Microdeletion 22q11.2 syndrome: Does thymus incidental surgical resection affect its immunological profile?

BACKGROUND: The del22q11 syndrome patients present immunological abnormalities associated to thymus alterations. Up to 75% of them present cardiopathies and thymus is frequently removed during surgery. The thymectomy per se has a deleterious effect concerning lymphocyte subpopulations, and T cell function. When compared to healthy controls, these patients have higher infections propensity of variable severity. The factors behind these variations are unknown. We compared immunological profiles of del22q11.2 Syndrome patients with and without thymectomy to establish its effect in the immune profile. METHODS: Forty-six del22q11.2 syndrome patients from 1 to 16 years old, 19 of them with partial or total thymectomy were included. Heart disease type, heart surgery, infections events and thymus resection were identified. Immunoglobulin levels, flow cytometry for lymphocytes subpopulations and TREC levels were determined, and statistical analyses were performed. RESULTS: The thymectomy group had a lower lymphocyte index, both regarding total cell count and when comparing age-adjusted Z scores. Also, CD3+, CD4+ and CD8+ lower levels were observed in this group, the lowest count in those patients who had undergone thymus resection during the first year of life. Their TREC level median was 23.6/µL vs 16.1µL in the non-thymus group (p=0.22). No differences were identified regarding immunoglobulin levels or infection events frequencies over the previous year. CONCLUSION: Patients with del22q11.2 syndrome subjected to thymus resection present lower lymphocyte and TREC indexes when compared to patients without thymectomy. This situation may be influenced by the age at the surgery and the time elapsed since the procedure.

Use of a temporary inferior vena cava filter during pregnancy in patients with thromboembolic events.

There are circumstances in the management of thromboembolic events during pregnancy when anticoagulant therapy is either contraindicated or not advisable, such as when pulmonary embolism (PE) or deep venous thrombosis is diagnosed close to term, given the risk of bleeding during delivery. In these cases, the thromboembolic risk can be controlled using temporary inferior vena cava filters (T-IVCFs). We present the case of a pregnant woman with thrombophilia who remained at rest for eight weeks due to an amniotic prolapse and for whom the placement of a T-IVCF was decided at 32 weeks' gestation after anticoagulant therapy had failed. An emergency caesarean section was performed at 33 weeks' gestation due to placental abruption following the spontaneous onset of preterm labour. The risk of bleeding during delivery when high doses of heparin are used, and the risk of PE when the heparin dose is decreased, needs to be evaluated versus the risks related to T-IVCF placement procedure and, as such, a review of the published experience in this field is warranted. We have concluded that T-IVCFs can be a safe alternative treatment for pregnant women in whom anticoagulation therapy is either contraindicated or not advisable.

Fucoxanthin in association with vitamin C acts as modulators of human neutrophil function.

INTRODUCTION: Neutrophils provide the first line of defense of the innate immune system by phagocytosing, killing and digesting bacteria and fungi. During this process, neutrophils produce reactive oxygen species (ROS), which in excess, can damage the cells themselves and surrounding tissues. The carotenoid fucoxanthin (Fc) has been studied concerning its antioxidant and anti-inflammatory actions. Vitamin c (Vc) also demonstrates potent antioxidant action. This study aimed to evaluate the effect of Fc (2 µM) in association with Vc (100 µM) on functional parameters of human neutrophils in vitro. MATERIALS AND METHODS: We evaluated the migration and phagocytic capacity, intracellular calcium mobilization, ROS production (O2(·)⁻, H2O2, HOCl), myeloperoxidase activity, profile of antioxidant enzymes, phosphorylation of p38 MAPK and p65 NFκB subunit, GSH/GSSG ratio and release of pro-inflammatory cytokines (TNF-α and IL-6) in neutrophils under different stimuli. RESULTS: We verified an increase in phagocytic capacity for all treatments, together with an increase in intracellular calcium only in cells treated with Fc and Fc + Vc. ROS production was reduced by all treatments, although Vc was a better antioxidant than Fc. Phosphorylation of the p-65 subunit of NFκB was reduced in cells treated with Fc + Vc and release of TNF-α and IL-6 was reduced by all treatments. These findings indicate that the regulation of inflammatory cytokines by neutrophils is not exclusively under the control of the NFκB pathway. Fc reduced the activity of some antioxidant enzymes, whereas Vc increased GR activity and the GSH/GSSG ratio. CONCLUSION: In conclusion, the results presented in this study clearly show an immunomodulatory effect of the carotenoid fc alone or in combination with Vc on the function of human neutrophils.

Etomidate in the treatment of Cushing syndrome.

Cushing syndrome is a metabolic disease caused by chronic exposure to high levels of glucocorticoids. It can present as an endocrine emergency due to a rapid increase in circulating cortisol leading to increased risk of cardiovascular disease and infection. Etomidate rapidly reduces plasma cortisol levels by inhibiting the action of 11ß-hidroxilase. We report the case of a patient with severe hypercortisolaemia accompanied by metabolic and psychiatric disorders in whom administration of etomidate reduced preoperative levels of cortisol.

EEG Interchannel Causality to Identify Source/Sink Phase Connectivity Patterns in Developmental Dyslexia.

While the brain connectivity network can inform the understanding and diagnosis of developmental dyslexia, its cause-effect relationships have not yet enough been examined. Employing electroencephalography signals and band-limited white noise stimulus at 4.8 Hz (prosodic-syllabic frequency), we measure the phase Granger causalities among channels to identify differences between dyslexic learners and controls, thereby proposing a method to calculate directional connectivity. As causal relationships run in both directions, we explore three scenarios, namely channels' activity as sources, as sinks, and in total. Our proposed method can be used for both classification and exploratory analysis. In all scenarios, we find confirmation of the established right-lateralized Theta sampling network anomaly, in line with the assumption of the temporal sampling framework of oscillatory differences in the Theta and Gamma bands. Further, we show that this anomaly primarily occurs in the causal relationships of channels acting as sinks, where it is significantly more pronounced than when only total activity is observed. In the sink scenario, our classifier obtains 0.84 and 0.88 accuracy and 0.87 and 0.93 AUC for the Theta and Gamma bands, respectively.

Risk factors for lymphedema after breast surgery: A prospective cohort study in the era of sentinel lymph node biopsy.

INTRODUCTION: The Objective was to investigate the incidence of lymphedema after breast cancer treatment and to analyze the risk factors involved in a tertiary level hospital. METHODS: Prospective longitudinal observational study over 3 years post-breast surgery. 232 patients undergoing surgery for breast cancer at our institution between September 2013 and February 2018. Sentinel lymph node biopsy (SLNB) or axillary lymphadenectomy (ALND) were mandatory in this cohort. In total, 201 patients met the inclusion criteria and had a median follow-up of 31 months (range, 1-54 months). Lymphedema was diagnosed by circumferential measurements and truncated cone calculations. Patients and tumor characteristics, shoulder range of motion limitation and local and systemic therapies were analyzed as possible risk factors for lymphedema. RESULTS: Most cases of lymphedema appeared in the first 2 years. 13.9% of patients developed lymphedema: 31% after ALND and 4.6% after SLNB (p < 0.01), and 46.7% after mastectomy and 11.3% after breast-conserving surgery (p < 0.01). The lymphedema rate increased when axillary radiotherapy (RT) was added to radical surgery: 4.3% for SLNB alone, 6.7% for SLNB + RT, 17.6% for ALND alone, and 35.2% for ALND + RT (p < 0.01). In the multivariate analysis, the only risk factors associated with the development of lymphedema were ALND and mastectomy, which had hazard ratios (95% confidence intervals) of 7.28 (2.92-18.16) and 3.9 (1.60-9.49) respectively. CONCLUSIONS: The main risk factors for lymphedema were the more radical surgeries (ALND and mastectomy). The risk associated with these procedures appeared to be worsened by the addition of axillary radiotherapy. A follow-up protocol in patients with ALND lasting at least two years, in which special attention is paid to these risk factors, is necessary to guarantee a comprehensive control of lymphedema that provides early detection and treatment.

High prevalences of infection with Giardia intestinalis genotype B among children in urban and rural areas of Argentina.

The protozoan parasite most frequently associated with diarrhoea worldwide is Giardia intestinalis. In 2005, a study was initiated to identify the genotypes of this parasite infecting children in the Argentinian provinces of Buenos Aires, Mendoza and Chaco, and to explore the associations between the genotype detected in a child, the characteristics of the child's household and the child's clinical presentation. Overall, 998 children (504 boys and 494 girls) aged between 2-14 years, with or without symptoms, were enrolled. The G. intestinalis in 94 of the 117 stool samples found positive for the parasite by microscopy were successfully genotyped by PCR. Seventy-seven of the children were found to be infected with genotype B only and 14 with genotype AII only, three children being found to have mixed (AII and B) infections. Only genotype B was detected in children from rural areas (P<0·05) and most Giardia detected in children from households with a piped water supply were also of this genotype (P<0·05). The other household characteristics investigated (quality of building, history of flooding, type of sanitation, level of overcrowding, and presence/absence of pet dogs) had no significant effect on the genotype distribution. Children infected with genotype AII were significantly younger than those infected with genotype B (P<0·05) and there was a significant positive association between infection with genotype B and abdominal pain (P<0·05). Diarrhoea was not, however, found to be significantly associated with genotype-AII or genotype-B infection. This is the first published report on the Giardia genotypes circulating in the provinces of Mendoza and Chaco. The results indicate the importance of asymptomatic children in the transmission of Giardia among the young.

Birth of a healthy infant after bone marrow-derived cell therapy.

Bone marrow-derived cell (BMDC) therapy has numerous applications as potential biological cells for use in regenerative medicine. Here, we present an original case of endometrial atrophy associated with genital tuberculosis in a woman who achieved a live birth with BMDC. This 27-year-old woman came to our center with endometrial atrophy and primary infertility. She had a past history of genital tuberculosis and amenorrhea. Her husband's semen quality was normal. The patient was counseled for hysteroscopy due to thin endometrium and advised in vitro fertilization (IVF) with donor eggs in lieu of poor ovarian reserve. Several attempts of IVF with hormone replacement therapy (HRT) were made, but the desired thickness of the endometrium was not achieved. Uterine artery injection of BMDC through interventional radiology was given, followed by HRT for three months, which resulted in improved endometrium. This was subsequently followed by IVF with donor egg. The treatment resulted in the conception and delivery of a 3.1-kg baby boy through lower segment caesarean section with no antenatal, intranatal or postnatal complications. Recently, there has been massive interest in stem cells as a novel treatment method for regenerative medicine, and more specifically for the regeneration of human endometrium disorders like Asherman syndrome and thin endometrium, which was the reason behind using this strategy for treatment.

Birth of a healthy infant after bone marrow-derived cell therapy / 대한생식의학회지

Bone marrow-derived cell (BMDC) therapy has numerous applications as potential biological cells for use in regenerative medicine. Here, we present an original case of endometrial atrophy associated with genital tuberculosis in a woman who achieved a live birth with BMDC. This 27-year-old woman came to our center with endometrial atrophy and primary infertility. She had a past history of genital tuberculosis and amenorrhea. Her husband’s semen quality was normal. The patient was counseled for hysteroscopy due to thin endometrium and advised in vitro fertilization (IVF) with donor eggs in lieu of poor ovarian reserve. Several attempts of IVF with hormone replacement therapy (HRT) were made, but the desired thickness of the endometrium was not achieved. Uterine artery injection of BMDC through interventional radiology was given, followed by HRT for three months, which resulted in improved endometrium. This was subsequently followed by IVF with donor egg. The treatment resulted in the conception and delivery of a 3.1-kg baby boy through lower segment caesarean section with no antenatal, intranatal or postnatal complications. Recently, there has been massive interest in stem cells as a novel treatment method for regenerative medicine, and more specifically for the regeneration of human endometrium disorders like Asherman syndrome and thin endometrium, which was the reason behind using this strategy for treatment.

Birth of a healthy infant after bone marrow-derived cell therapy / 대한생식의학회지

Bone marrow-derived cell (BMDC) therapy has numerous applications as potential biological cells for use in regenerative medicine. Here, we present an original case of endometrial atrophy associated with genital tuberculosis in a woman who achieved a live birth with BMDC. This 27-year-old woman came to our center with endometrial atrophy and primary infertility. She had a past history of genital tuberculosis and amenorrhea. Her husband’s semen quality was normal. The patient was counseled for hysteroscopy due to thin endometrium and advised in vitro fertilization (IVF) with donor eggs in lieu of poor ovarian reserve. Several attempts of IVF with hormone replacement therapy (HRT) were made, but the desired thickness of the endometrium was not achieved. Uterine artery injection of BMDC through interventional radiology was given, followed by HRT for three months, which resulted in improved endometrium. This was subsequently followed by IVF with donor egg. The treatment resulted in the conception and delivery of a 3.1-kg baby boy through lower segment caesarean section with no antenatal, intranatal or postnatal complications. Recently, there has been massive interest in stem cells as a novel treatment method for regenerative medicine, and more specifically for the regeneration of human endometrium disorders like Asherman syndrome and thin endometrium, which was the reason behind using this strategy for treatment.

Green tea polyphenols change the profile of inflammatory cytokine release from lymphocytes of obese and lean rats and protect against oxidative damage.

This study aimed to investigate whether green tea polyphenols (GT) modulate some functional parameters of lymphocytes from obese rats. Male Wistar rats were treated with GT by gavage (12 weeks/5 days/week; 500 mg/kg of body weight) and obesity was induced by cafeteria diet (8 weeks). Lymphocytes were obtained from mesenteric lymph nodes for analyses. In response to the cafeteria diet we observed an increase in activity of the metabolic enzyme hexokinase, ROS production, MnSOD, CuZnSOD and GR enzyme activities and proliferation capacity of the cells (baseline), whereas IL-10 production was decreased. Obese rats treated with GT decreased cell proliferation (under ConA stimulation). Hexokinase and G6PDH activity, ROS production and MnSOD, CuZnSOD, GPx and GR enzymes remained increased, accompanied by an increase in Nrf2 mRNA level. There was a decrease in pro-inflammatory IL-2, IL-6, IL-1ß, TNF-α cytokines that were accompanied by a decrease in the mRNA level of TRL4 while IL-10 production was increased in obese rats treated with GT. GT treatment of lean rats showed similar results to that of obese rats treated with GT, indicating that the effects of GT are independent of diet. Foxp3 and IRF4 mRNA levels were increased by GT. In conclusion, cafeteria diet modulated the function of lymphocytes from lymph nodes, increasing ROS production and decreasing anti-inflammatory IL-10, which could contribute to the inflammatory state in obesity. GT reduced ROS production, improving the redox status and reducing pro-inflammatory cytokine production by lymphocytes, suggesting that GT treatment may be driving lymphocytes to a more anti-inflammatory than pro-inflammatory microenvironment.

Elevated cAMP in intestinal epithelial cells during experimental cholera and salmonellosis.

Cholera and salmonellosis are two diarrheal diseases in which intestinal tissue cyclic adenosine monophosphate (cAMP) concentrations are elevated. Investigations of each experimental disease were initiated to identify the specific intestinal cells containing the elevated cAMP. Epithelial cells were eluted from the mucosa of infected and control intestinal loops of adult rabbits, after which the cAMP content of the epithelial cell fractions and the lamina propria cells was extracted and assayed. The identity of the epithelial cells (in the villus tip-to-crypt cell gradient) was monitored by measuring their intracellular alkaline phosphatase activity, while scanning electron microscopy was used to visualize the effects of infection and cell elution techniques. Clearly, in both experimental cholera and salmonellosis, elevated cAMP levels were associated with crypt epithelial cells. Villus tip epithelial cells from either infection tended to contain less cAMP than those of noninfected control tissue. In Salmonella-infected loops, it was apparent that cAMP was also elevated in lamina propria cell fractions. Lamina propria cells from V. cholerae-infected intestinal loops contained only basal levels of cAMP. In vitro exposure of isolated intestinal cells from normal rabbit intestine to a cell-free lysate of Salmonella resulted in elevation of cAMP in the epithelial cells and lamina propria cells. We conclude that in experimental cholera and salmonellosis, significant elevation of the cAMP levels occurred in intestinal crypt cells, consistent with an enterotoxin-mediated mechanism. In Salmonella-infected loops, it was unclear if the increased concentration of cAMP in lamina propria cells was generated by enterotoxin released from the invasive salmonellae or by prostaglandins formed during the inflammatory response to the bacteria, or by both mechanisms.

Phage typing combined with pulsed-field gel electrophoresis and random amplified polymorphic DNA increases discrimination in the epidemiological analysis of Salmonella enteritidis strains.

Phage typing (PT) combined with pulsed-field gel electrophoresis (PFGE) and a random amplified polymorphic DNA (RAPD) fingerprinting method was used to characterize Salmonella enteritidis strains. Twenty-four epidemiologically unrelated isolates, sampled from diverse ecological niches and fifteen isolates from four well-defined outbreaks of foodborne gastroenteritis, were studied. Seven phage types, with a predominance of PT 4 (63% of isolates), were observed when analysing the epidemiologically unrelated group. PT 4 was detected in all of the ecological niches studied, including food and fecally polluted river and beach water. The discriminatory power for phage typing, the average probability that the typing system will assign a different type to two unrelated strains randomly sampled in the microbial population, was 0.62. Ten PFGE pattern types were obtained with Xba I restriction endonuclease enzyme among the unrelated isolates; thirteen isolates belonged to PFGE pattern type 1 and the rest of the PFGE types were assigned to one or two isolates. The Dice coefficient clustered the similarities of the PFGE patterns between 80-100%. PFGE showed a discriminatory power of 0.72. Five clearly distinct RAPD patterns were observed with the OPS-19 oligonucleotide, but the discrimination obtained was low (0.46). The combination of the three typing methods increased the number of types to seventeen, giving high discrimination (0.92). Seven of the isolates recovered from various ecological niches belonged to the combination PT 4/PFGE 1/RAPD A and other combinations were unique or included only two strains. The four epidemiologically well-defined foodborne outbreaks were associated with the PT 4 phage type. In two of the outbreaks, other phage types (PT 7a and RDNC) were also observed in two isolates. Most of the isolates belonging to the foodborne outbreaks had an identical PFGE pattern (PFGE pattern type 1), but a difference in a restriction band was observed in an isolate belonging to an outbreak. Two RAPD patterns were observed in the outbreaks; RAPD pattern type A was detected in three of the four outbreaks. When the combined typing method was applied to the study, high concordance was observed and most of the outbreak strains belonged to the combination PT 4/PFGE 1/RAPD A. It is concluded that the combination of phage type with PFGE and RAPD provides a powerful discriminatory tool for the epidemiological analysis of unrelated and related strains of S. enteritidis.

The peripheral analgesic effect of morphine, codeine, pentazocine and d-propoxyphene.

The prostaglandin hyperalgesia and tail immersion tests were used to evaluate the analgesic action of morphine, codeine, d-propoxyphene and pentazocine following intraperitoneal, intraplantar and intracerebroventricular administration to rats. In the prostaglandin hyperalgesia test, all drugs produced a dose-dependent analgesia by the various routes. The rank order of potency after intraperitoneal administration was morphine (100) greater than d-propoxyphene (4) greater than pentazocine (2) greater than codeine (1). Although morphine (ID50 = 4 micrograms) was a very potent analgesic when given intracerebroventricularly, very shallow dose-response curves were obtained with the other substances which promoted less than 30% of inhibition at doses up to 250 micrograms. In the paw, morphine (ID50 = 5 micrograms) was only 5-8 times more potent than pentazocine, propoxyphene and codeine. Thus, in contrast with morphine, intraplantar administration of codeine, pentazocine and d-propoxyphene is much more effective than intracerebroventricular administration. In the tail immersion test the smallest intraperitoneal doses which affected the reaction time were 9 mg/kg morphine, 16.2 mg/kg codeine and pentazocine and 48.6 mg/kg d-propoxyphene. When injected intracerebroventricularly morphine (10 micrograms) was the only opiate that caused a detectable analgesic effect. In the prostaglandin hyperalgesia test, a small dose of naloxone (1 micrograms) given into the rat paw significantly antagonized the analgesic effect of d-propoxyphene, codeine and pentazocine administered either intraperitoneally or intraplantarly. These results clearly indicate that a method involving or mimicking inflammatory hyperalgesia is much more sensitive in detecting opiate analgesia than a method which uses heat as a nociceptive stimulus. Furthermore, our results support the proposition that part of the overall analgesia which follows the systemic administration of opiates is due to a peripheral antinociceptive action.

The role of opioids in the analgesic response of rats during the estrous cycle.

The analgesic response was evaluated by the tail immersion test in female rats during each phase of the estrous cycle. The reaction time (mean +/- SEM) for tail withdrawal from the hot water bath was faster during proestrus (5.78 +/- 0.28 s) and decreased significantly during estrus (5.31 +/- 0.30 s) and diestrus 1 (5.40 +/- 0.21 s). Blockade of opiate receptors with naloxone (2 mg/kg, ip) increased the sensitivity to the noxious stimulus only during proestrus (6.46 +/- 0.42 vs 5.02 +/- 0.41 s). These results suggest that the effects of gonadal steroids on nociception may involve an opioid pathway.

Sex-related differences in the analgesic response to the rat tail immersion test.

The analgesic response was evaluated by the tail immersion test in adult male (N = 30), female (N = 21) and androgenized female Wistar rats (N = 15). The reaction time for tail withdrawal from the hot water bath was faster for male than for female rats (3.48 +/- 0.12 vs 6.46 +/- 0.42 s). The reaction time of androgenized female rats was similar to that of male rats (3.08 +/- 0.16 s). Blockade of opiate receptors with naloxone (2 mg/kg, ip) decreased the sensitivity to the noxious stimuli in males (4.08 +/- 0.10 s) and in androgenized females (3.69 +/- 0.19 s) but increased it in female rats (5.01 +/- 0.41 s). These data show sex-related differences in the analgesic response evaluated by the tail immersion test and indicate that administration of androgens to newborn female rats affects their pain sensitivity.

Participation of opioid receptors in the modulation of the analgesic response by adrenal and gonadal glands.

The involvement of opioid receptors in the analgesic response was evaluated by the tail-immersion test in simultaneously adrenalectomized and ovariectomized female Wistar rats (210-250 g). The reaction time (mean +/- SEM) for tail withdrawal from hot water decreased significantly 2 weeks after surgery (3.52 +/- 0.20 s) when compared to intact animals (6.09 +/- 0.23 s). Hormonal replacement with dexamethasone (50 micrograms/day) did not affect reaction time (3.38 +/- 0.19 s). However, this response was restored by combined adrenal and gonadal steroid substitution (estradiol 5 micrograms/day and progesterone 1.5 micrograms 6 h before the tests) therapy (5.11 +/- 0.45 s in animals treated with dexamethasone plus estradiol and 5.04 +/- 0.43 s in animals treated with dexamethasone plus estradiol plus progesterone). Naloxone (2 mg/kg) decreased the reaction time of animals treated with adrenal and gonadal steroids (5.11 +/- 0.45 vs 4.15 +/- 0.44 s and 5.04 +/- 0.43 vs 3.87 +/- 0.28 s, respectively, before and after naloxone) but failed to decrease it in rats treated with dexamethasone only (3.88 +/- 0.18 vs 4.34 +/- 0.25 s, before and after naloxone). These observations indicate that gonadal steroids are the most important steroid factors involved in the reaction time to tail immersion in hot water and confirm other reports that the opioid pathways modulating the neuronal circuitry require the presence of these hormones.

Prevalence and severity of dental fluorosis in a Mexican community with above-optimal fluoride concentration in drinking water.

The purpose of this study was to determine the prevalence and severity of dental fluorosis in children living in a community at 2066 m above sea level. The water fluoride concentration of this community was 2.8 ppm. The population selected encompassed 10-12-yr-old schoolchildren who were life-long residents of the area. The modified Dean Index was used to estimate the severity of fluorosis. A total of 93 children participated in the study. They all showed evidence of dental fluorosis. Fifty-seven percent had moderate fluorosis, and 19% severe fluorosis. The high prevalence and severity of fluorosis in the population examined emphasized the need to study the factors determining dental fluorosis in Mexican communities.

Toxicological findings in a fatal ingestion of methamphetamine.

This paper presents the case history of a fatality caused by the complications brought about by the presence of methamphetamine and ethanol. Drug concentrations are reported from samples obtained approximately 15 min after the subject was last observed to be chewing what was then believed to be gum, 3 h after the initial toxic symptoms were displayed, 6, 11, and 22 h later. The subjects conditions deteriorated over the course of this time, and he was declared dead 33 h after the initial display of toxic symptoms. The toxicological findings and concentration levels of the reported biological specimens concurred with the expected findings in a case of methamphetamine toxicity.

[Quasispecies and molecular evolution of viruses]. / Cuasiespecies y evolución molecular de virus.

Ribonucleic acid (RNA) viruses evolve as complex distributions of genetically different but closely related variants termed viral quasispecies. The precise genome of a quasispecies cannot be defined, since the consensus genome is an average of many variants. The dynamics of quasispecies has considerable implications for the understanding of the adaptability and pathogenic potential of viruses, and in addition, for the design of preventive and therapeutic measures for the diseases caused by these viruses. The authors summarise current knowledge on the structure of quasispecies, and the biological implications of this structure.