Ana A. Weil

Patients with Suspected Herpes Simplex Encephalitis: Rethinking an Initial Negative Polymerase Chain Reaction Result

A statewide encephalitis diagnostic project of the California State Department of Health Services found that herpes simplex virus 1 DNA may not be detectable by molecular methods early in the clinical course of herpes simplex encephalitis.

Clinical Outcomes in Household Contacts of Patients with Cholera in Bangladesh

BACKGROUND Multiple Vibrio cholerae infections in the same household are common. The objective of this study was to examine the incidence of V. cholerae infection and associated clinical symptoms in household contacts of patients with cholera and to identify risk factors for development of severe dehydration in this cohort. METHODS Household contacts of hospitalized patients with cholera were observed with frequent clinical assessments and collection of serum and rectal swab samples for culture for a period of 21 days after presentation of the index case. RESULTS One-half (460 of 944) of all contacts reported diarrhea during the study period, and symptoms most frequently began 2 days after presentation of the index case. Antibiotics were used by 199 (43%) of 460 contacts with diarrhea. Results of rectal swab cultures for V. cholerae were positive for 202 (21%) of 944 contacts, and 148 (73%) infected contacts experienced diarrhea. Significant dehydration developed in 26 contacts; predictors of dehydration included vomiting, each additional day of diarrhea, and blood group O status. CONCLUSIONS In urban Bangladesh, the burden of diarrheal illness among household contacts of patients with cholera is higher than was previously estimated, and prophylactic intervention is feasible, because the majority of symptomatic cases of V. cholerae infection in contacts begin soon after presentation of the index case. Re-evaluation of targeted chemoprophylaxis for household contacts of patients with cholera may be warranted.

Gut Microbial Succession Follows Acute Secretory Diarrhea in Humans

ABSTRACT Disability after childhood diarrhea is an important burden on global productivity. Recent studies suggest that gut bacterial communities influence how humans recover from infectious diarrhea, but we still lack extensive data and mechanistic hypotheses for how these bacterial communities respond to diarrheal disease and its treatment. Here, we report that after Vibrio cholerae infection, the human gut microbiota undergoes an orderly and reproducible succession that features transient reversals in relative levels of enteric Bacteroides and Prevotella. Elements of this succession may be a common feature in microbiota recovery from acute secretory diarrhea, as we observed similar successional dynamics after enterotoxigenic Escherichia coli (ETEC) infection. Our metagenomic analyses suggest that multiple mechanisms drive microbial succession after cholera, including bacterial dispersal properties, changing enteric oxygen and carbohydrate levels, and phage dynamics. Thus, gut microbiota recovery after cholera may be predictable at the level of community structure but is driven by a complex set of temporally varying ecological processes. Our findings suggest opportunities for diagnostics and therapies targeting the gut microbiota in humans recovering from infectious diarrhea. IMPORTANCE Disability after diarrhea is a major burden on public health in the developing world. Gut bacteria may affect this recovery, but it remains incompletely understood how resident microbes in the digestive tract respond to diarrheal illness. Here, we observed an orderly and reproducible succession of gut bacterial groups after cholera in humans. Genomic analyses associated the succession with bacterial dispersal in food, an altered microbial environment, and changing phage levels. Our findings suggest that it may one day be feasible to manage resident bacterial populations in the gut after infectious diarrhea. Disability after diarrhea is a major burden on public health in the developing world. Gut bacteria may affect this recovery, but it remains incompletely understood how resident microbes in the digestive tract respond to diarrheal illness. Here, we observed an orderly and reproducible succession of gut bacterial groups after cholera in humans. Genomic analyses associated the succession with bacterial dispersal in food, an altered microbial environment, and changing phage levels. Our findings suggest that it may one day be feasible to manage resident bacterial populations in the gut after infectious diarrhea.

Memory B Cell Responses to Vibrio cholerae O1 Lipopolysaccharide Are Associated with Protection against Infection from Household Contacts of Patients with Cholera in Bangladesh

ABSTRACT Vibrio cholerae O1 causes cholera, a dehydrating diarrheal disease. We have previously shown that V. cholerae-specific memory B cell responses develop after cholera infection, and we hypothesize that these mediate long-term protective immunity against cholera. We prospectively followed household contacts of cholera patients to determine whether the presence of circulating V. cholerae O1 antigen-specific memory B cells on enrollment was associated with protection against V. cholerae infection over a 30-day period. Two hundred thirty-six household contacts of 122 index patients with cholera were enrolled. The presence of lipopolysaccharide (LPS)-specific IgG memory B cells in peripheral blood on study entry was associated with a 68% decrease in the risk of infection in household contacts (P = 0.032). No protection was associated with cholera toxin B subunit (CtxB)-specific memory B cells or IgA memory B cells specific to LPS. These results suggest that LPS-specific IgG memory B cells may be important in protection against infection with V. cholerae O1.

Memory T-Cell Responses to Vibrio cholerae O1 Infection

ABSTRACT Vibrio cholerae O1 can cause diarrheal disease that may be life-threatening without treatment. Natural infection results in long-lasting protective immunity, but the role of T cells in this immune response has not been well characterized. In contrast, robust B-cell responses to V. cholerae infection have been observed. In particular, memory B-cell responses to T-cell-dependent antigens persist for at least 1 year, whereas responses to lipopolysaccharide, a T-cell-independent antigen, wane more rapidly after infection. We hypothesize that protective immunity is mediated by anamnestic responses of memory B cells in the gut-associated lymphoid tissue, and T-cell responses may be required to generate and maintain durable memory B-cell responses. In this study, we examined B- and T-cell responses in patients with severe V. cholerae infection. Using the flow cytometric assay of the specific cell-mediated immune response in activated whole blood, we measured antigen-specific T-cell responses using V. cholerae antigens, including the toxin-coregulated pilus (TcpA), a V. cholerae membrane preparation, and the V. cholerae cytolysin/hemolysin (VCC) protein. Our results show that memory T-cell responses develop by day 7 after infection, a time prior to and concurrent with the development of B-cell responses. This suggests that T-cell responses to V. cholerae antigens may be important for the generation and stability of memory B-cell responses. The T-cell proliferative response to VCC was of a higher magnitude than responses observed to other V. cholerae antigens.

Antigen-Specific Memory T Cell Responses after Vaccination with an Oral Killed Cholera Vaccine in Bangladeshi Children and Comparison to Responses in Patients with Naturally Acquired Cholera

ABSTRACT Young children, older children, and adults develop comparable levels and durations of immunity following cholera. In comparison, young children receiving oral killed cholera vaccines (OCV) develop a lower level and shorter duration of protection than those of older children and adults. The reasons for this are unclear. We investigated OCV-induced memory T cell responses in younger and older children and compared responses to those in children with cholera. We found that patients with cholera developed significant levels of toxin-specific effector memory T cells (TEM) with follicular helper and gut-homing characteristics. Older children (6 to 14 years of age) receiving two doses of OCV containing recombinant cholera toxin B subunit (rCTB) had more modest TEM responses with follicular helper and gut-homing characteristics, but younger vaccinees (24 to 71 months of age) did not develop TEM responses. The TEM response correlated positively with subsequent IgG memory B cell responses specific to rCTB in older vaccinees. Cytokine analyses indicated that cholera patients developed significant Th1, Th17, and Th2 responses, while older children receiving vaccine developed more modest increases in Th1 and Th17 cells. Younger vaccinees had no increase in Th1 cells, a decrease in Th17 cells, and an increase in regulatory T (Treg) cells. Our findings suggest that T cell memory responses are markedly diminished in children receiving OCV, especially young children, compared to responses following naturally acquired cholera, and that these differences affect subsequent development of memory B cell responses. These findings may explain the lower efficacy and shorter duration of protection afforded by OCV in young children.

Vibrio cholerae O1 Infection Induces Proinflammatory CD4 T-Cell Responses in Blood and Intestinal Mucosa of Infected Humans†

ABSTRACT Vibrio cholerae O1 is a noninvasive enteric pathogen and serves as a model for studies of mucosal immunity. Although symptomatic V. cholerae infection induces durable protection against subsequent disease, vaccination with oral killed whole-cell V. cholerae stimulates less long-lasting protection against cholera. In this study, we demonstrated that cholera induces an early proinflammatory cellular immune response that results in priming of Th1- and Th17-type cytokine responses to ex vivo antigenic stimulation and an increase in the ratio of Th1 to Th2 CD4+ T-cell responses. Comparable priming of Th1 and Th17 responses, with an increased ratio of Th1 to Th2 CD4+ T-cell responses, was not observed in subjects who received two doses of the oral cholera vaccine Dukoral (a whole-cell cholera toxin B subunit containing [WC-CTB] vaccine). These findings suggest that natural V. cholerae infection induces an early, proinflammatory cellular immune response, despite the apparent lack of clinical signs of inflammation. The failure of the WC-CTB vaccine to activate equivalent, CD4+ T-cell responses is a potential explanation for the shorter duration of protection following immunization with this vaccine. Additional studies are needed to determine whether these early T-cell-mediated events predict the subsequent duration of immunologic memory.

Cholera: Lessons from Haiti and Beyond

Cholera is an acute, severe diarrheal disease caused by Vibrio cholerae that affects millions of people each year. Without prompt rehydration, death can occur within hours of the onset of symptoms. In October 2010, cholera emerged in Haiti, and the resulting large epidemic continues today. As of August 29, 2011, more than 439,000 cases have been reported in Haiti, with over 6,200 deaths. This review covers important features of epidemiology, pathogenesis, treatment and prevention of cholera, with a focus on the ongoing epidemic in Haiti.

Fecal Microbiota Transplant: Benefits and Risks

We commend the authors of “Weight Gain After Fecal Microbiota Transplantation” for describing this case of obesity after a fecal microbiota transplant (FMT). Fecal microbiota transplant is a highly effective therapy for recurrent Clostridium difficile infection (r-CDI), and the authors discuss possible unintended consequences in a patient after successful FMT, which could be due to alteration of the gut microbiota. Strengths of this study include (1) detailed information about the clinical course of the patient receiving FMT for r-CDI and (2) characteristics of the FMT donor, the patient’s daughter. This experience led to a change in FMT donor policy at the authors’ institution. The authors do not identify the mechanism for transmission of the obese phenotype, directly demonstrate a causal relationship, or study the patient’s microbiome over time. They do identify several factors that may have contributed to weight gain after FMT in the patient. These include, but are not limited to, resolution of CDI, antibiotic use, treatment for Helicobacter pylori infection, stress related to illness, older age, and genetic factors. There is no discussion of eating patterns or changes in eating patterns in these related and presumably cohabitating individuals. These possibilities aside, there is a growing body of data exploring the relationship between host body mass index (BMI), host metabolism, and the gut microbiota. The transmission of an obese phenotype after therapeutic FMT for r-CDI has not been reported previously, to our knowledge. There are differences in the gut microbial structure between lean and obese individuals [1]. A complex relationship exists between BMI and gut microbes, and this association cannot be reduced to a correlation between specific bacterial taxonomic groups and host BMI [2, 3]. Studies of the gut microbiome in monozygotic twins with discordant BMIs have advanced the knowledge of the gut microbe-host BMI interaction by demonstrating transmissibility and reversibility of the obese phenotype. In studies by Ridaura et al [4], germ-free mice receiving a stool lavage from an obese twin developed significantly greater adiposity than mice infused with the lean twin’s microbiota, and this effect was lessened when the 2 groups were cohoused (mice are normally coprophagic). The expression of microbial genes important for detoxification and stress responses were more prominent in germ-free mice that received the obese twin microbiome compared with the lean twin flora [4]. There is also new evidence that host genetics influence the structure of the gut microbiota, and in a study of more than 400 twin pairs, specific bacterial taxa were found to be more “heritable” than others [5]. It is possible and perhaps even likely that the weight gain in the case reported was influenced not only by microbial communities transmitted during FMT, but also by genetic factors common to the FMT donor and recipient. In controlled, randomized, and doubleblinded human studies described by Vrieze et al [6], transfer of a leanmicrobiota to individuals with metabolic syndrome was associated with improved insulin sensitivity when compared with controls (individuals with metabolic syndrome who received an infusion of their own stool). In this study, butyrate-producing bacterial strains (known to activate intestinal gluconeogenesis) were increased in both lean stool samples and lean individual’s intestinal biopsies [6]. Animal studies have shown that a relative paucity of butyrate-producing bacteria in the gut is associated with increased insulin resistance, and butyrate supplementation can reverse insulin resistance in diet-induced obesity in mice [7, 8]. A reduction in butyrate-producing bacteria can be achieved using antimicrobial agents directed at Gram-positive organisms, and by this mechanism, a loss of butyrate-producing organisms has been suggested as an explanation for the increase in BMI observed in patients treated with vancomycin for treatment of infective endocarditis [9, 10]. Bacterial products from the gut have been shown to enter the serum and affect distal organs. A recent murine study showed that manipulating gut flora in germ-free maternal mice affected the Received 22 December 2014; accepted 14 January 2015. Correspondencer: Ana A. Weil, MD, MPH, Infectious Diseases, Massachusetts General Hospital, 55 Fruit St., GRJ 520, Boston, MA 02114 (aweil@partners.org). Open Forum Infectious Diseases

Bacterial Shedding in Household Contacts of Cholera Patients in Dhaka, Bangladesh

Multiple Vibrio cholerae infections within the same household are common. Household contacts of patients with cholera were observed with daily clinical assessments and collection of rectal swab cultures for nine days after presentation of the index case. During the follow-up period, 71 (24%) of 294 household contacts developed a positive V. cholerae rectal swab, signifying bacterial shedding. The average length of bacterial shedding was 2.0 days (95% confidence interval 1.7-2.4). However, 16 (5%) of 294 contacts shed V. cholerae for ≥ 4 days. In a multivariate analysis, malnutrition was predictive of long-term shedding (odds ratio = 1.4, 95% confidence interval = 1.3-13, P = 0.02). High rates of V. cholerae infection and bacterial shedding among household contacts of cholera patients represent an opportunity for intervention to reduce V. cholerae transmission.