**10. Conclusion**

354 Non-Flavivirus Encephalitis

highly microfilaremic patients, the antifilarial activity of African traditional herbal remedies may be of interest. Most of these plants are well accepted and tolerated, and preliminary cytotoxicity results are encouraging (Mengome et al., 2010). There is currently no evidence of the existence of a symbiont in *Loa loa* (McGarry et al., 2003; Buttner et al., 2003), that might warrant concurrent antibiotic therapy for patients with loasis. Because *Loa loa* infection often goes undiagnosed, cases of encephalitis in *Loa loa* endemic areas may be attributed to viruses, bacteria or other parasites. This underdiagnosis is due partly to the lack of a simple, specific and rapid diagnostic test available at points of treatment for use by non specialists. Some candidate antigens have been identified and produced (Azzibrouck et al., 2010). Although spontaneous encephalitis may be caused by the adult worm, life-threatening forms are generally due to massive death of microfilaria. However, in endemic areas, about one-third of infected persons are microfilaremic and only 5% are strongly microfilaremic, the remainder being amicrofilaremic (Van Hoegaerden et al., 1986; Dupont et al., 1988). The fact that these latter persons live permanently in areas of continuous transmission without becoming microfilaremic points to the existence of a natural control mechanism. Further studies of these subjects could help to find ways of clearing microfilaria without triggering encephalitis. Noteworthy immunological differences have been found between microfilaremic and amicrofilaremic subjects. The latter patients exhibit a stronger immune response against *Loa loa* antigens, both qualitatively and quantitatively (Pinder et al., 1988; Pinder et al., 1992; Egwang et al., 1988a; Egwang et al., 1988b;Egwang et al.,1989; Akue et al., 1997; Akue et al., 1998; Baize et al.,1997; Akue & Devaney, 2002). Finally, more work is needed to determine the role of

immune complex deposition in the onset of encephalitis in patients with loaisis.

Fig. 9. *Loa loa* adult worm

The risk of *Loa loa* encephalitis must be taken in to account when managing patients in and from endemic areas. This severe form can occur spontaneously or be triggered by antifilarial treatment in highly microfilaremic patients. The underlying mechanism appears to include embolism following massive death of microfilaria, genetic polymorphism of biological drug carriers, and immunological processes. More work is needed to develop a diagnostic test, as well as new drugs and possibly a vaccine. Further characterization of *Loa loa* encephalitis in endemic regions and in animal models is needed to understand the mechanisms underlying the onset and outcome of encephalitis in patients with loaisis.
