Pathophysiology of airway viral infections

The treatment of mild upper respiratory tract infections - a position paper with recommendations for best practice

Following the waning severity of COVID-19 due to vaccination and the development of immunity, the current variants of SARS-CoV-2 often lead to mild upper respiratory tract infections (MURTIs), suggesting it is an appropriate time to review the pathogenesis and treatment of such illnesses. The present article reviews the diverse causes of MURTIs and the mechanisms leading to symptomatic illness. Different symptoms of MURTIs develop in a staggered manner and require targeted symptomatic treatment. A wide variety of remedies for home treatment is available, including over-the-counter drugs and plant-derived substances. Recent pharmacological research has increased the understanding of molecular effects, and clinical studies have shown the efficacy of certain herbal remedies. However, the use of subjective endpoints in these clinical studies may suggest limited validity of the results. In this position paper, the importance of patient-centric outcomes, including a subjective perception of improved well-being, is emphasized. A best practice approach for the management of MURTIs, in which pharmacists and physicians create an improved multi-professional healthcare setting and provide healthcare education to patients, is proposed. Pharmacists act as first-line consultants and provide patients with remedies, considering the individual patient's preferences towards chemical or plant-derived drugs and providing advice for self-monitoring. Physicians act as second-line consultants if symptoms worsen and subsequently initiate appropriate therapies. In conclusion, general awareness of MURTIs should be increased amongst medical professionals and patients, thus improving their management.

Effects of Highly Bioavailable Curcumin Supplementation on Common Cold Symptoms and Immune and Inflammatory Functions in Healthy Japanese Subjects: A Randomized Controlled Study

This study aimed to investigate the effects of 12-week consumption of highly bioavailable curcumin (150 mg/day of Theracurmin Super [TS-P1] or Theracurmin [CR-033P]) on common cold symptoms, immune function, and inflammatory markers. A randomized, double-blind, placebo-controlled study was conducted from November 2021 to May 2022 on 99 healthy Japanese adults. Using a computerized random number generator, each subject was randomly assigned to one of the following three groups: TS-P1, CR-033P, or placebo (n = 33 per group). For 12 weeks, each group consumed the four capsules that were given to them daily. The cumulative number of days for which common cold symptoms persisted was set as the primary outcome. Immunity parameters, inflammatory parameters, liver function parameters, and physical examination results were additional outcomes. A safety assessment was also performed. Ninety-four subjects completed the study, and the per protocol set included 30 subjects in the placebo group, 32 subjects in the TS-P1 group, and 33 subjects in the CR-033P group. The cumulative number of days for which common cold symptoms persisted was significantly lower in the TS-P1 and CR-033P groups than that in the placebo group. No adverse effects were observed. Consumption of highly bioavailable curcumin, TS-P1 or CR-033P (150 mg/day), for 12 weeks reduced the number of days for which common cold symptoms persisted in healthy Japanese adults.

Neurotrophin Regulation and Signaling in Airway Smooth Muscle

Structural and functional aspects of bronchial airways are key throughout life and play critical roles in diseases such as asthma. Asthma involves functional changes such as airway irritability and hyperreactivity, as well as structural changes such as enhanced cellular proliferation of airway smooth muscle (ASM), epithelium, and fibroblasts, and altered extracellular matrix (ECM) and fibrosis, all modulated by factors such as inflammation. There is now increasing recognition that disease maintenance following initial triggers involves a prominent role for resident nonimmune airway cells that secrete growth factors with pleiotropic autocrine and paracrine effects. The family of neurotrophins may be particularly relevant in this regard. Long recognized in the nervous system, classical neurotrophins such as brain-derived neurotrophic factor (BDNF) and nonclassical ligands such as glial-derived neurotrophic factor (GDNF) are now known to be expressed and functional in non-neuronal systems including lung. However, the sources, targets, regulation, and downstream effects are still under investigation. In this chapter, we discuss current state of knowledge and future directions regarding BDNF and GDNF in airway physiology and on pathophysiological contributions in asthma.

Rhinovirus-16 increases ATP release in A549 cells without concomitant increase in production

Human rhinovirus (RV) is the most common cause of upper respiratory tract infection (URTI) and chronic airway disease exacerbation. Cough is present in 50–80% of URTI cases, accompanied by heightened airway hypersensitivity, yet no effective treatment currently exists for this infectious cough. The mechanism by which RV causes cough and airway hypersensitivity in URTI is still unknown despite recent advances in potential therapies for chronic cough.

The effect of RV-16 infection (MOI 1) on intracellular ATP stores and ATP release in A549 alveolar epithelial cells was measured.

RV-16 infection was found to significantly increase (by 50% from basal at 24 h) followed by decrease (by 50% from basal at 48 and 72 h) intracellular ATP concentrations, while increasing ATP release (from 72 h) independently of secondary stimulation. This effect was mimicked by intercellular adhesion molecule 1 receptor binding alone through ultraviolet-inactivated sham control. In addition, RV-16-infected cells became more sensitive to secondary stimulation with both hypotonic and isotonic solutions, suggestive of a hypersensitive response. These responses were not mediated via increased TRPV4 or pannexin-1 whole-cell expression as determined by Western blotting. Interestingly, the increased ATP release seen was not a result of increased mitochondrial ATP production.

Thus, this is the first report demonstrating that RV-16 infection of airway epithelial cells causes hypersensitivity by increasing ATP release. These finding provide a novel insight into the process by which viruses may cause cough and identify a potential target for treatment of viral and post-viral cough.

Rhinovirus-infected airway epithelial cells (A549) show increased ATP release with and without a secondary stimulation (mechanical or hypotonic), which may account for increased cough sensitivity seen during respiratory viral infectionshttps://bit.ly/3eABEY9

How does rhinovirus cause the common cold cough?

Cough is a protective reflex to prevent aspiration and can be triggered by a multitude of stimuli. The commonest form of cough is caused by upper respiratory tract infection and has no benefit to the host. The virus hijacks this natural defence mechanism in order to propagate itself through the population. Despite the resolution of the majority of cold symptoms within 2 weeks, cough can persist for some time thereafter. Unfortunately, the mechanism of infectious cough brought on by pathogenic viruses, such as human rhinovirus, during colds, remains elusive despite the extensive work that has been undertaken. For socioeconomic reasons, it is imperative we identify the mechanism of cough. There are several theories which have been proposed as the causative mechanism of cough in rhinovirus infection, encompassing a range of different processes. Those of which hold most promise are physical disruption of the epithelial lining, excess mucus production and an inflammatory response to rhinovirus infection which may be excessive. And finally, neuronal modulation, the most convincing hypothesis, is thought to potentiate cough long after the original stimulus has been cleared. All these hypotheses will be briefly covered in the following sections.

The duration of cough in patients with H1N1 influenza

BACKGROUND

Cough is one of common symptoms of influenza, the cough duration and prevalence of postinfectious cough (PIC) after viral upper respiratory tract infection has not been well described.

OBJECTIVES

We aim to investigate the duration of cough and prevalence of PIC and its relation with acute symptoms, airway inflammation and cough sensitivity in patients with H1N1 influenza.

METHODS

Patients with acute symptoms of H1N1 influenza were enrolled and followed up until cough relived. Spirometry, induced sputum test, capsaicin challenge test were conducted in patients with PIC. Cough sensitivity was presented as logarithm of provocative concentration inducing five or more coughs (logC5).

RESULTS

A total of 141 cases with H1N1 influenza were enrolled. In patients with H1N1 influenza, 97.2% of them complained cough. The duration of cough was as following: <1 week (73.0%); 1-2 weeks (7.8%); 2-3 weeks (7.8%); ≥3 weeks (8.5%). Twelve (8.5%) patients had cough lasting more than 3 weeks (PIC), 4 (2.8%) patients developed chronic cough (>8 weeks). Acute symptoms, spirometry, bronchial responsiveness and sputum differential cell count were similar between patients with PIC and those without PIC, however, there was a higher prevalence of previous PIC (58.3% vs 14.7%, P < 0.05) and elevated cough sensitivity (lgC5: 1.18 ± 0.58 vs 2.73 ± 0.33, P < 0.01) in patients with PIC as compared with the patients without PIC.

CONCLUSIONS

Acute cough is common in patients with H1N1 PIC, only a few of patients develop chronic cough. Acute symptoms cannot predict PIC which is related with previous PIC and increased cough sensitivity.

Brain-derived neurotrophic factor in the airways

In addition to their well-known roles in the nervous system, there is increasing recognition that neurotrophins such as brain derived neurotrophic factor (BDNF) as well as their receptors are expressed in peripheral tissues including the lung, and can thus potentially contribute to both normal physiology and pathophysiology of several diseases. The relevance of this family of growth factors lies in emerging clinical data indicating altered neurotrophin levels and function in a range of diseases including neonatal and adult asthma, sinusitis, influenza, and lung cancer. The current review focuses on 1) the importance of BDNF expression and signaling mechanisms in early airway and lung development, critical to both normal neonatal lung function and also its disruption in prematurity and insults such as inflammation and infection; 2) how BDNF, potentially derived from airway nerves modulate neurogenic control of airway tone, a key aspect of airway reflexes as well as dysfunctional responses to allergic inflammation; 3) the emerging idea that local BDNF production by resident airway cells such as epithelium and airway smooth muscle can contribute to normal airway structure and function, and to airway hyperreactivity and remodeling in diseases such as asthma. Furthermore, given its pleiotropic effects in the airway, BDNF may be a novel and appealing therapeutic target.

Airway smooth muscle in airway reactivity and remodeling: what have we learned?

It is now established that airway smooth muscle (ASM) has roles in determining airway structure and function, well beyond that as the major contractile element. Indeed, changes in ASM function are central to the manifestation of allergic, inflammatory, and fibrotic airway diseases in both children and adults, as well as to airway responses to local and environmental exposures. Emerging evidence points to novel signaling mechanisms within ASM cells of different species that serve to control diverse features, including 1) [Ca(2+)]i contractility and relaxation, 2) cell proliferation and apoptosis, 3) production and modulation of extracellular components, and 4) release of pro- vs. anti-inflammatory mediators and factors that regulate immunity as well as the function of other airway cell types, such as epithelium, fibroblasts, and nerves. These diverse effects of ASM "activity" result in modulation of bronchoconstriction vs. bronchodilation relevant to airway hyperresponsiveness, airway thickening, and fibrosis that influence compliance. This perspective highlights recent discoveries that reveal the central role of ASM in this regard and helps set the stage for future research toward understanding the pathways regulating ASM and, in turn, the influence of ASM on airway structure and function. Such exploration is key to development of novel therapeutic strategies that influence the pathophysiology of diseases such as asthma, chronic obstructive pulmonary disease, and pulmonary fibrosis.

Altitude-related cough

Altitude-related cough is a troublesome condition of uncertain aetiology that affects many visitors to high altitude. The traditionally held belief that it was due solely to the inspiration of cold, dry air was refuted by observations and experiments in long duration hypobaric chamber studies. It is likely that altitude-related cough is a symptom of a number of possible perturbations in the cough reflex arc that may exist independently or together. These include loss of water from the respiratory tract; respiratory tract infections and sub-clinical high altitude pulmonary oedema. The published work on altitude-related cough is reviewed and possible aetiologies for the condition are discussed.

Cough reflex sensitivity is increased in guinea pigs with parainfluenza virus infection

The purpose of this study was to investigate for the change in cough reflex sensitivity (CRS) caused by parainfluenza virus type 3 (PIV3) infection. Guinea pigs were randomized into a vehicle control, an asthma control, or 1 of 4 PIV3-inoculated groups (referred to as postinfection day [PID] 6, 12, 28, and 42 groups). Evidence of viral protein and nucleic acid within the lung confirmed successful PIV3 infection. Plethysmography was used to assess CRS and airway reaction and airway inflammation was assessed via bronchoalveolar lavage fluid cytology and lung histopathology. Compared with the vehicle control group, CRS was significantly increased in all PID groups (P <.05) in concert with an obvious airway hyperresponsiveness in the PID 6 group. Though a small increase in CRS in the asthma control group was noted, it was not significant compared to the vehicle control group. Total cell counts from the bronchoalveolar lavage fluid of all PIV3-inoculated groups increased markedly and the number of lymphocytes was significantly increased in the PID 6 and PID 12 groups. The lung pathology of PIV3-inoculated animals showed airway inflammation without pneumonia in the acute infectious phase. The temporal and spatial variation of CRS may be the essential mechanism of cough caused by PIV3.

Buying time-the immune system determinants of the incubation period to respiratory viruses

Respiratory viruses cause disease in humans characterized by an abrupt onset of symptoms. Studies in humans and animal models have shown that symptoms are not immediate and appear days or even weeks after infection. Since the initial symptoms are a manifestation of virus recognition by elements of the innate immune response, early virus replication must go largely undetected. The interval between infection and the emergence of symptoms is called the incubation period and is widely used as a clinical score. While incubation periods have been described for many virus infections the underlying mechanism for this asymptomatic phase has not been comprehensively documented. Here we review studies of the interaction between human pathogenic respiratory RNA viruses and the host with a particular emphasis on the mechanisms used by viruses to inhibit immunity. We discuss the concept of the "stealth phase", defined as the time between infection and the earliest detectable inflammatory response. We propose that the "stealth phase" phenomenon is primarily responsible for the suppression of symptoms during the incubation period and results from viral antagonism that inhibits major pathways of the innate immune system allowing an extended time of unhindered virus replication.

A randomized double blind placebo controlled clinical evaluation of extract of Andrographis paniculata (KalmCold) in patients with uncomplicated upper respiratory tract infection

A randomized, double blind placebo controlled clinical study was conducted to evaluate the efficacy of KalmCold, an extract of Andrographis paniculata, in patients with uncomplicated upper respiratory tract infection (URTI). The assessment involved quantification of symptom scores by Visual Analogue Scale. Nine self evaluated symptoms of cough, expectoration, nasal discharge, headache, fever, sore throat, earache, malaise/fatigue and sleep disturbance were scored. A total of 223 patients of both sexes were randomized in two groups which received either KalmCold (200 mg/day) or placebo in a double blind manner. In both the treatments, mean scores of all symptoms showed a decreasing trend from day 1 to day 3 but from day 3 to day 5 most of the symptoms in placebo treated group either remained unchanged (cough, headache and earache) or got aggravated (sore throat and sleep disturbance) whereas in KalmCold treated group all symptoms showed a decreasing trend. Within groups, mean scores of symptoms in both the groups decreased significantly (p < or = 0.05) from day 1 to day 3 and day 5 while from day 3 to day 5 all symptoms except expectoration in placebo group did not improve significantly whereas in KalmCold treated group all symptoms improved significantly (p < or = 0.05) except earache. Comparing mean between both groups, all symptoms at day 1 and day 3 were found to be the same while at day 5 all symptoms except earache in KalmCold treated group improved significantly (p < or = 0.05) than placebo group. Similarly, within groups, overall scores of all symptoms in both the groups decreased significantly (p < or = 0.05) from day 1 to day 3 and day 5 while from day 3 to day 5 placebo group did not improve significantly whereas KalmCold treated group showed significant improvement (p < or = 0.05). On between groups analysis, KalmCold group showed significant reduction (p < or = 0.05) in overall symptom scores as compared to placebo group. In both placebo and KalmCold treated groups, there were only a few minor adverse effects with no significant difference in occurrence (Z = 0.63; p > 0.05). The comparison of overall efficacy of KalmCold over placebo was found to be significant (p < or = 0.05) and it was 2.1 times (52.7%) higher than placebo. The findings of this study revealed that KalmCold was effective in reducing symptoms of upper respiratory tract infection.

Mechanisms of symptoms of common cold and flu

It is the familiar symptoms of sore throat, runny nose, sneezing, and nasal congestion, muscle aches, chilliness and fever, etc., that define the common cold and flu syndromes as self-diagnosed illnesses. Although there is much information about the molecular biology of the viruses that cause the common cold and flu syndromes, there is relatively little research on the immunological, physiological and pathophysiological mechanisms involved in generating the symptoms. This chapter studies the mechanisms that cause local symptoms associated with local inflammation of the airway (sore throat, sneezing, rhinorrhoea and purulent nasal discharge, nasal congestion, sinus pain, watery eyes and cough), and the mechanisms that cause systemic symptoms associated with release of cytokines from leukocytes (headache, chilliness and fever, psychological effects, malaise and mood changes, loss of appetite, and muscle aches and pains).

Eosinophils and their interactions with respiratory virus pathogens

Eosinophils are implicated in the pathophysiology of respiratory virus infection, most typically in negative roles, such as promoting wheezing and bronchoconstriction in conjunction with virus-induced exacerbations of reactive airways disease and in association with aberrant hypersensitivity responses to viral vaccines. However, experiments carried out in vitro and in vivo suggest positive roles for eosinophils, as they have been shown to reduce virus infectivity in tissue culture and promote clearance of the human pathogen, respiratory syncytial virus in a mouse challenge model. The related natural rodent pathogen, pneumonia virus of mice (PVM), is highly virulent in mice, and is not readily cleared by eosinophils in vivo. Interestingly, PVM replicates in eosinophils and promotes cytokine release. The molecular basis of virus infection in eosinophils and its relationship to disease outcome is currently under study.

Prevalence, pathogenesis, and causes of chronic cough

Cough is a reflex action of the respiratory tract that is used to clear the upper airways. Chronic cough lasting for more than 8 weeks is common in the community. The causes include cigarette smoking, exposure to cigarette smoke, and exposure to environmental pollution, especially particulates. Diseases causing chronic cough include asthma, eosinophilic bronchitis, gastro-oesophageal reflux disease, postnasal drip syndrome or rhinosinusitis, chronic obstructive pulmonary disease, pulmonary fibrosis, and bronchiectasis. Doctors should always work towards a clear diagnosis, considering common and rare illnesses. In some patients, no cause is identified, leading to the diagnosis of idiopathic cough. Chronic cough is often associated with an increased response to tussive agents such as capsaicin. Plastic changes in intrinsic and synaptic excitability in the brainstem, spine, or airway nerves can enhance the cough reflex, and can persist in the absence of the initiating cough event. Structural and inflammatory airway mucosal changes in non-asthmatic chronic cough could represent the cause or the traumatic response to repetitive coughing. Effective control of cough requires not only controlling the disease causing the cough but also desensitisation of cough pathways.

Cytokine modulation of muscarinic receptors in the murine intestine

The extent to which gut motility and smooth muscle contractility are altered by intestinal inflammation depends on the nature of the underlying immune activation. The muscarinic receptor on smooth muscle plays a critical role in mediating acetylcholine-driven motor function. We examined the ability of cytokines to influence muscarinic receptor characteristics on intestinal longitudinal muscle and related the findings to studies on carbachol-induced contraction. Cells were isolated from longitudinal muscle myenteric plexus (LMMP). Cytokine receptor expression, muscle contractility, and muscarinic agonist receptor characteristics were examined by agonist displacement of [N-methyl-(3)H]scopolamine ([(3)H]NMS) binding. The TGF-beta1 receptor (543 bp) and the IFN-gamma receptor 1 (660 bp) were identified on smooth muscle cells. Scatchard analysis revealed dissociation constant and maximum binding values for [(3)H]NMS of 2.6 nM and 2.4 x 10(4) sites/cell, respectively, in control cells. Nematode infection was accompanied by a reduction in inhibitory constant of the high-affinity sites (K(H)), and this was independent of signal transduction and activator of transcription 6. Preincubation with TGF-beta1 enhanced longitudinal muscle contractility and decreased the K(H) to 2.2 pM (increased muscarinic receptor affinity), whereas preincubation with IFN-gamma increased the K(H) to 0.4 muM (decreased muscarinic receptor affinity) and decreased longitudinal muscle contractility. Preincubation of LMMP with IL-13 decreased the K(H) to 0.2 nM. Cytokines exert differential effects on the muscarinic receptor on intestinal longitudinal smooth muscle. These findings explain the basis for altered muscle contractility observed in Th1 and Th2 models of inflammation, as well as in the post-nematode-infected state.

Action of anti-tussive drugs on the emetic reflex of Suncus murinus (house musk shrew)

The cough and emetic reflexes involve a synchronized firing of motor neurones involved in respiratory control. Tachykinin NK1 receptor antagonists and 5-HT1A receptor agonists are examples of centrally acting drugs that reduce cough and emesis. In the present studies, therefore, we examined the possibility that other classes of drugs known to reducing cough have anti-emetic properties to prevent emesis induced by diverse challenges. We examined the potential of codeine (1-10 mg/kg), baclofen (1-10 mg/kg), scopolamine (0.3-10 mg/kg), diphenhydramine (1-10 mg/kg), imperialine (1-30 mg/kg) and verticine (0.3-3 mg/kg) to inhibit emesis induced by nicotine (5 mg/kg, s.c.), copper sulphate (120 mg/kg, intragastric), and provocative motion (4 cm horizontal displacement, delivered at 1 Hz) in Suncus murinus (house musk shrew). Only codeine had broad inhibitory properties (P<0.05) to antagonize emesis induced by all challenges with ID50 values ranging from 1.2 to 2.3 mg/kg. Baclofen antagonized emesis induced by nicotine (maximum reduction was 44.9%, P<0.05) and motion (maximum reduction was 97.3%, P<0.01), but potentiated copper sulphate-induced emesis (maximum potentiation was 73.0%, P<0.05). Scopolamine antagonized copper sulphate-induced emesis (maximum reduction was 61.2%, P<0.05) and imperialine antagonized nicotine-induced emesis (maximum reduction was 30.2%, P<0.01), but verticine potentiated motion-induced emesis (maximum potentiation was 60.0%, P<0.05). Diphenhydramine did not significantly reduce emesis induced by any of the challenges (P>0.05). In conclusion, codeine has broad inhibitory anti-emetic actions but a known ability to reduce coughing does not necessarily predict broad inhibitory anti-emetic properties.

Altitude-related cough

Cough is a troublesome condition which affects many visitors to high altitude. Traditionally it has been attributed to the inspiration of the cold, dry air which characterizes the high altitude environment. This aetiology was brought into question by observations and experiments in long duration hypobaric chamber studies in which cough still occurred despite controlled temperature and humidity. Anecdotally however, exercise, possibly via the associated increase in ventilation, does appear to precipitate cough at altitude. It is likely that the term, altitude-related cough, covers a number of conditions and aetiologies. These aetiologies are discussed and include water loss from the respiratory tract; high altitude pulmonary oedema; acute mountain sickness; bronchoconstriction; respiratory tract infections; vasomotor rhinitis and post-nasal drip; and alterations in the central control of respiration. We hypothesize that there are two forms of altitude-related cough: a cough which may occur at relatively low altitudes and which is related to exercise and persists despite descent and a cough which does not occur at altitudes below 5000-6000 m and which improves rapidly with descent to lower altitude. The treatment of altitude-related cough is symptomatic and frequently ineffective. Further work is required to understand the nature and aetiology of the cough which occurs at high altitude before effective therapies can be developed.

Infection with the cestode Hymenolepis diminuta induces changes in acetylcholine metabolism and muscarinic receptor mRNA expression in the rat jejunum

Total and neuron-specific uptake of [3H] choline into smooth muscle/myenteric plexus (SM/MP) preparations from the jejunum of rats infected with five Hymenolepis diminuta for 30 days compared to uninfected rats was significantly increased, as was choline acetyltransferase activity and acetylcholine biosynthesis. Although acetylcholinesterase and total cholinesterase activity levels in SM/MP preparations from infected rats were not significantly different from uninfected animals, pseudocholinesterase activity was significantly elevated in infected rats. Infection resulted in a significant elevation in the relative expression of muscarinic 2 (M2) receptor mRNA in jejunum compared to uninfected rats. Conversely, in rats infected with 50 worms for 30 days, the relative expression of muscarinic 1 (M1) receptor mRNA in the jejunum was significantly depressed, while the expression of M2 receptor mRNA was not significantly different from that in five worm infections. The relative expression of muscarinic 3 receptor mRNA was unaffected by infection. The present study shows that infection of rats with low numbers of an enteric cestode leads to a significant modulation of the cholinergic components of the myenteric plexus and M2 receptor mRNA, and that large number of worms result in suppression in the relative expression of M1 receptor mRNA.

The physiology of cough

Cough is comprised of three phases (inspiratory, compressive and expiratory) and serves as a vital defensive mechanism for lung health. It prevents pulmonary aspiration, promotes ciliary activity and clears airway debris. The importance of an intact cough mechanism is reflected in the occurrence of pulmonary problems when cough is inefficient. Cough efficiency is dependent on physical/mechanical aspects (respiratory muscles, mucus, airway calibre and larynx) and integrity of the neurophysiological pathway of cough. The understanding of the latter has progressed significantly (albeit mostly in animals) with the discovery of vanniloid receptors (and subtypes) and, more recently, by the characterisation of distinct cough receptors. However, the relative contributions of previously described airway afferents/receptors to cough are still disputed. Plasticity of the peripheral and central afferent pathways in cough has recently been shown to be important in pathological states associated with increased cough. To date, little is known of the developmental aspects of cough.

Understanding the symptoms of the common cold and influenza

The common cold and influenza (flu) are the most common syndromes of infection in human beings. These diseases are diagnosed on symptomatology, and treatments are mainly symptomatic, yet our understanding of the mechanisms that generate the familiar symptoms is poor compared with the amount of knowledge available on the molecular biology of the viruses involved. New knowledge of the effects of cytokines in human beings now helps to explain some of the symptoms of colds and flu that were previously in the realm of folklore rather than medicine-eg, fever, anorexia, malaise, chilliness, headache, and muscle aches and pains. The mechanisms of symptoms of sore throat, rhinorrhoea, sneezing, nasal congestion, cough, watery eyes, and sinus pain are discussed, since these mechanisms are not dealt with in any detail in standard medical textbooks.

Acute and chronic cough

Individuals are generally content to self-medicate for acute cough. It is only when the cough becomes persistent that they seek medical assistance. It is not known why patients cough in association with an acute upper respiratory tract infection (URTI), although interest has focused on how viruses may influence airway sensory nerve function and contribute to heightened cough reflex sensitivity. Why some patients develop a persistent cough following a viral URTI is also unclear. Much more is known about the causes and aggravants of chronic cough although there is no broad agreement as to the best way to manage such patients. Asthma, upper gastrointestinal dysfunction and rhinitis are frequently associated with chronic cough, although the impact of cough in suppurative lung disease and interstitial lung fibrosis is rarely considered. The development of effective treatments for cough remains a challenge and will require co-operation between clinicians, scientists and the pharmaceutical industry.