The first arriving virus shapes within-host viral diversity during natural epidemics

Viral diversity has been discovered across scales from host individuals to populations. However, the drivers of viral community assembly are still largely unknown. Within-host viral communities are formed through co-infections, where the interval between the arrival times of viruses may vary. Priority effects describe the timing and order in which species arrive in an environment, and how early colonizers impact subsequent community assembly. To study the effect of the first-arriving virus on subsequent infection patterns of five focal viruses, we set up a field experiment using naïve Plantago lanceolata plants as sentinels during a seasonal virus epidemic. Using joint species distribution modelling, we find both positive and negative effects of early season viral infection on late season viral colonization patterns. The direction of the effect depends on both the host genotype and which virus colonized the host early in the season. It is well established that co-occurring viruses may change the virulence and transmission of viral infections. However, our results show that priority effects may also play an important, previously unquantified role in viral community assembly. The assessment of these temporal dynamics within a community ecological framework will improve our ability to understand and predict viral diversity in natural systems.

Sequential acquisition of human papillomavirus infection between genital and oral anatomic sites in males

Oral human papillomavirus (HPV) is associated with increasing rates of HPV-associated oropharyngeal cancer (OPC) in men. Sequential infection from one site to another has been demonstrated at the cervix and anus. Thus, risk of an oral HPV infection after a genital infection of the same type in the HPV infection in men study was investigated. Samples from 3140 men enrolled in a longitudinal cohort were assessed for sequential genital to oral infection with one of nine HPV types (HPV 6, 11, 16, 18, 31, 33, 45, 52 and 58); and then also sequential, same-type oral to genital infection. Incidence rate ratios (IRRs) compared rates of oral HPV among men with and without prior genital infection of the same type. Risk of sequential HPV infections were assessed using Cox proportional hazards model. Incidence of an oral HPV infection was significantly higher among men with a prior genital infection of the same type for any of the 9 HPV types (IRR: 2.3; 95% CI: 1.7-3.0). Hazard ratio of a sequential genital to oral HPV infection was 2.3 (95% CI: 1.7-3.1) and 3.5 (95% CI: 1.9-6.4) for oral to genital infection. Both changed minimally after adjustment for age, country, circumcision, alcohol use, lifetime sexual partners and recent oral sex partners. HPV infections at one site could elevate risk of a subsequent genital or oral HPV infection of the same type in men, emphasizing the importance of vaccination to prevent all HPV infections.

Sequential Acquisition of Human Papillomavirus Infection at Genital and Anal Sites, Liuzhou, China

Little is known about the risk for acquiring a concordant human papillomavirus (HPV) infection in a genital (or anal) site after an anal (or genital) HPV infection. We collected 3 sets of anogenital specimens at 6-month intervals from 2,309 men and 2,378 women in Liuzhou, China, and tested these specimens for HPV. The risk for sequential anal HPV infection in participants with a previous genital HPV infection was higher than for participants without an infection (hazard ratio [HR] 4.4, 95% CI 3.4–5.8 for women and HR 2.6, 95% CI 1.4–4.6 for men). For sequential genital HPV infection, women with a previous anal infection had a higher risk (HR 1.9, 95% CI 1.2–3.1), but no major difference was found for men (HR 0.7, 95% CI 0.2–1.9). Our study indicates that autoinoculation might play a major role in anogenital HPV transmission, in addition to direct sexual intercourse, especially for anal infection in women.

Detection of Respiratory Syncytial Virus or Rhinovirus Weeks After Hospitalization for Bronchiolitis and the Risk of Recurrent Wheezing

BACKGROUND

In severe bronchiolitis, it is unclear if delayed clearance or sequential infection of respiratory syncytial virus (RSV) or rhinovirus (RV) is associated with recurrent wheezing.

METHODS

In a 17-center severe bronchiolitis cohort, we tested nasopharyngeal aspirates (NPA) upon hospitalization and 3 weeks later (clearance swab) for respiratory viruses using PCR. The same RSV subtype or RV genotype in NPA and clearance swab defined delayed clearance (DC); a new RSV subtype or RV genotype at clearance defined sequential infection (SI). Recurrent wheezing by age 3 years was defined per national asthma guidelines.

RESULTS

Among 673 infants, RSV DC and RV DC were not associated with recurrent wheezing, and RSV SI was rare. The 128 infants with RV SI (19%) had nonsignificantly higher risk of recurrent wheezing (hazard ratio [HR], 1.31; 95% confidence interval [CI], .95-1.80; P = .10) versus infants without RV SI. Among infants with RV at hospitalization, those with RV SI had a higher risk of recurrent wheezing compared to children without RV SI (HR, 2.49; 95% CI, 1.22-5.06; P = .01).

CONCLUSIONS

Among infants with severe bronchiolitis, those with RV at hospitalization followed by a new RV infection had the highest risk of recurrent wheezing.

Sequential infection can decrease virulence in a fish-bacterium-fluke interaction: Implications for aquaculture disease management

Hosts are typically infected with multiple strains or genotypes of one or several parasite species. These infections can take place simultaneously, but also at different times, i.e. sequentially, when one of the parasites establishes first. Sequential parasite dynamics are common in nature, but also in intensive farming units such as aquaculture. However, knowledge of effects of previous exposures on virulence of current infections in intensive farming is very limited. This is critical as consecutive epidemics and infection history of a host could underlie failures in management practices and medical intervention of diseases. Here, we explored effects of timing of multiple infections on virulence in two common aquaculture parasites, the bacterium Flavobacterium columnare and the fluke Diplostomum pseudospathaceum. We exposed fish hosts first to flukes and then to bacteria in two separate experiments, altering timing between the infections from few hours to several weeks. We found that both short-term and long-term differences in timing of the two infections resulted in significant, genotype-specific decrease in bacterial virulence. Second, we developed a mathematical model, parameterized from our experimental results, to predict the implications of sequential infections for epidemiological progression of the disease, and levels of fish population suppression, in an aquaculture setting. Predictions of the model showed that sequential exposure of hosts can decrease the population-level impact of the bacterial epidemic, primarily through the increased recovery rate of sequentially infected hosts, thereby substantially protecting the population from the detrimental impact of infection. However, these effects depended on bacterial strain-fluke genotype combinations, suggesting the genetic composition of the parasite populations can greatly influence the degree of host suppression. Overall, these results suggest that host infection history can have significant consequences for the impact of infection at host population level, potentially shaping parasite epidemiology, disease dynamics and evolution of virulence in farming environments.

Importance of Sequence and Timing in Parasite Coinfections

Coinfections by multiple parasites predominate in the wild. Interactions between parasites can be antagonistic, neutral, or facilitative, and they can have significant implications for epidemiology, disease dynamics, and evolution of virulence. Coinfections commonly result from sequential exposure of hosts to different parasites. We argue that the sequential nature of coinfections is important for the consequences of infection in both natural and man-made environments. Coinfections accumulate during host lifespan, determining the structure of the parasite infracommunity. Interactions within the parasite community and their joint effect on the host individual potentially shape evolution of parasite life-history traits and transmission biology. Overall, sequential coinfections have the potential to change evolutionary and epidemiological outcomes of host-parasite interactions widely across plant and animal systems.

Sequential Infection of Aedes aegypti Mosquitoes with Chikungunya Virus and Zika Virus Enhances Early Zika Virus Transmission

In urban settings, chikungunya, Zika, and dengue viruses are transmitted by Aedes aegypti mosquitoes. Since these viruses co-circulate in several regions, coinfection in humans and vectors may occur, and human coinfections have been frequently reported. Yet, little is known about the molecular aspects of virus interactions within hosts and how they contribute to arbovirus transmission dynamics. We have previously shown that Aedes aegypti exposed to chikungunya and Zika viruses in the same blood meal can become coinfected and transmit both viruses simultaneously. However, mosquitoes may also become coinfected by multiple, sequential feeds on single infected hosts. Therefore, we tested whether sequential infection with chikungunya and Zika viruses impacts mosquito vector competence. We exposed Ae. aegypti mosquitoes first to one virus and 7 days later to the other virus and compared infection, dissemination, and transmission rates between sequentially and single infected groups. We found that coinfection rates were high after sequential exposure and that mosquitoes were able to co-transmit both viruses. Surprisingly, chikungunya virus coinfection enhanced Zika virus transmission 7 days after the second blood meal. Our data demonstrate heterologous arbovirus synergism within mosquitoes, by unknown mechanisms, leading to enhancement of transmission under certain conditions.

Effect of maternally derived antibody on sequential infection with highly virulent bursal disease virus in newly hatched broilers

Maternally derived antibodies (MDAs) are important for protection against very virulent infectious bursal disease virus (vvIBDV). In this study, 5-day-old commercial broilers with non-uniform MDA titers (with a coefficient of variation of 50%) were challenged with vvIBDV and given free contact with each other during a 2-week period. The chicks were assigned to four MDA-titer subgroups, GI-1 (very low MDA), GI-2 (low MDA), GI-3 (medium MDA), and GI-4 (high MDA). Transient symptoms of infection were observed in 35.7% of challenged birds. Body weight gain was significantly lower in GI-2, GI-3, and GI-4 birds than in an unchallenged control group. Seroconversion was observed in GI-1 birds and some GI-2 birds. The frequency of virus shedding via the cloaca in vvIBDV-challenged birds increased from 7.1% of GI birds at 5 days post inoculation (dpi) to 35.7% at 14 dpi. The timing of virus shedding was progressively later from GI-1 to GI-4. At 14 dpi, significant atrophy of the bursa of Fabricius (BF) was observed in GI birds compared with GII controls; atrophy was most severe in GI-1 birds and least severe in GI-4 birds. BF lesion scores decreased from GI-1 to GI-4. The proportion of birds with IBDV antigen in the BF at 14 dpi was higher in GI-2 and GI-3 than in GI-1 and GI-4, whereas the viral load in positive birds increased from GI-1 to GI-4. Our results indicate that high levels of MDAs would protect chicks from initial vvIBDV infection but that progressive decay of these MDAs would result in delayed infection by virus shedding in initially infected birds with low MDA titers, resulting in continuous circulation of the virus in a flock with non-uniform MDA titers.

An experimental conflict of interest between parasites reveals the mechanism of host manipulation

Parasites can increase their host's predation susceptibility. It is a long-standing puzzle, whether this is caused by host manipulation, an evolved strategy of the parasite, or by side effects due to, for example, the parasite consuming energy from its host thereby changing the host's trade-off between avoiding predation and foraging toward foraging. Here, we use sequential infection of three-spined sticklebacks with the cestode Schistocephalus solidus so that parasites have a conflict of interest over the direction of host manipulation. With true manipulation, the not yet infective parasite should reduce rather than enhance risk taking because predation would be fatal for its fitness; if host behavior is changed by a side effect, the 2 parasites would add their increase of predation risk because both drain energy. Our results support the latter hypothesis. In an additional experiment, we tested both infected and uninfected fish either starved or satiated. True host manipulation should act independently of the fish's hunger status and continue when energy drain is balanced through satiation. Starvation and satiation affect the risk averseness of infected sticklebacks similarly to that of uninfected starved and satiated ones. Increased energy drain rather than active host manipulation dominates behavioral changes of S. solidus-infected sticklebacks.

Magnetoresponsive virus-mimetic nanocapsules with dual heat-triggered sequential-infected multiple drug-delivery approach for combinatorial tumor therapy

Stimuli-responsive drug-delivery systems constitute an appealing approach to direct and restrict drug release spatiotemporally at the specific site of interest. However, it is difficult for most systems to affect every cancer cell in a tumor tissue due to the presence of the natural tumor barrier, leading to potential tumor recurrence. Here, core-shell magnetoresponsive virus-mimetic nanocapsules (VNs), which can infect cancer cells sequentially and double as a magnetothermal agent fabricated through anchoring iron oxide nanoparticles in a single-component protein (lactoferrin) shell, are reported. With large payload of hydrophilic/hydrophobic anticancer cargos, doxorubicin and palictaxel, VNs can simultaneously give a rapid drug release and intense heat while applying an external high-frequency magnetic field (HFMF). Furthermore, after being liberated from dead cells by HFMF manipulation, the constructive VNs can sequentially infect neighboring cancer cells and deliver sufficient therapeutic agents to next targeted sites. With high efficiency for sequential cell infections, VNs have successfully eliminated subcutaneous tumor after a combinatorial treatment. These results demonstrate that the VNs could be used for locally targeted, on-demand, magnetoresponsive chemotherapy/hyperthermia, combined with repeated cell infections for tumor therapy and other therapeutic applications.