Disease Reservoirs: Animate or inanimate sources which normally harbor disease-causing organisms and thus serve as potential sources of disease outbreaks. Reservoirs are distinguished from vectors (DISEASE VECTORS) and carriers, which are agents of disease transmission rather than continuing sources of potential disease outbreaks.Fresh Water: Water containing no significant amounts of salts, such as water from RIVERS and LAKES.Rodentia: A mammalian order which consists of 29 families and many genera.Zoonoses: Diseases of non-human animals that may be transmitted to HUMANS or may be transmitted from humans to non-human animals.Animals, Wild: Animals considered to be wild or feral or not adapted for domestic use. It does not include wild animals in zoos for which ANIMALS, ZOO is available.Phytoplankton: Free-floating minute organisms that are photosynthetic. The term is non-taxonomic and refers to a lifestyle (energy utilization and motility), rather than a particular type of organism. Most, but not all, are unicellular algae. Important groups include DIATOMS; DINOFLAGELLATES; CYANOBACTERIA; CHLOROPHYTA; HAPTOPHYTA; CRYPTOMONADS; and silicoflagellates.Eutrophication: The enrichment of a terrestrial or aquatic ECOSYSTEM by the addition of nutrients, especially nitrogen and phosphorus, that results in a superabundant growth of plants, ALGAE, or other primary producers. It can be a natural process or result from human activity such as agriculture runoff or sewage pollution. In aquatic ecosystems, an increase in the algae population is termed an algal bloom.Cladocera: A suborder of CRUSTACEA, order Diplostraca, comprising the water fleas. They are benthic filter feeders that consume PHYTOPLANKTON. The body is laterally compressed and enclosed in a bivalved carapace, from which the head extends.Virus Latency: The ability of a pathogenic virus to lie dormant within a cell (latent infection). In eukaryotes, subsequent activation and viral replication is thought to be caused by extracellular stimulation of cellular transcription factors. Latency in bacteriophage is maintained by the expression of virally encoded repressors.Rivers: Large natural streams of FRESH WATER formed by converging tributaries and which empty into a body of water (lake or ocean).Water Microbiology: The presence of bacteria, viruses, and fungi in water. This term is not restricted to pathogenic organisms.Phylogeny: The relationships of groups of organisms as reflected by their genetic makeup.Rodent Diseases: Diseases of rodents of the order RODENTIA. This term includes diseases of Sciuridae (squirrels), Geomyidae (gophers), Heteromyidae (pouched mice), Castoridae (beavers), Cricetidae (rats and mice), Muridae (Old World rats and mice), Erethizontidae (porcupines), and Caviidae (guinea pigs).Chiroptera: Order of mammals whose members are adapted for flight. It includes bats, flying foxes, and fruit bats.Population Density: Number of individuals in a population relative to space.Zooplankton: Minute free-floating animal organisms which live in practically all natural waters.BrazilSeasons: Divisions of the year according to some regularly recurrent phenomena usually astronomical or climatic. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)Peromyscus: A genus of the subfamily SIGMODONTINAE consisting of 49 species. Two of these are widely used in medical research. They are P. leucopus, or the white-footed mouse, and P. maniculatus, or the deer mouse.Water Movements: The flow of water in enviromental bodies of water such as rivers, oceans, water supplies, aquariums, etc. It includes currents, tides, and waves.Hantavirus Infections: Infections with viruses of the genus HANTAVIRUS. This is associated with at least four clinical syndromes: HEMORRHAGIC FEVER WITH RENAL SYNDROME caused by viruses of the Hantaan group; a milder form of HFRS caused by SEOUL VIRUS; nephropathia epidemica caused by PUUMALA VIRUS; and HANTAVIRUS PULMONARY SYNDROME caused by SIN NOMBRE VIRUS.Water Supply: Means or process of supplying water (as for a community) usually including reservoirs, tunnels, and pipelines and often the watershed from which the water is ultimately drawn. (Webster, 3d ed)Urinary Reservoirs, Continent: Structures which collect and store urine and are emptied by catheterization of a cutaneous stoma or internal diversion to the urethra. The reservoirs are surgically created during procedures for urinary diversion.Disease Vectors: Invertebrates or non-human vertebrates which transmit infective organisms from one host to another.Hantavirus: A genus of the family BUNYAVIRIDAE causing HANTAVIRUS INFECTIONS, first identified during the Korean war. Infection is found primarily in rodents and humans. Transmission does not appear to involve arthropods. HANTAAN VIRUS is the type species.Environmental Monitoring: The monitoring of the level of toxins, chemical pollutants, microbial contaminants, or other harmful substances in the environment (soil, air, and water), workplace, or in the bodies of people and animals present in that environment.HIV-1: The type species of LENTIVIRUS and the etiologic agent of AIDS. It is characterized by its cytopathic effect and affinity for the T4-lymphocyte.