Ecology, epidemiology and control of infectious diseases (2009FBDBMW)
Institution
Universiteit Antwerpen (UA)
This document includes a full summary of all content seen in the classes taught by Wim Van Bortel of the course Ecology, epidemiology and control of infectious diseases given in the first Master in Biomedical Sciences: Infectious and Tropical Diseases. Caution: this document does not include the le...
Ecology, epidemiology and control of infectious diseases (2009FBDBMW)
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Ecology: partim Wim van Bortel
MALARIA: VECTORS & DYNAMICS OF TRANMISSION 18/10
VECTOR-BORNE DISEASES
In zoonotic diseases, you need an animal reservoir where the pathogen circulates
before spill-over to humans. Environment: everything from ecology to climate..
THE ROLE OF THE VECTOR
Vector transmission is also a biological process. First pick-up: vector takes up the
pathogen (often vectors aren’t infected as larvae/nymphae), then there is
replication / transformation of the pathogen in the vector species. In the end, transmission must
happen to transfer the pathogen to another host. Eg via mechanical transmission: eg biting flies.
Vector competence = the ability of a vector to acquire, maintain and transmit a pathogen. Certain
species can carry certain pathogens.
- Cycle in the vector:
o Inf. blood meal - journey of pathogen in vector - salivary glands / mouth parts /
faeces
- Sometimes vertical transmission: from female mosquito to offspring
In zoonotic diseases, the vector functions as a bridge between the animal reservoir and humans (eg
West Nile Virus). In anthroponotic diseases you don’t need a reservoir for maintenance and
transmission (eg malaria, dengue: both originally zoonotic diseases).
Mosquitos are diptera: 6 legs and 1 pair of wings (2 wings). Cullicoidea are steekmuggen. Cullicidae
are subdivided in anophelinae and culicinae. Anophelinae conclude the genus anopheles, culicinae
include the genera Culex and Aedes.
Anopheles:
- ~3500 mosquito species & ~465 Anopheles species. Among the Anopheles:
o ~70 species are capable to transmit Plasmodium
o ~40 species are important vectors
Has to do with vector competence but also the species
Anopheles develop from egg to larvae to pupae to adult. Larvae need to air-breath so they are found
at the surface of the water.
A female only has to copulate once and can then produce viable eggs for the rest of her life
(spermatheca). A blood meal is needed for egg development, so only females blood feed. The
gonotrophic cycle takes 2-3 days in tropical situations.
- Anopheles larval breeding sites in an African setting: standing water, breeding sites are
everywhere and man-made.
, - Anopheles larval breeding sites in an Asian setting: breakkish water, open spaces, in
Cambodya in forested areas, shade. In Northern Vietnam: anopheles minimus lives in small
rivers. SO different species have different ecology and larval ecology.
o Anopheles mostly likes clean water, rural areas. The risk on malaria is lower in the
city
BIOLOGY AND ECOLOGY
- Anthropophilic species: prefer to feed on humans
- Zoophilic species: ornithophilic: birds, mammophilic: mammals
- Nycthemeral cycle: nocturnal/diurnal/ at dusk & down
o Anopheles are nocturnal; Tiger mosquitos bite during the day
DIVERSITY OF ANOPHELES AND IMPLICATIONS FOR MALARIA EPIDEMIOLOGY
If you try to present the burden of a disease by making the size of the continent
bigger. This is Africa: 90% of malaria cases are reported from Africa.
2 species that cause Malaria:
- Falciparum: primarily in Africa Most life threatening (incubation period 6-
7 D)
- Vivax: primarily in Latin-America and Asia
The 4 plasmodium species are carried by many different mosquitos. The different mosquito species
differ from continent to continent and country to country. Examples: Anopheles gambiae, funestus
and arabiensis in Africa, minimus in Asia, albimanus in central & south America, dirus, minimus and
epiroticus in Southeast Asia.
EXAMPLE 1: UGANDA
In 7 villages mosquitos were collected by human landing collections: identify them & see if they’re
infected by plasmodium. Human landing collections: in 3 houses indoor and outdoor during 6 nights.
The annual entomological inoculation rate (EIR) = BMN x SI. You calculate the number of bites /
man / night estimated by the human landing collections multiplied by infected adults. SI = sporozoite
index. These are the parasites in the salivary glands of the mosquitos that can be transferred to
humans: proportion of mosquitos with sporozoites, estimated from ELISA results.
Graph 1: there is a relationship between the annual EIR and the R 0.
- How many potential infectious bites can a person get during 1
year in a specific village
- In some villages: very large AEIR
- Graph 2: the contribution of the different species to the AEIR:
almost 87% due to Anopheles funestus in Apac.
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