  This paper examines the interplay of the effect of cross immunity and
antibody-dependent enhancement (ADE) in mutistrain diseases. Motivated by
dengue fever, we study a model for the spreading of epidemics in a population
with multistrain interactions mediated by both partial temporary cross immunity
and ADE. Although ADE models have previously been observed to cause chaotic
outbreaks, we show analytically that weak cross immunity has a stabilizing
effect on the system. That is, the onset of disease fluctuations requires a
larger value of ADE with small cross immunity than without. However, strong
cross immunity is shown numerically to cause oscillations and chaotic outbreaks
even for low values of ADE.
