Review: Wetlands and invertebrate disease hosts: Are we asking for trouble?

Abstract

Wetlands provide a range of benefits to society, and yet in South Africa wetlands continue to be affected by human activities. Considerable effort is now being directed towards rehabilitation of degraded wetlands and the construction of artificial systems to treat effluent and stormwater. At the same time, wetlands provide potential habitat for vectors or intermediate hosts (collectively referred to in this document as 'invertebrate disease hosts': IDHs), of parasites implicated in the transmission of such important diseases as malaria and schistosomiasis (bilharzia). The present review considers, for the 2 major IDHs (mosquitoes and schistosome-transmitting snails), the type of habitat required by the water-dependent life stage and the ways in which wetland degradation, rehabilitation and creation may affect the availability of suitable habitat. General practical measures for minimising pest species, particularly mosquitoes, are included. This review also highlights other issues that require research and testing in the South African context, including: the IDHs implicated in less well-known diseases (both of humans and animals) and the control of mosquitoes and schistosome-transmitting snails through biomanipulation. We conclude that in regions of the country where the diseases are prevalent there is the likelihood that wetland rehabilitation and creation could inadvertently encourage the IDHs responsible for transmitting malaria and schistosomiasis. Assessment of the potential risks and benefits of a proposed wetland modification needs to be undertaken in a holistic manner using an adaptive framework that recognises the critical need to balance human and environmental health. Possible ways of controlling IDHs both in an environmentally-and socio-friendly manner need to be investigated using a multidisciplinary approach engaging invertebrate biologists, health care officials, wetland scientists and also sociologists and economists.

Wetlands as Settings for Human Health: Incorporating Ecosystem Services and Health Impact Assessment into Water Resource Management

“…(1) Urban wetlands protected for nature conservation (with the protection designed to support and regulate ecosystem services) can also support the presence of mosquitoes and other vectors, and in so doing, they can expose humans to vector-borne diseases (see Malan et al 2009), and (2) the presence of large woody debris in rivers (which regulates services, slows down water flows, and contributes to the trophic web as a supporting service) is an occupational and recreational hazard for swimming or boating and may even lead to a loss of life.…”

Tyre track pools and puddles – Anthropogenic contributors to aquatic biodiversity

“…An exception is the work of Bilton et al (2008) who examined the ecology and conservation status of a set of fluctuating and temporary ponds which included some formed on ancient cart tracks, in gateways and along hedgerows. Tank tracks on the military training area on Salisbury Plain (UK) are known to be important as habitats for fairy shrimp, Chirocephalus diaphanous and in Poland controlled use of 4WD vehicles and tractors has been suggested as a way of supporting suitable habitat for 2 branchiopod species Branchipus schaefferi and Triops cancriformis Goldyn et al (2012) but most of the work specifically on tyre tracks and wheel ruts is concerned with damage to existing habitat and its repercussions (Thompson and Schlacher 2008) and their role in providing habitat for disease vectors in the tropics (Carlson et al 2004;Malan et al 2009). There has been no study specifically on the macroinvertebrate faunal communities of water-filled tyre tracks.…”

Mosquitoes and other aquatic insects in fallow field biotopes and rice paddy fields

“…Although fallow field biotopes are expected to contribute to the conservation of endangered aquatic animals, it is commonly believed that such wetlands pose a risk to human health because they serve as breeding sites for mosquitoes (Dale & Knight, 2008; Malan et al , 2009; O’Geen et al , 2010). Fallow field biotopes also become breeding habitats for vector mosquitoes of Japanese encephalitis, such as Culex tritaeniorhynchus Giles, which breed in rice fields in Asia.…”