Regina C. LaRocque

Susceptibility to Vibrio cholerae Infection in a Cohort of Household Contacts of Patients with Cholera in Bangladesh

Background Despite recent progress in understanding the molecular basis of Vibrio cholerae pathogenesis, there is relatively little knowledge of the factors that determine the variability in human susceptibility to V. cholerae infection. Methods and Findings We performed an observational study of a cohort of household contacts of cholera patients in Bangladesh, and compared the baseline characteristics of household members who went on to develop culture-positive V. cholerae infection with individuals who did not develop infection. Although the vibriocidal antibody is the only previously described immunologic marker associated with protection from V. cholerae infection, we found that levels of serum IgA specific to three V. cholerae antigens—the B subunit of cholera toxin, lipopolysaccharide, and TcpA, the major component of the toxin–co-regulated pilus—also predicted protection in household contacts of patients infected with V. cholerae O1, the current predominant cause of cholera. Circulating IgA antibodies to TcpA were also associated with protection from V. cholerae O139 infection. In contrast, there was no association between serum IgG antibodies specific to these three antigens and protection from infection with either serogroup. We also found evidence that host genetic characteristics and serum retinol levels modify susceptibility to V. cholerae infection. Conclusions Our observation that levels of serum IgA (but not serum IgG) directed at certain V. cholerae antigens are associated with protection from infection underscores the need to better understand anti–V. cholerae immunity at the mucosal surface. Furthermore, our data suggest that susceptibility to V. cholerae infection is determined by a combination of immunologic, nutritional, and genetic characteristics; additional factors that influence susceptibility to cholera remain unidentified.

Blood Group, Immunity, and Risk of Infection with Vibrio cholerae in an Area of Endemicity

ABSTRACT Individuals with blood group O are more susceptible than other individuals to severe cholera, although the mechanism underlying this association is unknown. To assess the respective roles of both intrinsic host factors and adaptive immune responses that might influence susceptibility to infection with Vibrio cholerae, we prospectively followed a cohort of household contacts of patients with cholera in Bangladesh. In this study, we made the novel observation that persons with blood group O were less likely than those with other blood groups to become infected with V. cholerae O1 (odds ratio [OR], 0.67; 95% confidence interval [CI], 0.53 to 0.85; P = 0.008). Consistent with prior studies, however, household contacts with blood group O were more likely to develop severe illness if infected with V. cholerae O1 (OR, 2.3; 95% CI, 0.98 to 5.59; P = 0.05). While blood group O protected significantly against infection with V. cholerae O1, there was no evidence of protection against V. cholerae O139. A multivariate analysis demonstrated that the association between blood group O and protection from infection with V. cholerae O1 was independent of age, gender, and baseline anti-cholera toxin and vibriocidal antibody titers. Based on this epidemiologic evidence, we propose a hypothesis for understanding the association between blood group O and the risk of infection with V. cholerae O1 and O139 as well as the risk of developing severe symptoms once infected.

Leptospirosis during Dengue Outbreak, Bangladesh

We collected acute-phase serum samples from febrile patients at 2 major hospitals in Dhaka, Bangladesh, during an outbreak of dengue fever in 2001. A total of 18% of dengue-negative patients tested positive for leptospirosis. The case-fatality rate among leptospirosis patients (5%) was higher than among dengue fever patients (1.2%).

Meeting cholera's challenge to Haiti and the world: a joint statement on cholera prevention and care.

Cholera in Haiti: Acute-on-Chronic Long before the devastating earthquake on January 12, 2010, Haiti struggled beneath the burdens of intractable poverty and ill health. The poorest country in the Western Hemisphere, Haiti also faces some of the highest rates of maternal and infant mortality—widely used indicators of the robustness of a health system—in the world ([S1] in Text S1; [2], [3]). The October 2010 cholera outbreak is the most recent of a long series of affronts to the health of Haitis population; it is yet another acute symptom of the chronic weakness of Haitis health, water, and sanitation systems. Water and sanitation conditions highlight these systemic weaknesses. In 2002, Haiti ranked last out of 147 countries for water security [4], [5]. Before the earthquake struck, only half of the population in the capital, Port-au-Prince, had access to latrines or other forms of modern sanitation, and roughly one-third had no access to tap water [6]. Across the country, access to sanitation and clean water is even more limited: only 17% of Haitians had access to adequate sanitation in 2008, and 12% received treated water [7]. Not surprisingly, diarrheal diseases have long been a significant cause of death and disability, especially among children under 5 years of age [6]. The cholera outbreak began less than a year after a 7.0-magnitude earthquake took the lives of more than 300,000 people and left nearly 1.5 million homeless [6]. Almost 1 million Haitians still live in spontaneous settlements known as internally displaced persons (IDP) camps [8]. While post-earthquake conditions in Haiti were ripe for outbreaks of acute diarrheal illness, cholera was deemed “very unlikely to occur” by the United States Centers for Disease Control and Prevention (CDC) and other public health authorities [9]. Cholera had never before been reported in Haiti [S2] [10], [11]; health providers were unprepared for an influx of patients presenting with acute watery diarrhea. The cholera epidemic has been most severe in rural areas and large urban slums. Rural communities were charged with hosting hundreds of thousands of displaced people after the earthquake, placing greater demands on their already-scarce resources, including water. Surface water drawn directly from the source or piped from rivers and streams constitutes the principal supply of drinking water in rural Haiti. The lack of adequate piping, filtration, and water treatment systems (including chlorination) made these rural regions vulnerable to the rapid spread of waterborne disease. While most IDP camps have been supplied with potable water, large urban slums have had to rely on existing water sources—some of them containing Vibrio cholerae—and have therefore been vulnerable to rapid disease spread. Most slums also have poor sanitation infrastructure. Since the first cases were reported in Saint-Marc and Mirebalais, cholera has spread to every department in Haiti, and to other countries, too [S3] [12]–[14]. Public suspicion (ultimately validated by genomic sequence analyses [15]) of the strains link to South Asia, home to a group of United Nations peacekeepers stationed in central Haiti, triggered blame and violence that interfered with response efforts. As we have learned from the global AIDS pandemic and other infectious disease epidemics, cycles of accusation can continue for years, diverting attention and resources from the delivery of care and prevention services [16]. Systemic problems that brought cholera to epidemic levels in Haiti will (unless addressed) continue to facilitate its spread. As a disease of poverty, cholera preys upon the bottom of the social gradient; international trade, migration, and travel—from South Asia or elsewhere—open direct channels for pathogens that follow social fault lines.

Transcriptional Profiling of Vibrio cholerae Recovered Directly from Patient Specimens during Early and Late Stages of Human Infection

ABSTRACT Understanding gene expression by bacteria during the actual course of human infection may provide important insights into microbial pathogenesis. In this study, we evaluated the transcriptional profile of Vibrio cholerae, the causative agent of cholera, in clinical specimens from cholera patients. We collected samples of human stool and vomitus that were positive by dark-field microscopy for abundant vibrios and used a microarray to compare gene expression in organisms recovered directly from specimens collected during the early and late stages of human infection. Our results reveal that V. cholerae gene expression within the human host environment differs from patterns defined in in vitro models of pathogenesis. tcpA, the major subunit of the essential V. cholerae colonization factor, was significantly more highly expressed in early than in late stages of infection; however, the genes encoding cholera toxin were not highly expressed in either phase of human infection. Furthermore, expression of the virulence regulators toxRS and tcpPH was uncoupled. Interestingly, the pattern of gene expression indicates that the human upper intestine may be a uniquely suitable environment for the transfer of genetic elements that are important in the evolution of pathogenic strains of V. cholerae. These findings provide a more detailed assessment of the transcriptome of V. cholerae in the human host than previous studies of organisms in stool alone and have implications for cholera control and the design of improved vaccines.

Antigen-Specific Memory B-Cell Responses to Vibrio cholerae O1 Infection in Bangladesh

ABSTRACT Cholera, caused by Vibrio cholerae, is a noninvasive dehydrating enteric disease with a high mortality rate if untreated. Infection with V. cholerae elicits long-term protection against subsequent disease in countries where the disease is endemic. Although the mechanism of this protective immunity is unknown, it has been hypothesized that a protective mucosal response to V. cholerae infection may be mediated by anamnestic responses of memory B cells in the gut-associated lymphoid tissue. To characterize memory B-cell responses to cholera, we enrolled a cohort of 39 hospitalized patients with culture-confirmed cholera and evaluated their immunologic responses at frequent intervals over the subsequent 1 year. Memory B cells to cholera antigens, including lipopolysaccharide (LPS), and the protein antigens cholera toxin B subunit (CTB) and toxin-coregulated pilus major subunit A (TcpA) were enumerated using a method of polyclonal stimulation of peripheral blood mononuclear cells followed by a standard enzyme-linked immunospot procedure. All patients demonstrated CTB, TcpA, and LPS-specific immunoglobulin G (IgG)and IgA memory responses by day 90. In addition, these memory B-cell responses persisted up to 1 year, substantially longer than other traditional immunologic markers of infection with V. cholerae. While the magnitude of the LPS-specific IgG memory B-cell response waned at 1 year, CTB- and TcpA-specific IgG memory B cells remained significantly elevated at 1 year after infection, suggesting that T-cell help may result in a more durable memory B-cell response to V. cholerae protein antigens. Such memory B cells could mediate anamnestic responses on reexposure to V. cholerae.

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.

Incomplete Correlation of Serum Vibriocidal Antibody Titer with Protection from Vibrio cholerae Infection in Urban Bangladesh

The serum vibriocidal antibody is the only recognized predictor of protection from cholera, but no seroepidemiological data have been gathered since the emergence of Vibrio cholerae O139. We assessed the association between the vibriocidal antibody titer and protection from cholera in an endemic setting. Although a higher baseline vibriocidal titer correlated with protection from V. cholerae O1, infection still developed in some contacts with very high titers. No association between baseline vibriocidal titer and protection from V. cholerae O139 infection was found. Our findings suggest that the vibriocidal antibody is an incomplete predictor of protection from V. cholerae infection.

Pre‐travel Health Advice‐Seeking Behavior Among US International Travelers Departing From Boston Logan International Airport

BACKGROUND Globally mobile populations are at higher risk of acquiring geographically restricted infections and may play a role in the international spread of infectious diseases. Despite this, data about sources of health information used by international travelers are limited. METHODS We surveyed 1,254 travelers embarking from Boston Logan International Airport regarding sources of health information. We focused our analysis on travelers to low or low-middle income (LLMI) countries, as defined by the World Bank 2009 World Development Report. RESULTS A total of 476 survey respondents were traveling to LLMI countries. Compared with travelers to upper-middle or high income (UMHI) countries, travelers to LLMI countries were younger, more likely to be foreign-born, and more frequently reported visiting family as the purpose of their trip. Prior to their trips, 46% of these travelers did not pursue health information of any type. In a multivariate analysis, being foreign-born, traveling alone, traveling for less than 14 days, and traveling for vacation each predicted a higher odds of not pursuing health information among travelers to LLMI countries. The most commonly cited reason for not pursuing health information was a lack of concern about health problems related to the trip. Among travelers to LLMI countries who did pursue health information, the internet was the most common source, followed by primary care practitioners. Less than a third of travelers to LLMI countries who sought health information visited a travel medicine specialist. CONCLUSIONS In our study, 46% of travelers to LLMI countries did not seek health advice prior to their trip, largely due to a lack of concern about health issues related to travel. Among travelers who sought medical advice, the internet and primary care providers were the most common sources of information. These results suggest the need for health outreach and education programs targeted at travelers and primary care practitioners.

Transmission of Vibrio cholerae Is Antagonized by Lytic Phage and Entry into the Aquatic Environment

Cholera outbreaks are proposed to propagate in explosive cycles powered by hyperinfectious Vibrio cholerae and quenched by lytic vibriophage. However, studies to elucidate how these factors affect transmission are lacking because the field experiments are almost intractable. One reason for this is that V. cholerae loses the ability to culture upon transfer to pond water. This phenotype is called the active but non-culturable state (ABNC; an alternative term is viable but non-culturable) because these cells maintain the capacity for metabolic activity. ABNC bacteria may serve as the environmental reservoir for outbreaks but rigorous animal studies to test this hypothesis have not been conducted. In this project, we wanted to determine the relevance of ABNC cells to transmission as well as the impact lytic phage have on V. cholerae as the bacteria enter the ABNC state. Rice-water stool that naturally harbored lytic phage or in vitro derived V. cholerae were incubated in a pond microcosm, and the culturability, infectious dose, and transcriptome were assayed over 24 h. The data show that the major contributors to infection are culturable V. cholerae and not ABNC cells. Phage did not affect colonization immediately after shedding from the patients because the phage titer was too low. However, V. cholerae failed to colonize the small intestine after 24 h of incubation in pond water—the point when the phage and ABNC cell titers were highest. The transcriptional analysis traced the transformation into the non-infectious ABNC state and supports models for the adaptation to nutrient poor aquatic environments. Phage had an undetectable impact on this adaptation. Taken together, the rise of ABNC cells and lytic phage blocked transmission. Thus, there is a fitness advantage if V. cholerae can make a rapid transfer to the next host before these negative selective pressures compound in the aquatic environment.