VBD control

Question 1

Hoe would you stop the transmission of VBD?

Answer 1

• 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

Question 2

What was the problem with the yellow fever vaccine?

Answer 2

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.

Question 3

What is RTS,S/AS01?

Answer 3

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.

Question 4

What makes RTS,S different from malaria vaccine candidates currently under development?

Answer 4

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.

Question 5

What is the efficacy of the RTS,S vaccine?

Answer 5

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%.

Question 6

Going back to this vectorial capacity equation: what do you think it tells us about how we might hope to control these diseases?

Answer 6

• Less Vectors!
• Stop biting
• Increase mortality particularly before EIP

Question 7

What are Insecticide treated nets (ITNs)

Answer 7

• The main personal protection measure.
• Protects against malaria-transmitting mosquitoes (mainly Anopheles gambiae) that tend to bite at night.

Question 8

What protection do ITNs provide?

Answer 8

• 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

Question 9

Individual vs community protection

Answer 9

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).

1. Reducing the size of the mosquito population
2. Killing mosquitoes before they get old enough to transmit malaria
3. 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.

Question 10

What are Larvicides?

Answer 10

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.

Question 11

What are pros of larvicides?

Answer 11

• Complements other control strategies.
• Can target mosquitoes that bite outdoors and on animals.

Question 12

What are cons of larvicides?

Answer 12

• Identifying breeding sites can be very difficult.
• Larvicide needs to be frequently reapplied (weekly).
• Need to consider environmental feasibility.

Question 13

Ultra low volume spraying

Answer 13

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.

Question 14

Indoor residual spraying

Answer 14

• 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:

1. Repelling them from sprayed houses
2. Killing mosquitoes that rest on sprayed walls

Question 15

Vector control in sub saharan Africa

Answer 15

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.

Question 15

What are methods for controlling mosquitos?

Answer 15

• Removal of stagnant water (draining swamps, removing old tires). Not always possible, given the rainy season in some environments.
• Investing in more secure housing, windows, doors, screens.
• Monitor agriculture, construction, irrigation (these activities can generate breeding sites).

Requires collaboration between community members and vector control officers. It can be difficult to evaluate the success of environmental campaigns.

Question 16

What are some methods for controlling ticks?

Answer 16

• Removing host harborage areas
• Removing leaf litter and plant debris from landscaped areas
• Trimming tall grass and overhanging shrubs
• Maintaining wooded trails
• Using woodchip barriers

Requires collaboration between community members and vector control officers. It can be difficult to evaluate the success of environmental campaigns.

Question 17

Survival of vectors in vector borne diseases

Answer 17

Because of the long period many of these pathogens spend in the vector they are very sensitive to vector survival

This is some survival data from a mosquito vector in the lab, These mosquitoes were living the good life, but even so look how few actually survival the EIP.

Question 18

Lure-and-kill strategy traps

Answer 18

• Traps emit chemicals to mimic a mammal’s scent:
  
  • CO2 (propane-burning device),
  • Lactic acid,
  • Sugary scent.
  • Smelly socks also produce attractive odors.
• Females are drawn towards the trap, sucked in, and collected.
• Useful for monitoring; but typically too inefficient for suppression.

Question 19

Lethal ovitraps:

Answer 19

• Also use the lure-and-kill
• Females lay eggs in the trap, which are unable to emerge.
• Number of eggs can help identify mosquito breeding hotspots.

Question 20

Attractive toxic sugar bait

Answer 20

• Mosquito sugar feeding:
  
  • Both sexes sugar feed from flowers, etc.
  • Females require blood to produce eggs.
• Toxic sugar bait
  
  • Spray sugar feeding sites with toxic sugar bait.
  • Provide bait stations with sheltered, sprayed vegetation.
  • Most effective in dry locations.

Question 21

Reproductive vontrol strategies

Answer 21

controlling vector populations with male releases
An exciting new set of tools coming into more common use are reproductive control strategies.
They are being increasing considered as part of control kit for arbovirus vectors and notable the WHO recently released guidance for one of these strategies indicating they are here to stay.
There are many different versions of these strategies, but they share some common elements.

Question 22

Inseecticide treated cattle

Answer 22

Treating cattle with insecticide can reduce the incidence of malaria by killing mosquitoes that feed on both humans and cattle.

Treating cattle with insecticide has been trialled successfully in Pakistan, but African field trials haven’t produced very promising results.

Question 23

Pros of insecticide cattle

Answer 23

Complements other strategies in locations where vectors are largely zoophilic.

Question 24

Cons of insecticide cattle

Answer 24

- Mosquitoes tend to feed from legs of cattle. - Cattle rub their legs on the ground when they sleep/sit, leading to a short insecticidal half-life. - Mosquitoes feed for shorter times on treated cattle.

Question 25

Mouse Targeted Devices: Tick Tubes

Answer 25

Tick tubes are host-targeted devices filled with cotton nesting materials laced with Permethrin. When the tubes are placed in mouse breeding habitats (e.g. stone walls, brush piles, wood piles) mice will use the materials and place it in their nests causing any live ticks to detach and die. Tick tubes are biodegradable and the risk for environmental contamination is extremely low.

Question 26

Deer Targeted Devices: 4-Poster Bait Stations

Answer 26

4-poster bait station consists of a central feed bin for baiting deer and two application stations at either end of the unit. As deer feed on the corn bait the device forces them to rub against applicator rollers which apply pesticide to the ears, neck, head, and shoulders, where the majority of the adult ticks are attached and feeding.

Question 27

What is Ivernectin

Answer 27

IVM is a drug commonly used in Africa to treat onchocerciasis and lymphatic filariasis and has recently been suggested as a new form of malaria control IVM is taken by humans; mosquitoes feeding on the humans ingest some of the drug which has a **toxic effect** As a result their **lifespan is greatly reduced** The mosquito dies before the malaria parasites develop into sporozoites (the stage infectious to humans), thus preventing onwards transmission Recent field study shows promise- Cumulative malaria incidence was reduced in the intervention group (estimated mean 2·00 episodes per child) compared with the control group (2·49 episodes per child; risk difference –0.49).