Naegleria Fowleri in Thailand, 2003

Between 1988 and 2003, Naegleria fowleri was studied extensively in Thailand. The distribution of N. fowleri has been studied in many provinces since 1988. During 2001-2003, we received financial support from Mahidol University to study the distribution of pathogenic Naegleria spp in water reservoirs in central, northern, and western parts of Thailand. With these funds, research was conducted in Bangkok (Taling Chan District), Saraburi, Nakhon Nayok, Nakhon Sawan, Sukhothai, Prachuap Khiri Khan, Surat Thani and Chumphon Provinces. Studies indicated that pathogenic strains of Naegleria belonging to the species fowleri were found in Saraburi and Surat Thani, and could be identified by external morphology, molecular weight, isoenzyme patterns and cytopathogenicity. However, the development of therapeutic drug treatment is still problematic because of the high mortality rate and rapid progression of disease. Since 1970, the effects of numerous drugs and chemical agents have been studied; there are continuing efforts to develop new drugs in vitro and in vivo, because the current treatment of primary amebic meningoencephalitis remains ineffective for most patients. A study of the in vitro effect of various antifungal drugs and the drug combination 5-fluorouracil and amphotericin B on pathogenic Naegleria spp was published in 2002. In was concluded that amphotericin B, in combination with 5-fluorouracil was still the most effective treatment for pathogenic Naegleria spp infection. In addition, the IC50 of this drug combination was significantly lower than that of amphotericin B and 5-fluorouracil alone. Moreover, this drug combination has high synergistic activity and few side-effects in patients. These results emphasize the need for prompt treatment at an adequate minimum dosage by intrathecal route to arrest the disease. (Jariya et al, 1983). During the period 1983-2003, five cases were found in Thailand: 1 in Bangkok, 2 in Trat, 1 in Nakhon Pathom, and 1 in Suphan Buri Province (Somboonyosdech et al, 1987; Sirinavin et al, 1989; Poungvarin and Jariya, 1991). From the available information, it is reasonable to conclude that Naegleria fowleri is found primarily in central, eastern, and northeastern parts of Thailand (Jariya et al, 1988) corresponding to the provinces where PAM occurred. According to published survey reports, a thermophilic Naegleria spp (42 ̊C) was found in Lopburi (Jariya et al, 1997) and in Bangkok (Taling Chan District) (Tiewcharoen et al, 2004). After this survey, isolation and specific identification of the pathogenicity of Naegleria spp in central, northern, and western parts of Thailand (Saraburi, Nakhon Nayok, Nakhon Sawan, Sukhothai, Prachuap Khiri Khan, Chumphon, and Surat Thani provinces) was carried out. Isoenzyme patterns of the ameba isolates were significantly positive for malic, malate dehydrogenase and esterase enzymes when compared with those of the reference strains (Figs 1-5). These results showed that the distribution of thermophilic Naegleria spp in Saraburi was 0.39% (1/258), and 0.77% (2/258) in Surat Thani Province. It was concluded that biochemical analysis using the selection of isoenzymes was necessary to distinguish Naegleria fowleri from many strains of thermophilic Naegleria spp. However, the isoenzyme method of analysis yielded a correlation of intraspecific isoenzyme variations. Currently, there are plans to use Correspondence: Supathra Tiewchareen, Department of Parasitology, Faculty of Medicine at Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand. Tel: 66 (0) 2419-7000 Ext 6500 E-mail: [email protected] INTRODUCTION The free-living ameba, Naegleria fowleri, is the causative agent of primary amebic meningoencephalitis (PAM), a fatal disease of the central nervous system. Naegleria fowleri infection is acquired while swimming or diving in freshwater lakes, ponds and man-made pools (Sugita et al, 1999). Although PAM is rare, patients almost always die within 5-7 days of infection. The speed with which the disease progresses stresses the need for an overview study of its distribution (Tiewcharoen et al, 2001) identification, pathogenicity (Jarolim et al, 2000) and of the amebicidal drugs used to treat it (Tiewcharoen et al, 2003). Accurate information supplies the basic knowledge the Thai Department of Public Health needs to plan effective strategies to prevent and control this disease. DISTRIBUTION AND IDENTIFICATION The initial description of Naegleria fowleri was published in 1970 (Carter, 1970). The first case of PAM in Thailand was reported from Si Sa Ket Province