VBD control Flashcards
Hoe would you stop the transmission of VBD?
- Vector borne disease have to go through a vector. It is extremely rare that these kinds of infections can move from host to host directly
- One way of breaking the transmission cycle is to eliminate people from becoming infected or limiting their ability to pass the infection on to a new vector
- We are working towards doing this by using drugs that clear the infection from humans and also vaccinating them to prevent infection
What was the problem with the yellow fever vaccine?
Yellow fever vaccineis avaccinethat protects againstyellow fever.Yellow feveris a viral infection that occurs in Africa and South America. Most people begin to develop immunity within ten days and 99 percent are protected within one month ofvaccination, and this appears to be lifelong
Dengvaxia- which had an efficacy of 80.2% in the study—mightincreasedisease severity in some recipients, as happened with a dengue vaccine given to 1 million children in the Philippines before[the problem became clear]
Unlike Sanofi’s efficacy trials of Dengvaxia, Takeda assessed, prevaccination, whether participants in its study had antibodies from a previous dengue infection. About one in four participants were seronegative, and although no obvious signs of vaccine-induced harm occurred, theNEJMpaper notes the overall vaccine efficacy in this group dropped to 74.9%. What’s more, the vaccine offered no dengue protection against serotype 3 to these people—for unknown reasons.
What is RTS,S/AS01?
RTS,S/AS01 (RTS,S) is the world’s first malaria vaccine that has been shown to provide partial protection against malaria in young children. The vaccine acts againstPlasmodiumfalciparum, the most deadly malaria parasite globally and the most prevalent in Africa.1The vaccine has been recommended by WHO for pilot introduction in selected areas of 3 African countries. It will be evaluated for use as a complementary malaria control tool that could be added to (and not replace) the core package of WHO-recommended preventive, diagnostic and treatment measures.
What makes RTS,S different from malaria vaccine candidates currently under development?
RTS,S is the first, and to date, the only vaccine to show a protective effect against malaria among young children in a Phase 3 trial. Beginning in 2019, it will be the first malaria vaccine provided to young children through routine immunization programmes. Three sub-Saharan African countries will introduce the vaccine in selected areas as part of a large-scale pilot implementation programme.
What is the efficacy of the RTS,S vaccine?
The Phase 3 trial, conducted over 5 years (from 2009 to 2014), enrolled approximately 15000 young children and infants in 7 sub-Saharan African countries.2The trial sites within these countries represented a range of malaria transmission settings. Among children aged 5–17 months who received 4 doses of RTS,S, the vaccine prevented approximately 4 in 10 (39%) cases of malaria over 4 years of follow-up and about 3 in 10 (29%) cases of severe malaria,3with significant reductions also seen in overall hospital admissions as well as in admissions due to malaria or severe anaemia. The vaccine also reduced the need for blood transfusions, which are required to treat life-threatening malaria anaemia by 29%.
Going back to this vectorial capacity equation: what do you think it tells us about how we might hope to control these diseases?
- Less Vectors!
- Stop biting
- Increase mortality particularly before EIP
What are Insecticide treated nets (ITNs)
- The main personal protection measure.
- Protects against malaria-transmitting mosquitoes (mainly Anopheles gambiae) that tend to bite at night.
What protection do ITNs provide?
- Effective if used properly - ITNs can reduce clinical incidence by 50-62% compared to not using an ITN
- Long lasting, easy to use, cheap
- can delay emergence of drug resistance in the parasite
Individual vs community protection
Vector control provides individual level protection by preventing mosquito bites, either by repelling or killing mosquitoes.
It can also provide community level protection, vector control can protect entire communities by reducing transmission (here measured using R0).
- Reducing the size of the mosquito population
- Killing mosquitoes before they get old enough to transmit malaria
- Reducing levels of malaria in the community (herd immunity)
In regions of Africa such as Ifakara in Tanzania where high levels of bed net coverage have been achieved, there have been very large reductions in the numbers of mosquitoes that transmit malaria.
What are Larvicides?
Mosquitoes can be controlled by applying larvicides to breeding sites. Larvicides can be chemical poisons, bacteria or fungi.
A commonly used larvicide is Bacillus thuringiensis israelensis which interfere with larval digestive system.
What are pros of larvicides?
- Complements other control strategies.
- Can target mosquitoes that bite outdoors and on animals.
What are cons of larvicides?
- Identifying breeding sites can be very difficult.
- Larvicide needs to be frequently reapplied (weekly).
- Need to consider environmental feasibility.
Ultra low volume spraying
Indoor Residual Spraying (IRS) with insecticides are the cornerstones of nearly all modern large scale vector control campaigns.
The success of these interventions is based on killing or repelling female mosquitoes as they attempt to blood feed on humans.
Indoor residual spraying
- Indoor residual spraying (IRS) involves the application of a long-lasting insecticide to the inner walls of a house with a hand-compression sprayer.
IRS targets mosquitoes by:
- Repelling them from sprayed houses
- Killing mosquitoes that rest on sprayed walls
Vector control in sub saharan Africa
Between 2010 and 2012 approximately 320 million LLINs have been distributed in sub-Saharan Africa.
In the same period, 153 million people were protected by IRS every year.
These interventions have led to large numbers of lives saved. Between 2000 and 2010 it was conservatively estimated that bed nets prevented 843,000 deaths in children under 5 in sub-Saharan African.