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Category: Food Microbiology
Protozoan Parasites, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555819972/9781555819965.ch25-1.gif /docserver/preview/fulltext/10.1128/9781555819972/9781555819965.ch25-2.gifAbstract:
Protozoan parasites have been linked to human illnesses since antiquity and have been associated with outbreaks of foodborne and waterborne illness. Microorganisms such as amoebas, flagellates, ciliates, and coccidians are the most common in this group. Toxoplasma and Sarcocystis are most frequently associated with consumption of undercooked meats, whereas Cryptosporidium, Cyclospora, Cystoisospora, Giardia, and the amoebas are mostly associated with consumption of contaminated water and fresh produce (vegetables and fruits). Foodborne transmission of Trypanosoma cruzi has also been reported, particularly in South and Central America, when infected insects or their feces are consumed in fruit juice preparations. Cyclospora cayetanensis, a coccidian parasite, is endemic to various locations worldwide and was responsible for a number of U.S. foodborne-illness outbreaks in the 1990s as a result of consumption of imported berries and in the past 5 years after consumption of imported salad greens and cilantro. Sarcocystis infection has been diagnosed in ill travelers complaining of muscular pains; transmission was associated with consumption of improperly cooked meats from Southeast Asia. Most parasites are inactivated by heating at high temperatures and in some instances by prolonged storage under freezing conditions, but parasites are highly resistant to chemical disinfection. Increased travel to tropical areas and consumer demands for off-season produce have resulted in globalization of the food supply. Along with the advantages of globalization, the incidental spread of foodborne parasites has also increased. The biology, epidemiology, inactivation, treatment, and control of foodborne parasites are addressed in this chapter.
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Scanning electron micrographs of oocysts and excysting sporozoites of C. parvum. (A) Intact oocyst prior to excystation (magnification, ×11,200). (B) Three sporozoites (Sp) excysting from oocyst simultaneously via the cleaved suture (Su) (magnification, ×11,200). (C) Empty oocyst (magnification, ×11,200). (D) Excysted sporozoite (magnification, ×9,800). Ae, apical end. Reprinted from reference 224 .
Life cycle of Cryptosporidium. From reference 225 .
Acid-fast staining. (A) C. parvum. (B) C. cayetanensis. (C) C. belli. Bars = 20 μm.
C. cayetanensis oocysts. (A) Phase-contrast microscopy of unsporulated oocysts. (B) Oocysts (OO) in the process of excystation. Note the two sporozoites (SP) free of the sporocyst (SC). (C) Transmission electron microscopy of human small intestine showing Cyclospora intracellular stages. ME, merozoite.
Bright-field photomicrograph of unsporulated (A) and sporulated (B) C. belli oocysts.
Life cycle of T. gondii. From Dubey and Beattie ( 137 ).
Transmission electron micrographs of T. gondii. (A) Sporozoite in parasitophorous vacuole (Pv) of host cell (Hc) at 24 h after inoculation. Am, amylopectin granule; Co, conoid; Mn, microneme; Nu, nucleus of sporozoite; Rh, rhoptry. (B) Final stage of endodyogeny to form two daughter tachyzoites that are still attached to the posterior ends (arrowheads). DG, dense granules; HC, host cell; IT, intravacuolar tubules; M, mitochondrion; MC, microneme; MI, micropore; N, nucleus; RO, rhoptry. From Dubey and Beattie ( 137 ).
Scanning electron micrograph of G. lamblia trophozoites. One trophozoite shows the dorsal surface and the other shows the ventral surface with sucking disk and flagella.
Hematoxylin and eosin staining. (A) G. lamblia cyst with two nuclei and a trophozoite (a) and showing two nuclei and the median body visible at one pole (b). (B) B. coli cyst showing a large macronucleus and cilia beneath the cyst wall and trophozoite (a) and showing an oval macronucleus (b). (C) E. histolytica trophozoite showing a nucleus and a few red blood cells in the cytoplasm and cyst (a) and showing two of four nuclei and rod-shaped inclusion bodies with rounded ends (b). Courtesy of Lynne S. Garcia.