Biology Reference
In-Depth Information
INTRODUCTION
The geographic distribution of gastrointestinal (GI) geohelminths is
widespread, with various geographical areas of public health concern
including Africa, Southeast Asia, and Central and South America. It is
estimated that over one billion people are infected with Ascaris lum-
bricoides worldwide
1,2
with a notable prevalence in tropical areas where
lack of safe drinking water and poor sanitation practices lead to increased
exposure to infective eggs. Ascaris is found largely in developing coun-
tries and the epidemiological spread overlaps with that of several
important diseases of the tropics including human immunodeficiency
virus (HIV) and malaria (
Figure 4.1
). In areas where Ascaris is prevalent
“co-infection is the rule rather than the exception.”
3
Co-infection studies have steadily become more common although
funding has tended to be limited to the examination of Ascaris co-infection
on pathogens causing high levels of mortality. In this chapter, we outline
some of the general considerations in co-infection biology. We also review
available data looking at interactions and effects of Ascaris infection on
systemic co-infections with malaria or HIV. Possible effects of co-infecting
pathogens on Ascaris biology or pathology are seldom reported or dis-
cussed. In the third part of the chapter, we consider some of the hypo-
thetical interactions between Ascaris and co-infections that are more
localized to specific organs of the body, specifically the liver and lungs
(effects on Ascaris larval migration) and the gut (effects on egg hatching
and adult Ascaris survival and fecundity).
GENERAL CONSIDERATIONS FOR CO-INFECTION
INTERACTIONS IN ASCARIS LUMBRICOIDES-
INFECTED INDIVIDUALS
Disease severity in any infection is determined by a complex rela-
tionship between several different host and pathogen traits (
Tabl e 4. 1
).
Since pathogens have evolved to establish infection in hosts that are
often co-infected with another pathogen, the study of co-infection can
shed light on the biology and immunology of single infections that, in
many respects, are not the norm. This point is particularly relevant
when considering co-infections with Ascaris because of the high prev-
alence of this nematode infection in areas where many other diseases
thrive.
It is not known whether Ascaris infection increases the likelihood of
co-infection in a host. One study has reported that individuals who har-
bor higher (
5000 egg/g feces) intensities of A. lumbricoides infections
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