A general model of plant‐virus disease infection incorporating vector aggregation

Abstract

In plant-virus disease epidemiology, dynamical models have invariably incorporated a bilinear inoculation rate that is directly proportional to both the abundance of healthy (susceptible) hosts and the abundance of infective vectors. Similarly, the acquisition rate is usually assumed to be directly proportional to the abundance of nonviruliferous vectors and that of infectious hosts. These bilinear assumptions have been questioned for certain human diseases, and infection rates that incorporate power parameters of the variables have been proposed. Here, infection rates for plant-virus diseases that are of a more general form than the familiar bilinear terms are examined. For such diseases, the power parameter can be regarded as a measure of the spatial aggregation of the vectors or as a coefficient of interference between them, depending on the context.Field data of cassava mosaic virus disease (CMD) incidence were examined. When vector population density and disease incidence were high, disease progress curves over the first 6 months from planting could not be explained using models with bilinear infection rates. Incorporation of the new infection terms allowed the range of observed disease progress curve types to be described. New evidence of a mutually beneficial interaction between the viruses causing CMD and the whitefly vector, Bemisia tabaci, has shown that spatial aggregation of the vectors is an inevitable consequence of infection, particularly with a severe virus strain or a sensitive host. Virus infection increases both vector fecundity and the density of vectors on diseased plants. It is postulated that this enhances disease spread by causing an increased emigration rate of infective vectors to other crops. Paradoxically, within the infected crop, vector aggregation reduces the effective contact rate between vector and host and therefore the predicted disease incidence is less than when a bilinear contact rate is used.

Dinâmica temporal da população do ácaro Brevipalpus phoenicis e da leprose dos citros sob condições naturais de epidemia

“…Essa época foi precedida por contínua emissão de brotos e folhas novas. Para Zhang et al (2000), folhas e ramos novos são locais favoráveis à alimentação de vetores. A emissão de novos brotos parece atrair não apenas a população do ácaro, como também a população do ácaro virulífero, uma vez que a variável fenológica NBRONOV esteve positivamente associada à INPLSIN, conforme detectado pela regressão Poisson.…”

Starting the invasion pathway: the interaction between source populations and human transport vectors

“…Epidemiological studies of infectious diseases have shown that the rate of transmission and spread of a contagion are strongly influenced by the spatial aggregation of hosts, the relative proportions of these hosts that are susceptible or immune to infection, and by the rates of movement of infected hosts to uninfected populations (Power 1996;Zhang et al 2000). 'Hub-andspoke' or 'stepping stone' invasions are direct analogues of these models.…”

Population Dynamics, Demography, Dispersal and Spread of Bemisia tabaci

“…An additional factor that can aid invasion and displacement is the acceleration of population increase by the invader through mutualism with begomoviruses McKenzie 2002;Zhang et al 2000;Jiu et al 2007). observed that the B biotype showed greater egg-to-adult survival on pumpkin infected with the watermelon curly mottle strain of Squash leaf curl virus compared with uninfected plants.…”

“…observed that the B biotype showed greater egg-to-adult survival on pumpkin infected with the watermelon curly mottle strain of Squash leaf curl virus compared with uninfected plants. Zhang et al (2000) used modeling techniques to investigate increased vector fecundity, as well as vector density for B. tabaci feeding on cassava infected with Cassava mosaic virus, speculating that the interaction between virus and vector accelerated the spread of the vector and therefore the virus. Similarly, the B biotype laid more eggs on tomato plants infected with Tomato mottle virus than they did on uninfected plants (McKenzie 2002).…”