Tropic acid Tropical diseases

The alphaviruses are a group of 26 icosahedral, positive-sense RNA viruses primarily transmitted by mosquitoes [64]. These 700-A-diameter viruses are some of the simplest of the membrane-enveloped viruses, and members of this group cause serious tropical diseases with characteristic symptoms such as myositis, fever, rash, encephalitis, and polyarthritis [65]. The structures of two different alphavirus-Fab complexes have been determined by cryo-TEM Ross River virus (RR) and Sindbis virus (SIN) [66]. The amino acid sequences of the RR and SIN virus structural and nonstructural proteins are 49 and 64% identical, respectively [67]. The viral RNA genome and 240 copies of the capsid protein form the nucleocapsid core [68-73], and the El and E2 glycoproteins form heterodimers that associate as 80 trimeric spikes on the viral surface. Native SIN and RR lack the E3 glycoprotein because it disassociates from the spike complex after its display on the plasma membrane surface [74, 75]. El has a putative fusion domain that may facilitate host membrane penetration [76, 77]. E2 contains most of the neutralizing epitopes and is also probably involved in host cell recognition [78-80]. 

Diarrhea is a common problem that is usually self-limiting and of short duration. Increased accumulations of small intestinal and colonic contents are known to be responsible for producing diarrhea. The former may be caused by increased intestinal secretion which may be enterotoxin-induced, eg, cholera and E. col] or hormone and dmg-induced, eg, caffeine, prostaglandins, and laxatives decreased intestinal absorption because of decreased mucosal surface area, mucosal disease, eg, tropical spme, or osmotic deficiency, eg, disaccharidase or lactase deficiency and rapid transit of contents. An increased accumulation of colonic content may be linked to increased colonic secretion owing to hydroxy fatty acid or bile acids, and exudation, eg, inflammatory bowel disease or amebiasis decreased colonic absorption caused by decreased surface area, mucosal disease, and osmotic factors and rapid transit, eg, irritable bowel syndrome. 

Much of the toxicological interest in cyanide relating to mammals has focused on its rapid lethal action. However, its most widely distributed toxicologic problems are due to its toxicity from dietary, industrial, and environmental factors (Way 1981, 1984 Gee 1987 Marrs and Ballantyne 1987 Eisler 1991). Chronic exposure to cyanide is correlated with specific human diseases Nigerian nutritional neuropathy, Leber s optical atrophy, retrobulbar neuritis, pernicious anemia, tobacco amblyopia, cretinism, and ataxic tropical neuropathy (Towill etal. 1978 Way 1981 Sprine etal. 1982 Beminger et al. 1989 Ukhun and Dibie 1989). The effects of chronic cyanide intoxication are confounded by various nutritional factors, such as dietary deficiencies of sulfur-containing amino acids, proteins, and water-soluble vitamins (Way 1981). 

While insect control is more often a limiting factor in tropical bean production, there are several diseases that are serious in certain seasons and locations. Bean rust is one of the most widespread diseases, and it can be controlled effectively with protective fungicides, such as elemental sulfur and certain of the carbamic acid derivatives. The economics of bean production usually preclude any costly applications, however, and the problem has generally been turned over to the plant breeder to solve with resistant varieties. At present, the most practical control of bean anthracnose and the bean blights is through the use of clean seed and resistant varieties. Control with fungicides has always proved difficult and of doubtful value. 

Tropical sprue is a malabsorptive disease thought to be generated by specific t)q)es of infections. The disease involves diarrhea and is associated with the malabsorption of folate. Hence, its treatment may involve supplements of folic acid. 

Phyllanthus niruri L., a small plant which grows mainly in tropical and subtropical regions in Central and South American countries, and in India, is one of the most important traditional medicines used for the treatment of Jaundice, asthma, hepatitis and urolitic disease. Intensive chemical examinations of this plant have been carried out and several constituents such as lignans (79-81), alkaloids (82-84), flavonoids (85), tannins (86) and phthalic acid (87) have been identified. In addition, especially in this decade, several pharmacological experiments have also been reported (88, 89). In spite of many phytochemical and biochemical investigations, there have been only a few reports on tissue culture of this plant. 

ABSORPTION, DISTRIBUTION, AND ELIMINATION As with vitamin Bj, the diagnosis and management of folic acid deficiency depend on an understanding of the transport pathways and intracellular metabolism of the vitamin (Figure 53-10). Folates present in food are largely in the form of reduced polyglutamates, and absorption requires transport and the action of a pteroyl-glutamyl carboxypeptidase associated with mucosal cell membranes. The mucosae of the duodenum and upper part of the jejunum are rich in dihydrofolate reductase and can methylate most or aU of the reduced folate that is absorbed. Since most absorption occurs in the proximal small intestine, it is not unusual for folate deficiency to occur with jejunal disease. Both nontropical and tropical sprues are common causes of folate deficiency. 

Though the primary business of soybean processing is to produce animal protein feed, 17 to 20% of the soybean is an oil coproduct. In the 1960s, human health concerns about cholesterol caused an increase in demand for soybean oil. Food manufacturers shifted away from animal by-products as a source of fat or oil. Then in the 1970s, concerns arose about saturated fats from tropical oils. This caused another spike in demand as U.S. food manufacturers switched from palm oil to less saturated oils, such as soy. These events created significant opportunities for soybean oil to become the preferred oil for food manufacturers. Now evidence links the presence of trans-fatty acids, found in processed soybean oil, with heart disease. For some products, soybean oil is partially hydrogenated to improve products appearance, stability,... 

An example of sequential blocking is the use of a sulfadiazine with pyrimethamine 9.31) in toxoplasmosis, a protozoal disease (Wettingfeld, Rowe and Eyles, 1956). In this sequence, the sulfonamide blocks the incorporation of / -aminobenzoic acid into dihydrofolic acid, and the pyrimethamine prevents the reduction of this pteridine to tetrahydrofolic acid (Sections 9.3.2 and 9.3.3). In malaria, as early as 1959, Hurly made the observation that pyrimethamine and sulfadiazine potentiated one another to such a degree that the combination could actually cure Pl.falciparum infections. Thus, less than 0.1 m.e.d. (minimal effective dose) of pyrimethamine and 0.25 m.e.d. of sulfadiazine were, together, as effective as 1.0 m.e.d. of either drug separately. In current tropical medicine, Maloprim , a combination of pyrimethamine and dapsone 9.17) (the latter chosen because of its slow rate of excretion which matches that of pyrimethamine), forms an excellent replacement for chloroquine in cases of Pl.falciparum... 

Folic acid deficient humans develop a macrocytic hyperchromic anemia similar to that observed in vitamin Bi2 deficiency. Observations made on the undernourished population of Bombay prompted the discovery of the vitamin. In 1932, Will observed that macrocytic anemia occurred frequently among the people of Bombay and that the disease was readily cured by the addition of yeast to the diet. Folic acid deficiency also seems to be responsible for the macrocytic anemia that develops in cases of tropical sprue. 

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