Synergism between plant viruses: a mathematical analysis of the epidemiological implications

Abstract

Many virus diseases of plants are caused by a synergistic interaction between viruses within the host plant. Such synergism can induce symptoms more severe than would be caused by additive effects. In a synergistic interaction, the virus titre of both, one, or neither virus may be enhanced and, as a consequence, the rate of disease spread may be affected. An epidemiological model was developed in which transmission and loss rates were attributed to the different virus infection possibilities. Sharing the same host population implies competition, and this imposes an increased constraint on the survival of both viruses. It was shown that, in order to ensure virus survival in a mixed infection, the basic reproductive number should exceed a critical value which is larger than unity (R 0 . R c . 1). Here R 0 is used in the same sense as in the absence of superinfection. Increased virulence (equivalent to disease severity) in dually infected plants decreases the opportunities for both viruses to coexist, while increased virus transmission from dually infected plants increases such opportunities. The net effect of increased virulence and increased virus transmission on virus persistence was neutral if synergism caused the same proportional effect on both. Total host abundance was, however, reduced. The opportunity for virus persistence was increased if the enhancement of transmission exceeded that of virulence. Indeed, by this mechanism a virus which was nonviable alone could invade and persist in a chronic epidemic of another virus. Where the effect on virulence is greater than that on transmission, the viruses are likely to exclude each other, especially when the transmission rates of both viruses have intermediate values. In such cases, the final outcome is determined by both the parameter values and the initial state.

Cowpea Reaction to Single and Mixed Viral Infection with Blackeye Cowpea Mosaic Virus and Cowpea Yellow Mosaic Virus

“…The study also showed that mixed infection with BICMV and CYMV were more pathogenic than single viral inoculation. Zhang et al, (2000 and2001), had reported that viral interactions and coinfection with two independent unrelated viruses resulted in a much more serious disease than either virus in a single infection. This situation is often referred to as synergism ( ).…”

Mathematical models of the interrelated dynamics of hepatitis D and B

“…To date, there have been very few attempts in the literature to create a mathematical model of HBV-HDV dynamics. The earlier models of Zhang et al [6,7] are related in that they consider the competing dynamics of two viruses in a host plant population. The first known HBV-HDV model was proposed by Sousa and Cunha [8] and investigated numerically.…”

Expression of symptoms, viral coat protein and silencing suppressor gene during mixed infection of a N–Wi strain of potato virus Y and an asymptomatic strain of potato virus X

“…In the synergistic situations, either virus titre or the movement or both can be enhanced [35,43]. Breakdown of resistance by a co-infection with an unrelated virus is also an indication of a synergistic interaction [6,22,28,30].…”