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Trematode (fluke, distoma)
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pathogen
- Burkholderia pseudomallei
- potential biological weapon
epidemiology
- endemic South Asia, Southeastern Asia and Australia
- especially in Northeastern Thailand and Northern Australia
- Third ID death in Northeaster Thailand following after HIV and TB
- reason of localized distributions are unknown
- highly seasonal, most in rainy season
- stormy weather events like typhoon
transmission
- Burkholderia pseudomallei lives in soil and water
- close and repetitive contact to soil and freshwater, especially occupationally
- rice farmers in Thailand, Aboriginals in Australia
- most of cases unclear contact history
- immersion in freshwater or aspiration of freshwater like in tsunami may cause infection
- outbreak case mediated by contaminated water supply, disinfectant or detergents
incubation period
- 1-21 days after apparent exposure
- rarely long latency
- a case of 62 years after exposed in Viet Nam
- keep latent in macrophage for long time
- rational of long-term maintenance oral treatment
- where Burkholderia-containing macrophages are kept in human body is still unknown
risk factors
- 60-90% of cases have underlying conditions
- especially diabetes mellitus and chronic renal failure
- steroid, alcohol abuse, liver dysfunction, chronic lung disease, etc.
- HIV never predisposes to melioidosis
clinical course
- peak in 40-60 y/o
- male > female, presumably difference of exposure activity
- most asymptomatic or mild non-specific
- 60-70% of endemic area population show seroconversion until 4 y/o
- apparent case shows sepsis with fever and rigor
- 80% of apparent cases have pneumonia
- widespread consolidations or cavitations
- altered mental status
- jaundice
- diarrhea
- widespread metastatic abscesses
- liver, spleen, parotid gland, prostate in male, cutaneous, subcutaneous, keratitis
- parotitis/parotid abscess common in children in Thailand
- in endemic areas, melioidosis is the commonest cause of children's suppurative parotits
- hepatosplenic abscess common in Thailand
- prostatic abscess common in Australia
diagnosis
- Culture only
- oxidase positive gram negative rods resistant to aminoglycosides but susceptible to co-amoxiclav should be assumed as B. pseudomallei until proven otherwise
- serological or molecular test have low sensitivity and low specificity
- unevenly stained gram negative bipolar bacilli
treatment
- 2 weeks intensive parenteral antimicrobial
- ceftazidime or meropenem IV
- 12-20 weeks eradicative oral antimicrobial
- co-trimoxazole or co-amoxicluv PO
prognosis
- mortality of severe mellioidosis 40% in Thailand, 14% in Australia
- deaths within 48hrs after hospitalization common
- less mortal without underlying condition
- treatment response slow
- reinfection in 1-3.4% of survivors in long-term followup