Neorickettsia sennetsu as a Neglected Cause of Fever in South-East Asia.

Sabine Dittrich,Gareth D H Turner,Weerawat Phuklia,David J P Ferguson,Paul N Newton,Sayaphet Rattanavong,Stephen J Dumler,Vilada Chansamouth,Daniel H Paris,David H Walker

doi:10.1371/journal.pntd.0003908

Abstract

Neorickettsia sennetsu infection is rarely recognized, with less than 100 globally reported patients over the last 50 years. The disease is thought to be contracted by eating raw fish, a staple of many South-East Asian cuisines. In 2009, the first patient with sennetsu was identified in the Lao PDR (Laos), raising the question as to how common this organism and related species are in patients presenting with fever. We investigated the frequency of N. sennetsu infection at hospitals in diverse areas of Laos. Consenting febrile hospital inpatients from central (Vientiane: n = 1,013), northern (Luang Namtha: n = 453) and southern (Salavan: n = 171) Laos were screened by PCR for N. sennetsu, if no previous positive direct diagnostic test was available. A PCR-restriction fragment length polymorphism assay was developed to differentiate between N. sennetsu, Ehrlichia chaffeensis and Anaplasma phagocytophilum. To allow more detailed studies of N. sennetsu, culture was successfully established using a reference strain (ATCC VR-367), identifying a canine-macrophage cell line (DH82) to be most suitable to visually identify infection. After screening, N. sennetsu was identified and sequence confirmed in four (4/1,637; 0.2%) Lao patients. Despite the previously identified high seroprevalence of N. sennetsu antibodies in the Lao population (~17%), acute N. sennetsu infection with sufficient clinical signs to prompt hospitalization appears to be rare. The reservoir, zoonotic cycle and pathogenicity of N. sennetsu remain unclear and require further investigations.

Highlights

After the rediscovery of Neorickettsia sennetsu as a possible fish-borne cause of fever in 2009, it remained unclear to what extent this pathogen was responsible for disease in Laos and South-East Asia
Dishes prepared with raw or fermented fish are very commonly eaten in rural South-East Asia and the resulting burden of intestinal parasites is high
We describe the screening of ~1,600 patients from urban and rural Laos, finding N. sennetsu in diverse regions of the country

Summary

Introduction

Neorickettsia sennetsu was not reported for 24 years prior to the identification of a Lao patient with sennetsu in 2009 [1]. The resulting public health problem is illustrated by the high prevalence of intestinal parasites transmitted via undercooked fish [7,8,9]. The presence of both high parasitic disease burdens and high sennetsu seroprevalence in the population suggests that N. sennetsu could be an under recognized cause of fever [10]. The detection of N. sennetsu in a febrile Lao patient at our hospital, as well as in a single fish (Anabas testinudeus), highlighted unanswered questions regarding the prevalence, geographical distribution, zoonotic cycle, risk factors and pathogenicity of this rare pathogen [10]. We describe the development of tools to allow simple post-PCR identification as well as successful propagation of N. sennetsu in an endemic area, aiding timely public health interventions and future research on this organism [10,11]

Methods

Results

Discussion

Conclusion