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4.3.3 Host Diversity
Mosquitoes and ticks feed on a wide range of hosts, and their pathogens circulate in
diverse animal species. Lyme disease is caused by Borrelia burgdorferi, which is
transmitted to humans through the bite of Ixodes ticks. For Borrelia burgdorferi
sensu lato, a broad range of reservoir hosts have been identified, for instance nine
small mammals, seven medium-sized mammals and 16 bird species in Europe
(Gern et al. 1998), and eight small mammals in the USA (summarised in Salkeld
etÂ
al. 2008). As another example, the Zika virus is known to circulate in monkey and
wild mammal populations in Africa, and has been detected in domestic sheep, goats,
horses, cows, ducks, rodents, bats, orangutans and carabaos in Indonesia and
Pakistan (Vorou 2016). However, large knowledge gaps on the diversity of reservoir
hosts for mosquito- and tick-borne pathogens in old and new areas of distribution
still exist (Baráková et al. 2018; Hashiguchi et al. 2018). Certainly, these gaps will
never be closed given the complex dynamics of adaptations between pathogens,
vectors and hosts.
The conceptual model of the dilution effect in Lyme disease (Ostfeld and Keesing
2012) is the textbook example about how biodiversity on the level of the host spe-
cies can directly influence the transmission of an arthropod-transmitted disease.
Humans are aberrant hosts for the pathogen, because the pathogens cannot replicate
in humans. In a natural cycle of Borrelia burgdorferi, the bacteria are maintained by
small mammals and birds (reservoir hosts). The dilution effect model in the Lyme-
disease system states that the relative abundance of host individuals should be
evenly distributed across host species to decrease the potential for an encounter of
the tick with the most competent reservoir host. This model also applies to other
vector-host systems in which a generalist vector uses many host species of which
only a few are competent reservoir hosts (Swaddle and Calos 2008; Civitello et al.
2015). The smaller the risk for a host to become infected and thereby maintain and
release pathogens, the more species-diverse and abundant is the host community
(Civitello et al. 2013; Levi et al. 2016). However, this dilution effect is still under
academic debate (e.g. Civitello et al. 2015 and Salkeld et al. 2015), and there is an
urgent need for further research.
4.4 How to Manage VBDs?
Different public health measures exist, ranging from epidemic control through vec-
tor control (of mosquitoes, bugs, flies, fleas) and eradication of diseases through
vaccination, case treatment and breeding site elimination (WHO 2017b). Vector
control tools target specific life stages of arthropod vectors and are of a chemical
(e.g. pyrethroid insecticides), biological (e.g. Wolbachia bacteria) or transgenic
nature (e.g. genetically modified mosquitoes). Chemical insecticides are addition-
ally used for preventive measures such as insecticide-treated bed nets,
R. MĂĽller et al.
Biodiversity and Health in the Face of Climate Change
- Title
- Biodiversity and Health in the Face of Climate Change
- Authors
- Melissa Marselle
- Jutta Stadler
- Horst Korn
- Katherine Irvine
- Aletta Bonn
- Publisher
- Springer Open
- Date
- 2019
- Language
- English
- License
- CC BY 4.0
- ISBN
- 978-3-030-02318-8
- Size
- 15.5 x 24.0 cm
- Pages
- 508
- Keywords
- Environment, Environmental health, Applied ecology, Climate change, Biodiversity, Public health, Regional planning, Urban planning
- Categories
- Naturwissenschaften Umwelt und Klima