disease. In addition, identifying one particular parasite within an individual does not
indicate whether or not he/she has any other parasitic infections.
Most studies of parasitic infections are distributed in the following way: that is, a few
people have many parasites while most people have none or hardly any parasites. This
suggests that some people have a degree of immunity to certain infections.
Methods of examination must be taken into account. For instance if only stools are
examined, this will only reveal the presence of certain groups of parasites. It will not reveal
the presence of the metacestode stage of cestodes nor filarial nematodes. Blood samples
will show parasites associated with the circulating blood. Immunodiagnosis reveals the
presence of tissue or organ parasites, but is not very specific. An important aspect of any
epidemiological study is to ascertain whether or not the parasites found are zoonotic and
if they identify the animal hosts.
Poverty often goes together with poor housing, lack of clean fresh water, inadequate
sanitation, crowded living conditions and living in close proximity to domestic animals.
These conditions are often associated with disease and parasitic infections. Wet, muddy
and stagnant waters are frequently breeding grounds for vectors of infections.
A convenient method investigating the impact of parasitic infections in a community
is to examine the patient records from a local hospital or health clinic. Many such stud-
ies have been carried out and reported and provide some interesting information with
regard to parasite distribution in relation to the local topography and life styles etc. Such
a study was a survey of patients from the rural hospital of an isolated community in
Northern Namibia (Evans and Joubert 1989) (see Box 8.1).
An important finding was that many of those patients had more than one parasite, a
condition referred to as polyparisitism. The age and sex of the infected individuals
showed certain trends such as: More females were infected with hookworms — females
while doing the family washing tend spend more time on damp ground where the infec-
tious larvae live. S. mansoniwas found mainly in males — males spend more in contact
with water while fishing.
n 8.1.1 RURAL COMMUNITIES
Surveys of rural communities in a variety of geographical areas have revealed that indi-
viduals are frequently infected with more than one species of parasite. This condition was
clearly demonstrated in a series of investigations carried out by Buck et al. (1978) in the
following areas: Chad and Zaire in central Africa, areas containing both dry savannah and
humid wooded savannah; the low Amazon basin of Peru; and the semi-desert region of
Afghanistan.
EPIDEMIOLOGYn BOX 8.1
The total number of patients examined over 29 months was just over 4,000 and the major-
ity (72%) of these patients lived within a 5 km strip alongside a river.nThe mean annual temperature was 35°C with a range from +40°C to −4°C with no frost.
nThe annual rainfall was 600 mm, of which 64% fell between January to April.
nThe following types of parasite were detected by stool examinations of 518 patients (12.4%
of the total examined):
Ancylostoma braziliensisand A. caninum(6.8%); Strongyloides stercoralis(2.7%);
Hymenolepis nana(1%); Schistosoma mansoni(1%); Taeniaspp (0.9%).