Medical-Veterinary Entomology – Lecture 2

What is vectorial capacity?

Equation that measures pathogen transmission by mosquitoes, defined as the average number of new vertebrate infections per day from an index case.

Factors: mosquito-to-human ratio (m), human biting rate (a), daily mosquito survival (p), and pathogen latent period (n days).

What are the 4 components of vectorial capacity?

1. Number of mosquitoes per person

2. Feeding frequency and type

3. Survivorship

4. Vector competence

What is a bridge vector?

Biting arthropod transmitting a pathogen from an animal host to a human.

What is an enzootic vector?

Biting arthropod transmitting a pathogen from one animal host to another.

What is the Risk (Probability) of human infection equation?

Risk = A x Fm x P x Cv

A = vector abundance

Fm = fraction of human blood meals

P = infection prevalence in the vector

Cv = fraction of infected mosquitos that will transmit disease by a subsequent bite = vector competence

How is MIR (minimum infection rate) calculated?

MIR = (number of positive pools ÷ total specimens tested) × 1000

Define Endemic.

Disease regularly occurring in people within a certain area/community. (Greek: endemios, native + demos, people)

Define Epidemic.

Rapid spread of disease to many people in a population within a short time. (Greek: epi = upon/above + demos = people)

Define Pandemic.

Epidemic spread across multiple regions/continents, affecting many individuals. (Greek: pan = all + demos = people)

Define Enzootic.

Disease in non-human animals that is constantly present in a specific area at low incidence.

Define Epizootic.

Rapid spread of disease among non-human animals in a population within a short time. (Greek: epi = upon + zoon = animal)

Which invasive mosquitoes drive most recent epidemics?

• Culex pipiens,

• Cx. quinquefasciatus,

• Aedes albopictus,

• Aedes aegypti.
  

Diseases: Yellow fever, Dengue (DHF), West Nile encephalitis, Rift Valley fever, Chikungunya, Zika fever, Urban malaria.

what is the Mosquito (Culicidae) taxonomy?

Kingdom Animalia → Phylum Arthropoda → Class Insecta → Order Diptera → Family Culicidae → Subfamilies Anophelinae, Culicinae

Morphological difference in eggs between Anophelinae vs Culicinae

• Anophelinae: visible lateral floaters.

• Culicinae: no floaters.

Morphological difference in larvae between Anophelinae vs Culicinae

• Anophelinae: no respiratory siphon.

• Culicinae: highly visible siphon.

Morphological difference in adult females between Anophelinae vs Culicinae

• Anophelinae: palps as long as proboscis.

• Culicinae: palps smaller than proboscis.

Morphological difference in adult males between Anophelinae vs Culicinae

• Anophelinae: palps rounded extremities.

• Culicinae: palps tapered extremities.

Morphological difference in resting position between Anophelinae vs Culicinae

• Anophelinae: oblique to surface.

• Culicinae: parallel to surface.

Diseases transmitted by Anopheles gambiae complex

Malaria, human filariasis. A. gambiae (endophilic, endophagic), A. arabiensis (drier climates).

Diseases transmitted by Culex pipiens group

West Nile, St. Louis encephalitis, bird malaria.

• Temperate: Cx. pipiens form molestus (underground, autogenous)

• Tropical/subtropical: Cx. quinquefasciatus

Diseases transmitted by Aedes spp.

Dengue, Chikungunya, Zika, Yellow fever.

• Ae. aegypti: feral form (formosus) vs domestic form.

• Ae. albopictus: Asian tiger mosquito, cold-hardy, invasive.

Define Anthropophilic.

Preferring human hosts over animals (e.g., Anopheles gambiae).

Define Endophilic.

Mosquito that tends to rest indoors.

Define Endophagic.

Mosquito that feeds indoors.

Name three globally invasive Aedes mosquitoes and expansion timeline.

• Aedes aegypti: worldwide after 1500s (tropical)

• Aedes albopictus: worldwide after 1960s (tropical & temperate)

• Aedes japonicus japonicus: worldwide after 1990s (temperate)

How are anopheles eggs laid?

Later floats - eggs laid individually on water

How are aedes eggs laid?

No floats - eggs laid individually beside water

How are culex eggs laid?

no floats - eggs laid in rafts on water

How do anopheles larvae rest?

No siphon- rest parallel to water surface

How do aedes larvae rest?

Siphon - rest at an angle to water surface,

How do culex larvae rest?

Siphon - rest at an angle to water surface

What is the culex life cycle?

1. Eggs laid in raft at water surface

2. Larvae has a siphon and rest at an angle to water surface

3. Pupa takes air from water surface

4. Adult emerges at water surface from pupa