Nutrient Losses

Accelerated loss of nutrients from the body is probably the most important mechanism by which parasitic infections compromise the nutritional status of their host. Nutrient losses arise both directly and indirectly.

Direct losses occur during the feeding of the bloodsucking and tissue-invading parasites. Blood and tissue ingested by the worms forms part of the loss but the lesions caused by feeding and burrowing activity continue to ooze blood and tissue fluids after the parasites have moved on. Similarly, the passage of schistosome eggs through the tissues of the bladder or intestine is often accompanied by tissue damage and blood loss. Increased turnover and accelerated shedding of parasite-damaged enterocytes into the lumen of the GI tract is another mechanism of increased nutrient loss. Even though some of the nutrients lost into the lumen may be reabsorbed, the process is far from complete. Vomiting or diarrhea causes loss of electrolytes and important trace elements such as zinc.

Indirect losses arise from stimulation of the host's immunological and inflammatory mechanisms that are mobilized to combat the infection and repair tissue damage. Localized inflammation at the site of the parasite activity, often accompanied by lym-phocytic infiltration of tissues cause further damage to the mucosa, augmenting maldigestion, malabsorption, and nutrient losses as more damaged cells are shed. Activation of the systemic inflammatory system, i.e., the acute phase response, is a general reaction of the body to pathogen invasion or tissue damage. It results in a widespread cytokine-mediated catabolic response. Growth slows or ceases, muscle tissue is broken down to provide substrates for glu-coneogenesis and the repair of damaged cells, and a negative nitrogen balance ensues. Anorexia occurs and there are increased losses of amino acids, minerals, and vitamins in the urine and feces.

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