Database Reference
In-Depth Information
6.1 Chagas Disease Spread and Control Strategies
The model of this chapter can be used to explore how Chagas disease spreads in a
closed human population and how pursuing one or more of the following control
strategies might affect spread of the disease. These control strategies include the
following: improved housing structures, annual spraying, reservoir control, and con-
genital surveillance. The model consists of two sectors, one for the human popula-
tion showing the transmission of
T. cruzi
among humans. The second module shows
the life cycle of vector insects, and the transmission of
T. cruzi
from adults to in-
fected vectors.
The human population module (Figure 6.1) is based on 2002 estimated
Argentina's population size
2
, BIRTHRATE, and OVERALL DEATH RATE (NAT-
URAL DEATH RATE). We estimated the REPRODUCTIVE POPULATION from
the total population and also estimate the age and sex distribution of the population.
The initial number of SUSCEPTIBLE and INFECTED HUMANS is calculated
from the total population and prevalence rate of
T. cruzi
in Argentina
3
.
A human may acquire infection if borne to an infected mother. CONGENITAL
INFECTION RATE is calculated as the product of PREVALENCE OF
T. CRUZI
AMONG PREGNANT MOTHERS (0.055) and CONGENITAL TRANSMISSION
RATE (0.067)
4
. The majority of infected persons become infected by infected tri-
atomine bugs. The HUMAN INFECTION RATE is the probability that susceptible
humans become infected from these infection vectors:
)
∧
(
HUMAN INFECTION RATE
=
1
−
(
1
−
TRBH
CONT INF B
)
,
(6.1)
where TRBH is the probability that feeding of a bug on an uninfected human will
cause the human to acquire infection at a rate of 0.0008
5
.
CONT INF B is the average number of times an infected bug has had feeding
contact with a human. It is the product of the NUMBER OF INFECTED VEC-
TORS and the AVERAGE NUMBER OF FEEDINGS PER BUG EACH YEAR (5
times per year) divided by (TOTAL BLOOD SOURCE).
5
INFECTED HUMAN is
obtained from the product of HUMAN INFECTION RATE and SUSCEPTIBLE
HUMAN.
2
http://www.cia.gov/cia/publications/factbook/geos/ar.html
3
Gurtler, R.E., Cecere, M.C., Castanera, M.B., Canale, D., Lauricella, M.A., Chuit R., Cohen, J.E.
and E.L. Segura. 1996. Probability of infection with
Trypanosoma cruzi
of the vector Triatoma
infestans fed on infected humans and dogs in northwest Argentina. Am J Trop Med Hyg, 55(1),
24-31.
4
Blanco, S.B., Segura, E.L., Cura, E.L., Chuit, R., Tulian, L., Flores, I., Garbarino, G., Villalonga,
J.F. and R.E. Gurtler. 2000. Congenital transmission of
Trypanosoma cruzi
: an operational outline
for detecting and treating infected infants in northwestern Argentina. Trop Med Int Health, 5(4),
293-301.
5
Cohen, J.E. and R.E. Gurtler. 2001. Modeling household transmission of American Trypanoso-
miasis. Science, 293, 694-698.
