Urban dengue is common in most countries of the Americas, but has been rare in the United States for more than half a century. In 1999 we investigated an outbreak of the disease that affected Nuevo Laredo, Tamaulipas, Mexico, and Laredo, Texas, United States, contiguous cities that straddle the international border. The incidence of recent cases, indicated by immunoglobulin M antibody serosurvey, was higher in Nuevo Laredo, although the vector, Aedes aegypti, was more abundant in Laredo. Environmental factors that affect contact with mosquitoes, such as air-conditioning and human behavior, appear to account for this paradox. We conclude that the low prevalence of dengue in the United States is primarily due to economic, rather than climatic, factors.

Isolates of Borrelia turicatae, Borrelia parkeri, and the Florida canine borrelia (FCB) were examined to further phylogenetically characterize the identities of these spirochetes in the United States. DNA sequences of four chromosomal loci (the 16S rRNA gene, flaB, gyrB, and glpQ) were determined for eight isolates of B. turicatae and six isolates of B. parkeri, which grouped the spirochetes into two distinct but closely related taxa (>98% sequence identity) separate from Borrelia hermsii. The FCB was clearly separated with the group identified as B. turicatae, confirming this bacterium as a relapsing fever spirochete. Therefore, the potential for tick-borne relapsing fever in humans and other animals exists in Florida and future efforts are needed to determine the enzootic hosts and distribution of this spirochete in the southeastern United States. Analysis of plasmids demonstrated both linear and circular forms in B. turicatae but only linear plasmids in B. parkeri, which should be of interest to investigators concerned with plasmid diversity and evolution within this group of spirochetes.

In 1997, the Centers for Disease Control and Prevention, the Mexican Secretariat of Health, and border health officials began the development of the Border Infectious Disease Surveillance (BIDS) project, a surveillance system for infectious diseases along the U.S.-Mexico border. During a 3-year period, a binational team implemented an active, sentinel surveillance system for hepatitis and febrile exanthems at 13 clinical sites. The network developed surveillance protocols, trained nine surveillance coordinators, established serologic testing at four Mexican border laboratories, and created agreements for data sharing and notification of selected diseases and outbreaks. BIDS facilitated investigations of dengue fever in Texas-Tamaulipas and measles in California–Baja California. BIDS demonstrates that a binational effort with local, state, and federal participation can create a regional surveillance system that crosses an international border. Reducing administrative, infrastructure, and political barriers to cross-border public health collaboration will enhance the effectiveness of disease prevention projects such as BIDS.

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Hantaviruses are etiologic agents of hemorrhagic fever with renal syndrome, an acute illness characterized by acute renal insufficiency, proteinuria, and hemodynamic instability. Recently, a New World form of hantavirus disease, hantavirus pulmonary syndrome (HPS), was recognized; in this form, pulmonary edema is prominent, but renal insufficiency is generally lacking. HPS cases from the southeastern United States may be exceptional in that they have exhibited both pulmonary and renal manifestations. One case in Louisiana and one case in Florida were linked to infection by the distinct but closely related Bayou and Black Creek Canal hantaviruses, respectively. We report a nonfatal case of HPS caused by Bayou hantavirus that occurred in eastern Texas. Clinical manifestations included pulmonary and renal insufficiency and myositis, which had previously been observed in the patient from Florida. The occurrence of distinctive clinical abnormalities in HPS cases from the southeastern United States supports the concept that there are clinically significant differences between western and southeastern forms of HPS.

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culturing the Lyme disease spirochete Borrelia burgdorferi in 1985. This organism was subsequently isolated from blood, cerebrospinal fluid, joint fluid, skin, bone, and autopsy tissues from humans. Fluorescent-antibody tests with murine monoclonal antibodies confirmed that seven of these isolates were B. burgdorferi and that two others belonged to the genus Borrelia. Lyme disease, first recognized in 1975, is a tick-borne infection that can result in long-term rheumatologic or neurologic disorders. A spirochete isolated from Ixodes dammini in 1982 was later found to be the etiologic agent of the illness (6, 16). Since then, this bacterium, called Borrelia burgdorferi, has been detected in tissue specimens from patients who were diagnosed clinically as having Lyme disease (4, 5, 8, 9, 16). These specimens include blood, cerebrospinal fluid (CSF), joint fluids, and skin tissues. At the Texas Department of Health, we began culturing for B. burgdorferi during the spring of 1985. Blood, CSF, joint fluids, bone scrapings, autopsy tissues, and skin tissues from patients whose physicians suspected Lyme disease were submitted to our laboratory. These specimens were placed in modified BSK II medium in an attempt to isolate B. burgdorferi (1). Our findings are reported here. MATERIALS AND METHODS Specimens were collected by physicians and shipped overnight to the Texas Department of Health Laboratory in Austin. Blood, CSF, and joint fluids were sent either on wet or dry ice; skin and autopsy tissues were shipped in approximately 1 ml of either brain heart infusion or thioglycolate medium; and bone scrapings (from the right wrist of the patient) were placed directly into BSK II medium by the physician.

Between 1990 and 1992, ticks from eight Texas parks were collected and analyzed to determine the prevalence of spirochete-infected ticks. Borrelia spirochetes were detected in 1.03% of 5,141 Amblyomma americanum (L.) adults examined, a species Texas residents often encounter. No spirochetes were observed in the other tick species tested.