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Infectious Diseases and Vigilance – A Call for Multidisciplinary Military Medical Infectious Research
Tropical Medicine / Infectiology PDF

Infectious Diseases and Vigilance –
A Call for Multidisciplinary Military Medical Infectious Research

Lorenz Scheita, Reinhard Starkb, Sebastian Klapac, Gordon Vollertc, Marc Henniesd, Hagen Frickmannd

a Department of Internal Medicine, Bundeswehr Hospital Hamburg

b Department of Neurology, Bundeswehr Hospital Hamburg

c Research and Teaching Department, Institute of Maritime Medicine Kiel-Kronshagen and Section of Maritime Medicine, Christian-Albrechts-University Kiel

d Department of Microbiology and Hospital Hygiene, Bundeswehr Hospital Hamburg

Summary

Infectious diseases remain among the most frequent health-related events during military operations. This study investigates whether and to what extent indirect influences on behaviour and reaction times exist beyond the local or systemic infection pathology itself. This investigation is a narrative literature review. References were identified with the support of the German Armed Forces‘ Specialist Information Centre and using the NCBI PubMed database.

Existing data on associations between acute and chronic infectious diseases, as well as prolonged reaction times and related infection-associated behavioural changes, are superficial and incomplete. A comparatively robust data set exists for uncomplicated upper respiratory tract infections, a common condition, and for HIV (human immunodeficiency virus) infection, a disease currently requiring lifelong treatment. In summary, reaction time and other behavioural changes are described for various infectious diseases, with pathogen-specific patterns in occurrence, severity, and the time frame of manifestation. Cumulative effects of past and chronic infections can occur; for HIV, an association between effect size and severity of immunodeficiency has been described.

Infection-associated performance limitations have been repeatedly described, but available data remain fragmented, complicating risk assessments for military deployments. The potential relevance of delayed reaction time extensions in the later stages of infection and during convalescence, when soldiers may be declared fit for duty again, warrants further military medical investigation through a multidisciplinary collaboration between exercise physiology and infectious disease medicine.

Keywords: infection; reaction time; behaviour; combat readiness; deployment; risk assessment

Introduction and Background

Infectious diseases remain significant health risks during military deployments [27][29]. Historical deployment scenarios, such as the European Training Mission (EUTM) in Mali, illustrate that many infections are not inherently life-threatening and may not necessitate leave from duty if transmission prevention is justifiable [4]. However, infections can indirectly impair military performance to an operationally significant level, depending on conflict intensity. For instance, subclinical illnesses during maritime deployment can compromise essential watch and surveillance duties [9].

At the Military Infectious Diarrhoea Symposium (MIDAS) 2025, an academic exchange platform on deployment-related diarrhoea among NATO member states, a British colleague reported an interesting side effect observed in a study supported by the Military Infectious Disease Research Program on diarrhoea management [17]. A participant exhibited a specific reaction time extension from 1 to 3 seconds during the convalescence phase, even while feeling subjectively fit for duty. Due to the small sample size, the study [17] did not allow for systematic evaluation of reaction time effects; however, British colleagues noted a signal warranting further observation.

Unlike neurotropic pathogens, where neurological symptoms from neuroparenchymal involvement with prolonged convalescence or persistence are expected [19], the phenomenon observed by the British research team is not immediately self-explanatory. However, the following literature review suggests that effects of infectious diseases on vigilance and reaction time, which can be crucial during high conflict intensity phases, have been observed to a concerning degree. Our work provides an overview of existing evidence and aims to serve as a starting point for further military medical research in this area.

Methodology

For the narrative review, a search for theme-specific literature was conducted with the Bundeswehr’s Information Centre in Bonn, using open sources (NCBI PubMed, URL: https://pubmed.ncbi.nlm.nih.gov/), and the “Verbundkatalog FachInfoUstgBw”, using multiple search terms (including “reaction time extension,” “diarrhoea,” and “infectious disease”) and their English equivalents in various combinations. The suitability of works displayed by the search engines for inclusion was assessed by authors based on their expertise.

Results

Investigations into the relationships between infectious diseases and potential impacts on infected individuals’ reaction abilities are not new. As early as 1977, a working group proposed possible associations between neuromuscular transmission disorders and viral infections [18]. The following presents a selection of representative works on the associated occurrence of reaction time extensions and related neurological phenomena, as well as acute and chronic infections.

Observations in Acute Infections

Evidence regarding the effects of acute infections on attention and reaction time is most comprehensive for respiratory tract infections and is derived from epidemiological investigations, experimental human challenge studies, and animal models. Notably, a 2016 study conducted by researchers from the Karolinska Institute showed that cerebral replication of the 2009 H1N1 influenza A virus strain in immunodeficient mice lacking adaptive immunity resulted in narcolepsy-like sleep disruptions. These findings are consistent with previous reports indicating a potential immune-mediated mechanism underlying narcolepsy in humans after H1N1 influenza A infection.

Conversely, interactions between neurocognitive and neuroimmunological functions have been indicated, suggesting that neurocognitive impairments may enhance viral spread in acute respiratory viral infections [30]. This observation is based on a limited number of subjects from viral challenge experiments; verification or falsification with larger sample sizes is pending [30].

A British working group examining young adults with and without uncomplicated upper respiratory tract infections reported impairments in attention, mood, psychomotor skills, and information processing in infected individuals, with only mood correlating with symptom severity [23]. Attention and reaction time in uncomplicated upper respiratory infections are reduced, with infected individuals experiencing increased tension and anxiety [22].

A comparable reduction in attention and reaction time intensity was demonstrated for uncomplicated upper respiratory infections caused by rhinoviruses, endemic coronaviruses, and infections of unclear aetiology [20]. Reaction time effects do not appear directly dependent on nasopharyngeal airflow, as menthol application did not result in improvement [2]. An interesting temporal course was noted: while mood and psychomotor function were significantly impaired during the first week of non-complicated upper respiratory infections, attention impairments were detected in the second week of illness [6]. After recovery from uncomplicated respiratory infections, no significant differences in measurable reaction times compared to non-infected control subjects were detectable, at least in natural infections [21].

This contradicts viral challenge experiments for inducing uncomplicated upper respiratory infections, where reaction time delays persisted after clinical symptoms subsided [24]. Specific reaction time delays were observed in decision-bound reactions after influenza virus infection, while in other viral respiratory infections, reaction time extension was non-specific [24]. Animal experiments in cats suggest respiratory infections are associated with increased auditory excitability during sleep, indicating less deep and restful sleep as an etiological component [26].

Prolonged physical and psychological impairments post-acute respiratory infections have been repeatedly described, especially in connection with COVID-19. A British working group demonstrated episodic memory impairments up to six months post-infection and vigilance reductions up to nine months post-infection in individuals without significant early pandemic restrictions [32]. Long-COVID sufferers also showed marked cognitive slowdown compared to individuals without Long-COVID symptoms post-COVID-19 illness [31], not correlating with other symptoms such as fatigue, depression, sleep disorders, or PTSD. Table 1 provides a summary of the findings from the studies presented.

Tab. 1: Summary of Observations in Acute Infection

 

Observations in Chronic Infections

Studies on possible associations between reaction time and past or chronically persistent infections are available. A U.S. analysis examined aggregated effects of past and/or chronic infections with viral pathogens Cytomegalovirus (CMV), human herpesvirus 1 (HHV-1), human herpesvirus 2 (HHV-2), Hepatitis A virus (HAV), Hepatitis B virus (HBV), Hepatitis C virus (HCV), helminths Toxocara spp., and protozoan Toxoplasma gondii on neurocognitive function in young to middle adulthood. Adverse effects on information processing, learning, and memory were detectable, but not on reaction ability [5].

A differentiated picture emerged for specific infections in mice, where the murine equivalent to human Epstein-Barr virus (EBV) infection was induced with murine Gammaherpesvirus 68, short-term impairments in food intake behaviour, body weight, wheel-running activity, body temperature, and sleep were detectable 7 to 11 days post-virus inoculation. These parameters stabilised later on [15].

Reaction time slowing has also been described in individuals with human immunodeficiency virus (HIV) infection. Correlations with reaction time variability were shown in a small number of HIV-positive subjects with factors such as cognitive global status, adherence to antiretroviral medication, and nadir of immune status [3]. Motor impairments were frequently detectable in all stages of HIV infection, almost always present in the AIDS stage [13]. Psychomotor slowing and impaired attention in HIV patients correlated with reduced CD4+ T cell counts [14]. Reaction times were primarily prolonged in advanced HIV infection associated with decision-making [16]. In the absence of disease progression, HIV-associated changes in reaction time are generally considered mild [7]. Literature reports average reaction slowdowns of about 22 % compared to non-infected individuals [7].

Symptomatic HIV infection, without or with insufficient therapy, was associated with global cognitive slowing in modelling studies [8]. These results confirmed previous experiments simulating the AIDS dementia complex in animal models. Mice infected with LP-BM5 murine leukaemia virus (MuLV) exhibited learning and memory impairments, along with attention deficits [10]. SIV-infected macaques also showed movement and reaction time slowing [11]. Table 2 summarizes the results of the studies presented.

Tab. 2: Summary of Observations in Chronic Infection

 

Observations in Non-Infectious Inflammatory Stimuli

Results presented above may suggest inflammation generally dampens reaction capability. However, a recent Swiss study [1] on pollen exposure’s impact on cognitive abilities in allergy sufferers makes such a nonspecific reaction pattern unlikely. The exposure model interestingly led to no substantial changes in cognitive readiness, only a trend signal deemed statistically questionable by the authors [1]. Inflammatory conditions can be caused by various cellular and humoral immune system components, exhibiting big individual differences in expression [12].

Discussion

The findings reviewed herein underscore the heterogeneous and still incomplete nature of the evidence regarding infection-associated changes in reaction time and behavioural performance. Although respiratory tract infections [2][6][20–24] and HIV infection [3][7][8][13–16] constitute the best-studied models in this context, the overall body of evidence remains sparse. Notably, military medical investigations specifically addressing the operational relevance of such impairments are largely lacking. Against this background, the reaction time prolongation reported by the British research group following gastrointestinal infection cannot currently be interpreted conclusively. It may represent either a chance observation or an expression of pathogen-related neurocognitive effects that have thus far received insufficient scientific attention.

Despite the inconclusive data situation, the review yielded indications suggesting the latter. Herpesvirus infections in animal models [15] and uncomplicated upper respiratory infections in humans [6] demonstrated infection-associated behavioural changes manifesting in specific time windows not necessarily aligning with disease onset. The persistent reduction in vigilance months after early COVID-19 infections, even in individuals without subjective complaints [32], and the finding that reaction time extensions persist beyond clinically apparent disease in challenge experiments [24] make a pathogen-specifically heterogeneous association picture plausible.

This is supported by early studies showing pathogen-­specificity in infection-associated reaction time changes [24]. Conversely, a nonspecific inflammation-responsive phenomenon, as suggested by analyses of non-infectious inflammatory events, is unlikely [1]. Particularly in chronic infections, summation effects from various simultaneous or sequential infection events are indicated [5]. The patient’s immunological status seems to influence infection-induced reaction time changes, especially in HIV infection [13][14].

Conclusion

The very incomplete data regarding infections and reaction time changes are insufficient for assessing potential military medical risks related to delayed reaction capability in deployment situations. Multidisciplinary, cross-branch military medical research combining performance physiological and infectious medical expertise is advisable to address this topic academically. From practical considerations, investigations should focus on the time window immediately after regaining fitness for duty, as adverse or security-threatening functional consequences would be expected, especially then. This would account for behaviorally effective effects associated with later infection stages [6].

 

Key Messages

  • Infections can lead to reaction time changes beyond pathogen-specific local or systemic symptoms.
  • The data are fragmented and unsatisfactory for deriving risk assessments for deployment forces.
  • Occurrence, severity, and time frames of impairments, which can occur in the convalescence phase, show infection-specific patterns.
  • Cumulative effects of past and chronic infections, including immune status influences, have been described.
  • Interdisciplinary, cross-branch military medical research is advisable to assess infection-associated reaction time extensions more reliably, especially in later infection phases concerning fitness for duty in higher-intensity deployments.

References

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Manuscript Data

Citation

Scheit L, Stark R, Klapa S, Vollert G, Hennies M, Frickmann H. Infectious Diseases and Vigilance – A Call for Multidisciplinary Military Medical Infectious Research. WMM 2026;70(9E):8.

DOI: https://doi.org/10.48701/opus4-958

For the Authors

Lieutenant Colonel (MC) Prof. (APL) Dr. Hagen Frickmann

Department of Microbiology and Hospital Hygiene

Bundeswehr Hospital Hamburg

Lesserstraße 180, D-22049 Hamburg,

Email: hagenfrickmann@bundeswehr.org

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