Relation of HVJ (Sendai virus) production to cell growth phase in persistently infected mouse 3T3 cells

Resources, mortality, and disease ecology: Importance of positive feedbacks between host growth rate and pathogen dynamics

Resource theory and metabolic scaling theory suggest that the dynamics of a pathogen within a host should strongly depend upon the rate of host cell metabolism. Once an infection occurs, key ecological interactions occur on or within the host organism that determine whether the pathogen dies out, persists as a chronic infection, or grows to densities that lead to host death. We hypothesize that, in general, conditions favoring rapid host growth rates should amplify the replication and proliferation of both fungal and viral pathogens. If a host population experiences an increase in mortality, to persist it must have a higher growth rate, per host, often reflecting greater resource availability per capita. We hypothesize that this could indirectly foster the pathogen, which also benefits from increased within-host resource turnover. We first bring together in a short review a number of key prior studies which illustrate resource effects on viral and fungal pathogen dynamics. We then report new results from a semi-continuous cell culture experiment with SHIV, demonstrating that higher mortality rates indeed can promote viral proliferation. We develop a simple model that illustrates dynamical consequences of these resource effects, including interesting effects such as alternative stable states and oscillatory dynamics. Our paper contributes to a growing body of literature at the interface of ecology and infectious disease epidemiology, emphasizing that host abundances alone do not drive community dynamics: the physiological state and resource content of infected hosts also strongly influence host-pathogen interactions.

Replication of measles virus in Vero cells at elevated temperatures

In one-step growth experiment of measles virus (MV) in Vero cells at 39 C, the appearance of MV infectivity was delayed for 24 hr and the maximum titer was reduced by approximately 1,000-fold, when compared with those at 35 C. MV infectivity was thermolabile at the high temperature. Penetration was rather enhanced at 39 C. By Northern blot hybridization, viral RNAs including 50S genome-sized RNA and mRNAs were first detectable 24 hr post-infection (PI) at 35 C and 36 hr PI at 39 C, respectively. Rapid degradation of viral mRNAs was not observed in the infected cells at 39 C. The synthesis of N, F, and M proteins was relatively reduced at the high temperature and appearance of the other viral protein was delayed, in agreement with the time course of viral RNA synthesis. All these data suggest that less efficient synthesis of viral RNA, restriction of synthesis of N, F, and M proteins at translational level and thermolability of infectivity are all involved in the suppressed MV production in Vero cells at 39 C.

Influence of cellular functions on the evolution of persistent infections with Junin virus

Vero cell cultures persistently infected with Junin virus and subjected to different cultural conditions were established. The production of infectious plaque-forming virus, ts mutants and interfering viral particles was determined at different times during 110 days after infection. Carrier cultures maintained in stationary conditions continuously released PFU while proliferating persistent cultures exhibited a cyclical pattern which tends to a rapid PFU disappearance. Concomitantly, in stationary cultures the production of interfering particles was delayed and was lower than in actively growing persistent cells. The metabolic state of the infected cells did not affect the release of ts mutants. The results suggest that a cellular function is involved on the regulation of Junin virus persistent infections.