Human infection

Resistance to Tetracyclines. The tetracyclines stiU provide inexpensive and effective treatment for several microbial infections, but the emergence of acquired resistance to this class of antibiotic has limited their clinical usehilness. Studies to define the molecular basis of resistance are underway so that derivatives having improved antibacterial spectra and less susceptibiUty to bacterial resistance may be developed. Tetracyclines are antibiotics of choice for relatively few human infections encountered in daily clinical practice (104), largely as a result of the emergence of acquired tetracycline-resistance among clinically important bacteria (88,105,106). Acquired resistance occurs when resistant strains emerge from previously sensitive bacterial populations by acquisition of resistance genes which usually reside in plasmids and/or transposons (88,106,107). Furthermore, resistance deterrninants contained in transposons spread to, and become estabUshed in, diverse bacterial species (106). 

Coccidiosis is seen frequendy in puppies and kittens and is responsible for diarrhea and even death if the animals are maintained in unsanitary conditions. For dogs and cats there exists no satisfactory treatment however, the disease is self-limiting. Human infections can frequendy be traced to these animals. 

The starting point for the produchon of all microbial vaccines is the isolation of the appropriate microbe. Such isolates have been mostly derived from human infections and in some cases have yielded strains suitable for vaccine production very readily in other cases a great deal of manipulahon and selechon in the laboratory have been needed before a suitable strain has been obtained. 

Most of the strains associated with human infection belong to genogroup I (GI) or GII, while GUI viruses infect cattle, GPV viruses infect humans and canines, and GV viruses infect mice. 

Since HSV is only found in humans, infection may only be transmitted from infectious secretions onto mucosal surfaces (i.e., cervix or urethra) or abraded skin. It has also been noted that the virus may survive for a limited amount of time on environmental surfaces. 

Alves Oliveira LF, Moreno EC, Gazzinelli G, et al. Cytokine production associated with periportal fibrosis during chronic schistosomiasis mansoni in humans. Infect Immun 2006 74(2) 1215-1221. 

A knowledge of parasite life cycles is crucial in the understanding of the ways infection is acquired and spread, the pathogenesis of disease, and the ways in which disease might be controlled. Some parasites which infect only humans, such as Enterobius vermicularis (pinworm), have a narrow host specificity, whereas others such as Trichinella spiralis infect numerous species. When other animals harbor the same parasite stage as humans, these animal species may serve as reservoir hosts. Humans infected with a parasite stage usually seen in other animal species are referred to as accidental hosts. 

Human infections with Salmonella spp. and E. coli 0157 H7 are a common worldwide phenomenon. Livestock may serve as a source of several relevant human pathogenic microorganisms (Table 19.2). The most prevalent group is the enteric pathogens which include bacteria, viruses and parasites (i.e. protozoa and helminths). Animals may shed pathogens through excreta without... 

Toxoplasmosis. This disease is caused by Toxoplasma gondii, which normally causes an asymptomatic infection in healthy adults. This protozoan also infects a very wide variety of animals domestic cats are one source of human infection. Unlike Cryptosporidium, Toxoplasma is an intracellular parasite and can invade numerous organs of infected individuals. In AIDS patients, the... 

Srimanote, P., Paton, A. W., and Paton, J. C. (2002). Characterization of a novel type IV pilus locus encoded on the large plasmid of locus of enterocyte effacement-negative Shiga-toxigenic Escherichia coli strains that are virulent for humans. Infect. Immun. 70,3094-3100. 

There is concern that the virus can infect humans living in close proximity to the infected poultry/animals. As of May 31,2007, there have been 309 cases of humans infected, with 187 fatalities. Most of the cases were in Indonesia, Vietnam, Egypt, Thailand, and China. 

Table II lists the fermentation products licensed in the U.S. for parenteral or topical administration to animals. Most of these are also used to treat human infections. As important as these are for animal health, of far greater economic importance are the antibiotics that are incorporated into animal feeds.

Both types of resistance in animal bacteria can affect human health. Bacteria of animal origin that are resistant to a particular antibiotic may make this antibiotic ineffective for controlling human infections with pathogens bearing the kind of... 

In the more recent Chicago outbreak of Salmonellosis, which has been attributed to milk contaminated with a tetracycline-resistant strain of Salmonella typhimurium. there were two deaths verified as resulting from infections with the resistant strain of Salmonel la in 16 284 confirmed cases. If one pools these cases with those cited in the NRDC petition then the incidence of mortality (0.09%) is similar or than that of persons affected by antibiotic-sensitive Salmone1 la (0.21%) also cited by NRDC. Thus the similarity of risks of human infections with resistant and sensitive strains of SaImone 11a agrees with research data obtained in controlled experiments (Smith 15). 

Chase-Topping, M., Gaily, D., Low, C., Matthews, L., and Woolhouse, M. (2008). Super-shedding and the link between human infection and livestock carriage of Escherichia coli 0157. Nat. Rev. Microbiol. 6, 904-912. 

Anthrax, a disease caused by infection by Bacillus anthracis via spores, can be transmitted to humans or animals ruminants such as sheep, goats, cattle, and deer are most susceptible. The handling of infected animals or animal products may also lead to human infection. Recently, anthrax has been considered to be a potential candidate for bioterrorism activity. The spores are extremely hardy and may come into contact with humans through a cut or abrasion, through consumption of infected meat, or by inhalation. The Center for Disease Control (CDC) lists anthrax as a category A disease, and the only vaccine that currently exists has a number of drawbacks and health risks. 

The lack of human pathogenicity of plant viruses rules out the risks of human infection by exposure in the field or in food products to a plant virus. However, biological containment of the virus expression vector remains a primary safety concern as it can be considered a risk to the environment. This includes the spread of recombinant viruses to weeds... 

An anopheline mosquito inoculates plasmodium sporozoites to initiate human infection (Figure 52-1). Circulating sporozoites rapidly invade liver cells, and exoerythrocytic stage tissue schizonts mature in the liver. Merozoites are subsequently released from the liver and invade erythrocytes. Only erythrocytic parasites cause clinical illness. Repeated cycles of infection can lead to the infection of many erythrocytes and serious disease. Sexual stage gametocytes also develop in erythrocytes before being taken up by mosquitoes, where they develop into infective sporozoites. 

Gram-positive bacteria often carry surface proteins that interact with host tissues in establishing human infections. Protein A of Staphylococcus is a well-known... 

Ornithine decarboxylase is specifically inhibited by the enzyme-activated inhibitor a-difluoromethyl-ornithine, which can cure human infection with Trypanosoma brucei (African sleeping sickness) by interfering with polyamine synthesis.243-2443 In combination with inhibitors of spermidine synthase or S-adenosylmethionine decarboxylase,245 it can reduce polyamine levels and growth rates of cells. Another powerful inhibitor that acts on both ornithine and adenosylmethionine decarboxylases is the hydroxy-lamine derivative l-aminooxy-3-aminopropane 246... 

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