Environmental Engineering Reference
In-Depth Information
sterile, except for urinary schistosomiasis, typhoid, and leptospirosis carriers.
33
The prevalence of carriers differs by disease within an exposed population. For
example, the prevalence of amebic dysentery varies between 10 and 25 percent
and may be as high as 60 percent; shigellosis may be higher. Stoll has ventured to
hazard a guess of the prevalence of helminthic infections in the world.
10
He esti-
mates that at least 500 million persons harbor ascarids, 400 million other worms
(helminthes). Actually, a person who is ill with a helminthic disease probably
is infected with more than one parasite, since the conditions conducive to one
infection would allow additional species to be present.
The World Health Organization (WHO) estimates that 600 million people are
at risk and 300 million are afflicted by schistosomiasis (bilharziasis), usually
spread by wading in cercariae-infested water
11
In addition, it is estimated that
almost a quarter of the world's population suffers from one of four water-related
diseases: gastroenteritis, malaria, river blindness (onchocerciasis), or schistosomi-
asis A survey of U.S., state, and territorial public health laboratories by the CDC
in 1976 for frequency of diagnosis of intestinal parasitic infections in 414,820
stool specimens showed 15.6 percent contained one or more pathogenic or non-
pathogenic intestinal parasites, 3.8 percent were positive for
Giardia lamblia
,2.7
percent for
Trichuris trichiura
, 2.3 percent for
Ascaris lumbricoides
, 1.7 percent
for
Enterobius vermicularis
, and 0.6 percent for
Entamoeba histolytica
.
12
A study at a missionary college in east central China showed that 49 percent
of the students harbored parasitic worms, and a survey in an elementary school
in New Jersey found that 23 percent of the children were infected. In 1970,
Lease reported on the study of day care and elementary school programs in four
counties in South Carolina involving 884 children.
13
He found that 22.5 percent
of black children harbored
Ascaris
intestinal roundworms and, of the 52 white
children in the group, 13.5 percent had worms. Central sewage and water supply
was lacking. Persons living in rural areas had higher infection rates; infected
rural children also had twice the number of worms as infected children from
urban areas. A study involving 203 children ranging in age from six months to
six years in St. Lucia in the Caribbean showed that infection with
T. trichiura
was 84 percent,
A. lumbricoides
62 percent, hookworm 7 percent, and
To x o c a r a
canis
86 percent.
14
Since parasitic infection plus poor diet may result in serious
debility and perhaps death, preventive measures, including better sanitation and
hygienic practices, are essential.
The mouth, nose, throat, respiratory tract, and skin of humans are also reser-
voirs of microorganisms that directly cause a large group of illnesses.
Staphylo-
cocci
that produce enterotoxin are also found on the skin and mucous membranes,
in pus, feces, dust, and air, and in unsanitary food-processing plants. They are the
principal causes of boils, pimples, and other skin infections, and are particularly
abundant in the nose and throat of a person with a cold. It is no surprise, there-
fore, that
staphylococcus
food poisoning is one of the most common foodborne
diseases. Scrupulous cleanliness in food-processing plants, in the kitchen, and
among foodhandlers is essential if contamination of food with
salmonella
spp.,
staphylococci
,
clostridia
, and other microorganisms is to be prevented.
