Gross pathology associated with highly pathogenic avian influenza H5N8 and H5N1 in naturally infected birds in the UK (2020-2021)

BACKGROUND

Multiple outbreaks with highly pathogenic avian influenza virus (HPAIV) clade 2.3.4.4b viruses, including H5N8 and H5N1, have occurred in the United Kingdom, as well as in other European countries, since late 2020.

METHODS

This report describes the pathology among poultry species (chickens, turkeys, ducks, and pheasants) and captive birds (Black Swans, a whistling duck and peregrine falcons) naturally infected with HPAIV from 22 cases of HPAIV H5N8 and two cases of HPAIV H5N1 outbreaks investigated between October 2020 and April 2021.

RESULTS

On gross examination, pancreatic necrosis was easily identified and most commonly observed in galliformes infected with both subtypes of HPAIV but rarely in anseriformes. In addition, splenic necrosis was also frequently observed in chickens and turkeys infected with HPAIV H5N8. Other less common lesions included cardiac petechiae, serosal haemorrhages and ascites in a variety of species.

CONCLUSION

Given the widespread dissemination of HPAIV infection in susceptible avian species during autumn/winter 2020-2021, these data, when evaluated along with clinical information, is a valuable first step for both veterinarians and field services to evaluate gross pathology at post-mortem to support the diagnosis of HPAIV infection.

Intranasal Infection of Ferrets with SARS-CoV-2 as a Model for Asymptomatic Human Infection

Ferrets were experimentally inoculated with SARS-CoV-2 (severe acute respiratory syndrome (SARS)-related coronavirus 2) to assess infection dynamics and host response. During the resulting subclinical infection, viral RNA was monitored between 2 and 21 days post-inoculation (dpi), and reached a peak in the upper respiratory cavity between 4 and 6 dpi. Viral genomic sequence analysis in samples from three animals identified the Y453F nucleotide substitution relative to the inoculum. Viral RNA was also detected in environmental samples, specifically in swabs of ferret fur. Microscopy analysis revealed viral protein and RNA in upper respiratory tract tissues, notably in cells of the respiratory and olfactory mucosae of the nasal turbinates, including olfactory neuronal cells. Antibody responses to the spike and nucleoprotein were detected from 21 dpi, but virus-neutralizing activity was low. A second intranasal inoculation (re-exposure) of two ferrets after a 17-day interval did not produce re-initiation of viral RNA shedding, but did amplify the humoral response in one animal. Therefore, ferrets can be experimentally infected with SARS-CoV-2 to model human asymptomatic infection.

Substitution of warthog NF-κB motifs into RELA of domestic pigs is not sufficient to confer resilience to African swine fever virus

African swine fever virus (ASFV) causes a lethal, haemorrhagic disease in domestic swine that threatens pig production across the globe. Unlike domestic pigs, warthogs, which are wildlife hosts of the virus, do not succumb to the lethal effects of infection. There are three amino acid differences between the sequence of the warthog and domestic pig RELA protein; a subunit of the NF-κB transcription factor that plays a key role in regulating the immune response to infections. Domestic pigs with all 3 or 2 of the amino acids from the warthog RELA orthologue have been generated by gene editing. To assess if these variations confer resilience to ASF we established an intranasal challenge model with a moderately virulent ASFV. No difference in clinical, virological or pathological parameters were observed in domestic pigs with the 2 amino acid substitution. Domestic pigs with all 3 amino acids found in warthog RELA were not resilient to ASF but a delay in onset of clinical signs and less viral DNA in blood samples and nasal secretions was observed in some animals. Inclusion of these and additional warthog genetic traits into domestic pigs may be one way to assist in combating the devastating impact of ASFV.

Aspectos ecológicos de Telmatobius atacamensis (Anura: Telmatobiidae), un microendemismo de la Puna, Salta-Argentina

Telmatobius atacamensis es un anuro microendémico amenazado de la Puna salteña. En el presente estudio se identificaron los núcleos de reproducción caracterizando sus poblaciones. Para ello se realizó un muestreo anual en los ríos Los Patos y San Antonio, estableciéndose un total de diez sitios, registrándose pH, temperatura y conductividad eléctrica en los cuerpos de agua. Se empleó la técnica de encuentro visual (TEV) para la detección de los individuos. Se establecieron tres categorías de desarrollo larval, prometamórfico (G1), premetamórfico (G2) y clímax metamórfico (G3). Se identificaron seis núcleos reproductivos, cuatro en río San Antonio y dos en río Los Patos. Los individuos se localizaron en refugios subacuáticos con un rango reducido de conductividad eléctrica y uno amplio de temperatura mientras que el pH fue alcalino. Ambos ríos mostraron diferencias en cuanto a la frecuencia relativa de categorías de estadio larval. Las abundancias de esta etapa fue significativamente diferente entre ambos (ANOVA F= 109.41 p<0.000) siendo mayor para el río Los Patos. Los individuos adultos fueron registrados en ambos ríos durante todo el ciclo, con diferencias significativas en sus abundancias (T= 19.83 p<0.0001), resultando mayor para el río Los Patos. El presente trabajo aportaría información relevante para la evaluación del estado actual de conservación y la elaboración objetiva de estrategias para el diseño de monitores efectivos, comparaciones poblacionales futuras y protección de la especie.

The effect of BCG vaccination on macrophage phenotype in a mouse model of intranasal Mycobacterium bovis challenge

In order to develop improved vaccinations against tuberculosis, it is essential to understand the effect of vaccination on the immune response, and to overcome the mechanisms by which mycobacteria regulate this immune response. In this study, we examine the effect of intradermal vaccination with Mycobacterium bovis bacille Calmette-Guèrin on macrophage phenotype following intranasal challenge with virulent Mycobacterium bovis. Preserved lung tissues used in the present study were obtained from a previous vaccination trial in BALB/c mice. Vaccinated mice showed less extensive pulmonary lesions along with a significant decrease in bacterial lung burden when compared to control mice. Immunohistochemical markers of classically activated macrophages (iNOS) and alternatively activated macrophages (Arg1, FIZZ1) were applied to lung sections. Vaccination led to a statistically significant decrease in the number of Arg1+ macrophages. The presence of macrophages that expressed Arginase 1 in pulmonary lesions was much smaller than the presence of macrophages expressing iNOS. The low presence of Arg1+ macrophages induced by vaccination may be caused by Th1 polarization and may reduce alternative activation of macrophages, with an overall more effective intracellular killing of bacteria.

Two Single Incursions of H7N7 and H5N1 Low Pathogenicity Avian Influenza in U.K. Broiler Breeders During 2015 and 2016

Low pathogenicity (LP) avian influenza viruses (AIVs) have a natural reservoir in wild birds. These cause few (if any) overt clinical signs, but include H5 and H7 LPAIVs, which are notifiable in poultry. In the European Union, notifiable avian disease (NAD) demands laboratory confirmation with prompt statutory interventions to prevent dissemination of infection to multiple farms. Crucially, for H5 and H7 LPAIVs, movement restrictions and culling limit the further risk of mutation to the corresponding highly pathogenic (HP) H5 and H7 AIVs in gallinaceous poultry. An H7N7 LPAIV outbreak occurred during February 2015 at a broiler breeder chicken premise in England. Full genome sequencing suggested an avian origin closely related to contemporary European H7 LPAIV wild bird strains with no correlates for human adaptation. However, a high similarity of PB2, PB1, and NA genes with H10N7 viruses from European seals during 2014 was observed. An H5N1 LPAIV outbreak during January 2016 affecting broiler breeder chickens in Scotland resulted in rapid within-farm spread. An interesting feature from this case was that although viral tropism occurred in heart and kidney endothelial cells, suggesting HPAIV infection, the H5N1 virus had the molecular cleavage site signature of an LPAIV belonging to an indigenous European H5 lineage. There was no genetic evidence for human adaptation or antiviral drug resistance. The source of the infection was also likely to be via indirect contact with wild birds mediated via fomite spread from the nearby environment. Both LPAIV outbreaks were preceded by local flooding events that attracted wild waterfowl to the premises. Prompt detection of both outbreaks highlighted the value of the "testing to exclude" scheme launched in the United Kingdom for commercial gallinaceous poultry in 2014 as an early warning surveillance mechanism for NAD.

Ducks Are Susceptible to Infection with a Range of Doses of H5N8 Highly Pathogenic Avian Influenza Virus (2016, Clade 2.3.4.4b) and Are Largely Resistant to Virus-Specific Mortality, but Efficiently Transmit Infection to Contact Turkeys

Widespread H5N8 highly pathogenic avian influenza virus (HPAIV; clade 2.3.4.4b) infections occurred in wild birds and poultry across Europe during winter 2016-17. Four different doses of H5N8 HPAIV (A/wigeon/Wales/052833/2016 [wg-Wal-16]) were used to infect 23 Pekin ducks divided into four separate pens, with three contact turkeys introduced for cohousing per pen at 1 day postinfection (dpi). All doses resulted in successful duck infection, with four sporadic mortalities recorded among the 23 (17%) infected ducks, which appeared unrelated to the dose. The ducks transmitted wg-Wal-16 efficiently to the contact turkeys; all 12 (100%) turkeys died. Systemic viral dissemination was detected in multiple organs in two duck mortalities, with limited viral dissemination in another duck, which died after resolution of shedding. Systemic viral tropism was observed in two of the turkeys. The study demonstrated the utility of Pekin ducks as surrogates of infected waterfowl to model the wild bird/gallinaceous poultry interface for introduction of H5N8 HPAIV into terrestrial poultry, where contact turkeys served as a susceptible host. Detection of H5N8-specific antibody up to 58 dpi assured the value of serologic surveillance in farmed ducks by hemagglutination inhibition and anti-nucleoprotein ELISAs.

Muscarinic Receptors, from Synaptic Plasticity to its Role in Network Activity

Acetylcholine acting via metabotropic receptors plays a key role in learning and memory by regulating synaptic plasticity and circuit activity. However, a recent overall view of the effects of muscarinic acetylcholine receptors (mAChRs) on excitatory and inhibitory long-term synaptic plasticity and on circuit activity is lacking. This review focusses on specific aspects of the regulation of synaptic plasticity and circuit activity by mAChRs in the hippocampus and cortex. Acetylcholine increases the excitability of pyramidal neurons, facilitating the generation of dendritic Ca²⁺-spikes, NMDA-spikes and action potential bursts which provide the main source of Ca²⁺ influx necessary to induce synaptic plasticity. The activation of mAChRs induced Ca²⁺ release from intracellular IP₃-sensitive stores is a major player in the induction of a NMDA independent long-term potentiation (LTP) caused by an increased expression of AMPA receptors in hippocampal pyramidal neuron dendritic spines. In the neocortex, activation of mAChRs also induces a long-term enhancement of excitatory postsynaptic currents. In addition to effects on excitatory synapses, a single brief activation of mAChRs together with short repeated membrane depolarization can induce a long-term enhancement of GABA A type (GABA_A) inhibition through an increased expression of GABA_A receptors in hippocampal pyramidal neurons. By contrast, a long term depression of GABA_A inhibition (iLTD) is induced by muscarinic receptor activation in the absence of postsynaptic depolarizations. This iLTD is caused by an endocannabinoid-mediated presynaptic inhibition that reduces the GABA release probability at the terminals of inhibitory interneurons. This bidirectional long-term plasticity of inhibition may dynamically regulate the excitatory/inhibitory balance depending on the quiescent or active state of the postsynaptic pyramidal neurons. Therefore, acetylcholine can induce varied effects on neuronal activity and circuit behavior that can enhance sensory detection and processing through the modification of circuit activity leading to learning, memory and behavior.

Investigation into the Pathology of Idiopathic Systemic Amyloidosis in Four Captive Badgers (Meles meles)

Systemic idiopathic amyloidosis was described in four captive badgers (Meles meles). Two animals (B1 and B2) were not enrolled in any trial, while animals B3 and B4 took part in a vaccine efficacy study and had been challenged with Mycobacterium bovis. A full set of tissues was collected and processed routinely for histopathological, immunohistochemical and ultrastructural studies. Splenomegaly was found in three out of four animals. Histopathological evaluation revealed congophilic, permanganate-resistant systemic amyloid deposits in the tissues of all badgers. Animals B2 and B4 displayed a marked granulomatous response to amyloid within the spleen. Animals B1 and B2 also displayed clinicopathological findings suggestive of chronic kidney disease. Ultrastructural examination identified peculiar star-shaped arrays of amyloid. Immunohistochemical studies were unrewarding. Systemic amyloidosis should be considered among the differentials of wasting in captive badgers.

Subclinical BCG-osis in a Captive Badger (Meles meles) with Lymphoma

Subclinical systemic dissemination of Bacillus Calmette-Guérin (BCG) is described in a captive badger (Meles meles) with lymphoma. An adult female European badger was vaccinated per os with BCG and after 8 weeks post-mortem examination identified marked lymphadenomegaly and multinodular hepatic lesions. The histopathology and immunohistochemistry confirmed a multicentric T-cell lymphoma, associated with high BCG bacterial load in numerous tissues. The histology did not identify BCG-associated lesions. The scenario suggested that the T-cell lymphoma likely favoured the dissemination of the BCG ('BCG-osis'). Given that lymphoma is rare in badgers, this neoplasm should not interfere with the efficacy of large-scale vaccination programmes.

Detection of H3N8 influenza A virus with multiple mammalian-adaptive mutations in a rescued Grey seal (Halichoerus grypus) pup

Avian influenza A viruses (IAVs) in different species of seals display a spectrum of pathogenicity, from sub-clinical infection to mass mortality events. Here we present an investigation of avian IAV infection in a 3- to 4-month-old Grey seal (Halichoerus grypus) pup, rescued from St Michael's Mount, Cornwall in 2017. The pup underwent medical treatment but died after two weeks; post-mortem examination and histology indicated sepsis as the cause of death. IAV NP antigen was detected by immunohistochemistry in the nasal mucosa, and sensitive real-time reverse transcription polymerase chain reaction assays detected trace amounts of viral RNA within the lower respiratory tract, suggesting that the infection may have been cleared naturally. IAV prevalence among Grey seals may therefore be underestimated. Moreover, contact with humans during the rescue raised concerns about potential zoonotic risk. Nucleotide sequencing revealed the virus to be of subtype H3N8. Combining a GISAID database BLAST search and time-scaled phylogenetic analyses, we inferred that the seal virus originated from an unsampled, locally circulating (in Northern Europe) viruses, likely from wild Anseriformes. From examining the protein alignments, we found several residue changes in the seal virus that did not occur in the bird viruses, including D701N in the PB2 segment, a rare mutation, and a hallmark of mammalian adaptation of bird viruses. IAVs of H3N8 subtype have been noted for their particular ability to cross the species barrier and cause productive infections, including historical records suggesting that they may have caused the 1889 pandemic. Therefore, infections such as the one we report here may be of interest to pandemic surveillance and risk and help us better understand the determinants and drivers of mammalian adaptation in influenza.

Transmission dynamics between infected waterfowl and terrestrial poultry: Differences between the transmission and tropism of H5N8 highly pathogenic avian influenza virus (clade 2.3.4.4a) among ducks, chickens and turkeys

H5N8 highly-pathogenic avian influenza viruses (HPAIVs, clade 2.3.4.4) have spread globally via migratory waterfowl. Pekin ducks infected with a UK virus (H5N8-2014) served as the donors of infection in three separate cohousing experiments to attempt onward transmission chains to sequentially introduced groups of contact ducks, chickens and turkeys. Efficient transmission occurred among ducks and turkeys up to the third contact stage, with all (100%) birds becoming infected. Introduction of an additional fourth contact group of ducks to the turkey transmission chain demonstrated retention of H5N8-2014's waterfowl-competent adaptation. However, onward transmission ceased in chickens at the second contact stage where only 13% became infected. Analysis of viral progeny at this contact stage revealed no emergent polymorphisms in the intra-species (duck) transmission chain, but both terrestrial species included changes in the polymerase and accessory genes. Typical HPAIV pathogenesis and mortality occurred in infected chickens and turkeys, contrasting with 5% mortality among ducks.

Health outcomes, utilization, and equity in Chile: an evolution from 1990 to 2015 and the effects of the last health reform

OBJECTIVE

Chile is an attractive case study because of the deep political changes that it underwent over a short period of time: from a universal health service (60s), through a neoliberal reform (70s) and onto a series of legislative reforms (80s-90s). This article aims to explore and assess the evolution of health outcomes, equity, and utilization in Chile through the last period of these reforms (1990-2015).

STUDY DESIGN

Standardized health equity analysis.

METHODS

We conducted a standardized economic analysis on health equity and healthcare utilization using the ADePT software (by the World Bank) and using data from the Chilean National Socio-economic Survey. We evaluated trends of health equity and examined concentration curves of health utilization of healthcare services and health outcomes such as children/elder/pregnant nutritional status, self-reported health, and physical limitations.

RESULTS

Health outcomes such as nutritional problems in children and pregnant women were concentrated among the poor, while others such as high-relevance health conditions were similar for poorest and richest households. The concentration indexes for health outcomes suggested that income makes the distribution pro-poor. However, the opposite was true for age, in which the probability of health problems among rich individuals increased with age. The concentration curves for utilization of healthcare services showed that dental visits, laboratory exams, specialty visits, and hospitalizations were concentrated on the richest households, while the use of emergency services and preventive medicine were highly concentrated among poor individuals.

CONCLUSIONS

Although a positive trend in the increase of healthcare service use among income groups was observed, a significant impact of the latest health reform was not observed.

Novel Salmonella Variant Associated with Mortality in Two Great Spotted Woodpeckers (Dendrocopos major)

Two adult Great Spotted Woodpeckers (Dendrocopos major) from separate sites in Great Britain were examined postmortem in 2013 and 2016. A Salmonella sp. was isolated from multiple tissues in both birds. Histopathology and immunohistochemistry confirmed disseminated salmonellosis. Whole-genome sequencing and biochemical analyses putatively identified both isolates as a novel variant of Salmonella enterica subsp. enterica serovar Hessarek (S. Hessarek). Salmonellosis has seldom been reported in Piciformes, and never before in association with S. Hessarek infection. These findings, therefore, add to current knowledge regarding the range of wild bird species susceptible to this Salmonella serovar, and our understanding of the pathogens affecting Great Spotted Woodpeckers, in particular.

Detection of non-notifiable H4N6 avian influenza virus in poultry in Great Britain

A 12-month pilot project for notifiable avian disease (NAD) exclusion testing in chicken and turkey flocks in Great Britain (GB) offered, in partnership with industry, opportunities to carry out differential diagnosis in flocks where NAD was not suspected, and to identify undetected or undiagnosed infections. In May 2014, clinical samples received from a broiler breeder chicken premises that had been experiencing health and production problems for approximately one week tested positive by avian influenza (AI) real-time reverse transcription polymerase chain reaction (RRT-PCR). Following immediate escalation to an official, statutory investigation to rule out the presence of notifiable AI virus (AIV; H5 or H7 subtypes), a non-notifiable H4N6 low pathogenicity (LP) AIV was detected through virus isolation in embryonated specific pathogen free (SPF) fowls' eggs, neuraminidase inhibition test, cleavage site sequencing and AIV subtype H4-specific serology. Premises movement restrictions were lifted, and no further disease control measures were implemented as per the United Kingdom (UK) legislation. Phylogenetic analysis of the haemagglutinin and neuraminidase genes of the virus revealed closest relationships to viruses from Mallard ducks in Sweden during 2007 and 2009. In June 2014, clinical suspicion of NAD was reported in a flock of free-range laying chickens elsewhere in GB, due to increasing daily mortality and reduced egg production over a five-day period. An H4N6 LPAIV with an intravenous pathogenicity index of 0.50 was isolated. This virus was genetically highly similar, but not identical, to the virus detected during May 2014. Full viral genome analyses showed characteristics of a strain that had not recently transferred from wild birds, implying spread within the poultry sector had occurred. A stalk deletion in the neuraminidase gene sequence indicated an adaptation of the virus to poultry. Furthermore, there was unexpected evidence of systemic spread of the virus on post-mortem. No other cases were reported. Infection with LPAIVs often result in variable clinical presentation in poultry, making detection of disease more difficult.

Salmonella Enteritidis ST183: emerging and endemic biotypes affecting western European hedgehogs (Erinaceus europaeus) and people in Great Britain

The impacts of hedgehog (Erinaceus europaeus) Salmonella infection on public health and on animal welfare and conservation are unknown. We isolated Salmonella Enteritidis multi-locus sequence-type (ST)183 from 46/170 (27%) hedgehog carcasses (27 S. Enteritidis phage type (PT)11, 18 of a novel PT66 biotype and one with co-infection of these PTs) and from 6/208 (3%) hedgehog faecal samples (4 PT11, 2 PT66) from across Great Britain, 2012–2015. Whole genome phylogenetic analysis of the hedgehog isolates and ST183 from people in England and Wales found that PT11 and PT66 form two divergent clades. Hedgehog and human isolates were interspersed throughout the phylogeny indicating that infections in both species originate from a common population. PT11 was recovered from hedgehogs across England and Scotland, consistent with endemic infection. PT66 was isolated from Scotland only, possibly indicating a recent emergence event. People infected with ST183 were four times more likely to be aged 0–4 years than people infected by the more common ST11 S. Enteritidis. Evidence for human ST183 infection being non-foodborne included stronger correlation between geographic and genetic distance, and significantly increased likelihood of infection in rural areas, than for ST11. These results are consistent with hedgehogs acting as a source of zoonotic infection.

Pathobiological investigation of naturally infected canine rabies cases from Sri Lanka

Background

The recommended screening of rabies in ‘suspect’ animal cases involves testing fresh brain tissue. The preservation of fresh tissue however can be difficult under field conditions and formalin fixation provides a simple alternative that may allow a confirmatory diagnosis. The occurrence and location of histopathological changes and immunohistochemical (IHC) labelling for rabies in formalin fixed paraffin embedded (FFPE) canine brain is described in samples from 57 rabies suspect cases from Sri-Lanka. The presence of Negri bodies and immunohistochemical detection of rabies virus antigen were evaluated in the cortex, hippocampus, cerebellum and brainstem. The effect of autolysis and artefactual degeneration of the tissue was also assessed.

Results

Rabies was confirmed in 53 of 57 (93%) cases by IHC. IHC labelling was statistically more abundant in the brainstem. Negri bodies were observed in 32 of 53 (60.4%) of the positive cases. Although tissue degradation had no effect on IHC diagnosis, it was associated with an inability to detect Negri bodies. In 13 cases, a confirmatory Polymerase chain reaction (PCR) testing for rabies virus RNA was undertaken by extracting RNA from fresh frozen tissue, and also attempted using FFPE samples. PCR detection using fresh frozen samples was in agreement with the IHC results. The PCR method from FFPE tissues was suitable for control material but unsuccessful in our field cases.

Conclusions

Histopathological examination of the brain is essential to define the differential diagnoses of behaviour modifying conditions in rabies virus negative cases, but it is unreliable as the sole method for rabies diagnosis, particularly where artefactual change has occurred. Formalin fixation and paraffin embedding does not prevent detection of rabies virus via IHC labelling even where artefactual degeneration has occurred. This could represent a pragmatic secondary assay for rabies diagnosis in the field because formalin fixation can prevent sample degeneration. The brain stem was shown to be the site with most viral immunoreactivity; supporting recommended sampling protocols in favour of improved necropsy safety in the field. PCR testing of formalin fixed tissue may be successful in certain circumstances as an alternative test.

Outcome of Patients with Venous Thromboembolism and Factor V Leiden or Prothrombin 20210 Carrier Mutations During the Course of Anticoagulation

BACKGROUND

Individuals with factor V Leiden or prothrombin G20210A mutations are at a higher risk to develop venous thromboembolism. However, the influence of these polymorphisms on patient outcome during anticoagulant therapy has not been consistently explored.

METHODS

We used the Registro Informatizado de Enfermedad TromboEmbólica database to compare rates of venous thromboembolism recurrence and bleeding events occurring during the anticoagulation course in factor V Leiden carriers, prothrombin mutation carriers, and noncarriers.

RESULTS

Between March 2001 and December 2015, 10,139 patients underwent thrombophilia testing. Of these, 1384 were factor V Leiden carriers, 1115 were prothrombin mutation carriers, and 7640 were noncarriers. During the anticoagulation course, 160 patients developed recurrent deep vein thrombosis and 94 patients developed pulmonary embolism (16 died); 154 patients had major bleeding (10 died), and 291 patients had nonmajor bleeding. On multivariable analysis, factor V Leiden carriers had a similar rate of venous thromboembolism recurrence (adjusted hazard ratio [HR], 1.16; 95% confidence interval [CI], 0.82-1.64), half the rate of major bleeding (adjusted HR, 0.50; 95% CI, 0.25-0.99) and a nonsignificantly lower rate of nonmajor bleeding (adjusted HR, 0.66; 95% CI, 0.43-1.01) than noncarriers. Prothrombin mutation carriers and noncarriers had a comparable rate of venous thromboembolism recurrence (adjusted HR, 1.00; 95% CI, 0.68-1.48), major bleeding (adjusted HR, 0.75; 95% CI, 0.42-1.34), and nonmajor bleeding events (adjusted HR, 1.10; 95% CI, 0.77-1.57).

CONCLUSIONS

During the anticoagulation course, factor V Leiden carriers had a similar risk for venous thromboembolism recurrence and half the risk for major bleeding compared with noncarriers. This finding may contribute to decision-making regarding anticoagulation duration in selected factor V Leiden carriers with venous thromboembolism.