Vector
- Slovak term: Slovenský termín
- An organism that acts as an essential intermediate host or definite host for a human pathogen and that plays an active role in its transmission (WHO 2003).
- Excludes mechanical carriers of infective materials (such as houseflies and cockroaches), strictly passive intermediate hosts (e.g. the snail hosts of schistosomiasis) and reservoir species (e.g. foxes carrying rabies) (WHO 2003).
- An insect or other animal which normally transports an infectious agent that constitutes a public health risk (WHO 2005).
Explanation
Epidemiologically, the most important characteristic of vector species is vectorial capacity. Vectorial capacity is defined as the rate (usually daily) at which a bloodsucking insect population generates new inoculations from a currently infectious case. Vectorial capacity is the product of the eight components; vector longevity is a key component. It is a measure of potential rather than actual rate of transmission, because it includes no parasitological information. The vectorial capacity and other related measures of the potential rate of transmission are particularly advantageous under two circumstances:
- when the fraction of vectors which are infected is too small to measure reliably - this is typical in epidemic (rather than endemic) areas, where infection rates are often of the order of 0.1% and impossibly large sample sizes (e.g. more mosquitoes than can be dissected) are required to detect significant changes in such small rates;
- when an explanation for the variation in infection rake is needed - in this context, the theory of vectorial capacity clearly explains why transmission rate is particularly sensitive to changes in the daily survival rate of vectors. The concept of vectorid capacity does not apply to snails as intermediate hosts, though snail abundance and longevity are important epidemiological variables(WHO 2009).
Example
Anopheles mosquitoes are vectors of malaria (WHO 2003). True biting insects such as Anopheles mosquitoes for malaria, intermediate hosts such as snails for schistosomiasis and animal reservoirs such as rodents for leishmaniasis (WHO 2009).
References
- WHO, WMO and UNEP (2003) Climate change and human health: risks and responses
- WHO (2005) International Health Regulations
- WHO(2009) Health impact assessment glossary: E-learning modules.
