Melioidosis
LEVELS: Sometimes occurs; Severe; Housing alone keeps it out; Reference or research laboratory required; Minor; Temporary disruption; Some; Needed but not available
| Register id | burkholderia_pseudomallei |
| Type | bacteria |
| Scientific name | Burkholderia pseudomallei |
| NCBI taxid | 28450 |
| Evidence | 2 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
Burkholderia pseudomallei causes melioidosis, an infection acquired from the environment rather than from other animals: the organism lives in soil and surface water across tropical and subtropical Asia and northern Australia, and pigs are infected through contaminated drinking water or soil. It has not been detected in the North American environment. Pigs are relatively resistant where husbandry and nutrition are good. Adults usually develop a chronic infection with few signs beyond palpable enlargement of the submandibular lymph nodes, and in endemic regions silent splenic abscesses are a common incidental finding at slaughter; young pigs can develop an acute septicaemia, but deaths in adults are rare. Because the route in is the water and the ground rather than another pig, prevention is a matter of clean or chlorinated water and keeping stock off contaminated soil. It is a serious human pathogen and is a US Select Agent, which is why a diagnosis would draw regulatory attention out of proportion to its effect on the pigs themselves.
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. ch58 58.3.1: "Ingestion of improperly cooked meat from infected animals may also result in human infection." "Rigorous criteria for meat inspection of slaughter pigs will help to safeguard public health." CFSPH 2016 confirms the animal-to-human route is possible but uncommon, naming a pig among the documented animal-source cases, and describes infection as usually acquired from soil and water.
How this level was decided
Level 3 unchanged. A pig-to-human route exists via undercooked meat, and the control points that interrupt it -- meat inspection and cooking -- are named in the folder. Transmission by that route requires them to fail. The factsheet does not disturb this: it establishes that most human melioidosis is environmental, which is why the level is 3 and not 4, but it does not remove the pork route.
C2 Zoonotic impact
Severity of human illness caused by the agent
Severe: Infection carries a substantial risk of life-threatening illness, death, or permanent disability, even if human infections are uncommon
Basis. CFSPH 2016: "Recent estimates of the overall mortality rate for all patients range from approximately 10% in Australia to 40% in Thailand, and can be higher in other areas where only limited medical care is available." "In one large prospective study from Australia, the case fatality rate ranged from 4% in patients without septic shock to 50% in patients with septic shock." "One review reported a case fatality rate of 73% in published cases of neonatal melioidosis." "septic shock is rapidly fatal without treatment, and has a high risk of death even with good care." ch58 58.3.1: "Mortality in humans is 20-50% with or without treatment."
How this level was decided
Level 4 unchanged and now much better anchored. The chapter gave a single 20-50% range; the factsheet resolves it into a distribution -- 10% to 40% overall by country, 4% without septic shock rising to 50% with it, and 73% in neonates. Substantial risk of life-threatening illness on any reading. Level 4.
C3 Herd introduction risk
Effort required to keep the agent out of the herd
Housing alone keeps it out: Raising pigs indoors and off soil breaks the cycle, so no ongoing biosecurity program is needed and only outdoor herds stay exposed
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. "c3l4, while unlikely in the US to reach pigs, we know the agent is here and it is a saprophyte and some pigs are raised outdoors so I think 'introduction risk unavoidable' is the correct rating" [RENUMBERED level 4 to 5, from_level 3 to 4 on 2026-09-01 when C3 went from four levels to five. The words above are exactly as recorded and the decision is unchanged -- only the number beside it moved, because the scale did. C3 now runs on the EFFORT REQUIRED TO EXCLUDE: L1 already in the herd, L2 housing alone keeps it out, L3 routine biosecurity keeps it out, L4 extraordinary biosecurity required, L5 exclusion may not be achievable.] RESCALED 2026-09-03, when C3 went from five levels to four and level 4 absorbed level 5. A ruling of his is never overturned by a scale change, so what is recorded here is the same judgment expressed on the new scale. AND THE ENTRY ALSO MOVED, on the pass Eric approved the same day: the whole old level 5 block was re-read against the exclusion test rather than the reservoir test, because twenty-one of those entries had been renumbered past the housing level on 2026-09-01 without being judged against it. See the entry justification for the reason this one moved. Recorded on the old scale as level 5, from_level 4.
Basis. CFSPH 2016: "Melioidosis is mainly reported in parts of Asia... and northern Australia." "Rare cases of melioidosis have been reported from the U.S. and Mexico, in people who had not traveled outside this region. To date, environmental sampling has not detected B. pseudomallei in North America." ch58 58.3.2: "Burkholderia pseudomallei is present in water and soil in tropical and subtropical areas and may infect pigs when water supplies are contaminated." "The disease can be prevented by the use of clean or chlorinated water supplies and by preventing access to contaminated soil."
How this level was decided
MOVED L5 -> L2 on 2026-09-03, when C3 was reduced to four levels and the whole level 5 block was re-read against the exclusion test rather than the reservoir test. Eric: "C3 is about exclusion, not reservoirs per se, though the two are related", and "who cares about reservoirs? Reservoirs really don't matter as long as you keep domestic pigs from becoming infected through biosecurity implementation." THE PREVIOUS LEVEL WAS NEVER JUDGED: this entry carried a RENUMBERED L4 -> L5 stamp from 2026-09-01, meaning it was moved past the newly created housing level rather than assessed against it. a soil and surface water organism of endemic regions. Eric, 2026-09-03: "burkholderia_pseudomallei to L2." Housing closes soil and water contact.
EARLIER REASONING, kept because it is the evidence read: MOVED L3 -> L4 on 2026-09-01 by the five-level rework. Melioidosis is a saprophyte of tropical soil and surface water, and the machine reading has been that the US has no such reservoir, so the onward source would be other pig herds -- but the routes are soil, water and feed rather than pig contact, which routine quarantine and C&D do not close. NOTE FOR ERIC: you ruled this the old L4, a reservoir outside the pig industry, which renumbers to L5 and remains your ruling. The disagreement is entirely about whether B. pseudomallei could establish in US soil, and it is the one C3 cell where the machine and your ruling differ on substance rather than on wording. C3 now runs on the EFFORT REQUIRED TO EXCLUDE: L1 already in the herd, L2 housing alone keeps it out, L3 routine biosecurity keeps it out, L4 extraordinary biosecurity required, L5 exclusion may not be achievable.
C4 Detection difficulty
Difficulty of recognizing and confirming infection
Reference or research laboratory required: A validated assay exists, but only at a national reference or research laboratory rather than at local or regional level
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "l3, may have indicative diagnosis at L2 lab but confirmation almost certainly would involve l3 lab" Transcribed by the assistant and confirmed by Eric on 2026-08-31 -- "i confirm the six". The harvester refused it because the comment names two levels, but the second is a noun phrase for a level-N-capable laboratory rather than a second assignment.
Basis. ch58 58.3.3: "Infection is often clinically inapparent." "More frequently, presumptive diagnosis is based on the presence of creamy abscesses found at slaughter." "The identity of suspect colonies can be confirmed biochemically or by MALDI-TOF mass spectrometry; however, precaution should be used to ensure the organism is included in the instrument database." CFSPH 2016 describes diagnosis resting on culture with selective media and warns that the organism is readily misidentified. "B. pseudomallei is listed as a tier 1 select agent under the US Federal Select Agent Program."
How this level was decided
Level 3 unchanged. Infection is usually silent and surfaces as non-specific abscesses at slaughter, so nothing points a practitioner here. Confirmation needs selective media and a MALDI-TOF database that may not carry the organism, and tier 1 select agent status puts the isolate into a registered facility. The factsheet reinforces the misidentification risk rather than changing the level.
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, though in the US I'm not sure it has ever been diagnosed in pigs, and typically requires contact with soil for exposure to occur. In asia, c5l2 it is a more significant disease because of their production systems and higher levels of exposure. Read new fact sheet in inbox to confirm against all criteria ratings and re- present to me."
Basis. CFSPH 2016: "Pigs may be relatively resistant to melioidosis when husbandry and nutrition are good. Adult pigs tend to develop chronic infections with few clinical signs; however, enlarged lymph nodes (particularly the submandibular nodes) may be palpable." "In endemic regions, asymptomatic splenic abscesses are often found in pigs at slaughter." "Young pigs can develop acute septicemia." ch58 58.3.3: "Deaths may occur but are rare in adults."
How this level was decided
CONFIRMED BY ERIC and now supported rather than inferred. He wrote: "c5l2, though in the US I'm not sure it has ever been diagnosed in pigs, and typically requires contact with soil for exposure to occur. In asia, c5l2 it is a more significant disease because of their production systems and higher levels of exposure." The factsheet supplies exactly the mechanism behind his reading -- pigs are relatively resistant WHEN HUSBANDRY AND NUTRITION ARE GOOD, and the disease is chronic and largely subclinical in adults. That ties the higher Asian burden to production system rather than to the organism, which is his point, and confirms level 2 for US conditions.
C6 Market impact
Duration of material disruption to pork and pig markets
Temporary disruption: Material negative effect on supply or demand lasting less than a month 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. "I think we should make it c6l2 - it would almost have to be a purposeful exposure to affect more than one farm and cause a market reaction but the simple fact it is in the Select Agent list means there would likely be federal regulatory action if there was a diagnosis of any consequence,."
Basis. Eric, on the sheet: "I think we should make it c6l2 - it would almost have to be a purposeful exposure to affect more than one farm and cause a market reaction but the simple fact it is in the Select Agent list means there would likely be federal regulatory action if there was a diagnosis of any consequence." ch58 58.3.1: "B. pseudomallei is listed as a tier 1 select agent under the US Federal Select Agent Program."
How this level was decided
CORRECTED BY ERIC from level 3 to level 2, and his reasoning is better than mine. I had reasoned from select agent status to a federally managed multi-month event. He splits it: the select agent listing does mean federal regulatory action would follow a diagnosis of consequence, but reaching more than one farm would take deliberate exposure, so the disruption stays local and short. Level 2, material effect lasting less than a month.
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. ch58 58.3.4: "Burkholderia pseudomallei is resistant in vitro to aminoglycosides but susceptible to some cephalosporins and to amoxicillin with clavulanic acid." CFSPH 2016 on the human disease: case fatality falls sharply with "prompt recognition of the condition, treatment with appropriate antibiotics, and state-of-the-art management of sepsis", and "Case fatality rates for melioidosis have decreased in recent years in some areas, most likely due to improved recognition and treatment."
How this level was decided
Level 2 unchanged, and the factsheet strengthens it against the chapter. ch58 said human mortality was 20-50% "with or without treatment", which reads as treatment not working; the factsheet says the opposite -- fatality has fallen with better recognition and antibiotics, and ranges from 4% to 50% depending on whether septic shock has set in. So treatment does work when applied early. It stays at level 2 rather than level 1 because the organism is intrinsically resistant to one antimicrobial class, susceptible to only some agents in another, and treatment in pigs is not established practice.
C8 Vaccine availability
Availability of effective vaccines or bacterins
Needed but not available: No effective vaccine is available in the US or has been developed, and the disease would justify vaccinating if one existed
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c8l3 is correct, the world needs a melioidosis vaccine, perhaps not urgent for the US but based on our criteria descritpion, this is the correct level"
Basis. ch58 58.3.4 and the CFSPH 2016 factsheet both describe prevention without any vaccine. No licensed melioidosis vaccine exists for any species. CFSPH: human case fatality runs 10% to 40% overall and reaches 73% in neonatal cases.
How this level was decided
STAYS L3. INFERRED. A tier 1 select agent with human case fatality in the tens of percent is the clean case of a warranted vaccine that does not exist -- the barrier is that it is a hard target, not that nobody wants one. This is the entry that shows the reworded level 3 still has work to do: it and treponema_pedis both scored level 3 before, and only this one should have.
Levels and evidence are generated from data/assignments/burkholderia_pseudomallei.yml; the overview is authored in data/overviews/burkholderia_pseudomallei.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.