Understanding the incidence and timing of rabies cases in domestic animals and wildlife in south-east Tanzania in the presence of widespread domestic dog vaccination campaigns

The “Zero by 30” strategic plan aims to eliminate human deaths from
dog-mediated rabies by 2030, and domestic dog vaccination is a vital
component of this strategic plan. In areas where domestic dog vaccination
has been implemented, it is important to assess the impact of this
intervention. Additionally, understanding temporal and seasonal trends in
the incidence of animal rabies cases may assist in optimizing such
interventions. Data on the incidence of probable rabies cases in domestic
and wild animals were collected between January 2011 and December 2018 in
thirteen districts of south-east Tanzania where jackals comprise over 40%
of reported rabies cases. Vaccination coverage was estimated over this
period, as five domestic dog vaccination campaigns took place in all
thirteen districts between 2011 and 2016. Negative binomial generalized
linear models were used to explore the impact of domestic dog vaccination
on the annual incidence of animal rabies cases, whilst generalized
additive models were used to investigate the presence of temporal and/or
seasonal trends. Increases in domestic dog vaccination coverage were
significantly associated with a decreased incidence of rabies cases in
both domestic dogs and jackals. A 35% increase in vaccination coverage was
associated with a reduction in the incidence of probable dog rabies cases
of between 78.0 and 85.5% (95% confidence intervals ranged from 61.2 to
92.2%) and a reduction in the incidence of probable jackal rabies cases of
between 75.3 and 91.2% (95% confidence intervals ranged from 53.0 to
96.1%). A statistically significant common seasonality was identified in
the monthly incidence of probable rabies cases in both domestic dogs and
jackals with the highest incidence from February to August and lowest
incidence from September to January. These results align with evidence
supporting the use of domestic dog vaccination as part of control
strategies aimed at reducing animal rabies cases in both domestic dogs and
jackals in this region. The presence of a common seasonal trend requires
further investigation but may have implications for the timing of future
vaccination campaigns.