Human population, disease outbreaks

Epizootic 1. Denoting a temporal pattern of disease occurrence in an animal population in which the disease occurs with a frequency clearly in excess of the expected frequency in that population during a given time interval. 2. An outbreak (epidemic) of disease in an animal population often with the implication that it may also affect human populations. 

Influenza is the most widespread acute infectious disease of humans. Annually, influenza accounts for the increase in morbidity and mortality rate all over the world. For example, every winter about 300 000 patients in the US are hospitalized and 30000 0000 patients die as a result of influenza infection. The morbidity and mortality rates due to influenza infection are increased dramatically in cases of pandemic outbreaks. In the 20th century, there were three pandemics — the pandemic of Spanish influenza in 1918, caused by a virus of antigenic formula HlNl the pandemic of Asian influenza of 1957, caused by a virus of antigenic formula H2N2 the pandemic of 1968 caused by a virus with antigenic formula H3N2. These pandemics are characterized by a morbidity rate from 30% to 60% of the population and are accompanied by dramatic increases of pneumonia number and general mortality. The pandemic of Spanish influenza of 1918, which took the lives of 1-2% of the entire human population, was especially serious. Almost the entire world was stricken with the first influenza pandemic of the third millennium caused by strain A/California/04/2009 (HlNl). 

On occasion, the virus spreads beyond the affected individual. The intermediate cycle of yellow fever transmission occurs in humid or semi-humid savannahs of Africa and can produce small-scale epidemics in rural villages. Semi-domestic mosquitoes infect both monkey and human hosts and increased contact between man and infected mosquito leads to disease. This is the most common type of outbreak observed in recent decades in Africa. Urban yellow fever results in large explosive epidemics when travelers from rural areas introduce the virus into areas with high human population density. Domestic mosquitoes, most notably Aedes aegypti, carry the virus from person to person. These outbreaks tend to spread outward from one source to cover a wide area. 

Plague is characterized by periodic disease outbreaks in rodent populations, some of which have a high death rate. During these outbreaks, hungry infected fleas that have lost their normal hosts seek other sources of blood, thus increasing the increased risk to humans and other animals frequenting the area. 

At the same time, global travel and rise of imports and exports have made people aware of the possibility of global outbreaks of disease. Because 60 percent of infections contracted by human beings and 75 percent of emerging diseases have their origin in animals, maintaining a healthy animal population worldwide is essential to maintaining a healthy human population, which provides the workforce... 

An often over-looked aspect of surveillance for bioterror events is surveillance of animal populations. Several of the agents considered to have bioterror potential are diseases of animals, for example, anthrax and brucellosis (Franz et al., 2001 Inglesby et al., 1999 USAM-RIID, 2005). A covert attack may first become apparent when animals become ill. The need to coordinate information from medical and veterinary sources was illustrated by the epidemiologic investigation during the 1999 West Nile Virus outbreak in New York City. Investigators found that there had been an outbreak in birds several weeks prior to the human outbreak (Fine Lay-ton, 2001). The current surveillance plan for monitoring West Nile Virus infection in the U.S. includes sentinel surveillance of several animal populations (CDC, 2003). 

Although the role of ochratoxins in human pathogenesis is stiU speculative, the lesions of nephropathy in humans were reported to be similar to those observed in porcine nephropathy [104]. Outbreaks of kidney disease (Balkan endemic nephropathy) in rural populations in Bulgaria, Romania, Tunisia and the former Yugoslavia were associated with ochratoxin A [104—106]. These correlations were... 

Hayes (5) has also reviewed the contribution of pesticides to the control of human diseases spread by arthropods and other vectors. Outbreaks of malaria, louse-borne typhus, plague, and urban yellow fever, four of the most important epidemic diseases of history, have been controlled by use of the organochlorine insecticides, especially DDT. In fact, the single most significant benefit from pesticides has been the protection from malaria. Today malaria eradication is an accomplished fact for 619 million people who live in areas once malarious. Where eradication has been achieved it has stood the test of time. An additional 334 million people live in areas where transmission of the parasite is no longer a major problem. Thus, about 1 billion people, or approximately one-fourth of the population of the world, no longer live under the threat of malaria. 

Venezuelan equine encephalitis (VEE) is a virus that is naturally transmitted from horse to horse by mosquitoes. Humans can also get the virus from the infected mosquito. Each year, thousands of persons acquire the disease naturally from mosquito bites. Human outbreaks usually follow an epidemic among the horse population. Humans infected can infect mosquitoes for up to 72 hours. Once a mosquito becomes infected, it remains so for life. 

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