEEK-LONG FEBRILE SICKNESS with any combination of chills, conjunctival suffusion, severe headache, myalgia of lower back and legs, abdominal pain, vomiting, and diarrhea. IN APPROXIMATELY 5-10% OF CASES, THE CLINICAL COURSE PROGRESSES RAPIDLY TO INCLUDE ICTERUS, RENAL FAILURE, COUGH, DYSPNEA, AND HEMOPTYSIS THAT MAY BE FATAL."
How this level was decided
Level 3, and the chapter supplies the numbers rather than an adjective, which is rare in this criterion. Clinically important illness is common -- a week of fever severe enough to stop work -- and it requires medical treatment; death and permanent disability are uncommon at 5-10% progressing to the severe form, of which only a fraction are fatal. That is the level 3 label almost exactly. THE ARGUMENT FOR LEVEL 4 is that the severe form is Weil's disease with renal failure and pulmonary haemorrhage, and level 4 asks only for a SUBSTANTIAL risk of life-threatening illness. It is not taken because the chapter puts that outcome at one case in ten or twenty, against a background where most infections are asymptomatic.
C3 Herd introduction risk
Effort required to keep the agent out of the herd
Routine biosecurity keeps it out: Quarantine of incoming stock, transport and fomite control, cleaning and disinfection, and the usual monitoring reliably exclude it
Basis. ch52 52.4: "pigs are infected by SEROVARS MAINTAINED BY PIGS OR BY SEROVARS MAINTAINED BY OTHER ANIMAL SPECIES present in the area... PIGS ACT AS MAINTENANCE HOSTS FOR SEROVARS BELONGING TO SEROGROUPS POMONA AND AUSTRALIS, while serovars in serogroups Icterohemorrhagiae, Grippotyphosa, and Tarassovi are among the more commonly identified INCIDENTAL INFECTIONS in swine." 52.1: "TRANSMISSION IS BY DIRECT OR INDIRECT CONTACT WITH A CARRIER PIG OR OTHER ANIMAL. INTERRUPTION OF TRANSMISSION FROM INFECTED PIGS OR OTHER HOSTS TO SUSCEPTIBLE PIGS IS THE CRITICAL FACTOR IN CONTROL." 52.9: "THE MAIN MANAGEMENT FACTOR IN THE CONTROL OF LEPTOSPIROSIS IS THE PREVENTION OF DIRECT OR INDIRECT CONTACT WITH FREE-LIVING VECTORS OR OTHER DOMESTIC STOCK. STRICT BIOSECURITY SHOULD BE IMPLEMENTED, INCLUDING STRINGENT RODENT CONTROL PROGRAMS."
How this level was decided
Level 3. The chapter names the programme and every item is on the level 3 list: quarantine and testing of incoming stock, exclusion of other domestic species, and rodent control. NOTE HOW THE TWO HALVES OF THE EPIDEMIOLOGY SPLIT ACROSS YOUR C3 TEST and still land on the same level. The pig-maintained serovars, Pomona and Australis, arrive in carrier pigs -- other pigs, which housing does nothing about. The incidental serovars arrive from rodents and other stock -- which housing and rodent control do address, and would be level 2 on their own. The entry covers both, and the routine programme is what excludes them together. NOT LEVEL 4: nothing here needs filtration, treated feed or costly carrier testing.
C4 Detection difficulty
Difficulty of recognizing and confirming infection
Laboratory-dependent: The presentation does not point to this disease specifically, but local or regional laboratories can confirm it with a validated assay once it is suspected
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c4l2, numerous methods available at local and regional labs, commonly tested for in many species including pigs"
Basis. ch52 52.8: "THE MILD, OFTEN INAPPARENT CLINICAL SIGNS OF ACUTE LEPTOSPIROSIS MAKE CLINICAL DIAGNOSIS DIFFICULT, AND THE LACK OF SPECIFICITY OF LESIONS MAKES PATHOLOGICAL DIAGNOSIS DIFFICULT; THEREFORE, DIAGNOSIS IS USUALLY BASED ON THE RESULTS OF LABORATORY TESTS. Laboratory tests for leptospirosis fall into two groups: (i) INDIRECT SEROLOGICAL TESTS to assess antibody levels and (ii) DIRECT TESTS THAT DETECT THE ORGANISM. THE SELECTION OF TESTS DEPENDS ON THE PURPOSE OF TESTING AND THE AVAILABILITY OF DIAGNOSTIC ASSAYS." The purposes named are confirmation of clinical disease, herd status for control or eradication, and individual status for introduction into a closed herd or for trade.
How this level was decided
INFERRED. Level 2 -- laboratory-dependent. The chapter is explicit that neither the clinical picture nor the lesions will make the diagnosis, so this is not level 1; and it treats serology and direct detection as routinely selectable tools, including for individual animals being moved or traded, which is not how a reference-laboratory-only assay is described. That is level 2. THE CELL IS INFERRED RATHER THAN SUPPORTED because the folder does not name a specific assay or state where it is run -- the phrase "THE AVAILABILITY OF DIAGNOSTIC ASSAYS" is a hedge, and leptospiral serology by microscopic agglutination is in practice a specialised service. IF YOU KNOW THAT US LABORATORIES SEND LEPTOSPIRA SEROLOGY OUT rather than running it, this is level 3.
C5 Production cost
Financial impact on the infected farm's cost of production
Minor: Small and generally short-lived losses with little effect on overall cost of production
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c5l2, minor significance across the industry though do get anectdotal reports of outbreaks"
Basis. ch52 52.1: "Leptospirosis is A CAUSE OF REPRODUCTIVE LOSS IN BREEDING HERDS and has been reported in swine from all parts of the world; however, KNOWLEDGE OF THE INCIDENCE AND ECONOMIC IMPACT OF THE DISEASE IS LARGELY CONFINED TO ARGENTINA AND BRAZIL, AND TO THE INTENSIVE PIG INDUSTRIES OF THE NORTHERN HEMISPHERE, AUSTRALIA, AND NEW ZEALAND, WHERE ITS IMPORTANCE HAS APPARENTLY DECLINED. ENDEMIC INFECTION IN A HERD OF SWINE MAY PRODUCE LITTLE EVIDENCE OF CLINICAL DISEASE, BUT WHEN IT IS FIRST INTRODUCED INTO A SUSCEPTIBLE BREEDING HERD, OR DURING PERIODS OF WANING HERD IMMUNITY, IT CAN CAUSE VERY APPRECIABLE LOSSES THROUGH INFERTILITY, ABORTION, AND THE DELIVERY OF STILLBORN OR WEAK PIGLETS."
How this level was decided
INFERRED. Level 2 -- small and generally short-lived losses. The standing note SCORING/production_cost_impact decides this cell, and the chapter hands over the finding it asks for: in the intensive pig industries of the northern hemisphere, which includes US production, the IMPORTANCE OF THIS DISEASE HAS APPARENTLY DECLINED, and endemic infection produces little evidence of clinical disease. That is your Erysipelothrix and porcine parvovirus reasoning -- score what the industry actually sees. THE ARGUMENT FOR LEVEL 3 is the introduction event: "VERY APPRECIABLE LOSSES" of fertility and whole litters when it first enters a susceptible breeding herd. That is a real event and it is why the level is inferred rather than supported; on your Menangle rule it is the exception, not the general case.
C6 Market impact
Duration of material disruption to pork and pig markets
Negligible: Little or no material disruption to supply or demand when disease occurs on one or more farms
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c6l1, no reason to think the market would react, this is an old disease"
Basis. Leptospirosis has been reported in swine worldwide and is endemic in US herds, with its importance in intensive northern-hemisphere production having apparently declined (ch52 52.1). No trade measure, movement restriction or consumer response to a swine leptospirosis diagnosis is recorded anywhere in the chapter.
How this level was decided
INFERRED. Level 1 under the standing note SCORING/market_impact: an agent long endemic and routinely diagnosed in US pigs with no market move ever observed. NOTE THAT THE ZOONOSIS DOES NOT LIFT IT, on the reasoning you gave for anthrax: leptospirosis is a well-known occupational infection across several livestock sectors and dogs, so a diagnosis in pigs is not a novel event that would attract market attention.
C7 Treatment potential
Potential for treatment to improve outcomes
Some: Treatment exists but is inconsistent, requires extralabel use, or works only in some circumstances
Basis. ch52 52.9: "Control of leptospirosis is dependent on the combined use of three strategies: ANTIBIOTIC THERAPY, VACCINATION, AND MANAGEMENT. Unfortunately, THESE OPTIONS ARE NOT ALL AVAILABLE IN EVERY COUNTRY... In some countries, STREPTOMYCIN, THE MOST USEFUL ANTIBIOTIC for leptospiral treatment and control programs, IS NO LONGER AVAILABLE FOR VETERINARY USE... Especially since it is known that ANTIBIOTICS ALONE WILL NOT ELIMINATE PIG-MAINTAINED LEPTOSPIRAL INFECTIONS FROM INDIVIDUAL CARRIERS or control infection in herds. DESPITE CLAIMS by some authors that either systemic streptomycin... or oral tetracyclines... WILL ELIMINATE CARRIERS, OTHERS HAVE REPORTED THAT THESE REGIMES DO NOT WORK. Work on the use of alternative antibiotic therapy regimes indicates that OXYTETRACYCLINE, TYLOSIN, OR ERYTHROMYCIN MAY BE EFFECTIVE IN ELIMINATING POMONA FROM THE KIDNEYS of experimentally infected pigs."
How this level was decided
Level 2, and the chapter argues it out on the page. Treatment exists and is one of the three pillars of control, so this is not level 3; but it works only in some circumstances, which the chapter demonstrates rather than asserts -- published claims that streptomycin or tetracycline eliminate carriers are contradicted by other published work, antibiotics alone will not clear pig-maintained infection from carriers, and the most useful drug has been withdrawn from veterinary use in some countries. The alternatives that did clear kidneys did so in EXPERIMENTALLY infected pigs.
C8 Vaccine availability
Availability of effective vaccines or bacterins
Available but inconsistent: Commercial or autogenous vaccines exist in the US but protection may be inconsistent
Basis. ch52 52.9: "VACCINATION INDUCES IMMUNITY OF RELATIVELY SHORT DURATION. IMMUNITY TO INFECTION IS PROBABLY NEVER 100% AND, AT BEST, LASTS LITTLE MORE THAN 3 MONTHS... VACCINATION MARKEDLY REDUCES THE PREVALENCE OF INFECTION IN SWINE HERDS BUT WILL NOT ELIMINATE INFECTION. Improvements in bovine leptospirosis vaccines have resulted in protective immunity lasting approximately 12 months. THERE IS A NEED FOR THE DEVELOPMENT OF SIMILAR VACCINES FOR SWINE that should contain appropriate serovars of pig-maintained strains plus strains maintained by other regional hosts. MIXED GENOTYPE INFECTION of serovar Bratislava indicates that NATURAL INFECTION BY ONE GENOTYPE MAY NOT ALWAYS CONFER IMMUNITY TO INFECTION BY THE HETEROLOGOUS GENOTYPE OF THE SAME SEROVAR." Elsewhere: "VACCINES ARE NOT AVAILABLE IN MANY COUNTRIES."
How this level was decided
Level 2. Multivalent leptospiral bacterins are available in the US and markedly reduce infection prevalence, so this is not level 3; and the disease warrants vaccinating, so it is not the "not needed" half of level 1. What holds it at level 2 is stated in successive sentences: immunity is never complete, lasts little more than three months at best, does not eliminate infection, and may not cover a heterologous genotype of the same serovar. THE CHAPTER ALSO SAYS A BETTER VACCINE IS NEEDED and points at the bovine products as the model, which is the strongest form of the level 2 finding -- a product that exists and is not good enough, rather than a gap.
Levels and evidence are generated from data/assignments/leptospira_species.yml; the overview is authored in data/overviews/leptospira_species.md. Do not hand-edit this page — corrections go in data/assignments/CORRECTIONS.yml.
Quoted material marked Basis is from Zimmerman JJ, Karriker LA, Ramirez A, Schwartz KJ, Stevenson GW, Zhang J, eds. Diseases of Swine, 12th edition. Hoboken: Wiley Blackwell, 2025 — except where another source is named in the quotation itself.