Taking a bite out of nutrition and arbovirus infection

Nutrition is a key factor in host–pathogen defense. Malnutrition can increase both host susceptibility and severity of infection through a number of pathways, and infection itself can promote nutritional deterioration and further susceptibility. Nutritional status can also strongly influence response to vaccination or therapeutic pharmaceuticals. Arthropod-borne viruses (arboviruses) have a long history of infecting humans, resulting in regular pandemics as well as an increasing frequency of autochthonous transmission. Interestingly, aside from host-related factors, nutrition could also play a role in the competence of vectors required for transmission of these viruses. Nutritional status of the host and vector could even influence viral evolution itself. Therefore, it is vital to understand the role of nutrition in the arbovirus lifecycle. This Review will focus on nutritional factors that could influence susceptibility and severity of infection in the host, response to prophylactic and therapeutic strategies, vector competence, and viral evolution.

As the old adage goes, you are what you eat. Proper nutrition is a cornerstone of health, and malnutrition can seriously impair the function of the immune system, resulting in increased infections or a more severe disease. Imbalanced or inadequate nutrition can also affect responses to vaccines or drugs that are vital for protection and treatment against viruses. A mosquito is also a product of what it eats. Nutrition during development and adult lifecycle can affect the feeding behavior of mosquitoes, thereby affecting transmission of viral diseases. Arthropod-borne viruses (arboviruses) are a major global health concern, especially in areas impacted by malnutrition. Understanding how nutrition can affect both humans and mosquitoes in the context of these viruses is vital to combating these diseases.

Infections of the developing world

Access to critical care is rapidly growing in areas of the world where it was previously nonexistent and where infectious diseases often comprise the largest disease burden. Additionally, with crowding, mass migrations, and air travel, infectious diseases previously geographically confined are quickly spread across the planet, often in shorter time frames than disease incubation periods. Hence, critical care practitioners must be familiar with infectious diseases previously confined to the developing world. This article reviews selected tropical diseases that are seen in diverse locales and often require critical care services.

North American encephalitic arboviruses

Arboviruses continue to be a major cause of encephalitis in North America, and West Nile virus neuroinvasive disease is now the dominant cause of encephalitis. Transmission to humans of North American arboviruses occurs by infected mosquitoes or ticks. Most infections are asymptomatic or produce a flulike illness. Rapid serum or cerebrospinal fluid IgM antibody capture ELISA assays are available to diagnosis the acute infection for all North American arboviruses. Unfortunately, no antiviral drugs are approved for the treatment of arbovirus infection and current therapy is supportive.

Arboviruses and their vectors in the Pacific--status report

Three arboviruses have already caused epidemics in various Pacific Island countries and territories, and currently represent a direct threat to public health. The diseases concerned are all mosquito-borne and should be kept under careful surveillance. Dengue fever, which is a worldwide major public health problem, is mainly transmitted in the Pacific by the Aedes aegypti vector but also by other mosquitoes of this genus with varying ranges. Epidemic polyarthritis due to the Ross River virus is endemic in Australia. At least one major epidemic has occurred in the Pacific where various vector mosquito species occur. Japanese encephalitis is a zoonosis that can be transmitted to humans by mosquitoes of the genus Culex. Its area of distribution in Asia is expanding and the possibility of fresh incursions into the region should be borne in mind. This paper reviews the situation regarding these diseases in the Pacific and provides information on the way they are transmitted as well as on the biology of the mosquito vectors.

The global emergence/resurgence of arboviral diseases as public health problems

During the past 20 years there has been a dramatic resurgence or emergence of epidemic arboviral diseases affecting both humans and domestic animals. These epidemics have been caused primarily by viruses thought to be under control such as dengue, Japanese encephalitis, yellow fever, and Venezuelan equine encephalitis, or viruses that have expanded their geographic distribution such as West Nile and Rift Valley fever. Several of these viruses are presented as case studies to illustrate the changing epidemiology. The factors responsible for the dramatic resurgence of arboviral diseases in the waning years of the 20th century are discussed, as is the need for rebuilding the public health infrastructure to deal with epidemic vector-borne diseases in the 21st century.

[Arbovirus infections. From virus, mosquitoes, animals and humans]

Arboviruses occur throughout the world in plants and animals: reptiles, birds and mammals including man. These relatively recent RNA-containing viruses have great evolutionary potential and are a major cause of epidemics. Arboviruses exhibit a dual life cycle involving continual transmission to and from the vertebrate host and arthropod vector which ingests or inoculates the agent during blood meals. Agents belong to many different viral families and represent an important source of emerging diseases. Because of the mode of transmission is vectorial, spread can enhanced by man-made changes in the ecosystem. This risk is often underestimated. The population explosion provides a great opportunity for the progression of these arboviruses.

In vivo reassortment of Thogoto virus (a tick-borne influenza-like virus) following oral infection of Rhipicephalus appendiculatus ticks

Arboviruses with segmented genomes have the potential to reassort in both their vertebrate hosts and arthropod vectors. Reassortment of Thogoto virus, a tick-borne orthomyxo-like virus, has been demonstrated following dual infection of hamsters by temperature-sensitive mutants. To investigate whether similar events can occur in ticks, Rhipicephalus appendiculatus larvae and nymphs were dually infected by interrupted feeding on viraemic hamsters. Wild-type reassortant virus was isolated from the ticks 12 to 15 days after engorgement. Following moulting, nymphs and adults transmitted reassortant virus to uninfected hamsters. This is the first reported evidence that a tick-borne arbovirus can reassort in vivo in a naturally infected arthropod vector. The relative roles of vector and vertebrate host in generating and perpetuating reassortant viruses in nature are discussed.

Effect of Sindbis birus infection on survival of mice in the cold

Mice infected with 10(9) plaque-forming units (PFU) of Sindbis virus 9 h prior to exposure to cold (5 degrees C) died more rapidly after entering the new environment than saline-injected control mice. The early deaths occurred in animals singly housed without bedding and only when food was withheld. Because deaths could be prevented by providing the infected animals with food, it was concluded that metabolic alteractions resulting from the virus infection were responsible for the deaths. As evidence, corticosteroid-inducible hepatic enzymes did not respond to hydrocortisone administration in virus-infected mice housed at 5 degrees C. Phosphoenolpyruvate carboxykinase (PEPCK) (EC 4.1.1.32) was induced significantly in control mice held at 5 degrees C for 5 h, but failed to induce in infected mice in the cold. Tryptophan oxygenase (TO) (EC 1.13.11.11) activity was also induced in control mice at 5 degrees C, but was too low to be measured in livers of all infected mice including those exposed to cold. The conclusion that Sindbis virus-infected mice were unable to make the metabolic adjustments required for survival at 5 degrees C was further indicated by severe hypoglycemia and rapid drop in rectal temperature that occurred in infected mice after 5 h in the cold.