Foodborne Animal Parasites 687
Because bovine and porcine animals serve as intermediate hosts for these parasites, their potential
as foodborne pathogens to humans is obvious.
Cryptosporidiosis
The protozoan Cryptosporidium parvum was first described in 1907 in asymptomatic mice, and
for decades now it has been known to be a pathogen of at least 40 mammals and varying numbers
of reptiles and birds. Although the first documented human case was not recorded until 1976, this
disease has a worldwide prevalence of 1–4% among patients with diarrhea,
104 and it appears to be
increasing. In England and Wales for the 5 years 1985–1989, the numbers of identified cases were
1874, 3694, 3359, 2838, and 7769, respectively.
2 This disease was the fourth most frequent cause of
diarrhea during the period noted. It is estimated to cause infections in from 7 to 38% of AIDS patients
in some hospitals.
104 The prevalence of C. parvum in diarrheal stools is similar to that of Giardia
lamblia.
104 In humans, the disease is self-limiting in immunocompetent individuals, but it is a serious
infection in the immunocompromised, such as AIDS patients. The protozoan is known to be present
in at least some bodies of water (see below) and thus exists the potential for food transmission. The
fecal–oral route of transmission is the most important, but indirect transmission by food and milk is
known to occur.
C. parvum is an obligate intracellular coccidian parasite that carries out its life cycle in one host.
Following ingestion of the thick-walled oocysts, they excyst in the small intestine and free sporozoites
and penetrate the microvillous region of host enterocytes, where sexual reproduction leads to the
development of zygotes. They invade host cells by disrupting their own membrane as well as that of
the host. Host cell actin polymerization at the interface between the parasite and the host cell cytoplasm
has been found to be necessary for infection.
30 About 80% of the zygotes form thick-walled oocysts
that sporulate within host cells.
24 The environmentally resistant oocysts are shed in feces, and the
infection is transmitted to other hosts when they are ingested.
The oocysts of C. parvum are spherical to ovoid and average 4.5–5.0 µm in size. Each sporulated
oocyst contains four sporozoites. The oocysts are highly resistant in the natural environment and
may remain viable for several months when kept cold and moist.
24 They have been reported to be
destroyed by treatments with 50% or more ammonia and 10% or more formalin for 30 minutes.
24 The
latter investigator has reported that temperatures above 60
◦ C and below −20
◦ C may kill C. parvum
oocysts. The organism is destroyed by high-temperature, short time (HTST) milk pasteurization.
Holding oocysts at 45
◦ C for 5–20 minutes has been reported to destroy their infectivity.
1 In one study,
infectivity was lost after 2 months when cysts were stored in distilled water or at 15–20
◦ C within
2 weeks or at 37
◦ C in 5 days.
92 In the latter study, cysts did not survive freezing even when stored in a
variety of cryoprotectants. The survival of C. pavum oocysts of human and ovine origins in still natural
mineral waters was assessed in a study in Scotland. When added to mineral waters and held at 20
◦ C, a
progressive decline in viability of both types was noted, but viability remained unaltered when stored
for 12 weeks at 4
◦ C.
73 Commonly used disinfectants are ineffective against the oocysts,
10 and this has
been demonstrated for ozone and chlorine compounds. For a 90% or more inactivation of C. parvum
oocysts, 1 ppm ozone required 5 minutes, 1.3 ppm chlorine dioxide required 60 minutes, and 80 ppm
each of chlorine and monochloramine required about 90 minutes.
62 The oocysts were 14 times more
resistant to ClO 2 than Giardia cysts, and these investigators suggested that disinfection alone should
not be relied upon to inactivate C. parvum oocysts in water.
Human cryptosporidiosis may be acquired by at least one of five known transmission routes:
zoonotic, person-to-person, water, nosocomial (hospital acquired), or food. Zoonotic transmission
Because bovine and porcine animals serve as intermediate hosts for these parasites, their potential
as foodborne pathogens to humans is obvious.
Cryptosporidiosis
The protozoan Cryptosporidium parvum was first described in 1907 in asymptomatic mice, and
for decades now it has been known to be a pathogen of at least 40 mammals and varying numbers
of reptiles and birds. Although the first documented human case was not recorded until 1976, this
disease has a worldwide prevalence of 1–4% among patients with diarrhea,
104 and it appears to be
increasing. In England and Wales for the 5 years 1985–1989, the numbers of identified cases were
1874, 3694, 3359, 2838, and 7769, respectively.
2 This disease was the fourth most frequent cause of
diarrhea during the period noted. It is estimated to cause infections in from 7 to 38% of AIDS patients
in some hospitals.
104 The prevalence of C. parvum in diarrheal stools is similar to that of Giardia
lamblia.
104 In humans, the disease is self-limiting in immunocompetent individuals, but it is a serious
infection in the immunocompromised, such as AIDS patients. The protozoan is known to be present
in at least some bodies of water (see below) and thus exists the potential for food transmission. The
fecal–oral route of transmission is the most important, but indirect transmission by food and milk is
known to occur.
C. parvum is an obligate intracellular coccidian parasite that carries out its life cycle in one host.
Following ingestion of the thick-walled oocysts, they excyst in the small intestine and free sporozoites
and penetrate the microvillous region of host enterocytes, where sexual reproduction leads to the
development of zygotes. They invade host cells by disrupting their own membrane as well as that of
the host. Host cell actin polymerization at the interface between the parasite and the host cell cytoplasm
has been found to be necessary for infection.
30 About 80% of the zygotes form thick-walled oocysts
that sporulate within host cells.
24 The environmentally resistant oocysts are shed in feces, and the
infection is transmitted to other hosts when they are ingested.
The oocysts of C. parvum are spherical to ovoid and average 4.5–5.0 µm in size. Each sporulated
oocyst contains four sporozoites. The oocysts are highly resistant in the natural environment and
may remain viable for several months when kept cold and moist.
24 They have been reported to be
destroyed by treatments with 50% or more ammonia and 10% or more formalin for 30 minutes.
24 The
latter investigator has reported that temperatures above 60
◦ C and below −20
◦ C may kill C. parvum
oocysts. The organism is destroyed by high-temperature, short time (HTST) milk pasteurization.
Holding oocysts at 45
◦ C for 5–20 minutes has been reported to destroy their infectivity.
1 In one study,
infectivity was lost after 2 months when cysts were stored in distilled water or at 15–20
◦ C within
2 weeks or at 37
◦ C in 5 days.
92 In the latter study, cysts did not survive freezing even when stored in a
variety of cryoprotectants. The survival of C. pavum oocysts of human and ovine origins in still natural
mineral waters was assessed in a study in Scotland. When added to mineral waters and held at 20
◦ C, a
progressive decline in viability of both types was noted, but viability remained unaltered when stored
for 12 weeks at 4
◦ C.
73 Commonly used disinfectants are ineffective against the oocysts,
10 and this has
been demonstrated for ozone and chlorine compounds. For a 90% or more inactivation of C. parvum
oocysts, 1 ppm ozone required 5 minutes, 1.3 ppm chlorine dioxide required 60 minutes, and 80 ppm
each of chlorine and monochloramine required about 90 minutes.
62 The oocysts were 14 times more
resistant to ClO 2 than Giardia cysts, and these investigators suggested that disinfection alone should
not be relied upon to inactivate C. parvum oocysts in water.
Human cryptosporidiosis may be acquired by at least one of five known transmission routes:
zoonotic, person-to-person, water, nosocomial (hospital acquired), or food. Zoonotic transmission