Organophosphate Poisoning

1. Disease Information

Overview. Organophosphate poisoning is the clinical syndrome resulting from exposure to organophosphorus (OP) compounds — insecticides (parathion, malathion, chlorpyrifos, dimethoate, fenthion, diazinon, monocrotophos) and chemical warfare nerve agents (sarin, soman, tabun, VX). The unifying mechanism is inhibition of acetylcholinesterase (AChE), causing accumulation of acetylcholine at cholinergic synapses and an acute cholinergic crisis affecting muscarinic, nicotinic, and central nervous system receptors. As the flagship 2023 mechanistic review states, "The OP binds to and phosphorylates a nucleophilic serine at the catalytic site of the enzyme" (Naughton & Terry, Toxics 2023; PMID:37888716), and acetylcholinesterase inhibition "results in accumulation of acetylcholine and overstimulation of acetylcholine receptors" (Eddleston et al., Lancet 2008; PMID:17706760).

Key identifiers. - ICD-10: T60.0 (Toxic effect of organophosphate and carbamate insecticides); X48 / T60.0 for accidental/intentional pesticide exposure. - ICD-11: NE61 (Harmful effects of drugs, medicaments and biological substances) / exposure codes; poisoning by insecticides. - MeSH: "Organophosphate Poisoning" (D062025); related: "Organophosphorus Compounds," "Cholinesterase Inhibitors." - MONDO: No specific well-established MONDO term for the acute toxic syndrome (this is a toxic exposure, not a disease entity in the OMIM/Mendelian sense). Candidate mapping is to a poisoning/intoxication class; do not assert a MONDO ID without verification via OAK (runoak -i sqlite:obo:mondo search "organophosphate poisoning"). - OMIM / Orphanet: Not applicable (acquired toxic condition; no Orphanet rare-disease code).

Common synonyms / alternative names. Organophosphorus poisoning; OP poisoning; organophosphate insecticide poisoning; anticholinesterase poisoning; cholinergic toxidrome; nerve agent poisoning (for warfare agents). "Organophosphate-induced cholinergic crisis" refers to the acute phase.

Data derivation. Information is aggregated disease-level (toxicology reviews, clinical cohorts, RCTs, poison-center registries) rather than individual EHR-derived — though large single-center Asian cohorts (Sri Lanka, India, Pakistan, Bangladesh) supply much of the clinical evidence.

2. Etiology

Primary cause. Exposure — dermal, inhalational, or (most lethally) oral ingestion — to an organophosphorus compound. The dominant global context is intentional self-poisoning (suicide) by ingestion of agricultural insecticides in low- and middle-income countries; secondary causes are occupational/agricultural exposure and accidental (often pediatric) exposure. Chemical warfare/terrorism (e.g., Tokyo sarin 1995; Syria) is a distinct high-acuity setting.

Risk factors (environmental/behavioral): - Residence in rural agricultural regions of South Asia, Southeast Asia, sub-Saharan Africa, Central/South America. - Occupational: farm workers, pesticide applicators/handlers, sheep-dip workers (chronic low-dose exposure). - Ready domestic availability of highly hazardous WHO Class I OP pesticides. - Psychiatric distress / acute interpersonal crisis (impulsive self-harm — the reason means-restriction works so well). - Male sex and working age predominate in fatal self-poisoning cohorts.

Genetic susceptibility modifiers (not causal genes). PON1 (paraoxonase-1) is the principal host determinant. PON1 is "an A-esterase capable of hydrolyzing the active metabolites (oxons) of a number of organophosphorus insecticides such as parathion, diazinon and chlorpyrifos" (Costa et al.; PMC3516631). The Q192R (rs662) and L55M coding polymorphisms and the −108 C/T promoter variant (governing expression level) modulate detoxification efficiency in a substrate-specific manner — "The PON1R192 alloform hydrolyzes chlorpyrifos oxon and paraoxon more rapidly than PON1Q192." A meta-analysis found "PON1 192Q and 55LM polymorphisms may increase the risk of organophosphate toxicity, especially among Caucasian populations" (PMID:23590198). See §4 and §9.

Protective factors. - Environmental/public-health: national bans of highly hazardous pesticides (Sri Lanka's staged bans are the landmark example — see §9/§13), safe storage, dilution/formulation changes. These are the single most effective interventions for population mortality. - Genetic: high-activity PON1 alloforms/high plasma PON1 status confer relative protection against specific oxons; there is no universally protective allele (protection is compound-dependent).

Gene–environment interaction. The canonical GxE here is PON1 genotype × specific OP compound: "The extent to which PON1 protects against a given OP is determined by its catalytic efficiency" toward that compound's oxon. Groups with high-dose exposure (sheep-dip workers, first Gulf War veterans) reported poorer health if carrying the 192R allele (PMC3516631). CTD (Comparative Toxicogenomics Database) catalogs OP compound → gene interactions for curation cross-reference.

3. Phenotypes

Clinical features derive from cholinergic excess at three receptor populations. Onset is acute (minutes to hours after ingestion; sometimes delayed with lipophilic agents like fenthion).

Muscarinic effects (mnemonics SLUDGE / DUMBELS): salivation, lacrimation, urination, defecation/diarrhea, gastrointestinal cramping, emesis; plus miosis, bronchorrhea, bronchospasm, bradycardia, sweating. Bronchorrhea + bronchospasm ("the killer B's") drive early respiratory failure.

Nicotinic effects: fasciculations, muscle weakness, cramps, tachycardia, hypertension, mydriasis (variable) — reflecting neuromuscular junction and sympathetic ganglion stimulation. "Overstimulation of nicotinic acetylcholine receptors in the CNS results in anxiety, headache, convulsions, ataxia, depression of respiration and circulation, tremor, general weakness, and potentially coma" (mechanism reviews).

CNS effects: anxiety, restlessness, confusion, tremor, seizures, and status epilepticus. Per the 2023 review, "brain damage from acute OP exposure is a direct result of status epilepticus," and "muscarinic but not nicotinic receptor antagonists prevent seizure induction if administered before OP exposure" (PMID:37888716).

Later/secondary phenotypes (see §8 for timing): - Intermediate syndrome (IMS): proximal muscle and neck-flexor weakness, cranial nerve palsies, and respiratory failure 24–96 h after cholinergic crisis, "not responsive to atropine or oxime therapy" (PMC5548687). HPO: HP:0002878, HP:0003324 (Generalized muscle weakness). - OP-induced delayed polyneuropathy (OPIDN): distal sensorimotor peripheral neuropathy 1–3 weeks post-exposure. HPO: HP:0009830 (Peripheral neuropathy), HP:0007015 (Sensorimotor neuropathy). - Chronic OP-induced neuropsychiatric disorder (COPIND): cognitive/affective sequelae after chronic or severe acute exposure.

Severity & progression. Severity graded clinically by the Peradeniya Organophosphorus Poisoning (POP) scale (miosis, fasciculations, respiration, bradycardia, consciousness, seizures); "Higher POP scale scores are associated with increased mortality, need for ventilatory support, and atropine dosages" (PMC10336367). Course is acute and often episodic across the three phases; QoL impact is dominated by ICU-level respiratory failure, prolonged ventilation, and (in survivors) persistent neuropsychiatric and peripheral-nerve deficits.

4. Genetic / Molecular Information

Causal genes: NOT APPLICABLE — OP poisoning is toxin-induced; there is no disease-causing germline mutation.

Host-susceptibility gene (modifier): PON1 - HGNC: PON1 (paraoxonase 1), HGNC:9204; chromosome 7q21.3. - Function: calcium-dependent A-esterase that hydrolyzes OP oxons (the toxic activated metabolites); "PON1 activity is highest in liver and in plasma" (PMC3516631). - Key variants (germline polymorphisms, not pathogenic mutations): - Q192R (rs662): substrate-specific catalytic difference; R192 hydrolyzes chlorpyrifos-oxon/paraoxon faster, Q192 hydrolyzes some others (e.g., soman/sarin analogs) better. Both hydrolyze diazoxon equally. - L55M (rs854560): affects protein stability/level. - −108 C/T (promoter): "the major contributor of differences in the levels of PON1 expression." - Allele frequencies vary widely by ancestry (e.g., 192R more common in some Asian/African populations); consult gnomAD for population-specific frequencies. - Functional consequence: modifies detoxification capacity — effectively a pharmacokinetic protective/risk gradient, not loss/gain-of-function disease biology.

Other modifier candidates: BCHE (butyrylcholinesterase) genotype affects plasma pseudocholinesterase scavenging capacity; carboxylesterase (CES1/CES2) contributes to OP scavenging in some species (large in rodents, minor in humans — relevant to model translation, §15). These are secondary.

Epigenetics / chromosomal abnormalities: Not applicable to the acute syndrome. Some experimental and epidemiological work links chronic/developmental OP exposure to DNA-methylation changes (neurodevelopmental cohorts), but this is not part of the acute poisoning entity.

5. Environmental Information

Environmental / chemical agents (the etiology itself). Representative OP insecticides — with CHEBI suggestions for curation: - Parathion (CHEBI:27928), methyl-parathion, chlorpyrifos (CHEBI:34631), malathion (CHEBI:6651), diazinon (CHEBI:34682), dimethoate (CHEBI:34706), monocrotophos, fenthion, dichlorvos (CHEBI:4498). - Nerve agents: sarin (CHEBI:75701), soman, tabun, VX. - Detoxification/therapeutic chemicals: atropine (CHEBI:16684), pralidoxime (CHEBI:8354), obidoxime, diazepam (CHEBI:49575).

WHO hazard classification (Class Ia/Ib "extremely/highly hazardous") predicts case fatality — the basis for regulatory bans.

Lifestyle factors. Alcohol co-ingestion at the time of self-poisoning worsens outcome; occupational non-use of personal protective equipment increases dermal/inhalational absorption in agricultural workers.

Infectious agents: Not applicable (aspiration pneumonia is a complication, not a cause).

6. Mechanism / Pathophysiology

Causal chain (upstream → downstream):

1. OP absorption and bioactivation. Parent thion OPs (P=S) are metabolized by hepatic cytochrome P450 to the active oxon (P=O) form; PON1 competes by hydrolyzing oxons (detoxification branch). Pathways: KEGG "Metabolism of xenobiotics by cytochrome P450."
2. AChE inhibition (primary lesion). The oxon phosphorylates the catalytic serine of acetylcholinesterase (AChE, ACHES/ACHE; EC 3.1.1.7): "The OP binds to and phosphorylates a nucleophilic serine at the catalytic site of the enzyme" (PMID:37888716). GO terms: GO:0003990 (acetylcholinesterase activity), GO:0004104 (cholinesterase activity), GO:0042135 (neurotransmitter catabolic process).
3. "Aging." The phosphorylated enzyme can undergo dealkylation ("aging"), after which it becomes irreversibly inhibited and no longer reactivatable by oximes — the pharmacological rationale for giving oximes early. Aging half-time is compound-specific (minutes for soman; hours–days for many insecticides).
4. Acetylcholine accumulation → receptor overstimulation. Acetylcholine (CHEBI:15355) accumulates at synapses; overstimulation of muscarinic (CHRM1-5) and nicotinic (CHRNA/CHRNB) acetylcholine receptors. GO: GO:0007271 (synaptic transmission, cholinergic), GO:0007213 (G-protein-coupled acetylcholine receptor signaling). Clinical cholinergic toxidrome results (§3).
5. CNS excitotoxicity. Cholinergic overactivity triggers seizures/status epilepticus; downstream, "the amygdala displays a rapid increase in extracellular glutamate after exposure to soman" — a glutamatergic secondary phase that sustains seizures and neuronal injury even after cholinergic control (PMID:37888716).
6. Calcium overload, mitochondrial dysfunction, oxidative stress. "Excess Ca++ disrupts the function of mitochondria, leading to ATP depletion and oxidative stress"; "oxidative stress and inflammation play an important role in neuronal damage caused by chronic OP exposure." GO: GO:0006954 (inflammatory response), GO:0006979 (response to oxidative stress), GO:0006915 (apoptotic process). This drives neuronal necrosis/apoptosis and long-term brain damage.
7. Respiratory failure (the proximate cause of death). Convergence of bronchorrhea/bronchospasm (muscarinic), diaphragmatic/intercostal weakness (nicotinic neuromuscular block), and central respiratory depression (CNS).

Distinct secondary mechanisms: - Intermediate syndrome (IMS): post-synaptic neuromuscular dysfunction and receptor downregulation from prolonged ACh excess; correlates with sustained AChE inhibition and specific agents (dimethoate, fenthion, monocrotophos). - OPIDN: mechanistically separate — covalent inhibition and "aging" of neuropathy target esterase (NTE / PNPLA6), "localised to the cytoplasmic face of the endoplasmic reticulum," which normally deacylates ER phosphatidylcholine; its inhibition "may perturb the metabolism of important membrane phospholipids," causing distal axonopathy (PMC5548687). Newer work implicates TRPA1 channel activation: "a variety of organophosphates, exemplified by malathion, activates TRPA1 but not other neuronal TRP channels" (Cell Discovery 2017, celldisc201724). GO: GO:0004622-type phospholipase activity; NTE = PNPLA6 (HGNC:16268).

Molecular profiling. Candidate severity biomarkers beyond cholinesterase include serum S100B and amyloid-β (PMC10579114) and creatine phosphokinase (CPK) for muscle involvement (PMC9662705); these are prognostic, not diagnostic.

7. Anatomical Structures Affected

Organ / system level: - Nervous system (primary): central (UBERON:0001017 CNS — brain seizures/excitotoxicity), peripheral/autonomic, neuromuscular junction. - Respiratory system (UBERON:0001004): bronchi (bronchorrhea/bronchospasm), diaphragm (UBERON:0001103) — respiratory failure. - Cardiovascular (UBERON:0004535): brady-/tachyarrhythmia, QT prolongation. - Gastrointestinal (UBERON:0005409): hypersalivation, cramping, diarrhea. - Eye (UBERON:0000970): pupil (miosis via iris sphincter), lacrimal gland (UBERON:0001817). - Exocrine glands: salivary (UBERON:0001044), sweat glands. - Skeletal muscle (UBERON:0001134): fasciculation, weakness, rhabdomyolysis.

Cell types (CL suggestions): - Cholinergic neurons (CL:0000108 cholinergic neuron). - Skeletal muscle fibers / motor endplate (CL:0000188 cell of skeletal muscle). - Peripheral neurons and Schwann cells (CL:0002573) — OPIDN axonopathy. - Bronchial smooth muscle and secretory (goblet) cells; cardiac pacemaker cells.

Subcellular (GO cellular component): synaptic cleft (GO:0043083), neuromuscular junction (GO:0031594), endoplasmic reticulum (GO:0005783 — NTE localization), mitochondria (GO:0005739 — Ca²⁺/oxidative injury).

Localization / lateralization: systemic and bilateral/symmetric; miosis is bilateral; OPIDN is length-dependent and symmetric distal.

8. Temporal Development

Three temporally distinct phases (a hallmark of OP toxicology):

1. Acute cholinergic crisis — onset minutes to a few hours (delayed/prolonged with lipophilic agents like fenthion, which can relapse over days). Duration ~24–72 h; the phase in which most deaths occur.
2. Intermediate syndrome (IMS) — "occurs 24–96 hours after exposure," after apparent recovery from cholinergic signs; proximal/respiratory muscle weakness; "the patient usually recovers within 2 or 3 weeks"; atropine/oxime-unresponsive (PMC5548687). A critical window because respiratory arrest can occur in a conscious, seemingly recovering patient ("type II respiratory failure," Eddleston 2008).
3. OPIDN — delayed, 1–3 weeks (typically ~2 weeks) after exposure; progressive distal sensorimotor neuropathy; recovery partial and slow over months, often incomplete.

Onset pattern: acute for the syndrome overall; subacute/delayed for IMS and OPIDN. Course: episodic/multiphasic rather than continuously progressive. Critical intervention window: the first minutes–hours (decontamination, atropine, early oxime before "aging"); and vigilant monitoring across the 1–4 day IMS window.

9. Inheritance and Population (Epidemiology)

Global burden. OP self-poisoning is a major global health problem. Pesticide self-poisoning overall causes roughly 110,000–168,000 deaths per year; a systematic review estimated "around one in seven of global suicides were due to pesticide self-poisoning" (~110,000/year, 2010–2014). Eddleston et al. attribute "around two-thirds of these deaths — a total of 200,000 a year" to organophosphorus pesticides specifically (PMID:17706760; earlier BJPsych global-response analysis, Gunnell & Eddleston, PMID:16946353 / PMC2493385).

Case fatality. "Medical management is difficult, with case fatality generally more than 15%" and reported ranges of 15–30% in Asian hospital cohorts (Eddleston 2008). Fatality is compound-dependent (dimethoate, fenthion, parathion far more lethal than malathion/chlorpyrifos).

Geographic distribution. Concentrated in rural low- and middle-income countries — South Asia (Sri Lanka, India, Bangladesh), Southeast Asia, China, sub-Saharan Africa, and parts of Central/South America — where highly hazardous OP insecticides are agriculturally available. The Sri Lankan pesticide-ban natural experiment is the landmark demonstration that means restriction cuts population suicide rates (Lancet Global Health, 2017).

Demographics. Male predominance and working-age (roughly 15–45 y) predominance in fatal self-poisoning; a separate pediatric accidental-exposure population exists. Occupational chronic exposure affects agricultural workers of both sexes.

Genetics (host): No inheritance pattern for the disease (it is acquired). PON1 susceptibility alleles follow ordinary Mendelian codominant polymorphism inheritance with ancestry-dependent allele frequencies (see §4). Penetrance/expressivity concepts do not apply to a toxic exposure.

10. Diagnostics

Diagnosis is primarily clinical (exposure history + cholinergic toxidrome), supported by:

Laboratory / biomarkers (LOINC-codable): - Red-cell (erythrocyte) acetylcholinesterase (RBC AChE) — best surrogate for synaptic AChE; "direct measurement of red blood cell acetylcholinesterase activity indicates the degree of toxicity, and sequential measurement could be used to assess treatment response" (PMID:17913691). LOINC ~ "Acetylcholinesterase [Enzymatic activity/volume] in RBC." - Plasma butyrylcholinesterase (BChE / pseudocholinesterase) — "more easily available but may not correlate with severity of poisoning and cannot be used to guide treatment," though useful as an exposure biomarker; "serum cholinesterase can fall to about 40% before any symptoms occur and up to 70–80% before symptoms become severe" (PMID:25189163 / PMC4224972; PMID:17913691). - CPK (muscle injury / severity prediction; PMC9662705); amylase; arterial blood gas (respiratory failure); electrolytes; lactate. - Emerging: S100B, amyloid-β as severity biomarkers (PMC10579114).

Functional / electrophysiology: ECG (bradycardia, QT prolongation, arrhythmia — prognostic); repetitive nerve stimulation / EMG shows decrement-increment and can predict/confirm intermediate syndrome; nerve conduction studies for OPIDN.

Imaging: chest X-ray for aspiration pneumonia/ARDS (a complication, not diagnostic).

Clinical severity criteria: Peradeniya Organophosphorus Poisoning (POP) scale (PMC10336367); POP correlates with mortality, ventilation need, and atropine requirement.

Genetic testing: Not diagnostic. PON1 genotyping is a research/exposure-susceptibility tool, not a clinical diagnostic (GTR lists PON1 assays for research contexts).

Differential diagnosis: carbamate poisoning (same toxidrome, spontaneously reversible carbamylation, oximes usually unnecessary/controversial), nerve-agent exposure, muscarine-containing mushroom poisoning, nicotine toxicity, cholinergic drugs, and non-toxic causes of miosis/coma (opioids — miosis but no SLUDGE, no bronchorrhea).

11. Outcome / Prognosis

Mortality. Case fatality 15–30% in resource-limited cohorts, dominated by early respiratory failure and later IMS-related respiratory arrest, aspiration pneumonia, and ARDS (§9). Death is driven by agent lethality, ingested dose, time-to-treatment, and access to ICU ventilation.

Prognostic factors: ingested compound (dimethoate/fenthion/parathion worst), POP severity score, depth/duration of cholinesterase inhibition, GCS/coma at presentation, need for intubation, hypotension, and time to atropinization. Elevated CPK and persistent low RBC AChE predict complicated courses.

Morbidity in survivors: - Intermediate syndrome — prolonged ventilation, ICU complications; usually recovers over 2–3 weeks. - OPIDN — distal weakness/sensory loss with slow, often incomplete recovery; long-term disability. - COPIND / neuropsychiatric sequelae — persistent cognitive impairment, depression, anxiety, EEG changes after severe/repeated exposure. - Anoxic brain injury from prolonged seizures/respiratory failure.

Recovery potential: with prompt aggressive supportive care (early intubation, adequate atropinization) survival is good for many insecticides; nerve agents and the most lethal insecticides carry high mortality despite treatment.

12. Treatment

Management rests on decontamination + resuscitation + antidotes (atropine, oxime, benzodiazepine) — MAXO suggestions noted.

Immediate / supportive (MAXO:0000950 supportive care): airway protection and early intubation/mechanical ventilation for respiratory failure/secretions (MAXO for mechanical ventilation / oxygen administration); IV access, fluids; skin/GI decontamination (remove clothing, wash skin; activated charcoal if early and airway protected). Staff PPE to prevent secondary contamination.

Antidotes (pharmacotherapy — MAXO:0000058 / administration of drug):

1. Atropine (CHEBI:16684) — competitive muscarinic antagonist; the mainstay, benefit well established. Give by doubling-dose titration: "a regimen of doubling doses, with the aim of raising the pulse above 80 beats per minute and systolic blood pressure above 80 mm Hg," continuing "until the heart rate is more than 80 bpm, the systolic BP is more than 80 mm Hg, and the chest is clear" (Eddleston 2008, PMID:17706760; doubling-dose vs ad hoc comparison PMID:18784205). Does not treat nicotinic (muscle weakness) effects. Watch for atropine toxicity (agitation, hyperthermia, ileus).
2. Oximes — pralidoxime (CHEBI:8354) / obidoxime — reactivate phosphorylated AChE before aging. WHO regimen: "pralidoxime chloride 2 g IV over 20–30 min, follow with an infusion of pralidoxime 0.5–1 g/h" (Eddleston 2008). Efficacy is genuinely uncertain: a Cochrane review concluded current evidence is insufficient to show benefit or harm and does not support the WHO regimen; a 2020 meta-analysis of RCTs found "the risk of mortality and the need for ventilator support were not significantly different," with "a significant increase in the incidence of intermediate syndrome in the pralidoxime group" — "pralidoxime was not shown to be beneficial" (PMID:32257715 / PMC7117609; earlier systematic review PMID:11978898). Curate this as a genuine evidence controversy (SUPPORT vs REFUTE evidence items).
3. Benzodiazepine — diazepam (CHEBI:49575) — for seizures/agitation and neuroprotection: "Acutely agitated patients will benefit from treatment with diazepam" (Eddleston 2008); first-line for OP/nerve-agent seizures (with midazolam increasingly preferred pre-hospital).

Pharmacogenomics: PON1 status influences endogenous detoxification (§4) but is not yet used to guide antidote dosing.

Experimental / investigational therapies: novel reactivators (e.g., experimental oxime K027 vs pralidoxime/obidoxime, PMC6547910), CNS-penetrant oxime prodrugs, bioscavengers (recombinant/plasma-derived butyrylcholinesterase as a stoichiometric scavenger), magnesium sulfate and clonidine as adjuncts, lipid emulsion, and — for nerve-agent neuroprotection — the Src-kinase inhibitor saracatinib (soman model, PMC12270223). Search ClinicalTrials.gov for active adjunct trials (magnesium, sodium bicarbonate, fresh frozen plasma/BChE).

Treatment algorithm summary: decontaminate → secure airway/ventilate → atropine titrated to secretions/HR/BP → oxime early (per local protocol, acknowledging weak evidence) → benzodiazepine for seizures → ICU monitoring for intermediate syndrome across days 1–4 → rehabilitation for OPIDN.

13. Prevention

Primary prevention (the highest-impact lever): - Regulatory bans of highly hazardous OP pesticides — WHO-endorsed; Sri Lanka's staged bans produced large national declines in suicide with negligible agricultural cost (Lancet Global Health 2017). This population-level means restriction is the single most effective intervention. - Safer formulations, dilution, and secure household/community storage (lockboxes). - Occupational: PPE, closed application systems, worker training, exposure limits (EPA/WHO).

Secondary prevention: occupational cholinesterase surveillance of pesticide handlers (baseline + periodic RBC AChE/BChE; remove from exposure at defined depression thresholds — "cholinesterase depression among pesticide handlers," PMID:25189163); early recognition and rapid treatment of exposures.

Tertiary prevention: ICU monitoring to preempt IMS respiratory arrest; rehabilitation for OPIDN; psychiatric follow-up and safety planning for self-poisoning survivors to prevent repetition.

Public-health / behavioral: integrated suicide-prevention (means restriction remains dominant over individual counseling given impulsivity), agricultural extension education, and poison-center infrastructure. Immunization/prophylaxis: for anticipated nerve-agent exposure only, military pretreatment with pyridostigmine (reversible carbamate that shields a fraction of AChE) plus auto-injector atropine/oxime kits — not applicable to civilian insecticide poisoning.

14. Other Species / Natural Disease

• Taxonomy affected: OPs are toxic across vertebrates and invertebrates (the insecticidal target is homologous insect AChE). Mammals studied include mouse (NCBITaxon:10090), rat (NCBITaxon:10116), guinea pig (NCBITaxon:10141), and non-human primates; birds and fish are ecotoxicologically important.
• Veterinary relevance: OP/carbamate toxicosis is a common companion-animal and livestock poisoning (dogs, cats, cattle, horses) from flea/tick products, dips, and agricultural exposure — same cholinergic toxidrome, treated with atropine ± pralidoxime. OMIA is not the relevant resource (no Mendelian trait); veterinary toxicology literature and VetCompass cover incidence.
• Comparative biology: the AChE mechanism is deeply evolutionarily conserved (single active-site serine across taxa), which is why OPs are broad-spectrum. A key cross-species caveat: rodents express high plasma carboxylesterase that scavenges OPs, conferring protection humans lack — a major translational confounder (§15).
• Cross-species susceptibility differences track carboxylesterase levels, PON1 orthologs, and body-size/dosing; guinea pigs (low carboxylesterase) better model human nerve-agent responses than rats/mice.
• Zoonotic/transmission: Not applicable (non-communicable toxic exposure).

15. Model Organisms

• Guinea pig (NCBITaxon:10141): historically preferred for nerve-agent/OP work because low plasma carboxylesterase mimics human pharmacokinetics; toxicity is "sex- and age-dependent and cannot be solely accounted for by acetylcholinesterase inhibition" (PMC2630363).
• Rat (NCBITaxon:10116): widely used for seizure/EEG, respiratory, and countermeasure studies (anesthetized-rat EEG/respiratory assays); confounded by high carboxylesterase.
• Genetically humanized mice (KIKO): a modern model — "a novel genetically modified mouse strain (KIKO) with nonfunctional serum carboxylesterase (Es1 KO) and an altered AChE gene expressing the human form (AChE KI)" — engineered to remove the rodent carboxylesterase scavenging confounder and express human-sequence AChE, improving translation for soman/nerve-agent countermeasure testing (PMC7918218; MALDI-MSI characterization PMC11172367).
• Model types available: knock-in (human AChE), knockout (Es1/serum carboxylesterase), and induced (agent-dosed) models. Resources: MGI, IMPC, IMSR.
• Phenotype recapitulation: models reproduce cholinergic crisis, seizures/status epilepticus, and respiratory failure, and support antidote/neuroprotectant screening (e.g., saracatinib in soman-poisoned models, PMC12270223; physostigmine adjunct in soman guinea pig, PMC3043258).
• Limitations: rodent carboxylesterase overprotection; species differences in oxime pharmacokinetics and in the human-specific chronicity of IMS/COPIND; nerve-agent models may not fully capture insecticide self-poisoning kinetics (huge ingested doses, slow absorption, prolonged redistribution of lipophilic agents).

Curation Notes & Ontology Cross-Reference Summary

• Nature of entry: environmental/toxic exposure syndrome — populate pathophysiology around AChE inhibition; treat PON1 as a SUSCEPTIBILITY/MODIFIER gene, not a causal gene; do not add inheritance blocks for the disease itself.
• Key genes: ACHE (HGNC:108), BCHE (HGNC:983), PON1 (HGNC:9204), PNPLA6/NTE (HGNC:16268).
• Key GO: GO:0003990 (acetylcholinesterase activity), GO:0007271 (cholinergic synaptic transmission), GO:0007213 (GPCR ACh receptor signaling), GO:0006979 (oxidative stress response), GO:0006954 (inflammation).
• Key CHEBI: acetylcholine (CHEBI:15355), atropine (CHEBI:16684), pralidoxime (CHEBI:8354), diazepam (CHEBI:49575), chlorpyrifos (CHEBI:34631), parathion (CHEBI:27928), sarin (CHEBI:75701).
• Key MAXO: supportive care (MAXO:0000950), pharmacotherapy/drug administration, mechanical ventilation, dietary/GI decontamination.
• Evidence controversy to encode explicitly: oxime/pralidoxime efficacy — pair a SUPPORT item (mechanistic reactivation rationale) with REFUTE/PARTIAL items from the 2020 RCT meta-analysis (PMID:32257715) and Cochrane review.

Primary Sources (verify each PMID with just fetch-reference before quoting in YAML)

Verification reminder for KB ingestion: every snippet above is drawn from search-surfaced abstracts/reviews; before committing any of these as evidence items, run just fetch-reference PMID:XXXX and confirm each snippet is an exact substring of the fetched abstract (per the dismech anti-hallucination SOP), and validate all HP/GO/CL/CHEBI/UBERON/MAXO term IDs and labels with just validate-terms-file. The oxime-efficacy claim in particular should be curated as a genuine SUPPORT-vs-REFUTE controversy, not a settled recommendation.

Sources: - Mechanisms of Organophosphate Toxicity and the Role of Acetylcholinesterase Inhibition (Toxics 2023) · PubMed - Management of acute organophosphorus pesticide poisoning (Lancet 2008 / PMC) · PubMed - Efficacy of Pralidoxime: Systematic Review & Meta-analysis (2020) - Oximes in acute OP pesticide poisoning: systematic review (2002) - Deaths from pesticide poisoning: a global response (BJPsych 2006) - Novel Clinical Toxicology and Pharmacology of OP Insecticide Self-Poisoning (Annu Rev) - PON1 as a genetic determinant of susceptibility to OP toxicity · PON1 Q192R/L55M meta-analysis - Blood AChE and BChE as biomarkers among pesticide handlers · RBC AChE and plasma BChE status - Delayed Polyneuropathy Induced by OP Poisoning (OPIDN) · TRPA1 mediates OPIDN (Cell Discovery) - Peradeniya OP Poisoning Scale assessment - Doubling doses vs ad hoc atropinization (2008) - KIKO humanized mouse model of soman toxicity · Guinea pig OP toxicity model - Organophosphate Toxicity — StatPearls

This report is ready to seed a dismech Organophosphate_Poisoning.yaml entry. The two most important curation cautions: treat it as a toxic-exposure entry (PON1 = susceptibility modifier, no causal gene/inheritance), and encode the oxime efficacy uncertainty as competing evidence rather than a recommendation.