Mosquitoes, Arboviruses

Front 1

What are the maintenance hosts, amplifiers hosts and incidental hosts in arboviruses?

Back 1

Maintenance: Wildlife (mammals, birds, reptiles etc.)

Domestic animals are amplifiers

Man is incidental host

Front 2

Two main arbovirus vectors?

Back 2

Aedes and Culex
Both urban and rural

Front 3

Aedes aegypti.
Features of adult:

Features of larvae:

Where do they rest?

When do they feed?

Back 3

Adult: Black and white and "lyre" pattern on thorax. Lie parallel

Larvae: Short fat siphon, Thrives in containers, around the home.

Rest: Indoors/Around the home.

Feed: On humans only, diurnally active, indoors and around the house.

Flight: Rarely >100m

Front 4

Aedes aegypti. Principle vector of..? (4)

Back 4

Zika

Yellow Fever (urban)

Chikungunya

Dengue

Front 5

Aedes albopictus.
Vector for?

Environments?

Active where and when?
Hosts?

Interesting issues?

Back 5

Vector for dengue and zika. (not important in YF)

Mainly rural, peri-urban and sometimes urban.

Diurnally active, mainly outdoors.

Range of hosts in addition to humans.

Responsible for epidemics of dengue/chikingunya outbreaks in Europe as becoming more common. However generally not an incredibly effective vector so not important for rise in zika and dengue.

Front 6

How did yellow fever spread to humans?

Back 6

Originally "Jungle" cycle with monkey reservoirs transmitted between themselves mosquito vectors (e.g. Aedes Africanus) that only bite monkeys.
Humans then come into contact with deforestation etc. and vectors with more wide palate bite both humans and monkeys.

Then transferred to urban areas with aegypti causing closed loop human spread.

Front 7

3 main control methods for Yellow Fever?

Back 7

Case finding

Mass vaccination

Vector control (Rare today)

Front 8

Culex.
Colour?

Feed when and on what?

Stay where?

Problem?

Breeding sites?

Back 8

Brown/Dull

Feed at night and will feed readily on birds, pigs and humans.

Stay both indoor and outdoors

Often the most apparent mosquitoes in a locality as very, very annoying.

C.Tritaeniorhynchus typically breeds in rice fields/drainage ditches.

Front 9

Main vector for Japanese Encephalitis?

Back 9

Culex tritaeniorhnchus (and other Culex species)

Front 10

Japanese encephalitis.
Maintenance hosts?

Amplifier hosts?

Back 10

Maintenance: Aquatic birds

Amplifier: Pigs

Front 11

Control of JE.

Vaccination vs Vector

Back 11

Vaccination: Humans and Pigs (Humans method of choice)

Vector control: Aerial spraying (polluting), Larval control (impractical), LLIN, Insecticide resistance a problem. Can consider introducing fish.

Front 12

Dengue.

Why increase?

Vaccine?
Vector control?

Back 12

Massive increase due to urbanisation and travel

New vaccine not active against all serovars.

Vector control:
Source reduction--> Elimination of vector breeding sites.

Larviciding --> Probably never going to fully take off. Originally organophosphate used now safe treatments such a pyriproxyfen.

Education and community involvement.

Fogging --> Does not work.

LLIN --> No evidence.

Front 13

Promising tools for future aedes aegypti control?

Back 13

1. Control of immature stages (Safe insecticides such as pyriproxyfen)

2. Control of adult mosquitoes --> Physical barrier and IRS

3. Innovative methods: GM mosquitoes. Using wolbachia symbiont infection to drive refractory genes into population

Front 14

Life cycle of mosquitoes in general.

Starting at blood feed.

Back 14

After blood feed --> Eggs laid after 3-4 days.

Larvae hatch from eggs after 2-3 days.

Larvae feed on microorganisms and grow through 4 instars.

Pupae form after 5-7 days.
Adult emerges after 36 hours.

Total length 10-14 days.

Front 15

Endophagy vs Exophagy.

Endophily vs Exophily (resting)

Back 15

Exo - Outside (e.g. Arabiensis)

Endo - Inside (e.g. Gambiae)

Front 16

How long on average does it take for a mosquito to become infective?

Back 16

10-14 days

Front 17

What is the sporozoite rate?

Back 17

%mosquitoes infective or infectious

Typically 5% in An.Gambiae in AFrica

Detect either by:

Dissection and microscopy for sporozoites

ELISA

PCR

Front 18

Vectorial capacity.

Essentially what is the numerator and the denominator?

Back 18

Numerator --> Man biting rate (Dependent on density of vectors to man and biting rate) x Probability of daily survival (to the power of incubation of parasite)

Denominator --> Log of probability of survival.

Front 19

What are the advantages of targeting adult mosquitoes with IRS and ITNs? (3)

Back 19

Very large number of breeding sites can make larval control unrealistic

Aquatic breeding sites require very frequent treatment. However last a long time on walls and nets.

Maturation of the parasite takes 10-12 days. Has a number of feeds in that time and therefore more and more chance of death.

Front 20

What class of insecticide is the only one recommended for nets?

How long will they last?

Back 20

Pyrethroids and will last <5 years.

Front 21

Insecticides for mosquitoes.
When was the last active ingredient invented?

Back 21

Pyrethroids in the 70s (Permethrin).

No new since! Only new in class.

Front 22

Larval Control

What 2 main ways are there.
And within those what options?
Is it used much in malaria?
Which diseases is it more used in?

Back 22

Source reduction:

Cover water, drain areas, remove objects filled with water. Difficult and expensive to do. Sometimes impossible or too environmentally degrading.

Chemical larviciding:

Certain chemical larvicides - Temephos

Can cover areas with oil

Can use biologicals such as Bacilius Thuringiensis (Specific to blackfly, midges and mosquitoes)

Insect growth regulators (methoprene)

Front 23

What is zooprophylaxis?

Back 23

In areas with animal seeking vectors --> Can use insecticides on the domestic animals.

Front 24

Other personnel protection from mosquitoes apart from LLIN/ITNs?

Back 24

Coils.

Deet

Fogging