Protozoa, toxicity

Fish are generally more susceptible to poisoning than microscopic plants or other animals as such they are a good indicator species. A summary of the concentrations of selected substances at which toxic effects have been detected in bacteria, algae, crustacia and protozoa is given in Table 16.14. 

IFN-y may also prove valuable in treating a variety of other conditions, and clinical trials for various indications are currently underway. This cytokine shows promise in treating leishmaniasis, a disease common in tropical and subtropical regions. The causative agent is a parasitic protozoan of the genus Leishmania. The disease is characterized by the presence of these protozoa inside certain immune cells, particularly macrophages. IFN-y appears to stimulate the infected macrophage to produce nitric oxide, which is toxic for the parasite. 

Bringmann. G. and Ktihn. G. Comparison of the toxicity thresholds of water pollntants to bacteria, algae and protozoa in the cell multiplication inhibition test. Water Res., 14(3) 231-241. 1980. 

As protozoa and nematodes live in pore water in the soil, most of the methods are adapted from toxicity tests designed for aquatic samples. Among the protozoa the tests with cihates Tetrahymena pyriformis, Tetrahymena thermophiia, Colpoda cucullus, Colpoda inflata, Colpoda steinii, Paramecium caudatum, and Paramecium aurelia have been developed [ 102,112-117]. It is the opinion of some authors that the sensitivity of infusorians is higher than that of microorganisms [115,116]. 

Ammonia is also the major nitrogenous end product in some of the simpler aquatic and marine animal forms, such as protozoa, nematodes, and even bony fishes, aquatic amphibia, and amphibian larvae. Such animals are called am-monotelic. But in many animals, NH3 is toxic, and its removal by simple diffusion is difficult. Thus, in terrestrial snails and amphibia, as well as in other animals living in environments in which water is limited, urea is the principal end product (fig. 22.6). Urea formation also helps to maintain osmotic balance with seawater in cartilagenous fishes. In such animals, most of the urea secreted by the kidney glomerulus is reabsorbed by the tubules. Indeed, the amount of nitrogen excreted by the kidneys of fishes is small com-... 

Mechanism of Action. Although the drug s exact mechanism of action is unknown, mefloquine may exert antimalarial effects similar to chloroquine that is, these drugs inhibit hemoglobin digestion in malarial parasites, thus causing heme by-products to accumulate within the protozoa and cause toxicity and death of this parasite.65... 

Mechanism of Action. The exact mechanism of quinine is not known. This drug probably exerts antimalarial effects similar to those of chloroquine—that is, inhibition of hemoglobin digestion and subsequent accumulation of toxic heme by-products that lead to death in susceptible protozoa.22... 

Clinical Use. lodoquinol (Diquinol, Yodoxin, other names) is used primarily to treat protozoal infections within the intestinal tract,51 and it is often combined with a second tissue amebicide, which kills protozoa at extraintestinal sites. For instance, iodoqui-nol may be combined with metronidazole to ensure the destruction of parasites throughout the body, lodoquinol is usually administered orally. Because iodoquinol is relatively toxic, the routine use of this drug has been replaced somewhat by other agents such as paromomycin, which may be somewhat safer. 

Mechanism of Action. Paromomycin acts selectively on protozoa within the intestinal lumen and destroys these parasites by a direct toxic effect. 

Gilron, G.L. and Lynn, D.H. (1998) Ciliated protozoa as test organisms in toxicity assessments, in P.G. Wells, K. Lee and C. Blaise (eds.), Microscale Testing in Aquatic Toxicology Advances, Techniques, and Practice, CRC Press, Boca Raton, FL, pp. 323-336. 

Bioassays appeared to fit the bill to perform this service to monitor chemical contamination. They have been around for a while. Until relatively recently, however, they remained in the realm of the laboratory. Only over the last two decades have they found a niche in testing for toxic chemicals in water and sediment, but not yet specifically as a tool for routine water quality monitoring. As Small-scale Freshwater Toxicity Investigations, Volumes 1 and 2 amply demonstrates, the science has now come of age. Assays based on bacteria, microscopic or multi-cellular algae, protozoa, invertebrates and vertebrates (freshwater fish cell cultures) are discussed in... 

Metabolic processes of fungi, bacteria, and protozoa act to degrade toxic substances in the water and soil environments. 

The greatest danger to humans from dinoflagellata toxins comes from the ingestion of shellfish, such as mussels and clams, that have accumulated the protozoa from sea water. In this form the toxic material is called paralytic shellfish poison. As little as 4 mg of this toxin, the amount found in several severely infested mussels or clams, can be fatal to a human. The toxin depresses respiration and affects the heart, resulting in complete cardiac arrest in extreme cases. 

Detoxification of dietary alleochemicals, which can be achieved by symbiotic bacteria or protozoa living in the rumen or intestines, or by liver enzymes which are specialized for the chemical modification of xenobiot-ics. This evolutionary trait is very helpful for Homo sapiens, since it endowed us with a means to cope with our man-made chemicals which pollute the environment. Carnivorous animals, such as cats, are known to be much more sensitive toward plant poisons (505). It was suggested that these animals, which do not face the problem of toxic food normally, are thus not adapted to the handling of allelochemicals. 

The modern period of chemotherapy, the treatment of disease by use of chemical substances, began with the work of Paul Fhrlich (1854-1916). It was known at the beginning of the present century that certain organic compounds of arsenic would kill protozoa, parasitic micro-organisms responsible for certain diseases, and Ehrlich set himself the task of synthesizing a large number of arsenic compounds, ill an effort to find one which would be at the same time toxic (poisonous) to protozoa irj the human body and non-toxic to the human host... 

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