Maternal antibodies contribute to sex-based difference in hantavirus transmission dynamics

Hantavirus maintenance and transmission in reservoir host populations

Hantaviruses are primarily hosted by mammalian species of the orders Rodentia, Eulipotyphla and Chiroptera. Spillover to humans is common, and understanding hantavirus maintenance and transmission in reservoir host populations is important for efforts to curtail human disease. Recent field research challenges traditional phases of virus shedding kinetics derived from laboratory rodent infection experiments. Organ infection sites in non-rodent hosts suggest similar transmission routes to rodents, but require direct assessment. Further advances have also been made in understanding virus persistence (and fadeouts) in fluctuating host populations, as well as occupational, recreational and environmental risk factors associated with spillover to humans. However, despite relevance for both intra-species and inter-species transmission, our understanding of the longevity of hantaviruses in natural environments remains limited.

Arenavirus Dynamics in Experimentally and Naturally Infected Rodents

Infectious diseases of wildlife are typically studied using data on antibody and pathogen levels. In order to interpret these data, it is necessary to know the course of antibodies and pathogen levels after infection. Such data are typically collected using experimental infection studies in which host individuals are inoculated in the laboratory and sampled over an extended period, but because laboratory conditions are controlled and much less variable than natural conditions, the immune response and pathogen dynamics may differ. Here, we compared Morogoro arenavirus infection patterns between naturally and experimentally infected multimammate mice (Mastomys natalensis). Longitudinal samples were collected during three months of bi-weekly trapping in Morogoro, Tanzania, and antibody titer and viral RNA presence were determined. The time of infection was estimated from these data using a recently developed Bayesian approach, which allowed us to assess whether the natural temporal patterns match the previously observed patterns in the laboratory. A good match was found for 52% of naturally infected individuals, while most of the mismatches can be explained by the presence of chronically infected individuals (35%), maternal antibodies (10%), and an antibody detection limit (25%). These results suggest that while laboratory data are useful for interpreting field samples, there can still be differences due to conditions that were not tested in the laboratory.

Puumala hantavirus infections in bank vole populations: host and virus dynamics in Central Europe

BACKGROUND

In Europe, bank voles (Myodes glareolus) are widely distributed and can transmit Puumala virus (PUUV) to humans, which causes a mild to moderate form of haemorrhagic fever with renal syndrome, called nephropathia epidemica. Uncovering the link between host and virus dynamics can help to prevent human PUUV infections in the future. Bank voles were live trapped three times a year in 2010-2013 in three woodland plots in each of four regions in Germany. Bank vole population density was estimated and blood samples collected to detect PUUV specific antibodies.

RESULTS

We demonstrated that fluctuation of PUUV seroprevalence is dependent not only on multi-annual but also on seasonal dynamics of rodent host abundance. Moreover, PUUV infection might affect host fitness, because seropositive individuals survived better from spring to summer than uninfected bank voles. Individual space use was independent of PUUV infections.

CONCLUSIONS

Our study provides robust estimations of relevant patterns and processes of the dynamics of PUUV and its rodent host in Central Europe, which are highly important for the future development of predictive models for human hantavirus infection risk.

Effects of sex and generation on hepatitis B viral load in families with hepatocellular carcinoma

AIM

To explore factors associated with persistent hepatitis B virus (HBV) infection in a cohort of hepatocellular carcinoma (HCC)-affected families and then investigate factors that correlate with individual viral load among hepatitis B surface antigen (HBsAg)-positive relatives.

METHODS

We evaluated non-genetic factors associated with HBV replication in relatives of patients with HCC. Relatives of 355 HCC cases were interviewed using a structured questionnaire. Demographics, relationship to index case, HBsAg status of mothers and index cases were evaluated for association with the HBV persistent infection or viral load by generalized estimating equation analysis.

RESULTS

Among 729 relatives enrolled, parent generation (P = 0.0076), index generation (P = 0.0044), mothers positive for HBsAg (P = 0.0007), and HBsAg-positive index cases (P = 5.98 × 10^-8) were associated with persistent HBV infection. Factors associated with HBV viral load were evaluated among 303 HBsAg-positive relatives. Parent generation (P = 0.0359) and sex (P = 0.0007) were independent factors associated with HBV viral load. The intra-family HBV viral load was evaluated in families clustered with HBsAg-positive siblings. An intra-family trend of similar HBV viral load was found for 27 of 46 (58.7%) families. Male offspring of HBsAg-positive mothers (P = 0.024) and older siblings were associated with high viral load.

CONCLUSION

Sex and generation play important roles on HBV viral load. Maternal birth age and nutritional changes could be the reasons of viral load difference between generations.

Age-related effects of chronic hantavirus infection on female host fecundity

1. Pathogens often cause detrimental effects to their hosts and, consequently, may influence host population dynamics that may, in turn, feed back to pathogen transmission dynamics. Understanding fitness effects of pathogens upon animal host populations can help to predict the risks that zoonotic pathogens pose to humans. 2. Here we determine whether chronic infection by Puumala hantavirus (PUUV) affects important fitness-related traits, namely the probability of breeding, reproductive effort and mother and offspring condition, in the bank vole (Myodes glareolus). Using 9 years empirical data in a PUUV endemic area in Central Finland, we found differences between reproductive characteristics of PUUV-infected and uninfected female bank voles. 3. Young infected females had a significantly higher, and old individuals lower, likelihood of reproducing than uninfected animals during the middle of the breeding season. The implication is that PUUV infection may have long-term deleterious effects that are observed at old age, while in young individuals, the infection may enhance breeding probability by directing resources towards current breeding. 4. Moreover, PUUV infection was related with the mother's body condition. Infected mothers were in poorer condition than uninfected mothers in the early breeding season, but were in better condition than uninfected mothers during the middle of the breeding season. Offspring body condition was positively associated with mother's body condition, which, in turn, was related to the PUUV infection status of the mother. 5. Our findings indicate that chronic infection may affect the reproduction of female hosts, but the effect is dependent on the host age. The effect of chronic hantavirus infection was small and density-independent and hence unlikely to contribute to the cyclic population dynamics of the host. However, the effects on a female's reproductive output might affect the abundance of young susceptible individuals in the population and hence influence the transmission and persistence of the pathogen. Although experimental and long-term capture-mark-recapture studies are required to further clarify the fitness effects of hantavirus infection and their consequences for pathogen dynamics, this study shows that the infection may have complex effects that are dependent on the age of the individual and the time of the breeding season.

Hantavirus immunology of rodent reservoirs: current status and future directions

Hantaviruses are hosted by rodents, insectivores and bats. Several rodent-borne hantaviruses cause two diseases that share many features in humans, hemorrhagic fever with renal syndrome in Eurasia or hantavirus cardiopulmonary syndrome in the Americas. It is thought that the immune response plays a significant contributory role in these diseases. However, in reservoir hosts that have been closely examined, little or no pathology occurs and infection is persistent despite evidence of adaptive immune responses. Because most hantavirus reservoirs are not model organisms, it is difficult to conduct meaningful experiments that might shed light on how the viruses evade sterilizing immune responses and why immunopathology does not occur. Despite these limitations, recent advances in instrumentation and bioinformatics will have a dramatic impact on understanding reservoir host responses to hantaviruses by employing a systems biology approach to identify important pathways that mediate virus/reservoir relationships.

Maternal antibodies contribute to sex-based difference in hantavirus transmission dynamics

Individuals often differ in their ability to transmit disease and identifying key individuals for transmission is a major issue in epidemiology. Male hosts are often thought to be more important than females for parasite transmission and persistence. However, the role of infectious females, particularly the transient immunity provided to offspring through maternal antibodies (MatAbs), has been neglected in discussions about sex-biased infection transmission. We examined the effect of host sex upon infection dynamics of zoonotic Puumala hantavirus (PUUV) in semi-natural, experimental populations of bank vole (Myodes glareolus). Populations were founded with either females or males that were infected with PUUV, whereas the other sex was immunized against PUUV infection. The likelihood of the next generation being infected was lower when the infected founders were females, underlying the putative importance of adult males in PUUV transmission and persistence in host populations. However, we show that this effect probably results from transient immunity that infected females provide to their offspring, rather than any sex-biased transmission efficiency per se. Our study proposes a potential contrasting nature of female and male hosts in the transmission dynamics of hantaviruses.