Thresholds for disease persistence in models for tick-borne infections
- From: "CaliforniaLyme" <CaliforniaLyme@xxxxxx>
- Date: 1 May 2005 08:17:06 -0700
1: J Theor Biol. 2003 Oct 7;224(3):359-76. Related Articles, Links
Thresholds for disease persistence in models for tick-borne infections
including non-viraemic transmission, extended feeding and tick
aggregation.
Rosa R, Pugliese A, Norman R, Hudson PJ.
Centre for Alpine Ecology, Viote del Monte Bondone, 38040 Trento,
Italy. rosa@xxxxxxxx
Lyme disease and Tick-Borne Encephalitis (TBE) are two emergent
tick-borne diseases transmitted by the widely distributed European tick
Ixodes ricinus. The life cycle of the vector and the number of hosts
involved requires the development of complex models which consider
different routes of pathogen transmission including those occurring
between ticks that co-feed on the same host. Hence, we consider here a
general model for tick-borne infections. We assumed ticks feed on two
types of host species, one competent for viraemic transmission of
infection, the second incompetent but included a third transmission
route through non-viraemic transmission between ticks co-feeding on the
same host. Since a blood meal lasts for several days these routes could
lead to interesting nonlinearities in transmission rates, which may
have important effects.We derive an explicit formula for the threshold
for disease persistence in the case of viraemic transmission, also for
the case of viraemic and non-viraemic transmission. From this formula,
the effect of parameters on the persistence of infection can be
determined. When only viraemic transmission occurs, we confirm that,
while the density of the competent host has always a positive effect on
infection persistence, the density of the incompetent host may have
either a positive effect, by amplifying tick population, or a negative
("dilution") effect, by wasting tick bites on an incompetent host. With
non-viraemic transmission, the "dilution" effect becomes less relevant.
On the other hand, if the nonlinearity due to extended feeding is
included, the dilution effect always occurs, but often at
unrealistically high host densities. Finally, we incorporated the
effects of tick aggregation on the hosts and correlation of tick stages
and found that both had an important effect on infection persistence,
if non-viraemic transmission occurred.
PMID: 12941594 [PubMed - indexed for MEDLINE]
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