MICRO: Global health priorities and brain worms Flashcards
What did the Alma Ata Declaration 1978 reinstate?
Reinstated the definition of health: a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity
What two factors does DALY encompass?
Morbidity and mortality
DALY = YLL + YLD
DALY = disability adjusted life years
- YLL= No of deaths * standard life expectancy at time of death - years of life lost
- YLD=No of incident cases * disability weight * average duration of case
Years of life lost due to premature mortality (YLLs)
Years of healthy life lost due to disability (YLDs)
What does 1 DALY mean?
1 DALY = 1 lost year of full healthy life lost
DALY vs QALY
DALY - thought of as years lost
QALY - thought of as years gained
What is a QALY?
- Measure of disease burden
- Includes both quantity and quality of life lived
- Used in assessing the value of a medical intervention
- Based upon the number of years of life that would be added by the intervention
What is 1 QALY?
A year in the hypothetical state of “perfect health” is worth 1 QALY.
Being deceased is worth 0 QALYs.
Other health states fall between 0 to 1
How are standard and new treatments compared in terms of benefit to the quality of life?
Patients receiving standard treatment will live for 1 year and quality of life will be 0.4 (0 = worst possible health/death, 1= perfect health)
Patients receiving new drug will live for 1 year 3 months (1.25 years), with a quality of life of 0.6.
The new treatment is compared with standard care in terms of the QALYs gained:
- Standard treatment: 1 (year’s extra life) x 0.4 = 0.4 QALY
- New treatment: 1.25 (1 year, 3 months extra life) x 0.6 = 0.75 QALY
Therefore, the new treatment leads to 0.35 additional QALYs (that is: 0.75 -0.4 QALY = 0.35 QALYs).
The cost of the new drug is assumed to be $10,000, standard treatment costs $3000.
The difference in treatment costs ($7000) is divided by the QALYs gained (0.35) to calculate the cost per QALY. The new treatment would cost $20,000 per QALY.
Why is QALY debated?
- What is perfect health? Not patient-centric
- There may be a health state worse than death
Case:
- 42 year old man originally from Ecuador
- 1 month occipital headache
- 3 generalised tonic-clonic seizures, spontaneous recovery
- 1 previous seizure in Ecuador 1985, no medications
- Works as a cleaner
- Lives with wife & 3 sons, 1 of whom has epilepsy (age 19)
- 5 cigarettes/week, occasional alcohol
Cystic lesion seen below.
Calcification is also seen (reverse) in the brain.
Cyst + calcification = Taenia solium cysticercosis
How would we manage this patient?
Epilepsy
- Anticonvulsants - phenytoin
- Advised not to drive
Cerebral inflammation and oedema
- Corticosteroids - dexamethasone
Kill viable cysticerci
- Cestocidal drugs - albendazole
Family screening
What is the source of Taenia solium cysticercosis?
Pork tapeworm larvae - common in all non-Muslim developing countries
What is Taenia solium cysticercosis often misdiagnosed as?
Commonest cause of adult-onset epilepsy in many countries, causes 20-30% of adult-onset epilepsy in Peru
What two tapeworms can cause intestinal infection/taeniasis in humans? How severe is taniasis?
- Intestinal infection with adult stage of large tapeworms
- T. solium
- T. saginata
- Generally non-fatal - usually asymptomatic, may live for many years and grow up to 30m.
- Eggs released intermittently - need 3 stool microscopies
What tapeworm causes cysticercosis? How severe is the infection?
Tissue infection with larval stage of T. solium
- Serious disease that usually involves the CNS. Infection may be fatal
How do pig get infected with porcine cysticercosis? What type of Taenia solium infection is caused by eating infected under-cooked pork?
Pig infection by:
- Pigs ingest tapeworm eggs in human faeces
- Parasites migrate to tissues & encyst - measly pork (“measly” = cystic)
Humans eating pigs only causes intestinal tapeworms.
Describe the life cycle of Taenia solium infections.
It is caught from other humans (faeces/GI spread) and cysticercosis is a dead end for the spread of the disease
What is the route of infection for human cysticercosis?
Ingestion of tapeworm eggs - in food contaminated with faeces
Usually travelling in non-Muslim areas
So vegetarians and meat eaters can all be affected
What sites are infected by cysticercosis?
ALL tissues in the body can be affecte (incl. muscle and heart, BRAIN)
Still a possible cause if it is endemic in the area where you live, despite you being vegan/vegetarian/never eating pork
What are the clinical features of neurocysticercosis?
Brain cysticerci are the most frequent cause of symptomatic disease
Clinical features depend on the immune response, number & site of cysts e.g.
- 65% epilepsy
- 24% raised intra-cranial pressure
- 22% headache
- 14% altered mental state
- Also stroke, blindness, spinal disease
How do neurocysticercosis parasites survive in the body?
Evade and suppress inflammation by…
- Sequestration/fibrous encapsulation
- Concomitant immunity
- Molecular mimicry/masking
- Modulation of host immunity
What is likely to be happening if you get symptoms with neurocysticercosis?
- Usually, living cysts are asymptomatic
- Symptoms mark cyst degeneration
- Associated with eosinophilic cellular influx
Death of cyst causes symptoms
What is the management of neurocysticercosis?
Anticonvulsant therapy e.g. phenytoin
Ventriculo-peritoneal shunt (if hydrocephalus occurs)
Cestocidal drugs (albendazole or praziquantel)
- Accelerate disappearance of viable cysticerci
- Cause transient inflammation around viable cysticerci
- Randomised trials suggest clinical benefit
Steroids for inflammation around dying cysts before / during / after treatment
- Partial effect for cyst degeneration/cestocidal therapy
- Inadequate for: chronic granulomatous inflammation
- Heavy infections – cestocidal therapy without steroids may be fatal
What caution should be taken when using anti-parasitic drugs for severe cysticercosis?
There may be a transient exacerbation - steroids should be added in severe cases to reduce inflammation (cestocidal therapy without steroids may be fatal)
What is a simple intervention used to reduce cysticercosis in developing countries?
Rice growth - pigs will go into these instead of eating human faeces
What causes taeniasis vs cysticercosis?
Taeniasis - ingestion of cysticerci in infected meat
Cysticercosis - ingestion of T. solium eggs by ingesting foods contaminated with faeces
