Transmission dynamics of an iridescent virus in an experimental mosquito population: the role of host density

Abstract

Abstract. 1. The transmission of insect pathogens cannot be adequately described by direct linear functions of host and pathogen density due to heterogeneity generated from behavioural or physiological traits, or from the spatial distribution of pathogen particles. Invertebrate iridescent viruses (IIVs) can cause patent and lethal infection or a covert sub-lethal infection in insects. Aedes aegypti larvae were exposed to suspensions of IIV type 6 at two densities. High larval density increased the prevalence of aggression resulting in potentially fatal wounding.2. The overall prevalence of infection (patent þ covert) was positively influenced by host density and increased with exposure time in both densities. The survival time of patently infected insects was extended by & 5 days compared with non-infected insects.3. Maximum likelihood models based on the binomial distribution were fitted to empirical results. A model incorporating heterogeneity in host susceptibility by inclusion of a pathogen-free refuge was a significantly better fit to data than an all-susceptible model, indicating that transmission is non-linear. The transmission coefficient (u) did not differ with host density whereas the faction of the population that occupied the pathogen-free refuge (P R ) was significantly reduced at high host density compared with the low density treatment.4. The transmission of free-living infective stages of an IIV in Ae. aegypti larvae is non-linear, probably because of density-related changes in the frequency of aggressive encounters between hosts. This alters host susceptibility to infection and effectively reduces the proportion of hosts that occupy the pathogen-free refuge.

Disease Dynamics and Persistence of Musca domestica Salivary Gland Hypertrophy Virus Infections in Laboratory House Fly (Musca domestica) Populations

“…This assumption has been challenged by several researchers (8,9,19,26). A linear relationship between transmission efficiency and densities of virus and hosts may exist only within a limited range of densities.…”

Natural invertebrate hosts of iridoviruses (Iridoviridae)

“…Characteristic gill disease was also reported in Mytilus edulis trossulus (Gould) from the Baltic Sea near Gdansk, Poland, but the causative agent was not identifi ed (Smolarz et al 2006). , Marina et al 2005. Different genera also have distinct thermal requirements during immature development and the replication of IIVs is thermolabile with complete inhibition at temperatures over 30°C.…”

“…This has led to a lack of interest in the study of these viruses and a resulting paucity of information concerning their biology and survival in invertebrate populations. Indeed, the mechanisms of transmission of most IIVs remain unclear, although cannibalism and wounding have been shown to be viable mechanisms in some species (Carter 1973, Grosholz 1992, Undeen & Fukuda 1994, Marina et al 2005, Williams & Hernández 2006. Nematodes and hymenopteran endoparasitoids can also transmit IIVs by introducing virus particles into susceptible hosts during the act of host penetration or oviposition, respectively (Mullens et al 1999, López et al 2000.…”

Larval Competition Extends Developmental Time and Decreases Adult Size of wMelPop Wolbachia-Infected Aedes aegypti

“…23 These deleterious effects on fitness may be explained by physical interference, 24 increased levels of pollution caused by natural waste released into the environment, 23,25 or through increased aggression leading to higher biting frequencies and increasing the incidence of disease transmission. 26 Larval competition between species has been proposed as the primary mechanism for recently observed shifts in species distributions of Ae. aegypti and Ae.…”