Topical application of DEET for schistosomiasis

Abstract

N, N-diethyl-m-toluamide (also known as DEET) is a broad-spectrum insect repellent that is used extensively against both human and animal pests, worldwide. Recent studies show that topical lipid formulations of DEET, such as LipoDEET, are highly effective in killing schistosome cercariae in the skin. Minimal systemic absorption, low manufacturing cost, and a wide range of activity against insects and schistosomes potentially makes compounds such as LipoDEET an excellent prophylactic agent against human and animal schistosomiasis in endemic areas, especially for travelers, until an effective vaccine is available.An effective vaccine for human or animal schistosomiasis remains elusive, despite the high incidence of these infections in several parts of the world [1]. Schistosomiasis is a water-borne infection. The infective stages of the parasite, called cercariae, are released into fresh water by infected snails from several species such as Biomphalaria spp., Oncomelania spp. and Bulinus spp. Therefore, minimizing water contact and/or destruction of schistosome-bearing snails in endemic areas are probably the best ways to prevent this infection. Indeed, the St Lucia Island project, which involved a 15-year intense schistosomiasis control programme in St Lucia, is probably one of the greatest success stories of schistosomiasis control, indicating that it is possible to control and eradicate schistosomiasis in a well-contained region such as an island [2]. However, restricting people and animals from coming in to close contact with infected water sources in endemic are as in the mainland is an impracticable and daunting task [3]. Snail control in the mainland is probably a much more complicated preposition than that performed in an Island because of the vast area involved, cost of chemical or biological application, changing climatic conditions and several ecological problems [4]. Despite these hurdles, there are a few promising reports of partial success in the control of Schistosoma japonicum infection in mainland China and Philippines as a result of improved hygiene measures [5]. Another alternative to control schistosomiasis in endemic areas is mass chemotherapy with praziquantel, the only effective drug against schistosomiasis. Unfortunately, there are indications of potential drug resistance against praziquantel [6]. Added to this is the declining trend of reduced investment of pharmaceutical industries in drug research for tropical diseases mainly because of the high cost of drug development and registration [7]. Despite our enormous efforts directed towards schistosomiasis control during the past 50 years, schistosomiasis continues to be a global problem and there appears to be no decline in the incidence [8].Infections with schistosomes occur when cercariae penetrate and enter into the body through intact skin. Therefore, blocking entry of cercariae into the skin could potentially control the infection. Over the years, several topical agents have been evaluated for their ability to block cercarial p...

In Vitro Assessment of Anthelmintic Activities ofRauwolfia vomitoria(Apocynaceae) Stem Bark and Roots against Parasitic Stages ofSchistosoma mansoniand Cytotoxic Study

“…Therefore, preventing such penetration of cercariae into the skin is also a potential form of transmission control [6]. Over the years, many topical agents have been evaluated for their ability to block penetration of cercariae into the skin and some of these compounds are highly effective but have not been used clinically due to their potential toxicity and difficulty in formulation and/or applying under field conditions [39]. These among other factors have stimulated the search for new agents that are safer and capable of providing such protection.…”

Current status and future prospects for a vaccine against schistosomiasis

“…It has been demonstrated that topical lipid formulations are highly effective at killing cercariae in the skin, thereby preventing infection. Indeed, in animals treated with a liposome-based DEET preparation, 100% protection against infection could be obtained and promising results were also obtained in a group of human volunteers visiting Lake Malawi [13].…”

Cream formulations protecting against cercarial dermatitis by Trichobilharzia

“…Similarly, it just can be speculated whether the poor effect of DEET (10%) was parasite, concentration and carrier related. Liposomal DEET (20%), however, was shown to provide complete protection against infection with S. mansoni (Salafsky et al 1999;Ramaswamy et al 2003). The inhibitory value of other agents decreasing penetration rates to a certain extent is hardly assessable.…”

“…For example, the insecticide dimethylphthalate (MacFarlane 1949), its derivative dibutylphthalate (Yang et al 1965) and the molluscicide niclosamide (Cherfas 1989;AbuElyazeed et al 1993) were reported to inhibit cercarial skin penetration with varying efficiency. Encouraging results were also obtained with the insect repellent N,N-diethyl-mtoluamide (DEET); its observed loss of protection due to absorption into the systemic circulation was recently outflanked by incorporating the drug in liposomes ("Lipo DEET") resulting in 100% protection (Salafsky et al 1999;Ramaswamy et al 2003). Studies with a novel human skin model indicate that a dimethicone-based cream offers a high level of protection (Ingram et al 2002).…”