A zooprophylaxis strategy using l-lactic acid (Abate) to divert host-seeking malaria vectors from human host to treated non-host animals

Abstract

Background: Zooprophylaxis is a technique in which blood-seeking vectors are diverted to non-host animals in order to lower blood-feeding rates on human hosts. The success of this technique depends on the host preference of the vector being targeted. The objective of this study was to evaluate the effect of l-lactic acid (Abate) to divert malaria mosquito, Anopheles gambiae from feeding on human host.Methods: A 14-month-old female goat was treated with Abate, a formulation incorporating l-lactic acid into a slowrelease matrix. This formulation was applied on the fur of the goat's back and neck. The treated animal was then presented to Anopheles gambiae sensu stricto (s.s.) as a prospective host in a semi-field environment ('mosquito sphere') together with either an untreated animal or a human. The number of mosquitoes caught to each host choice offered were compared. Results:Goat treated with the l-lactic acid formulation successfully attracted An. gambiae at higher rates (70.2%) than the untreated ones (29.8%). Furthermore, An. gambiae s.s. were attracted to a treated goat at an equivalent degree (47.3%) as to their preferred human host (52.7%), even when the preferred host was present in the same environment. Conclusions:The findings indicate that human host-seeking mosquitoes can be diverted into feeding on nonpreferred hosts despite the close proximity of their favoured host, hence reducing chances for the transmission of blood-borne parasites.

Dilution effects in disease ecology

“…Characterizing the amount of variation across hosts is an important frontier (see main text), particularly how it varies for different types of disease systems, and how those patterns influence dilution effects Proportion of ticks molting Macdonald, 1957;WHO, 1982). More recently, scientists have recommended using zooprophylaxis while simultaneously treating the added host species with insecticides to further reduce mosquito populations (Kemibala et al, 2020;Morona et al, 2017). The use of interspecific variation to manage transmission has been particularly well-characterised for Ribeiroia ondatrae, a trematode parasite of wildlife.…”

“…(Hall et al, 2009). How the abundance of hosts affects managed dilution effects, for example, for zooprophylaxis, has been a major question (Ault, 1994; Kemibala et al, 2020; Saul, 2003). This issue also dominated early conversations about the pathways by which natural dilution effects occur (Begon, 2008; Johnson et al, 2008; Keesing et al, 2010).…”

“…The World Health Organisation and others have recognised the potential of this ‘zooprophylaxis’ in the management of malaria and other vector‐borne diseases (Ault, 1994 ; Macdonald, 1957 ; WHO, 1982 ). More recently, scientists have recommended using zooprophylaxis while simultaneously treating the added host species with insecticides to further reduce mosquito populations (Kemibala et al, 2020 ; Morona et al, 2017 ).…”

“…Johnson et al, 2013b ; Luis et al, 2018 ; Strauss et al, 2018 ; Thieltges et al, 2008 ), other mechanisms have also been proposed in theory and described in at least some disease systems (Johnson & Thieltges, 2010 ; Keesing et al, 2006 ). For example, the presence of alternative hosts for vectors like ticks and mosquitoes can deflect vector meals away from high‐quality hosts, and also affect the abundance of vectors (Keesing et al, 2006 ), mechanisms that underlie zooprophylaxis (Ault, 1994 ; Kemibala et al, 2020 ; Saul, 2003 ). In the Lyme disease system, ticks that feed on some species are less likely to feed successfully (Figure 4 ) and also less likely to survive over the winter (Brunner et al, 2011 ; Keesing et al, 2009 ) (Figure 2e ).…”

“…Using dilution effects in managed systems requires careful consideration of which low‐quality hosts are most likely to reduce overall transmission, and whether the net effects of reducing transmission are worth any potential costs, such as the possibility of decreases in crop yield or harvesting efficiency (Smithson & Lenné, 1996 ). Recent studies of zooprophylaxis suggest that potential costs of adding low‐quality hosts, such as increases in vector abundance, might be mitigated, for example with the use of topical insecticides (Asale et al, 2017 ; Kemibala et al, 2020 ).…”