16 Malaria Elimination

Is it reasonable to set a goal of malaria elimination?

In most of africa, population mostly sits in hyperendemic and mesoendemic areas (2/3 of population)

In areas of less malaria transmission, its older people getting malaria, but total numbers of severe malaria are less.

In areas with epidemic area, you go from almost no cases to super high cases with an outbreak.

16.1 Why is there so much malaria in africa, but not in India or South America?

Sri Lanka eliminates malaria - 2016 Population 22 million, rural, GDP $3000 (middle income), mix of endemic and epidemic

  • In 1935 there was a population that killed 1.5% population
  • 1945 took up indoor residual spraying
  • 1958 WHO eradication programme
  • 1963 only 17 cases
  • 1964 IRS scaled back
  • 1967 1.5 million cases
  • 1983-2009 civil war
  • 1999 WHO support integrated control programme
  • 2012 last indigneous case
  • 2016 confirmed gone

16.2 Definitions

Eradication = gone forever, everywhere

Elimination = either gone for now in one place, or at very very low and stable levels

Control = limiting the number of caases

EIR = number of infected bites / year PPR CAR (clincal attack rate)

Basic Case Reproductive Rate (R0) - number of secondary cases arising from a single primary case, in one round of transmission, assuming no immunity in population

The R0 for measles: 15-18 TB: 2.1-2.2 Ebola: just below 3

16.3 Factors important in transmission of malaria?

  • Infrastructures
  • Water
  • Mosquito burden
  • Host immunity
  • Bed net usage
  • Environment
  • Mosquito burden
  • Duration of infection in man

16.4 What are the most effective tools in elimination?

  • Treating people - complex health system
  • Larvae - draining pools
  • Mosquitoes - bed nets/ddt
  • vaccine -
  • Environmental - development

All of these strategies need new tools to fight it. New modelling, testing, agents

16.5 India vs Africa

In most parts of asia and s america - R0 is 1

In most parts of equatorial africa - R0 is 500+

16.6 Ross MacDonald Equation

what are the factors that influence transmission? it’s dependent on female mosquites, and how often they bite humans (you need to square this as they bite twice), and how long these mosquites survive. people have to stay parasatemic, so you need to factor the speed that people get better in (the faster they get better, the less they have a chance to get infected)

R0 = (m.a2.pn)/-r.lnp

  • . = times
  • m = number of (f) mosquitoes per person
  • a = daily biting frequency (of man)
  • p = proportion of mosquitoes surviving each day (as a decimal)
  • n = number of days for the parasite to mature inside a mosquito
  • r = proportion of infected people recovering each day

  • lnp = some log correction

  • You improve treatment, you affect r.
  • You destroy larvae, you affect m
  • You kill mosquitoes, you affect p and
  • You vaccinate, you affect r

  • You change the environment, you affect all of them

The mcdonald equation was tested in the 1950’s through the WHO eradication program’s intervention. It stands up!

The biggest affect you can have on R0 through affecting a single variable, is through killing mosquitoes (affecting p). So the biggest affect is through killing off mosquitoes, through indoor residual spraying.

So why is africa different to asia? The mosquitoes are different!

The anopheles gambiae mosquito are extremely efficient, they have a long lifespan, they are hardy, they have a wide range of breeding sites, they almost eclusively bite humans.