Inter-relationship of Host and Environment
· 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
·
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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