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Chapter: Medicine Study Notes : Public Health

Inter-relationship of Host and Environment

Lifecycle: plasmodia in human blood -> mosquito sucks blood -> migrate into mosquito saliva glands -> passed on in next bite

Inter-relationship of Host and Environment


 


Malaria

 

·        Background: 

o   Lifecycle: plasmodia in human blood ® mosquito sucks blood ® migrate into mosquito saliva glands ® passed on in next bite 

o   Host factors: 

§  Sickle cell anaemia ® ¯contagious

§  Immunocompromised: kids, malnourished, concurrent infection, maybe AIDS

o   Pathogen factors: which strain

o   Vector attributes: right species of mosquito


·        Interventions:

o   Vector – Host relationship: Interrupt exposure eg nets, repellent, clothing

o   Host: general health, nutrition

o   Host – Pathogen relationship: chemoprophylaxis 

o   Pathogen: Air-conditioning ® ¯temp ® ¯plasmodium

o   Pathogen – Vector relationship: Remove infected hosts (ie cure them)

o   Vector: source reduction (spray, ¯water traps)


·        Effect of the environment:

o   Vector: if warm and wet breed faster

o   Host: if hot take clothes off and open windows


·        Pathogen: plasmodium replicated faster if warmer


Yellow Fever

 

·        Swotted for Public Health Test Question.  Source: Harrison‟s and CDC Website


·        Haemorrhagic fever with prominent hepatic necrosis

 

·        Incidence declining since the turn of the century. Outbreaks mainly now only in West Africa. South America also at risk


·        Urban Yellow Fever:

o  Spread by Aedes Aegytpi mosquito

o  Human – mosquito – human cycle.  Mosquitoes pass it to their offspring via ovary infection 

o  Deposit eggs in any container with water in or around homes (so can still get it if low rainfall or dry season) Þ women and children more at risk if they‟re around home a lot


·        Sylvatic Yellow Fever:

o  Mosquitoes infected from viraemic monkeys (monkey‟s don‟t get ill so are a continuing reservoir) 

o  Infects humans in or living around forests Þ men who do the hunting more at risk


·        Prevention (in addition to Malaria factors above): 

o  Put bed nets over infected people – stops onward transmission of infected people. They are viraemic for 3 – 6 days, following a 3 – 6 day incubation period.

o  Treatment is supportive only.  There is no chemoprophylaxis

o  Vaccination:

§  Safe, lasts for 10 years

§  Only vaccinate child < 12 months and pregnant women if high risk 

o  Epidemics occur if poor maintenance of vaccination and lack of plans for detection and response to epidemics

 

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Medicine Study Notes : Public Health : Inter-relationship of Host and Environment |


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