Flashcards in Worms and Hygiene Deck (23)
What are the symptoms of Enterobius vermicularis infection? What is its common name? 22:10
- Intense anal itching (pruritus; particularly at night, adult female lays up to 10,000 eggs in irritant mucus around anus; viable for up to 20 days)
- Long term infestation
What is the prevalence of Enterobius vermicularis infection in the UK? How is it transmitted?
- Most common nematode (roundworm - phylum) in the UK
- Affects up to 20% of children < 10 years
- Transmitted by faecal-oral infection, ingestion from contaminated linen or retro-infection (larvae crawl back up into colon)
What complications may arise from Enterobius vermicularis infection?
- Scratching can lead to excoriation (wearing off skin); risk of secondary infection
- Vulvitis; when worms transferred to the vagina/urethra; can result in severe pelvic inflammatory disease w/Enterobius infection and secondary E. coli infection
What are the long-term symptoms of untreated Enterobius vermicularis?
Persistent infestation can lead to:
- Loss of appetite
- Weight loss
- Cause of nocturnal enuresis (nocturnal bed-wetting) in children
What is the non-pharmacological approach to treating E. vermicularis?
- High standards of hygiene (sufficient if continued for several weeks)
- Washing bed sheets and clothes
- Vacuuming and damp dusting of surfaces
- Basic hand-washing hygiene/etiquette (inc. under nails)
- Wearing tight-fitting undergarments prevents scratching/cotton gloves
- Bathing every morning after waking up reduces re-infestation rates
What is the pharmacological management of E. vermicularis?
Mebendazole (everyone > 2 years)
- Single dose, with a second after two weeks (reinfection common)
- Does not kill eggs; use along w/hygiene measures
- Max. 8 x 100g chewable tablets to be sold at one time (Ovex)
What are the symptoms of Strongyloides stercoralis infection?
Also known as threadworm (dumb af; call E. vermicularis pinworm then)
- Pruritus 'larva currens'; larvae burrow through skin causing pruritus around feet and toes. Migrate via venous circulation to lungs; can cause pneumonitis (Loffler's syndrome, like Ascaris lumbricoides), then expectorated into the pharynx, swallowed and excreted via colon.
- Cutaneous, GI and pulmonary symptoms too maybe but no problems in > 60% of cases
>>> Can lead to Hyperinfestation; widespread dissemination of larvae, leading to systemic organ failure (together w/bacterial sepsis; usually only in immunocompromised e.g. chemotherapy
How prevalent is Strongyloides stercoralis? How is it transmitted?
- Not endemic in UK
- Picked up from travel abroad; prevalent (up to 20%) in sub-Saharan Africa, S. America, SE Asia (poor sanitation, or where human excrement used routinely as fertiliser
- Worms exist in soil as free-living worm, or parasitic filariform larvae; picked up by walking barefoot in soil
What is the pharmacological treatment for Strongyloides stercoralis infection? What adjuvant measures are there?
Post-referral to infectious diseases specialist:
- Ivermectin (Stromectol); only availible via special order manufacturers (unlicensed)
- Two doses administered 2 weeks apart (although not shown to be more efficacious than single dose)
- Covers 3-4 week period of larval maturation, reducing potential auto-reinfection
>>> Combine w/wearing shoes, avoiding walking in insanitary areas
How is hyperinfestation syndrome treated in Strongyloides stercoralis infection?
- Combination of daily ivermectin (2 weeks) and antibiotics to treat associated gram -ve bacterial infection, and intensive care support (multiple organ failure)
- Mortality still high w/treatment though
- Parenteral ivermectin sometimes given; but only availible as unlicensed veterinary formulation
What are the symptoms of Taenia saginata infection?
Taeniasis (usually asymptomatic):
- GI disturbances; abdominal discomfort, diarrhoea, loss of appetite and emaciation
- Anal pruritus when proglottids excreted
- Can reach 17m (small intestines ideal environment o accommodate)
What could infection with the pig tapeworm, Taenia solium lead to?
Cysticercosis; ingesting eggs/proglottids instead of cysts
- Human becomes intermediate host for parasite
- Worm can migrate to lungs etc., even neurocysticercosis (migration to brain); causing headache, seizures, meningitis and death.
How is Taenia spp. infection treated?
- Avoid raw meat (especially abroad)
- Personal hygiene; avoid reinfection w/eggs
- Broad-spectrum anthelminthic; praziquantel or niclosamide
- Available on named-patient basis only
- Co-prescribed with laxative (help remove head scolex) and antiemetic (stopping reinfection by vomiting and re-ingesting proglottids)
What is the hygiene hypothesis?
- Lower incidence of infection in early childhood = rapid 20th century rise in allergic diseases e.g. asthma/hayfever (allergic triad)
- Protective effects of large families and certain environments e.g. farms
>>> Stimulation of body's immune defences
What is the 'old friends' hypothesis?
- Immune stimulation part of evolutionary development; early commensal organisms (inc. parasites) may be more important than chickenpox in childhood etc.
> Microbial diversity theory that gut flora is key for priming and regulating immune system in pregnancy and breast feeding
What has been the result of losing the symbiotic relationship between parasites and viruses?
- Autoimmune and immunologically mediated disease (linked to cancers e.g. ALL, and autism)
>>> Parasites help down-regulate immune system through T-cells; protective benefit for parasite, potential positive benefit for humans.
What is disease modification and what morbidities could be helped?
- Moderate hookworm infections have beneficial effects on hosts suffering from diseases linked to overactive immune systems e.g asthma and allergy
- Small subset of people in Ethiopia infected with hookworm were half as likely to experience asthma or hayfever
- Potential benefits hypothesised for asthma, MS, Crohn's disease and Type 1 DM.
What are the aims of hookworm vaccines?
- Targets hookworm proteins Na-GST-1 and NA-APR-1
- To prevent severe hookworm in < 10 years, reduce anemia, cognitive and growth retardation
What is good personal hygiene? Why does it matter?
Important to avoid infestation (faecal-oral transmission):
- Hands; washed thoroughly in soap and water before and after handling/preparing food, before eating, after toilet/close contact w/animals
- Pets; dogs to be thoroughly de-wormed, avoid feeding w/raw meet or offal
How do UK regulations ensure environmental hygiene?
- Governing of human/animal sewage treatment and disposal; prevent contaminating rivers, freshwater
- Reduces likelihood of animals such as cows/sheep coming into contact w/contaminated pasture (breaks parasite life cycle); though concerns after widespread flooding
What standard of food hygiene should be generally maintained?
- Pork/beef/fish; cook thoroughly to kill eggs and larvae
- Freeing meat and fish; below -10ºC for > 48 hours kills tapeworm eggs and larvae, but thorough cooking/reheating still recommended
- Pickling; MAY kill fish tapeworm larvae/eggs
- Food hygiene v. important when travelling
What food inspection standards are maintained by the Food Standards Agency for meat?
Inspection at all stages in:
- Cutting premises
- Meat products premises