Update on non-vector transmission of dengue: relevant studies with Zika and other flaviviruses.

Human dengue virus infection without mosquito vector has been reported to occur as a result of mucocutaneous transmission, needlestick in patient care and laboratory accident, blood transfusion, bone marrow transplant, organ transplant, intrapartum and perinatal transmission, and breastfeeding. The emergence of Zika virus, another mosquito-borne flavivirus, has illustrated additional potential routes of non-vector transmission in humans. A recent study in another flavivirus, Japanese encephalitis virus, in pigs has also demonstrated non-vector transmission. We highlight some reports on dengue virus that have documented non-vector transmission and that are relevant to the transmission of Zika virus and other flaviviruses.

Dengue: update on epidemiology.

The epidemiology of dengue fever has undergone major shifts in recent decades. The global distribution has expanded to include more geographic areas. The intensity of transmission and the severity of infections have increased in areas where infection was already endemic. Multiple studies provide a clearer picture of the epidemiology and allow mapping of its distribution and change over time. Despite major efforts to control transmission, competent vectors now infest most tropical and subtropical regions; Aedes albopictus, also a competent vector, is able to survive in temperate areas, placing parts of Europe and North America at risk for local transmission. Many research teams in dengue-endemic areas are working to identify key local weather, vector, and other variables that would allow prediction of a likely epidemic early enough to permit interventions to avert it or blunt its impact.

Latent infection with Leishmania donovani in highly endemic villages in Bihar, India.

INTRODUCTION: Asymptomatic persons infected with the parasites causing visceral leishmaniasis (VL) usually outnumber clinically apparent cases by a ratio of 4-10 to 1. We describe patterns of markers of Leishmania donovani infection and clinical VL in relation to age in Bihar, India. METHODS: We selected eleven villages highly endemic for Leishmania donovani. During a 1-year interval we conducted two house to house surveys during which we collected blood samples on filter paper from all consenting individuals aged 2 years and above. Samples were tested for anti-leishmania serology by Direct Agglutination Test (DAT) and rK39 ELISA. Data collected during the surveys included information on episodes of clinical VL among study participants. RESULTS: We enrolled 13,163 persons; 6.2% were reactive to DAT and 5.9% to rK39. Agreement between the tests was weak (kappa = 0.30). Among those who were negative on both tests at baseline, 3.6% had converted to sero-positive on either of the two tests one year later. Proportions of sero-positives and sero-converters increased steadily with age. Clinical VL occurred mainly among children and young adults (median age 19 years). DISCUSSION: Although infection with L. donovani is assumed to be permanent, serological markers revert to negative. Most VL cases occur at younger ages, yet we observed a steady increase with age in the frequency of sero-positivity and sero-conversion. Our findings can be explained by a boosting effect upon repeated exposure to the parasite or by intermittent release of parasites in infected subjects from safe target cells. A certain proportion of sero-negative subjects could have been infected but below the threshold of antibody abundance for our serologic testing.

NDM-1 and the Role of Travel in Its Dissemination.

Antimicrobial resistance is a growing problem globally. The appearance and spread of bacteria that are resistant to most or all commonly available antibiotics has raised the specter of untreatable bacterial infections. The New Delhi metallo-beta-lactamase-1 (NDM-1) has received wide attention because of the extreme resistance it confers, its presence in many common pathogens, its rapid spread to multiple continents, and local nosocomial spread in some areas. Most early reports of infections were in individuals who had received medical care in the Indian subcontinent. This paper will explore the role of travelers in the movement of pathogens and microbial genetic material associated with resistance, with a special focus on the appearance and dispersal of bacteria carrying this mobile genetic element, bla (NDM-1), and the contributing factors, including growing long-distance travel and expansion of travel across international borders for medical, dental, and surgical care (medical tourism).

The role of the traveler in emerging infections and magnitude of travel.

Travel and trade have grown immensely. Travelers interact with people and microbes during their journeys, and can introduce infectious agents to new areas and populations. Studying illnesses in travelers is a source of knowledge into diseases of resource-poor regions and the control of these diseases. Travel-associated illnesses also serve to detect emerging infections.

Emergence and control of infectious diseases in China.

Infectious diseases remain the major causes of morbidity and mortality in China despite substantial progress in their control. China is a major contributor to the worldwide infectious disease burden because of its population size. The association of China with the rest of the world through travel and trade means that events in the country can affect distant populations. The ecological interaction of people with animals in China favours the emergence of new microbial threats. The public-health system has to be prepared to deal with the challenges of newly emerging infectious diseases and at the same time try to control existing diseases. To address the microbial threats, such as severe acute respiratory syndrome, the government has committed substantial resources to the implementation of new strategies, including the development of a real-time monitoring system as part of the infectious-disease surveillance. This strategy can serve as a model for worldwide surveillance and response to threats from infectious diseases.

Prevention of tick-borne diseases.

Ticks are a part of the landscape where humans live, work, and play. Because ticks carry a wide range of organisms that potentially can cause disease in humans, many studies have focused on ways to reduce risk of these diseases. Ticks have biologically complex interactions with microorganisms and with their vertebrate hosts, on whom they depend for blood meals and survival. To consider ways to reduce the burden of tick-borne diseases in humans, it is necessary to understand the biology and ecology of ticks and their interface with humans. In many areas, changes in land use, reforestation, and patterns of human settlements have led to more abundant tick populations, increasing rates of infections in ticks, and increasing contact with human populations. Warmer winter temperatures in temperate regions may extend the transmission season for some ticks and pathogens. Although much of the discussion in this article has focused on I. scapularis and the Lyme disease spirochete (because they have been studied extensively), other tick-pathogen pairs may differ in risk factors for infection and transmission dynamics. Interventions studied to reduce the burden of tick-borne diseases include changing the environment, controlling vertebrate hosts, killing ticks, altering the behavior of humans, treating tick bites, and trying to protect humans through immunologic means (vaccine). All of these approaches have limitations and drawbacks. From a public health perspective, a plan that employs multiple strategies may be most effective. This article has reviewed what is known about preventive interventions, including the vaccine.