pubhtlh 264 - week 4: food, mercury, & health

food-borne diseases

illness caused by injection of contaminated food

outbreak

• 2 or more cases of a similar illness among individuals who have had a common exposure

• Critical components of defintion

  • Same diagnosis or symptoms and signs suggestive of same illness

  • Clear association between cases, with or without a recognized common source

Under-Reporting Problem for FBDO

• Only a fraction of FBDOs are routinely reposted

  • Most household infections are not recognized or reported by people, doctors, or labs

  • Same pathogens in water and person-to-person (hard to pinpoint source

  • pathogens are unidentifiable

  • Passive surveillance system (waits for report than hunting for it)

  • Outbreaks that are most likely to be brought to the attention of public health authorities include those that are large or that can cause serious harm

Foodborne Diseases Pyramid - Passive Surveillance (top to bottom)

• surveillance

• lab survey

• physician survey

• pop survey

foodborne viruses

• Norovirus

• Hepatitis A

• Rotavirus

type of food hazards

• Naturally-occuring

• Added interntionally

  • farming practices (animals - antibiotics & growth hormones & vegetables/fruits - pesticides)

  • Food processing” food processing: food preservatives and other additives

• Added non-intentionally: e.g. bioaccumulation of pesticides, persistent lipohoic organic contaminants, and heavy metals in dish meat & mother’s breast milk

major chemical hazards associated with FBDOs in the U.S.

• Scombroid toxin/histamine

• Ciguatoxin

• Mycotoxins

• Control of Food-borne Disease

• from farm to table approach (shared responsbility along the supply chain)

  • Implementation analysis of good manufacturing practice & hazardous analysis critical control points

outbreack investigation steps

• confirm outbreak

  • establish baseline

  • verify the diagnosis

  • rule out other causes

• describe the outbreak

  • case definition

  • search for cases (time, place, person)

• determine the cause

  • hypothesis

  • chose a study design

  • environmental investigation

• implement control measures

  • immediate action

  • intervention types

  • monitoring

• communication & conclusion

  • public & internal updates

  • declare end of outbreak

Elemental mercury and pathways

• Elemental merury

  • heavy, silver-grey, metal; liquid at room temperature

  • Conducts electricity & mixed easily with other metals

• Elemental mercury exposure pathways

  • Respiratory: easily absorbed into bloodstream & crosses blood brain barrier

  • Skin & gastrointestinal: minimal

inorganic mercury & pathways

• Inorganic mercury

  • Mercurous, Hg1+ ot mercuric, Hg2+

  • Oxifixed mercury that combine with other chemicals elements to create salt forms

• Inorganic mercury exposure pathways

  • Gastrointestinal

  • Skin: poor systemic absorption unless exposed to large amounts

health effect of inorganic mercury

pink disease (acrodynie)

types of organic mercury

• Methylmercury

  • Used as a crop fungicide

  • Ubiquitous in envrionment since microorganism methylate elemental

• Ethylmercury

  • Thimerosal (C9H9HgNaO2S; 49% mercury by weight) used as an antisepticl/antifungal and vaccine preservative

• Phenylmercury

  • As persercative in paints and as disinfectant

accumulation of Methymercury in Fish

inorganic or elemental mercury —> biotransformation —> organic methylmercury —> bioaccumulation —> fish

• organic methylmercury binds to protein or meat of fish and cannot be removed by cooking or cleaning

organic mercury poisoning - minamata disease, japan, 1950s

• Seafood from the bay w/ mercury from an industrial source, many cases of neurotoxicity

• Most striking was the vulnerability of the fetal brain to mercury toxicity shown by the high rate of cerebral palsy in children born during this period

Minamata Disease - Fetal Effects

• Cerebral palsy

• Abnormal reflexed, involuntary movements

• Mental retardation in infants

• Developmental delays - some didn’t walk until age 7

Minamata Disease - Adults

• Parenthesis-numbness “pins & needles”

• Cerebellar ataxis, tremors, convulsions

• Constriction of visual fields, loss of smell

• Loss of hearing, dizziness, insomnia

• Speech disorder

• Cognitive impairment, such as inattention, excitement, hallucinosis, loss of intelligence

lifelong effects of organic mercury (MeHg)

• severe neurodevelopmental delays

• cognitive deficits (memory/attention)

• motor dysfunction (tremors, ataxia)

• vision/hearing loss

• cardiovascular issues

planting seed w/ organic mercury (MeHg)

The Incident: Iraq Grain Poisoning

• Seed grain (intended for planting, not eating) was treated with methylmercury as an antifungal agent to prevent rot in the soil.

• Failure of Risk Communication:

  • Language Barrier: The warning labels on the sacks were written in English and Spanish, which the local population did not understand.

  • Cultural Misinterpretation: The "Skull and Crossbones" symbol, widely recognized as "poison" in Western cultures, held no specific meaning or warning value in the Arab world at that time.

  • The Red Dye False Security: A red dye was added to the grain as a visual warning; however, people believed the poison was the dye itself. When they washed the grain and the water ran clear, they mistakenly thought they had "washed out" the poison.

Thimerosal (ethyl mercury; EtHg) in vaccine

• exceeded EPA recs in vaccine b/w 1930-march 2001

  • Since march 2001 all vaccines available thimerosal free

• The EPA guideline is based on prenatal exposure to methyl/mercury (MeHg) rather than postnatal exposure to EtHg

  • Prenatal exposure to MeHg is associated with neurodevelopmental abnormalities

  • EtHg and MeHg are structurally related chemicals. But more rapid excretion and low blood levels of EtHg were observed in experimental studies

Vaccine Theory

• 1998 Wakefield case of MMR association w/ gastrointestinal symptoms, autistic regression

• No evidence for a decrease in autism despite the exclusion fo thimerosal from nearly all childhood vacciens since 2001

fish & methylmercury (MeHg)

• fish is main source of exposure to MeHg

• Levels can also be high in predatory freshwater fish, such as pike, perch, tilapia

• typically about 0.05 to 1.4 ppm in fish

mercury recommendation - 2004 EPA/FDA

• Advices to avoiding harm to fetus and young children

  • Do not eat shark, swordfish, king mackerel, tilefish

  • Eat up to 12 oz (2 average meals) or a variety of fish and shellfish that are lower in mercury

  • For recreationally-caught fish…checl local advisories

  • Eat up to 6 oz of albacore/white tuna per week, and on other fish in the same week

Mercury Recommendation - 2008 EPA/FDA

• Benefits of seafood outweigh the health risks and that most people should eat more fish, even if they contain mercury

• For most people, the risk from mercury by eating fish and shellfish is not a health concern

• Pregnant women don’t eat enough fish

Mercury Recommendation - 2015 EPA/FDA

• pregnant women should consume 8-12 oz of seafood

• pregenant/breastfeeding & children should awais fish high in MeHg

Mercury Recommendation - 2019 EPA/FDA

• 8 oz of seafood for children per week

• 8-12 of seafood for pregnant/breastfeeding low in mercury