Search For New and Emerging Etiologic Agents

美国正在研究急性或慢性非甲、乙、丙、丁、戊型肝炎患者的临床样本，以寻找传播媒介的生物学、血清学或分子证据。暴发性非甲到戊型肝炎患者的诊断仍然是一个谜，可能感染了一种或多种以前未被识别的病毒。我们正试图找出这种疾病的病因。我们在印度、埃及和沙特阿拉伯进行的血清流行病学研究提供了另一种水传播肝炎病毒存在的证据。我们正试图从这些病人的临床标本中传播一种病原体。几年前，据报道一种肝炎病毒可从一名非甲、非乙肝炎患者传染给狨猴。该病菌可在狨猴中连续传播，已被部分鉴定。对GB病毒进行了克隆和测序，结果显示它是两种不同的病毒（GBV-A和GBV-B），每一种病毒都与丙型肝炎病毒以及以前未被识别的人类病毒（GBV-C）有远亲关系。已在灵长类动物和体外对GB试剂和新发现的人类病毒进行了研究。构建了GBV-B的感染性cDNA。新发现的人类病毒（GBV-C）被传播给黑猩猩，由此产生的感染具有特征。此外，在新大陆猴子身上发现了几种与GBV-A有关的新病毒。戊型肝炎病毒可能正在成为一个比以前认为的更大的公共卫生问题。我们正在研究它在全世界发展中国家和工业化国家的流行病学。获得猪感染戊型肝炎病毒（HEV）的血清学证据。从感染猪中分离到一株新的独特HEV毒株，并对其进行了鉴定。它被证明具有世界范围的分布。对猪操作人员和匹配的献血者进行的血清流行病学研究显示，猪操作人员体内HEV抗体过量，表明该病毒可能通过人畜共患传播。也获得了野生大鼠感染戊型肝炎病毒的类似血清学证据，目前正在寻找感染源。迄今为止，我们已成功地将该媒介从洛杉矶捕获的大鼠传播到同一物种的实验室大鼠（褐家鼠）。然而，传播一直很困难，这表明病毒以低滴度复制。我们在SCID大鼠中准备了一个相对高滴度的病毒池。确定大鼠HEV是否与人类感染有关的研究正在进行中。近年来，分子生物学的现代技术被用于发现新的病毒。目前，这些技术正被应用于从输血相关性肝炎患者中前瞻性收集血清，以寻找可能导致美国高达15%此类肝炎的新型肝炎病毒。为了提高特定病毒发现技术的灵敏度（即，那些能够在不考虑序列的情况下扩增独特序列的技术），我们对现有技术进行了修改，以提高检测的灵敏度。利用这项新技术，我们发现了两种以前未被识别的牛细小病毒，它们污染了大部分牛血清。这一发现对用牛血清制备的生物制剂的安全性具有启示意义。川崎病是一种危及幼儿生命的疾病。它具有传染病的流行病学特征。HVS正试图将一种假定的病原体从川崎病儿童急性期临床样本传播给非人灵长类动物。另一种新发现的病原体是严重急性呼吸系统综合征（SARS）的病原。我们正在相关动物模型系统中研究这种病毒的自然历史。

Clinical samples from patients with acute or chronic non-A, B, C, D, E hepatitis in the United States are being studied for biological, serological or molecular evidence of transmissible agents. Patients with fulminant non-A to E hepatitis remain a diagnostic enigma and may be infected with one or more previously unrecognized viruses. We are attempting to discover the etiology of this disease. Evidence for the existence of an additional water-borne hepatitis virus has come from our seroepidemiologic studies in India, Egypt and Saudi Arabia. We are attempting to transmit an agent from clinical specimens of such patients. Some years ago, a hepatitis virus was reported to be transmissible from a non-A, non-B hepatitis patient to marmoset (tamarin) monkeys. The agent, called the GB agent, could be serially transmitted in marmosets and was partially characterized. The GB agent was cloned and sequenced and shown to be two separate viruses (GBV-A and GBV-B), each distantly related to hepatitis C virus as well as to a previously unrecognized human virus (GBV-C). The GB agents and the newly discovered human virus have been studied in primates and in vitro. An infectious cDNA of GBV-B was constructed. The newly recognized human virus (GBV-C) was transmitted to chimpanzees and the resulting infection characterized. In addition, several new viruses, related to GBV-A, were discovered in New World monkeys. Hepatitis E virus may be emerging as a greater public health problem than previously thought. We are studying its epidemiology in developing and industrialized countries worldwide. Serologic evidence of infection of swine with hepatitis E virus (HEV) was obtained. A new and unique HEV strain was recovered from infected swine and characterized. It was shown to have a worldwide distribution. Seroepidemiological studies of swine handlers and matched blood donors have shown an excess of antibody to HEV in swine handlers, suggesting that the virus may be zoonotically spread. Similar serologic evidence for infection of wild rats with HEV has also been obtained and the infecting agent is being sought. To date we have successfully transmitted the agent from rats trapped in Los Angeles to laboratory rats of the same species (Rattus norvegicus). However, transmission has been difficult, suggesting that the virus replicates at low titer. We have prepared a relatively high-titered pool of the virus in SCID rats. Studies to determine if rat HEV is linked to human infection are in progress. Modern techniques of molecular biology have been used to discover new viruses in recent years. These are now being applied to prospectively collected sera from patients with transfusion-associated hepatitis in a search for new hepatitis viruses that may cause up to 15% of such hepatitis in the US. In an attempt to increase the sensitivity of specific virus discovery technologies (i.e., those capable of amplifying unique sequences without regard to the sequence), we have introduced modifications to existing techniques that have improved the sensitivity of the assay. Using the new technology, we have discovered two previously unrecognized bovine parvoviruses that contaminate most lots of bovine serum. This finding has implications for the safety of biologicals that are prepared with bovine serum. Kawasaki Disease is a life-threatening illness of young children. It has the epidemiologic characteristics of an infectious disease. The HVS is attempting to transmit a putative agent from acute phase clinical samples of children with Kawasaki Disease to nonhuman primates.Another newly recognized pathogen is the etiologic agent of Severe Acute Respiratory Syndrome (SARS). We are studying the natural history of this virus in relevant animal model systems.