BOOKS OF RtfiDIfGS - PAHO/WHO

- 97 -
R. F'RRICHS AND J. PRAWDA
where
R,.,= thc index of rabies risk for a barrio i at time i,
C, = hc relative proportion of barrio i dogs typically found in ihe streets.
X , ,=the number of susceptible dogs in barrio i at time t, and
i(j)=a subscript denoting neighboring barrios j,j= I ... 5 which surround
barrio i.
Since a rabid dog moves fromi barrio to barrio. the assu miiinIon is miade tlha tlhe sull
of the values of Cq(,)X,(), in each of the five neighboring barrios is equally as
important to the subsequent generation of rabies as the value of C,X, 1, ini barrio i
itself.
All values of R,., are ranked froni highest Lo lowest. A vaccinaling teaim aild truck
are sent to thi highliest ranked barrio. II tiher are numerous trucks, each one goes to a
separate high ranked barrio and remains there until the required proportion of
susceplible dcogs is vaccinated. Thereafcíer the trucks return at diffrcent timc periods
to the rabies center for reassignmieni to tle next highest raniked barrio. Tlhe most
important factor is that the vaccinators go house-to-house in the selected barrios and
vaccinate all susceptible dogs they encounter. Since the necessary informnation for the
formitula can be continuiously updated hy tile vaccinators with limited data collected
during their visit to the various barrios, we feel thlat the policy will be easy to operaite
and will require little supervision. Further details of this barrio ranking procedure are
published elsewhere (14].
Thc Preferred Vaccinaltion Policy is co*mpared in Figure 3 with a policy of no
vaccination. The term "VA" refeis Lo the fact that 70 percent of tihe susceptible cdogs
in the selected barrios were immunizei durIn; each visit by the vaccinators. Or
restated, it means that 30 percent of the barrio dog owners were either not home or
were urnwilling to cooperate with tl - rabies prevention prograni. As can be seen in
Figure 3 the Preferred Vaccination Policy greatly reduced the incidence of canine
rabies throughout tihe planning horizon. But al wiiat cost?
Comparing the three vaccination policies which we have shown so far. Table 1
in¡dicates that thc Preferred Vaccination Policy with 70 percent public cooperation
cost more than either of the otlher two policies. However, the cuniulative meanll
number of rabid dogs over the ten-year planning horizon is also reduced to a lower
level than either of the other two policies.
PREFERRED VACCINATION POLICY PROBLEM
80- n
70 1 - MEAN
60- Ki .95 confidence interval
50- 1
4 40-
30
20O
Q. 10 __....._______ _-
2 4 6 8 10 12
COST(USAdollars) per PREVENTED RABID DOGS
FIGURI: .1 ('omlpuler Simulalitn Experitmcnls: Cost ¡..r prevented rabi do
dd Juring a ten-ycar rc,
with the '-ilerred Vaccination Policy sel at diffcrcnt i.:vels of VA (percent vaccim;ted in ach .lv,
barrio) (m,':;;. 0.95 ?cfidence interval, 10 epidemic tr!:is per experiment).