The value and role of mosquito meshes in low resource and poor income settings: author’s reply

Abstract

We would like to thank Stephenson and Kingsnorth for the critical examination of our publication and would like to comment on the criticism expressed [1, 2]. Our research group has been working on the biocompatibility of mosquito and commercial meshes for several years, primarily to prove the equivalence of these meshes [3, 4]. During our investigations it became more and more apparent that the sterilization process itself is of crucial importance. Thus, we discovered that the process of steam sterilization also leads to changes in commercial meshes. We have recently tested mosquito meshes made of polyester and those made of polyethylene. The polyester mesh was purchased in Germany; the polyethylene mesh was sent to us from the USA with the information, documented several times, that it was manufactured by the company Amsa-Plastic in India. Despite several attempts, we have not succeeded in acquiring a mesh directly on the Internet or by telephone order from the company directly. From all of these meshes, 24 pieces of 6 × 11 cm size were produced and sterilized for the mechanical tests. The sterilization at 134 °C and 121 °C was performed in the central sterilization department of the Südstadt Clinic Rostock by the CE certified autoclave ECS 209 (WEBECO, Spain). Temperature fluctuations, as assumed by the authors, do not occur with this constantly maintained device. A sterilization temperature of 100 °C cannot be set with these autoclaves because they are not permitted in Europe, so we had to improvise. It was thus only for this particular relatively low temperature (100 °C) that we used the baby bottle steam sterilizer. As explained in our article, this temperature had been chosen in addition to the conventional sterilization temperatures mentioned above (134 °C, 121 °C) to simulate the situation in areas without electricity (and thus without autoclaves). The treatment of the meshes with penicillin/streptomycin and amphotericin took place with all mesh pieces only AFTER the sterilization and leads thus also to no impairment or even denaturation of the meshes. In contrast to the information provided by Stephenson et al., our chemical analyses showed that the mosquito mesh from India was not made of low-density polyethylene (LDPE) but instead of high-density polyethylene (HDPE). As described in our article, polyethylene is not optimally suited for steam sterilization. The thermal properties of polyethylene are very limited, as it starts to soften at 80 °C. The melting point of LDPE is 105 °C; that of HDPE is 137 °C. We cannot understand from our data why there was little or no shrinkage in the mesh used by both Stephenson et al. and Tongaonkar, both of whom we hold in high esteem. The chemical and physical properties of polyethylene cannot be influenced. It is possible that, as assumed in our article, other polymers (e.g. polypropylene) were temporarily part of the mesh, so that the degree of shrinkage was lower. We consider the argument that if a mesh shrinks, it should be discarded because of the low costs, to be debatable. As described in our investigations, sterilization changes the mechanical and chemical properties of the nets including the biocompatibility of the fibroblasts. If shrinkage is still acceptable, the effective porosity, elasticity and flexibility of the mesh will still change compared to the non-sterile mesh. Mitura et al. also showed nearly identical results for locally acquired meshes [5]. As already explained in our article, the composition of a manufacturer’s polymers can theoretically change daily due to new suppliers, so that a previously successfully implanted mesh suddenly no longer meets the minimum requirements. Therefore, Löfgren et al. * R. Wiessner [email protected]