Age distribution of dengue cases in southern Vietnam from 2000 to 2015.

BACKGROUND: Dengue is the most common vector-borne viral infection. In recent times, an increase in the age of cases with clinical dengue has been reported in the national surveillance system and published literature of Vietnam. This change not only alter the risk of transmission and disease burden in different populations but also will impact for prevention and control strategies. A retrospective study was conducted from 2000 to 2015 in 19 provinces of southern Vietnam to describe the changes in age distribution of dengue cases and circulating serotypes. METHODOLOGY/PRINCIPAL FINDINGS: The study is a time trend analysis of the data aggregated from the database of dengue surveillance system. The database consisted of clinically diagnosed and laboratory-confirmed cases of dengue in southern Vietnam from 2000 to 2015. In the study period, the mean age of dengue cases increased from 12.2 ± 8.8 years old (y/o) to 16.8 ± 13.3 y/o between 2000 and 2015. Majority of severe cases were observed in the age group of 5-9 y/o and 10-14 y/o. Overall, the mortality and case fatality rates (CFR) were lowest during 2010 to 2015, and all four serotypes of dengue were observed. CONCLUSIONS/SIGNIFICANCE: With the exception of severe form, the age distribution of clinical cases of dengue appears to be shifting towards older age groups. An increase in the mean age of clinical cases of dengue has been observed in southern Vietnam over the past decade, and the highest incidence was observed in age group of 5-14 y/o. All serotypes of dengue were in circulation.

Seroepidemiological study of Japanese encephalitis virus in Chiang Mai: Immunity and susceptibility 28 years after introduction of a vaccination programme.

BACKGROUND: Thailand has introduced a nationwide vaccination against Japanese encephalitis virus (JEV) into National Immunization Programme since the 1990's. To improve the understanding of immunity and susceptibility of the population after 28 years of a vaccination programme, we conducted a JEV seroepidemiological study in a JEV-endemic area of Thailand. METHODS: An age-stratified, population-based, seroepidemiological study was conducted in Chiang Mai, Thailand-a northern Thai province where is an endemic area of Japanese encephalitis. Nine districts were chosen based on administrative definition: rural (n = 3); urban (n = 3); and peri-urban (n = 3). Within each district, eligible participants were randomly selected from 3 age groups: adolescents (10-20 years); adults (21-50 years); and older adults/elderly (≥51 years) by computer randomization. Plaque reduction neutralization tests (PRNT50 and PRNT90) were performed to measure neutralizing antibodies to JEV. To account for the cross-reactivity of JEV and other flaviviruses, JEV seroprotection was defined according to age, previous history of JEV vaccination, and PRNT50/PRNT90 levels of study participants. RESULTS: Overall, 279 adolescents, 297 adults, and 297 older adults/elderly were enrolled from nine districts. Age-stratified, protocol-defined, cluster-adjusted JEV seroprotection rates were 61% (95% CI: 48-73%), 43% (95% CI: 31-57%), and 52% (95% CI: 37-67%) for adolescents, adults, and older adults/elderly, respectively. Living in peri-urban districts, having a history of prior dengue virus infection, and previously receiving mouse brain-derived JEV vaccine were significantly associated with seroprotection to JEV in adolescents. Older age and male sex were associated with seroprotection for adults; and only male sex was the associated factor for older adults/elderly (P <0.05). CONCLUSIONS: Approximately half of population living in a JEV-endemic area demonstrated seroprotection to JEV. Ongoing nationwide surveillance on JEV seropepidemiology is an important strategy to understand the evolving population-level immunity to JEV, and to help formulating the appropriate recommendations on JE immunization.

Estimating dengue transmission intensity from serological data: A comparative analysis using mixture and catalytic models.

BACKGROUND: Dengue virus (DENV) infection is a global health concern of increasing magnitude. To target intervention strategies, accurate estimates of the force of infection (FOI) are necessary. Catalytic models have been widely used to estimate DENV FOI and rely on a binary classification of serostatus as seropositive or seronegative, according to pre-defined antibody thresholds. Previous work has demonstrated the use of thresholds can cause serostatus misclassification and biased estimates. In contrast, mixture models do not rely on thresholds and use the full distribution of antibody titres. To date, there has been limited application of mixture models to estimate DENV FOI. METHODS: We compare the application of mixture models and time-constant and time-varying catalytic models to simulated data and to serological data collected in Vietnam from 2004 to 2009 (N ≥ 2178) and Indonesia in 2014 (N = 3194). RESULTS: The simulation study showed larger mean FOI estimate bias from the time-constant and time-varying catalytic models (-0.007 (95% Confidence Interval (CI): -0.069, 0.029) and -0.006 (95% CI -0.095, 0.043)) than from the mixture model (0.001 (95% CI -0.036, 0.065)). Coverage of the true FOI was > 95% for estimates from both the time-varying catalytic and mixture model, however the latter had reduced uncertainty. When applied to real data from Vietnam, the mixture model frequently produced higher FOI and seroprevalence estimates than the catalytic models. CONCLUSIONS: Our results suggest mixture models represent valid, potentially less biased, alternatives to catalytic models, which could be particularly useful when estimating FOI from data with largely overlapping antibody titre distributions.

Influenza in Malaysian adult patients hospitalized with community-acquired pneumonia, acute exacerbation of chronic obstructive pulmonary disease or asthma: a multicenter, active surveillance study.

BACKGROUND: Available data on influenza burden across Southeast Asia are largely limited to pediatric populations, with inconsistent findings. METHODS: We conducted a multicenter, hospital-based active surveillance study of adults in Malaysia with community-acquired pneumonia (CAP), acute exacerbation of chronic obstructive pulmonary disease (AECOPD) and acute exacerbation of asthma (AEBA), who had influenza-like illness ≤10 days before hospitalization. We estimated the rate of laboratory-confirmed influenza and associated complications over 13 months (July 2018-August 2019) and described the distribution of causative influenza strains. We evaluated predictors of laboratory-confirmed influenza and severe clinical outcomes using multivariate analysis. RESULTS: Of 1106 included patients, 114 (10.3%) were influenza-positive; most were influenza A (85.1%), with A/H1N1pdm09 being the predominant circulating strain during the study following a shift from A/H3N2 from January-February 2019 onwards. In multivariate analyses, an absence of comorbidities (none versus any comorbidity [OR (95%CI), 0.565 (0.329-0.970)], p = 0.038) and of dyspnea (0.544 (0.341-0.868)], p = 0.011) were associated with increased risk of influenza positivity. Overall, 184/1106 (16.6%) patients were admitted to intensive care or high-dependency units (ICU/HDU) (13.2% were influenza positive) and 26/1106 (2.4%) died (2.6% were influenza positive). Males were more likely to have a severe outcome (ICU/HDU admission or death). CONCLUSIONS: Influenza was a significant contributor to hospitalizations associated with CAP, AECOPD and AEBA. However, it was not associated with ICU/HDU admission in this population. Study registration, NMRR ID: NMRR-17-889-35,174.

Quantifying the annual incidence and underestimation of seasonal influenza: A modelling approach.

BACKGROUND: Seasonal influenza poses a significant public health and economic burden, associated with the outcome of infection and resulting complications. The true burden of the disease is difficult to capture due to the wide range of presentation, from asymptomatic cases to non-respiratory complications such as cardiovascular events, and its seasonal variability. An understanding of the magnitude of the true annual incidence of influenza is important to support prevention and control policy development and to evaluate the impact of preventative measures such as vaccination. METHODS: We use a dynamic disease transmission model, laboratory-confirmed influenza surveillance data, and randomized-controlled trial (RCT) data to quantify the underestimation factor, expansion factor, and symptomatic influenza illnesses in the US and Canada during the 2011-2012 and 2012-2013 influenza seasons. RESULTS: Based on 2 case definitions, we estimate between 0.42-3.2% and 0.33-1.2% of symptomatic influenza illnesses were laboratory-confirmed in Canada during the 2011-2012 and 2012-2013 seasons, respectively. In the US, we estimate between 0.08-0.61% and 0.07-0.33% of symptomatic influenza illnesses were laboratory-confirmed in the 2011-2012 and 2012-2013 seasons, respectively. We estimated the symptomatic influenza illnesses in Canada to be 0.32-2.4 million in 2011-2012 and 1.8-8.2 million in 2012-2013. In the US, we estimate the number of symptomatic influenza illnesses to be 4.4-34 million in 2011-2012 and 23-102 million in 2012-2013. CONCLUSIONS: We illustrate that monitoring a representative group within a population may aid in effectively modelling the transmission of infectious diseases such as influenza. In particular, the utilization of RCTs in models may enhance the accuracy of epidemiological parameter estimation.

Estimated dengue force of infection and burden of primary infections among Indian children.

BACKGROUND: Comprehensive, age-stratified dengue surveillance data are unavailable from India and many more dengue cases occur than are reported. Additional information on dengue transmission dynamics can inform understanding of disease endemicity and infection risk. METHODS: Using age-stratified dengue IgG seroprevalence data from 2556 Indian children aged 5-10 years, we estimated annual force of infection (FOI) at each of 6 sites using a binomial regression model. We estimated the ages by which 50 and 70% of children were first infected; and predicted seroprevalence in children aged 1-10 years assuming constant force-of-infection. Applying these infection rates to national census data, we then calculated the number of primary dengue infections occurring, annually, in Indian children. RESULTS: Annual force-of-infection at all sites combined was 11.9% (95% CI 8.8-16.2), varying across sites from 3.5% (95% CI 2.8-4.4) to 21.2% (95% CI 18.4-24.5). Overall, 50 and 70% of children were infected by 5.8 (95% CI 4.3-7.9) and 10.1 (95% CI 7.4-13.7) years respectively. In all sites except Kalyani, > 70% of children had been infected before their 11th birthday, and goodness-of-fit statistics indicated a relatively constant force-of-infection over time except at two sites (Wardha and Hyderabad). Nationwide, we estimated 17,013,527 children (95% CI: 14,518,438- 19,218,733), equivalent to 6.5% of children aged < 11 years, experience their first infection annually. CONCLUSIONS: Dengue force-of-infection in India is comparable to other highly endemic countries. Significant variation across sites exists, likely reflecting local epidemiological variation. The number of annual primary infections is indicative of a significant, under-reported burden of secondary infections and symptomatic episodes. TRIAL REGISTRATION: Registered retrospectively with clinicaltrials.gov ( NCT01477671 ; 18/11/2011) and clinical trials registry of India (ctri.nic.in; CTRI/2011/12/002243 ; 15/12/2011). Date of enrollment of 1st subject: 22/9/2011.

Serological Evidence of Japanese Encephalitis Virus Circulation in Asian Children From Dengue-Endemic Countries.

Background: Japanese encephalitis virus (JEV) is a zoonotic, mosquito-borne flavivirus, distributed across Asia. Infections are mostly mild or asymptomatic, but symptoms include neurological disorders, sequelae, and fatalities. Data to inform control strategies are limited due to incomplete case reporting. Methods: We used JEV serological data from a multicountry Asian dengue vaccine study in children aged 2-14 years to describe JEV endemicity, measuring antibodies by plaque reduction neutralization test (PRNT50). Results: A total 1479 unvaccinated subjects were included. A minimal estimate of pediatric JEV seroprevalence in dengue-naive individuals was 8.1% in Indonesia, 5.8% in Malaysia, 10.8% in the Philippines, and 30.7% in Vietnam, translating to annual infection risks varying from 0.8% (in Malaysia) to 5.2% (in Vietnam). JEV seroprevalence and annual infection estimates were much higher in children with history of dengue infection, indicating cross-neutralization within the JEV PRNT50 assay. Conclusions: These data confirm JEV transmission across predominantly urban areas and support a greater emphasis on JEV case finding, diagnosis, and prevention.

Geographic variation in dengue seroprevalence and force of infection in the urban paediatric population of Indonesia.

Understanding the heterogeneous nature of dengue transmission is important for prioritizing and guiding the implementation of prevention strategies. However, passive surveillance data in endemic countries are rarely adequately informative. We analyzed data from a cluster-sample, cross-sectional seroprevalence study in 1-18 year-olds to investigate geographic differences in dengue seroprevalence and force of infection in Indonesia. We used catalytic models to estimate the force of infection in each of the 30 randomly selected sub-districts. Based on these estimates, we determined the proportion of sub-districts expected to reach seroprevalence levels of 50%, 70% and 90% by year of age. We used population averaged generalized estimating equation models to investigate individual- and cluster-level determinants of dengue seropositivity. Dengue force of infection varied substantially across Indonesia, ranging from 4.3% to 30.0% between sub-districts. By age nine, 60% of sub-districts are expected to have a seroprevalence ≥70%, rising to 83% by age 11. Higher odds of seropositivity were associated with higher population density (OR = 1.54 per 10-fold rise in population density, 95% CI: 1.03-2.32) and with City (relative to Regency) administrative status (OR = 1.92, 95% CI: 1.32-2.79). Our findings highlight the substantial variation in dengue endemicity within Indonesia and the importance of understanding spatial heterogeneity in dengue transmission intensity for optimal dengue prevention strategies including future implementation of dengue vaccination programmes.

Dengue virus serotype distribution based on serological evidence in pediatric urban population in Indonesia.

BACKGROUND: Dengue is a febrile illness transmitted by mosquitoes, causing disease across the tropical and sub-tropical world. Antibody prevalence data and serotype distributions describe population-level risk and inform public health decision-making. METHODOLOGY/PRINCIPAL FINDINGS: In this cross-sectional study we used data from a pediatric dengue seroprevalence study to describe historical dengue serotype circulation, according to age and geographic location. A sub-sample of 780 dengue IgG-positive sera, collected from 30 sites across urban Indonesia in 2014, were tested by the plaque reduction neutralization test (PRNT) to measure the prevalence and concentration of serotype-specific neutralizing antibodies according to subject age and geography. PRNT results were obtained from 776 subjects with mean age of 9.6 years. 765 (98.6%) neutralized one or more dengue serotype at a threshold of >10 (1/dil). Multitypic profiles were observed in 50.9% of the samples; a proportion which increased to 63.1% in subjects aged 15-18 years. Amongst monotypic samples, the highest proportion was reactive against DENV-2, followed by DENV-1, and DENV-3, with some variation across the country. DENV-4 was the least common serotype. The highest anti-dengue antibody titers were recorded against DENV-2, and increased with age to a geometric mean of 516.5 [1/dil] in the oldest age group. CONCLUSIONS/SIGNIFICANCE: We found that all four dengue serotypes have been widely circulating in most of urban Indonesia, and more than half of children had already been exposed to >1 dengue serotype, demonstrating intense transmission often associated with more severe clinical episodes. These data will help inform policymakers and highlight the importance of dengue surveillance, prevention and control.

Correction: Dengue seroprevalence and force of primary infection in a representative population of urban dwelling Indonesian children.

[This corrects the article DOI: 10.1371/journal.pntd.0005621.].

Systematic review of seroepidemiological studies on Japanese encephalitis in the Republic of Korea.

BACKGROUND: Countries with strong vaccination programmes, including the Republic of Korea, have experienced changes in the epidemiology of Japanese encephalitis (JE), with an increase in cases seen among adults. However, the reasons for this increase are not clearly understood. This study describes the change in age-specific JE virus (JEV) seroprevalence over time in Korea, with a view to understanding this transition. METHODS: A search of Embase, MEDLINE, PubMed, KoreaMed, Korea Education and Research Information Service, National Library of Korea, and the Seoul National University Medical Library was conducted using the keywords 'Japanese encephalitis' combined with 'Korea', 'seroprevalence', 'seropositivity', 'seroepidemiology', 'serosurvey', 'immunity', and 'antibody'. RESULTS: Eighteen studies published between 1946 and 2012 were retrieved. In 1946, seropositivity was 51% in the 1-10 years age group, 79% in those aged 11-20 years, and 94% in those ≥61 years of age. In the 1970s, seropositivity in children and adolescents was low (10-59%); seropositivity in this group increased to 90-92% in 1984-1985, and increased further to 98% in 2012. Seropositivity among adults aged 41-50 years and 51-60 years in the 2010s ranged between 83.1% and 97.9% and between 77.5% and 98.3%, respectively. CONCLUSIONS: The implementation of the universal JE vaccination programme in the 1980s has increased the seroprevalence of JEV in Korea, especially in children who are targeted for vaccination.

Dengue seroprevalence and force of primary infection in a representative population of urban dwelling Indonesian children.

BACKGROUND: Indonesia reports the second highest dengue disease burden in the world; these data are from passive surveillance reports and are likely to be significant underestimates. Age-stratified seroprevalence data are relatively unbiased indicators of past exposure and allow understanding of transmission dynamics. METHODOLOGY/PRINCIPAL FINDINGS: To better understand dengue infection history and associated risk factors in Indonesia, a representative population-based cross-sectional dengue seroprevalence study was conducted in 1-18-year-old urban children. From October to November 2014, 3,210 children were enrolled from 30 geographically dispersed clusters. Serum samples were tested for anti-dengue IgG antibodies by indirect ELISA. A questionnaire investigated associations between dengue serologic status and household socio-demographic and behavioural factors. Overall, 3,194 samples were tested, giving an adjusted national seroprevalence in this urban population of 69.4% [95% CI: 64.4-74.3] (33.8% [95% CI: 26.4-41.2] in the 1-4-year-olds, 65.4% [95% CI: 69.1-71.7] in the 5-9-year-olds, 83.1% [95% CI: 77.1-89.0] in the 10-14-year-olds, and 89.0% [95% CI: 83.9-94.1] in the 15-18-year-olds). The median age of seroconversion estimated through a linear model was 4.8 years. Using a catalytic model and considering a constant force of infection we estimated 13.1% of children experience a primary infection per year. Through a hierarchical logistic multivariate model, the subject's age group (1-4 vs 5-9 OR = 4.25; 1-4 vs. 10-14 OR = 12.60; and 1-4 vs 15-18 OR = 21.87; p<0.0001) and the number of cases diagnosed in the household since the subject was born (p = 0.0004) remained associated with dengue serological status. CONCLUSIONS/SIGNIFICANCE: This is the first dengue seroprevalence study in Indonesia that is targeting a representative sample of the urban paediatric population. This study revealed that more than 80% of children aged 10 years or over have experienced dengue infection at least once. Prospective incidence studies would likely reveal dengue burdens far in excess of reported incidence rates.

Symptomatic Dengue Disease in Five Southeast Asian Countries: Epidemiological Evidence from a Dengue Vaccine Trial.

Dengue incidence has increased globally, but empirical burden estimates are scarce. Prospective methods are best-able to capture all severities of disease. CYD14 was an observer-blinded dengue vaccine study conducted in children 2-14 years of age in Indonesia, Malaysia, Thailand, the Philippines, and Vietnam. The control group received no vaccine and resembled a prospective, observational study. We calculated the rates of dengue according to different laboratory or clinical criteria to make inferences about dengue burden, and compared with rates reported in the passive surveillance systems to calculate expansion factors which describe under-reporting. Over 6,933 person-years of observation in the control group there were 319 virologically confirmed dengue cases, a crude attack rate of 4.6%/year. Of these, 92 cases (28.8%) were clinically diagnosed as dengue fever or dengue hemorrhagic fever by investigators and 227 were not, indicating that most symptomatic disease fails to satisfy existing case definitions. When examining different case definitions, there was an inverse relationship between clinical severity and observed incidence rates. CYD14's active surveillance system captured a greater proportion of symptomatic dengue than national passive surveillance systems, giving rise to expansion factors ranging from 0.5 to 31.7. This analysis showed substantial, unpredictable and variable under-reporting of symptomatic dengue, even within a controlled clinical trial environment, and emphasizes that burden estimates are highly sensitive to case definitions. These data will assist in generating disease burden estimates and have important policy implications when considering the introduction and health economics of dengue prevention and control interventions.

Recent epidemiological trends of dengue in the French territories of the Americas (2000-2012): a systematic literature review.

UNLABELLED: Dengue is a public health concern across the globe, and an escalating problem in the Americas. As part of a wider programme (covering Latin America and South East Asia) to characterize the epidemiology of dengue in dengue endemic areas, we undertook a systematic literature review to assess epidemiological trends (incidence, timing and duration of outbreaks/epidemics, age and sex distribution, serotype distribution, seroprevalence and disease severity) for dengue across the French Territories of the Americas (FTA), in French Guiana, Guadeloupe, Martinique, Saint Martin and Saint Barthélemy between 2000 and 2012 (CRD42012002341: http://www.crd.york.ac.uk/prospero/display_record.asp?ID=CRD42012002341). Of 413 relevant data sources identified, 45 were eligible for inclusion. A large proportion of the available data were from national surveillance reports, and 12 publications were from peer-reviewed journals. During the review period, 3-5 epidemics were identified in each of the island territories and French Guiana, and epidemics were often associated with a shift in the predominant circulating dengue virus serotype. Substantial gaps in epidemiological knowledge were identified. In particular, information regarding dengue virus genotype distribution, seroprevalence and age distribution of dengue were lacking. Additionally, much of the available data were from epidemic years; data from inter-epidemic periods were sparse. Nevertheless, the available epidemiological data showed that dengue is endemic across the FTA and suggest an evolution towards hyperendemicity, highlighting the need to continue the efforts with the existing surveillance programmes to assist in planning an effective vaccination programme once a dengue vaccine is deployed. PROTOCOL REGISTRATION: PROSPERO CRD42012002341.

Vaccination using phase I vaccine is effective to control Coxiella burnetii shedding in infected dairy cattle herds.

The effectiveness of the vaccination of dairy cows combined or not with antibiotics (i.e. oxytetracycline) to control Coxiella burnetii (Cb) shedding at herd level was investigated in 77 Q fever clinically affected herds. In addition to nulliparous heifers' vaccination, one out of the four following medical strategies was randomly assigned to dairy cows in each herd: vaccination (using a phase I vaccine) alone, vaccination combined with oxytetracycline, oxytetracycline alone or nothing. Their effectiveness to reduce Cb load in quarterly samples of bulk tank milk (BTM) and of pooled milk of primiparous (MP) was assessed through logistic hierarchical models. A significant reduction in Cb load was observed in herds where the vaccination of ≥80% of dairy cows was implemented; whereas the use of antibiotics was uneffective. Our findings support the interest of a whole vaccination strategy and provide evidence for decreasing the use of antibiotics in dairy cattle herds.

Effectiveness of vaccination and antibiotics to control Coxiella burnetii shedding around calving in dairy cows.

Effectiveness of phase 1 vaccine, combined or not with tetracycline, to control Coxiella burnetii vaginal shedding at calving in cows was assessed through a 13 months study in 22 Q fever clinically affected commercial dairy herds. Four medical strategies implemented at herd level but randomly assigned to cows (vaccination, vaccination and tetracycline, tetracycline, nothing) were compared. There was no significant interaction effect between vaccination and antibiotherapy. Tetracycline used once at drying off was associated with a lower risk of being detected shedder at calving (OR=0.40, CI 95% [0.21-0.75]), but had no significant effect on the bacterial load shed. Vaccination did not significantly prevent shedding but was significantly (OR=0.15, CI 95% [0.03-0.85]) associated with lower bacterial load shed. Thus, vaccination using a phase 1 vaccine and antibiotherapy using tetracycline is associated with a decrease in shedding in dairy cows and could contribute to reduce the bacterial load generated in the environment. To the best of our knowledge, this is the first study providing useful information for evidenced-based and rational use of medical strategy combining antibiotic and vaccination in infected dairy cattle herds.

Seroprevalence of Q fever in naturally infected dairy cattle herds.

Coxiella burnetii is the causal agent of Q fever, a worldwide spread zoonosis. Prevention of C. burnetii shedding in cattle is critical to control the spread of the pathogen between animals, and from animals to humans. Vaccination with a phase 1 vaccine has been shown to be effective in preventing shedding when implemented in still susceptible animals, even in infected cattle herds. The identification of these animals (dairy cows and nulliparous females) as targets for vaccination consequently is crucial. Hygiene measures conventionally also are implemented, but their relative impact on C. burnetii diffusion remains unknown. The objectives of this study therefore were to (i) describe the distribution of the within-herd apparent seroprevalence among cows and nulliparous females and (ii) to explore the association between management practices and herd characteristics on the one hand, and these seroprevalences on the other. In a sample of 100 naturally and clinically infected dairy herds, blood samples were taken systematically from all nulliparous females (older than 12 months) and cows, and serologically tested. Information on herd characteristics and management practices were collected through a questionnaire filled in by each farmer. The variation in within-herd seroprevalence among cows and the risk for a herd of having at least one seropositive nulliparous female were investigated using multivariate (linear and logistic respectively) regression models. Median within-herd seroprevalence was 0.32 (Q1=0.22; Q3=0.43). We observed a low to null (median=0.01; Q1=0; Q3=0.10) within-herd seroprevalence in nulliparous females contrary to a high value (median=0.42) and variability (Q1=0.28; Q3=0.56) in cows. Only a few herd characteristics and management practices were found to be related to seroprevalence. Within-herd seroprevalence in cows was found to be significantly (P<0.10) higher in herds (i) with a number of cows<46, (ii) with seasonal calving, and (iii) with grazing or contact through the fence with other ruminant herds. The risk of having at least one seropositive nulliparous female was increased in herds (i) with seasonal calving and (ii) where the foetus and/or the placenta of aborted cows were not systematically removed. Our findings support, in addition to the implementation of high level of hygiene measures, the relevance of vaccination (at least in nulliparous females) as a method to control the spread of C. burnetii within an infected herd, as vaccination is effective in susceptible animals and given that nulliparous females are mostly not infected even in infected herds.

Prevalence of Coxiella burnetii infection in domestic ruminants: a critical review.

Reliable detection of Coxiella burnetii is a critical point for the control of the spread of this zoonotic disease (Q fever), ruminants being considered as the main source for human infection as confirmed by the recent human outbreak in the Netherlands since 2007. Considering both public and animal health, providing consolidated prevalence data could be relevant within the decision process of public policy makers or producers organizations. The objective of this study was to conduct a critical review of the literature focused on the prevalence of C. burnetii infection at animal, herd and within-herd levels in cattle, goat and sheep. A qualitative assessment of the 69 selected publications, based on the analysis of the sampling frame and testing procedures, was also performed. While the number of publications increased recently, major methodological issues were still evidenced. These critical issues were related to (i) the absence of description of the sampling strategy and (ii) the lack of sensitivity of the testing procedure. The lack of well designed studies makes not possible to estimate accurately the current prevalence of the infection. Nevertheless, the literature review reported the detection of C. burnetii infection in the all 5 continents with a wide range whatever the species. The apparent prevalence was slightly higher in cattle (20.0% and 37.7% of mean apparent prevalence at animal and herd level respectively) than in small ruminants (around 15.0% and 25% respectively for animal and herd level in sheep and goat). The present conclusions and the current situation support the persistent need of conducting well designed studies, aiming at estimating the true prevalence of C. burnetii infection in the three main domestic ruminant species.