Dengue and dengue haemorrhagic fever: Indian perspective.

The relationship of this country with dengue has been long and intense. The ?rst recorded epidemic of clinically dengue-like illness occurred at Madras in 1780 and the dengue virus was isolated for the ?rst time almost simultaneously in Japan and Calcutta in 1943-1944. After the ?rst virologically proved epidemic of dengue fever along the East Coast of India in 1963-1964, it spread to allover the country.The ?rst full-blown epidemic of the severe form of the illness,the dengue haemorrhagic fever/dengue shock syndrome occurred in North India in 1996. Aedes aegypti is the vector for transmission of the disease. Vaccines or antiviral drugs are not available for dengue viruses; the only effective way to prevent epidemic degure fever/dengue haemorrhagic fever (DF/DHF) is to control the mosquito vector, Aedes aegypti and prevent its bite. This country has few virus laboratories and some of them have done excellent work in the area of molecular epidemiology,immunopathology and vaccine development. Selected work done in this country on the problems of dengue is presented here.

Effect of pretreatment with chromium picolinate on haematological parameters during dengue virus infection in mice.

BACKGROUND & OBJECTIVE: Dengue virus (DV) has caused severe epidemics of dengue fever (DF) and dengue haemorrhagic fever (DHF) and is endemic all over India. We have earlier reported that exposure of mice to hexavalent chromium [Cr(VI)] compounds increased the severity of dengue virus infection. Trivalent chromium picolinate (CrP) is used worldwide as micronutrient and nutritional supplement. The present study was therefore, carried out to investigate the effects of CrP on various haematological parameters during DV infection of mice. METHODS: The Swiss Albino smice were inoculated with dengue virus (1000 LD50, intracerebrally) and fed with chromium picolinate (CrP) in drinking water (100 and 250 mg/l) for 24 wk. Peripheral blood leucocytes and other haematological parameters, and spleens were studied on days 4 and 8 after virus inoculations and the findings were compared with those given only CrP and the normal control age matched mice. RESULTS: CrP in drinking water for 24 wk had no significant effects on peripheral blood cells of mice. On the other hand, there was significant decrease in different haematological parameters following inoculation of normal mice with DV. In CrP fed mice the effects of DV infection were abolished on most of the haematological parameters. INTERPRETATION & CONCLUSION: The findings of present study showed that the adverse effects of DV infection, specially on platelets and leucocytes, were abrogated by pretreatment of mice with CrP. The therapeutic utility of CrP in viral infections including dengue needs to be studied in depth.

Macrophage and dengue virus: friend or foe?

The cells of monocyte-macrophage (Mphi) lineage play important roles both in innate and adaptive immune responses. They are the first line of defence in body and their job is to phagocytose a foreign invader, the pathogen, digest it and remove it. Mphi help body in mounting the antigenspecific immune response by presenting the digested pathogen antigen in conjunction with major histocompatibility complex (MHC) class II molecules to recruit B and T lymphocytes response. Usually Mphi succeed in their job of eliminating most pathogens from the body but sometimes the pathogen strikes a "friendship" with them and starts using them for its benefit. A number of pathogens, including dengue virus (DV), subvert Mphi and use them for their replication, increasing the severity of damage to the body. This duality may be related to the fact that Mphi serve as efficient host cell for DV replication, in addition to being responsible for innate immunity and for initiating adaptive immune responses. This review gives a brief overview of the various roles of Mphi (enmity and friendship) during dengue virus infection.

A comparative study on rat intestinal epithelial cells and resident gut bacteria (ii) effect of arsenite.

OBJECTIVE: In order to use facultative gut bacteria as an alternate to animals for the initial gastrointestinal toxicity screening of heavy metals, a comparative study on rat intestinal epithelial cells and resident gut bacteria was undertaken. METHODS: in vitro growth rate of four gut bacteria, dehydrogenase (DHA) and esterase (EA) activity test, intestinal epithelial and bacterial cell membrane enzymes and in situ effect of arsenite were analysed. RESULTS: Growth profile of mixed resident population of gut bacteria and pure isolates of Escherichia coli, Pseudomonas sp., Lactobacillus sp., and Staphylococcus sp. revealed an arsenite (2-20 ppm) concentration-dependent inhibition. The viability pattern of epithelial cells also showed similar changes. DHA and EA tests revealed significant inhibition (40%-72%) with arsenite exposure of 5 and 10 ppm in isolated gut bacteria and epithelial cells. Decrease in membrane alkaline phosphatase and Ca2+ -Mg2+ -ATPase activities was in the range of 33%-55% in four bacteria at the arsenite exposure of 10 ppm, whereas it was 60%-65% in intestinal epithelial villus cells. in situ incubation of arsenite using intestinal loops also showed more or less similar changes in membrane enzymes of resident gut bacterial population and epithelial cells. CONCLUSION: The results indicate that facultative gut bacteria can be used as suitable in vitro model for the preliminary screening of arsenical gastrointestinal cytotoxic effects.

Effects of dengue virus infection on peripheral blood cells of mice exposed to hexavalent chromium with drinking water.

BACKGROUND & OBJECTIVE: The occupational and non-occupational exposure to hexavalent chromium Cr (VI) is common. The effect of chromium compromises the immune response of the host. Dengue virus (DV) infection causes various changes in the peripheral blood cells. It is, therefore, possible that the chromium toxicity may affect the disease process during DV infection. The present study aims to study the effects of dengue virus infection on peripheral blood cells of mice fed Cr (VI) with drinking water. METHODS: One group of mice was given ad libitum drinking water containing Cr (VI) and the other group used as the normal control mice was given plain water to drink. At the 3, 6 and 9 wk of Cr (VI) drinking, a set of mice from each group was inoculated intracerebrally (ic) with DV and studied at the 4th and 8th day post inoculation. RESULTS: It was observed that Cr (VI) drinking led to reduction in lymphocytes, haemoglobin and the haematocrit values while the granulocyte, monocyte and platelet counts were increased. On the other hand, most of the parameters were decreased following inoculation of normal mice with DV. In Cr (VI)-fed mice the effects of DV infection were minimal. The most significant finding of these experiments was that the reduction in platelet counts following inoculation with DV was markedly less in Cr (VI)-fed mice than that in DV-inoculated normal control mice. INTERPRETATION & CONCLUSION: Cr(VI) compounds have been declared as a potent occupational carcinogen. On the contrary, Cr(III) salts such as chromium polynicotinate, chromium chloride and chromium picolinate, are used as micronutrients and nutritional supplements, and have been shown to exhibit health benefits in animals and humans. Whether therapeutic doses of chromium (III) compounds may be able to prevent the DV-induced fall in platelet counts, needs to be investigated.

Dengue vaccines: problems and prospects.

The extent of cumulative disease burden caused by dengue virus has attained an unprecedented level in recent times with sharp increase in the size of human population at risk. Dengue disease presents highly complex medical, economic and ecologic problems. The surge in publications on the development of dengue vaccines, taking advantage of new generation of biotechnology techniques indicates the profound interest and urgency in the scientific and medical communities in combating this disease. This review summarizes the importance of critical subjects like pathogenesis of dengue haemorrhagic fever and inadequacy of animal model that have adversely affected dengue vaccine development. Further, the remarkable progresses so far made in dengue vaccine research not only employing a diverse range of new strategies but also re-using old techniques to improve the existing vaccines, have been presented. The efficacy and safety of some of the new vaccine candidates have been evaluated and proven in human preclinical/clinical trials. Besides the technical advancement in vaccine development, vaccine safety and vaccine formulation have been examined.

Effects of dengue virus infection on the spleen of male mice given hexavalent chromium with drinking water.

The present study was undertaken to investigate the effects of dengue virus (DV) infection in male mice given drinking water containing 250 ppm Cr (VI) and the normal control male mice given plain water to drink. On the basis of intake of water in 24 h, the average dose of Cr (VI) in each mouse was 14.8 mg/kg. After 3, 6, and 9 weeks of drinking Cr (VI), a set of five mice from each group were inoculated intracerebrally (ic) with a 1000 x LD(50) (100 times the lethal dose that kills 50% mice) dose of DV, and the effects on the spleen were studied at the fourth and eightth day postinoculation. It was observed that Cr (VI) drinking and DV infection led to reduction in the weight of the spleen, but the peak reduction was seen in Cr (VI)-fed mice infected with DV, being 30, 34, and 61% at 3, 6, and 9 weeks respectively. A similar response was seen with respect to the cytotoxic activity of spleen homogenates, phagocytic activity of macrophages, and the mitogenic response of spleen cells to concanavalin A from different groups of animals, being most marked (58 to 60%) at the ninth week of Cr (VI) drinking. This shows a summation of adverse effects of DV infection in mice preexposed to Cr (VI).

A comparative study on rat intestinal epithelial cells and resident gut bacteria: (I) effect of hexavalent chromium.

Toxicants including heavy metals reaching the intestine following ingestion through food and water primarily interact with an ecosystem of eukaryotic and prokaryotic cells. Gut bacteria having a dynamic interrelationship with intestinal epithelial cells are known to play important and specific metabolic, trophic, and protective functions. The present study was undertaken to compare the effects of hexavalent chromium on rat intestinal epithelial cells and the resident gut bacteria following in vitro and in vivo exposures. The survival rate and viability pattern of two types of cells were comparable. Under in vitro conditions, the gut bacteria were quick to reduce Cr (VI) in early time periods, while, at 30 h time, both types of cells showed similar capacity for the reduction of Cr (VI). Chromium intoxication (10 ppm of Cr (VI) in drinking water for 10 weeks) caused significant decrease in membrane alkaline phosphatase and Ca(2 +)-Mg(2 +)-ATPase activities of intestinal epithelial cells as well as of three gut bacteria viz. Escherichia coli, Pseudomonas sp, and Lactobacillus sp. Major structural membrane constituents like carbohydrates and phospholipids also showed significant decline in both types of cells. These findings indicate that 10 ppm and higher Cr concentrations may cause toxic insult, resulting in impaired intestinal functional efficacy. It also implies that the gut bacteria can be used at least for preliminary screening of heavy metals gastrointestinal toxicity.

Effects of chromium on the resident gut bacteria of rat.

The major nonoccupational source of chromium (Cr) for humans is through ingestion with food and water, but its effect on the gut microflora has not been studied. The present study was, therefore, undertaken to investigate the effects of chronic ingestion of potassium dichromate (chromium VI) on the resident gut bacteria of male Wistar rats. A group of rats was kept on drinking water containing 10 ppm chromium VI (Cr [VI]) (called Cr-stressed animals) and the other group was given plain water. After 10 weeks, Lactobacillus, Pseudomonas sp., and Escherichia coli were isolated from the cecum of the rats and various studies were performed. The most significant findings of the present study were the stimulation of growth of facultative gut bacteria from the Cr-stressed rats and the significant increase of growth even in the presence of lower concentrations of Cr. Furthermore, the capacity to reduce Cr (VI) was significantly decreased along with the increased tolerance of the bacteria to Cr (higher minimum inhibitory concentration [MIC] values), which was associated with the development of antibiotic resistance. The effects were most marked with the Pseudomonas sp. and least with the E. coli. The antibiotic resistance developed with the Lactobacillus may be a blessing in disguise, because the bacteria may continue to provide benefits even in patients given antibiotic therapy. The gut bacteria thus provide the first line of defense to the body by converting toxic Cr (VI) to a less toxic Cr (III) and may act as a prebiotic.

Suboptimal chlorine treatment of drinking water leads to selection of multidrug-resistant Pseudomonas aeruginosa.

The present study was undertaken to investigate the spectrum of bacteria present in the River Gomti water before and after chlorination for drinking purposes. We observed that the strains of Pseudomonas aeruginosa that survived chlorination on three out of seven occasions were resistant to almost all the antibiotics tested. The chlorine-resistant bacteria had mucoid colonies and grew better at 24 degrees C. All attempts to isolate the plasmid responsible for chlorine resistance were unsuccessful. Laboratory experiments using different strains of the P. aeruginosa in distilled water showed that only the resistant strain survived chlorine treatment at a dose of < or =500 microg/L. Similar results were obtained when water collected from seven different sites on the River Gomti was treated with graded doses of chlorine. At the higher dose of chlorine, all the bacteria died in 30 min, whereas with lower doses all the bacteria survived. The present study underscores the importance of measuring water chlorine concentrations to assure they are sufficiently high to remove pathogenic bacteria from drinking water. To our knowledge, this is the first report in the literature of the selection of multidrug-resistant bacteria by suboptimal chlorine treatment of water.

Gut microflora & toxic metals: chromium as a model.

The gastrointestinal tract (GIT) is exposed to various environmental pollutants including metals, that contaminate food and water which may have toxic effects on body. GIT has large amount of microbes that live in symbiosis and help the host in different ways. The resident gut microflora have a significant role to play in detoxification and elimination of the harmful metals from the body. Chromium is a naturally occurring heavy metal found commonly in environment in trivalent (Cr III) and hexavalent (Cr VI) forms. Cr (VI) compounds have been shown to be potent occupational carcinogens. The reduction of Cr (VI) to Cr (III) results in the formation of reactive intermediates that together with oxidative stress and oxidative tissue damage, and a cascade of cellular events including modulation of apoptosis regulatory gene p53 contribute to the cytotoxicity, genotoxicity and carcinogenicity of Cr(VI)-containing compounds. The data discussed here with reference to chromium show that gut microflora have a marked capacity to cope with the increased load of ingested metals and may contribute significantly in the protection against metal toxicity.

Various cells of the immune system and intestine differ in their capacity to reduce hexavalent chromium.

The cells of the immune system form a strong line of defence against foreign substances. The present study was undertaken to investigate the capacity of different cells of Wistar rats to reduce potentially carcinogenic hexavalent chromium (Cr-VI) into less toxic trivalent chromium in vitro. 5 x 10(6) cells were incubated with 10 or 25 microg ml(-1) of Cr (VI) in the form of K2Cr2O7 at 37 degrees C in the presence of 5% CO2 in air. At various time periods the remaining amount of Cr (VI) was measured and the percentage of Cr (VI) reduced was calculated. Among the single cell suspensions from the splenic cells a peak reduction of 55% was observed with the total spleen cells, 40% with the B-lymphocyte-enriched subpopulation, 10% with T-lymphocytes and 24% with the macrophages. The reduction by splenic and peritoneal macrophages was similar. Total thymocytes reduced 54% of the Cr (VI). Since the most common route of entry of chromium is through drinking water and food, intestinal cells were also investigated. Among the intestinal cells the maximum reduction of 100% (of 10 microg ml(-1)) was observed with the upper villus cells and 72% with the middle villus cells while reduction was the least (4%) with the crypt cells. The reduction in the intestinal loop in situ was 100%. The time taken by each cell type for the peak reduction to Cr (VI) was markedly different. The findings thus show that the capacity of different cells in the body differs vastly in their capacity and time taken to reduce hexavalent chromium. The most efficient handling of Cr (VI) by the intestine, due to the presence of a variety of cells and bacteria, protects the body from its adverse effects.

Seroprevalence of three emerging arboviral infections in Kuwaiti nationals.

Diseases caused by dengue, sandfly fever and hanta viruses pose a major health risk in many countries. We determined the threat of these arboviral infections through a serologic using enzyme linked immunosorbent assay (ELISA) based tests. Hantavirus-specific antibodies were also detected using immunofluorescence. Of 499 samples tested for dengue virus IgG antibodies l4% were as positive for dengue positive by all the ELISA tests. Among the 42 showing strong IgG reactivity, only 1 was positive for dengue virus IgM antibodies. All samples tested for IgG antibodies to sandfly fever virus were negative. Hantavirus antibodies were detected in 11% of the 46 samples from high-risk individuals. The low prevalences suggest that at present these infections are not a serious problem in Kuwait.

Seroprevalence of three emerging arboviral infections in Kuwaiti nationals

Diseases caused by dengue, s and fly fever and hanta viruses pose a major health risk in many countries. We determined the threat of these arboviral infections through a serologic using enzyme linked immunosorbent assay [ELISA] based tests. Hantavirus-specific antibodies were also detected using immunofluorescence. Of 499 samples tested for dengue virus IgG antibodies l4% were as positive for dengue positive by all the ELISA tests. Among the 42 showing strong IgG reactivity, only 1 was positive for dengue virus IgM antibodies. All samples tested for IgG antibodies to s and fly fever virus were negative. Hantavirus antibodies were detected in 11% of the 46 samples from high-risk individuals. The low prevalences suggest that at present these infections are not a serious problem in Kuwait

Effects of chromium on the immune system.

Chromium is a naturally occurring heavy metal found commonly in the environment in trivalent, Cr(III), and hexavalent, Cr(VI), forms. Cr(VI) compounds have been declared as a potent occupational carcinogen among workers in chrome plating, stainless steel, and pigment industries. The reduction of Cr(VI) to Cr(III) results in the formation of reactive intermediates that together with oxidative stress oxidative tissue damage and a cascade of cellular events including modulation of apoptosis regulatory gene p53, contribute to the cytotoxicity, genotoxicity and carcinogenicity of Cr(VI)-containing compounds. On the other hand, chromium is an essential nutrient required to promote the action of insulin in body tissues so that the body can use sugars, proteins and fats. Chromium is of significant importance in altering the immune response by immunostimulatory or immunosuppressive processes as shown by its effects on T and B lymphocytes, macrophages, cytokine production and the immune response that may induce hypersensitivity reactions. This review gives an overview of the effects of chromium on the immune system of the body.