Hepatotropic action of the virus of West Nile fever

An experimental infection of mice with West Nile Virus (WNFV) showed pronounced dystrophic changes in the hepatic parenchyma and expression of WNV antigens in the endothelium of hepatic capillaries and in hepatocyte cytoplasm, which testifies to the tropic action of WNFV to hepatic tissue.     

West Nile fever among residents of the Astrakhan region in 2002

Thirty-three persons infected with West Nile fever were detected in 2002 in the Astrakhan Region; the diagnosis was confirmed serologically and the maximal number of the infected was registered in August, same year. The indices of the specific humoral immunity varied from 3.3% to 27.1%. A monitoring determined the highest infection risk among the residents of the Volga middle delta.     

Agriculture-health interface in the field of epidemiology of vector-borne diseases and the control of vectors

This paper is a review of the interactions between agriculture and vector borne diseases. Rain forest clearing makes possible the development of heliophilous species of anophelines and snails leading to an increase of malaria and schistosomiasis in Africa. But in Asia, clearing is a control method against Anopheles balabacensis, an important malaria vector. Clearing of forest galleries is followed by the disappearance of shore-dwelling tsetse flies. Woodcutters and pioneer farmers are contaminated with arbovirus and leishmaniasis when entering in natural sylvatic foci of these diseases. Management of drinking water reduces guinea worm as well as cholera and other diarrhoeal diseases. More over when piped water becomes available people are no more obliged to store drinking water in containers where vectors use to breed. Reservoirs of dams offer large possibilities for the development of mosquitoes including anophelines vectors of malaria and filariasis and of snails hosts of schistosomiasis. The medical importance of these man-made breeding sites depends of the local epidemiological features of the diseases. Dam spillways provide breeding for blackflies and man-made foci of onchocerciasis have been described in West Africa. Irrigation channels mainly when non cleared of vegetation are good breeding places for anophelines and snails. Irrigated surfaces like rice fields are highly productive in anophelines and other dangerous species of Culicinae. Insecticides used in agriculture, mainly to control cotton and rice pests, have been at the origin of insecticide resistance of several anopheline species. On an other hand, sometimes rice pests control lead to the control of rice field mosquitoes until they become resistant, e.g. for Culex tritaeniorhynchus the vector of Japanese encephalitis in South Korea. Many international organizations have emphasized the role of intersectorial collaboration to control man-made vector borne diseases foci. Good planning of the infrastructures (e.g. twin spillways) and adequate maintenance are essential. Vector control in rice field is a puzzling question. Wet irrigation was a hope but it cannot be done everywhere. Biological control methods have not been proven to be very efficient. Even Bacillus thuringiensis H14 and B. sphaericus have severe limitation. New tools for intersectorial activities should be a goal for scientists imagination.     

The state of vector-borne diseases in Indonesia]

From epidemiological point of view, Indonesia is an extremely interesting area owing its insular structure and ecological, anthropological, cultural and economical diversity. As everywhere, vector-borne diseases are the result of complex and variable epidemiological systems, subject both to biogeographical rules and human activity. Two main arboviroses are present in Indonesia: dengue and Japanese encephalitis. Dengue appears as an endemoepidemic disease and is mostly circumscribed to urban areas. Haemorrhagic cases were first observed in 1968; since then, the incidence has been constantly increasing and the disease is now one of the principal causes of child lethality. Japanese encephalitis is a rural endemic disease transmitted by rice-field mosquitoes; its incidence remains relatively low since pigs, which are usual link-hosts for the virus, are uncommon in this mainly Muslem country. Human clinical cases are recorded from non-Muslem islands such as Bali or Irian Jaya which raises the question of immunisation for travellers. Recently, Japanese encephalitis was observed on east of the Wallace line which had been considered as the eastern cut-off line. Malaria is common throughout the country, Plasmodium vivax being the most frequent species. Some of the Anopheline vectors are related to brackish water as are coastal species; others have been favoured by rice growing. Several species bite and rest outdoors, rendering control measures complex. Moreover, chloroquine resistance is increasing in both P. falciparum and P. vivax. All three filaria species responsible for human lymphatic filariasis exist in Indonesia. Bancroft filariasis is present in rather limited foci on most of the islands; malayan filariasis is very prevalent on many islands, mostly in coastal areas, and Timor filariasis exist only on a few small islands. These parasitic diseases are cumulative and do not practically endanger the health of travellers. In the past, plague was common on Java island, but today, human cases are very rare. Scrub typhus is prevalent everywhere, as is murine typhus, being very frequent in harbour cities and one of the main causes of hospitalisation for febrile syndromes.. On the whole, the situation of several of these diseases has been worsening in Indonesia for about thirty years. Although epidemiological situations constantly evolve, two recent occurrences should be paid particular attention: -transmigration which is now a national priority and greatly facilitates the spread of many pathogens, arboviroses or chloroquine-resistant plasmodia, but also of rats, mosquitoes, etc. -deforestation due either to land-farming by Javanese transmigrants or to sudden climatic changes such as El Ni?o in 1997. Such deep ecological transformations may have considerable and unforeseeable consequences on the epidemiology of vector-borne diseases in Indonesia.     

Four human diseases with significant public health impact caused by mosquito-borne flaviviruses: West Nile,Zika, dengue and yellow fever

In this review we will discuss the epidemiology, clinical characteristics, diagnostic tests, pathologic features, treatment and disease prevention strategies for four mosquito-borne flaviviruses. West Nile and Zika viruses, once thought to be restricted geographically, emerged on the American continent in the first part of the 21st century. They have been constantly in the lay press and have caused a heightened awareness of emerging infections by the public, particularly given the manifestation of microcephaly in congenital Zika syndrome. Yellow fever and dengue viruses, with mosquito vectors similar to West Nile and Zika viruses, are endemic in many tropical areas of the world and produce frequent outbreaks. The global distribution of yellow fever and dengue viruses could also change and has great potential to do so. Factors that could contribute to reemergence of the diseases in areas of the world where they are currently only seen in travelers, include the presence of yellow fever and dengue virus vectors in temperate climates and growing urbanization. These two factors increase potential contact between vectors and naïve human hosts, thus could result in reemergence of yellow fever or dengue virus infections.     

Astrocytic morphological responses in different murine brain regions in the simulation of West Nile fever

The brains from the mice infected intraperitoneally (with development of these or those symptoms of viral encephalitis) or intramuscularly with the Astrakhan West Nile fever virus strain (AcT 986) was pathomorphologically studied. Clinicomorphological changes in the neurons and vessels of the microcirculatory bed were found in the dorsal regions of medulla oblongata. Immunohistochemicall analysis showed that mature and/or activated astrocytes increased in number, largely in the animals without clinical manifestations of encephalitis. The findings provide evidence that cerebral astrocytes play a protective and adaptive role that seems to depend on the biological properties of the pathogen.     

The influence of Poly I∶C on the course of infection in mice inoculated with West Nile Virus

Summary In mice infected intraperitoneally with a hundred per cent lethal dose of West Nile virus a significant reduction in mortality was found if treatment with the complex of synthetic polyriboinosinic and polycytidylic acids (Poly IC) was given four hours prior to or twenty hours after virus challenge.Treatment induced large amounts of circulating interferon a few hours after inoculation. Only a slight difference in maximum viraemia in the various groups was found, but viraemia developed later in the mice given Poly IC a few hours before virus injection. Infection of the brain developed later in the groups treated with Poly IC.Using various doses of West Nile virus almost the same mortality was found in the group given a lethal virus dose but treated with Poly IC and the group receiving sublethal virus dose and no Poly IC treatment. Maximum of viraemia was high in the former group, while in the latter group it was significantly lower. Therefore it is supposed that Poly IC in these experiments did not protect through an interferon mediated suppression of the viraemia but rather through an effect of the interferon exerted directly upon the target organ. A reduction of circulating HI antibodies was found in the group on which Poly IC had the most pronounced effect.     

Morphofunctional characteristics of antigen-presenting cells in lymph node in mice with experimental West Nile fever

Pronounced transformation of cells in mesenteric lymph nodes, mainly in the thymus-independent zone and sinuses, was detected in albino mice experimentally infected with West Nile fever (strain 986). Maximum antigen-presenting activity was exhibited by activated macrophages, minimum activity - by dendritic cells of lymphoid follicles.     

The past and present threat of vector-borne diseases in deployed troops

From time immemorial, vector-borne diseases have severely reduced the fighting capacity of armies and caused suspension or cancellation of military operations. Since World War I, infectious diseases have no longer been the main causes of morbidity and mortality among soldiers. However, most recent conflicts involving Western armies have occurred overseas, increasing the risk of vector-borne disease for the soldiers and for the displaced populations. The threat of vector-borne disease has changed with the progress in hygiene and disease control within the military: some diseases have lost their military significance (e.g. plague, yellow fever, and epidemic typhus); others remain of concern (e.g. malaria and dengue fever); and new potential threats have appeared (e.g. West Nile encephalitis and chikungunya fever). For this reason, vector control and personal protection strategies are always major requirements in ensuring the operational readiness of armed forces. Scientific progress has allowed a reduction in the impact of arthropod-borne diseases on military forces, but the threat is always present, and a failure in the context of vector control or in the application of personal protection measures could allow these diseases to have the same devastating impact on human health and military readiness as they did in the past.     

Cases of West Nile fever in Novosibirsk region in 2004, and the genotyping of its viral pathogen

Three cases of West Nile fever were registered for the first time in Novosibirsk region in 2004. The diagnosis was confirmed by revealing IgG against West Nile virus (three cases) and viral RNA (two cases). Sequence analysis of fragments of E protein gene showed that the virus belonged to Ia genotype.     

The effect of weather on some infectious diseases

For several years the Royal College of General Practitioners has been collecting data supplied by local doctors throughout Britain on some infectious diseases seen in their practices. We describe a method of computerisation of this information and statistical analyses. We are investigating the influence of external factors such as climate on the infectiousness of some diseases. A model is fitted involving a non homogeneous two-state Markov chain whose transition probabilities are governed by the explanatory data.     

Morphological and immunohistochemical changes in tissues of the lung, myocardium and kidney in experimental West Nile fever

An experimental infection of mice with West Nile virus (WNV) showed pronounced dystrophic changes in tissues of the kidneys and myocardium as well as expression of WNV antigens in cells of the lungs, kidneys and myocardium, which can denote tropism of WNV to tissues of the lungs, kidneys and myocardium.     

The influence of cold or isolation stress on neuroinvasiveness and virulence of an attenuated variant of West Nile virus

Summary The effect of cold or isolation stress on neuroinvasiveness and virulence was investigated in mice inoculated with an attenuated WNV (WN-25) strain.The WN-25 variant differed from the parent strain by its inability to kill mice after I.P. injection though it was able to immunize even after injection with low doses of virus. Exposure of inoculated mice for 5 minutes a day to cold water (1±0.5 °C) for 8 days resulted in 60% mortality, while in non-stressed infected mice no death was observed. Cold or isolation stress increased the virus level in the brain to 8.9 and 7.4 log 10 PFU as compared to no virus in the infected control. Moreover, it was found that virus level in the spleen of stressed mice reached 3.4 and 3.7 log 10 PFU respectively, while in non-stressed mice no virus was detected. The virus which was isolated from the brain of moribund stressed mice was extremely virulent: I.P. inoculation of as little as 10 PFU caused death to normal non-stressed mice.We suggest that cold or isolation stress conditions in mice inoculated with an attenuated strain induce a selection process. The virus which was isolated from the brain of stressed mice changes its virulence and kills like wild type WNV.     

Studies on West Nile virus infection by means of fluorescent antibodies

Summary By means of infectivity titration of tissues and fluorescein-labeled antibody staining, the pathogenesis of West Nile virus in suckling mice was studied. When mice were inoculated intracerebrally, antigens were first detected in the central nervous system and in mesenchymal tissue. When mice were inoculated intraperitoneally, antigens were first detected in mesenchymal tissue and the plexus of Auerbach in the digestive tract. Additional antigens were soon found in the entire nervous system, the blood vessels, the smooth and skeletal muscle and other connective tissues. Involvement of the major organs and lymph nodes was minimal until the last 2 days of infection. The rise of tissue infectivity titers generally paralleled the observed spread of viral antigens. Nervous tissue and mesenchymal tissue appeared to show equal susceptibility to primary viral invasion and growth. The possibility that the blood vessel wall is one of the primary sites of multiplication for WN virus is suggested.Aided in part by a grant from the National Foundation and by Research Grant E 2514, U. 8. Public Health Service, Department of Health, Education and Welfare.