Nonchromosomal birth defects and risk of childhood acute leukemia: An assessment in 15 000 leukemia cases and 46 000 controls from the Childhood Cancer and Leukemia International Consortium

Although recent studies have demonstrated associations between nonchromosomal birth defects and several pediatric cancers, less is known about their role on childhood leukemia susceptibility. Using data from the Childhood Cancer and Leukemia International Consortium, we evaluated associations between nonchromosomal birth defects and childhood leukemia. Pooling consortium data from 18 questionnaire-based and three registry-based case-control studies across 13 countries, we used multivariable logistic regression models to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for the association between a spectrum of birth defects and leukemia. Our analyses included acute lymphoblastic leukemia (ALL, n = 13 115) and acute myeloid leukemia (AML, n = 2120) cases, along with 46 172 controls. We used the false discovery rate to account for multiple comparisons. In the questionnaire-based studies, the prevalence of birth defects was 5% among cases vs 4% in controls, whereas, in the registry-based studies, the prevalence was 11% among cases vs 7% in controls. In pooled adjusted analyses, there were several notable associations, including (1) digestive system defects and ALL (OR = 2.70, 95% CI: 1.46-4.98); (2) congenital anomalies of the heart and circulatory system and AML (OR = 2.86, 95% CI: 1.81-4.52) and (3) nervous system defects and AML (OR = 4.23, 95% CI: 1.50-11.89). Effect sizes were generally larger in registry-based studies. Overall, our results could point to novel genetic and environmental factors associated with birth defects that could also increase leukemia susceptibility. Additionally, differences between questionnaire- and registry-based studies point to the importance of complementary sources of birth defect phenotype data when exploring these associations.

Associations between birth defects with neural crest cell origins and pediatric embryonal tumors

BACKGROUND

There are few assessments evaluating associations between birth defects with neural crest cell developmental origins (BDNCOs) and embryonal tumors, which are characterized by undifferentiated cells having a molecular profile similar to neural crest cells. The effect of BDNCOs on embryonal tumors was estimated to explore potential shared etiologic pathways and genetic origins.

METHODS

With the use of a multistate, registry-linkage cohort study, BDNCO-embryonal tumor associations were evaluated by generating hazard ratios (HRs) and 95% confidence intervals (CIs) with Cox regression models. BDNCOs consisted of ear, face, and neck defects, Hirschsprung disease, and a selection of congenital heart defects. Embryonal tumors included neuroblastoma, nephroblastoma, and hepatoblastoma. Potential HR modification (HRM) was investigated by infant sex, maternal race/ethnicity, maternal age, and maternal education.

RESULTS

The risk of embryonal tumors among those with BDNCOs was 0.09% (co-occurring n = 105) compared to 0.03% (95% CI, 0.03%-0.04%) among those without a birth defect. Children with BDNCOs were 4.2 times (95% CI, 3.5-5.1 times) as likely to be diagnosed with an embryonal tumor compared to children born without a birth defect. BDNCOs were strongly associated with hepatoblastoma (HR, 16.1; 95% CI, 11.3-22.9), and the HRs for neuroblastoma (3.1; 95% CI, 2.3-4.2) and nephroblastoma (2.9; 95% CI, 1.9-4.4) were elevated. There was no notable HRM by the aforementioned factors.

CONCLUSIONS

Children with BDNCOs are more likely to develop embryonal tumors compared to children without a birth defect. Disruptions of shared developmental pathways may contribute to both phenotypes, which could inform future genomic assessments and cancer surveillance strategies of these conditions.

Ethnic disparities in childhood leukemia survival by border residence: A Texas population-based analysis

BACKGROUND

The US-Mexico border is a medically underserved region where survival disparities have been observed in adults diagnosed and treated for various malignancies. Studies examining survival disparities among children living in this region and diagnosed with cancer are lacking. The objective of this study was to evaluate the impact of border residence on survival among children with acute lymphoblastic leukemia (ALL), acute myeloid leukemia (AML), and living near the Texas-Mexico border at the time of their diagnosis. The authors hypothesized that this group experiences inferior survival compared with patients with childhood leukemia living in nonborder areas.

METHODS

The authors conducted a retrospective survival analysis leveraging data from the Texas Cancer Registry. The study included patients aged birth to 19 years who were diagnosed with ALL or AML between 1995 and 2017. Cox proportional hazards models were used to evaluate the factors associated with the risk of death. Overall survival estimates were calculated using Kaplan-Meier methods.

RESULTS

During the study period, there were 6002 children diagnosed with ALL and 1279 diagnosed with AML. Inferior 5-year overall survival was observed among children with ALL living along the border region compared with those living in nonborder areas (77.5% vs. 85.8%). In adjusted models, children with ALL living along the border experienced a 30% increased hazard of death versus children living in nonborder areas. In contrast, for children with AML, survival estimates did not vary by border versus nonborder residence.

CONCLUSIONS

Living along the border was associated with inferior survival among children with ALL, but not among children with AML. Additional studies are urgently needed to identify the factors driving these disparities to effectively design multilevel interventions and influence state and national cancer control programs.

A population-based assessment of metastatic hepatoblastoma in Texas reveals ethnic disparities

Background

Hepatoblastoma (HB) is the most common primary liver cancer in children with emerging evidence that incidence is increasing globally. While overall survival for low risk hepatoblastoma is >90%, children with metastatic disease have worse survival. As identifying factors associated with high-risk disease is critical for improving outcomes for these children, a need for a further understanding of the epidemiology of hepatoblastoma is warranted. Therefore, we conducted a population-based epidemiologic study of hepatoblastoma in Texas, a large state characterized by ethnic and geographic diversity.

Methods

Information on children diagnosed with hepatoblastoma at 0-19 years of age for the period of 1995-2018 was obtained from the Texas Cancer Registry (TCR). Demographic and clinical variables including sex, race/ethnicity, age at diagnosis, urban-rural status, and residence along the Texas-Mexico border were evaluated. Multivariable Poisson regression was used to calculate adjusted incidence rate ratios (aIRRs) and 95% confidence intervals (CIs) for each variable of interest. Joinpoint regression analysis was used to determine the trend in incidence of hepatoblastoma, overall and by ethnicity.

Results

Overall, 309 children diagnosed with hepatoblastoma in Texas for the period of 1995-2018. Joinpoint regression analysis showed no joinpoints in the overall or the ethnic-specific analyses. Over this period, the incidence increased at 4.59% annually; with the annual percent change higher among Latinos (5.12%) compared to non-Latinos (3.15%). Among these children, 57 (18%) had metastatic disease at diagnosis. Factors associated with hepatoblastoma included male sex (aIRR = 1.5, 95% CI: 1.2-1.8, p = 0.002); infancy (aIRR = 7.6, 95% CI: 6.0-9.7, p < 0.001); and Latino ethnicity (aIRR = 1.3, 95% CI: 1.0-1.7, p = 0.04). Additionally, children living in rural areas were less likely to develop hepatoblastoma (aIRR = 0.6, 95% CI: 0.4-1.0, p = 0.03). While residence on the Texas-Mexico border association with hepatoblastoma approached statistical significance (p = 0.06) in unadjusted models, this finding did not remain significant after adjusting for Latino ethnicity. The two factors associated with being diagnosed with metastatic hepatoblastoma included Latino ethnicity (aIRR = 2.1, 95% CI: 1.1-3.8, p = 0.02) and male sex (aIRR = 2.4, 95% CI: 1.3-4.3, p = 0.003).

Conclusions

In this large population-based study of hepatoblastoma, we found several factors associated with hepatoblastoma and metastatic disease. The reasons for a higher burden of hepatoblastoma among Latino children is unclear but could be due to differences in geographic genetic ancestry, environmental exposures, or other unmeasured factors. Additionally, it is notable that Latino children were also more likely to be diagnosed with metastatic hepatoblastoma compared to non-Latino white children. To our knowledge, this has not been previously reported and warrants further study to delineate the causes of this disparity and identify interventions to improve outcomes.

The Epidemiology of Biliary Atresia: Exploring the Role of Developmental Factors on Birth Prevalence

OBJECTIVE

To identify key epidemiologic factors relevant to fetal development that are associated with biliary atresia.

STUDY DESIGN

This population-based registry study examined infants born in Texas between 1999 and 2014. Epidemiologic data relevant to fetal development were compared between cases of biliary atresia identified in the Texas Birth Defects Registry (n = 305) vs all live births (n = 4 689 920), and Poisson regression was used to calculate prevalence ratios (PRs) and 95% CIs.

RESULTS

The prevalence of biliary atresia over the study period was 0.65 per 10 000 live births. Biliary atresia was positively associated with female sex (adjusted PR, 1.68; 95% CI, 1.33-2.12), delivery before 32-37 weeks of gestation (adjusted PR, 1.64; 95% CI, 1.18-2.29), delivery before 32 weeks of gestation (adjusted PR, 3.85; 95% CI, 2.38-6.22), and non-Hispanic Black vs non-Hispanic White maternal race/ethnicity (adjusted PR, 1.54, 95% CI, 1.06-2.24), while biliary atresia was inversely associated with season of conception in the fall relative to spring (adjusted PR, 0.62; 95% CI, 0.45-0.86). In addition, biliary atresia was associated with maternal diabetes (adjusted PR, 2.34; 95% CI, 1.57-3.48), with a stronger association with pregestational diabetes compared with gestational diabetes. In subgroup analyses, these associations were present in isolated biliary atresia cases that do not have any additional birth defects.

CONCLUSIONS

Biliary atresia is associated with multiple factors related to fetal development, including pregestational maternal diabetes, female sex, and preterm birth. These associations also were observed in isolated cases of biliary atresia without other malformations or laterality defects. Our results are consistent with early life events influencing the pathogenesis of biliary atresia, and support further studies investigating in utero events to better understand etiology and time of onset.

Medical radiation exposure and risk of sporadic retinoblastoma

BACKGROUND

While there is evidence that parental exposure to medical radiation is associated with increased risk of sporadic bilateral retinoblastoma in offspring, this association has not been confirmed. Additionally, the relationship between paternal and maternal exposures and sporadic unilateral retinoblastoma has not been fully investigated.

PROCEDURE

Data were obtained from two large multicenter case-control studies of retinoblastoma. For the paternal analyses, 268 bilateral cases, 155 unilateral cases, and 358 controls were included. For the maternal analyses, 298 bilateral cases, 184 unilateral cases, and 404 controls were included. Logistical regression models were used to estimate odds ratios (OR) and 95% confidence intervals (CI) to evaluate the associations between parental exposures to medical radiation and sporadic retinoblastoma, while adjusting for potential confounders.

RESULTS

Paternal exposure to medical radiation was not significantly associated with sporadic bilateral retinoblastoma in offspring. However, increasing paternal exposure to gonadal radiation was associated with increased risk of unilateral retinoblastoma (P-trend = .03). Maternal history of upper and lower gastrointestinal (GI) series was associated with bilateral retinoblastoma (OR = 1.9, 95% CI: 1.1-3.2 and OR = 6.9, 95% CI: 2.9-16.4, respectively). However, there was no association between maternal exposure to medical radiation and unilateral retinoblastoma in offspring.

CONCLUSION

Our investigation adds to the evidence that medical radiation exposure in fathers as well as mothers prior to pregnancy may increase the risk of germline alterations leading to the development of retinoblastoma in their offspring. However, our findings could point to a more complex etiological framework for this important pediatric malignancy.

Cancer diagnostic profile in children with structural birth defects: An assessment in 15,000 childhood cancer cases

BACKGROUND

Birth defects are established risk factors for childhood cancer. Nonetheless, cancer epidemiology in children with birth defects is not well characterized.

METHODS

Using data from population-based registries in 4 US states, this study compared children with cancer but no birth defects (n = 13,111) with children with cancer and 1 or more nonsyndromic birth defects (n = 1616). The objective was to evaluate cancer diagnostic characteristics, including tumor type, age at diagnosis, and stage at diagnosis.

RESULTS

Compared with the general population of children with cancer, children with birth defects were diagnosed with more embryonal tumors (26.6% vs 18.7%; q < 0.001), including neuroblastoma (12.5% vs 8.2%; q < 0.001) and hepatoblastoma (5.0% vs 1.3%; q < 0.001), but fewer hematologic malignancies, including acute lymphoblastic leukemia (12.4% vs 24.4%; q < 0.001). In age-stratified analyses, differences in tumor type were evident among children younger than 1 year and children 1 to 4 years old, but they were attenuated among children 5 years of age or older. The age at diagnosis was younger in children with birth defects for most cancers, including leukemia, lymphoma, astrocytoma, medulloblastoma, ependymoma, embryonal tumors, and germ cell tumors (all q < 0.05).

CONCLUSIONS

The results indicate possible etiologic heterogeneity in children with birth defects, have implications for future surveillance efforts, and raise the possibility of differential cancer ascertainment in children with birth defects.

LAY SUMMARY

Scientific studies suggest that children with birth defects are at increased risk for cancer. However, these studies have not been able to determine whether important tumor characteristics, such as the type of tumor diagnosed, the age at which the tumor is diagnosed, and the degree to which the tumor has spread at the time of diagnosis, are different for children with birth defects and children without birth defects. This study attempts to answer these important questions. By doing so, it may help scientists and physicians to understand the causes of cancer in children with birth defects and diagnose cancer at earlier stages when it is more treatable.

Incidence and predictors of treatment-related conjugated hyperbilirubinemia during early treatment phases for children with acute lymphoblastic leukemia

Conjugated hyperbilirubinemia (CHB) and liver transaminase elevation are known complications of acute lymphoblastic leukemia (ALL) therapy, but host risk factors are poorly understood. Among 373 children diagnosed with ALL between 2011 and 2016, clinically significant CHB and transaminase elevation were observed in 15 (4.0%) and 12 (3.2%) children, respectively, during induction and consolidation. Body mass index ≥95th percentile (odds ratio 9.20, 95% confidence interval 2.56-32.96) was the only host factor independently associated with CHB, and no host factors were associated with transaminase elevation. Obese patients warrant closer monitoring of hepatic function to facilitate early intervention prior to the development of severe, adverse hepatic events.

Association Between Birth Defects and Cancer Risk Among Children and Adolescents in a Population-Based Assessment of 10 Million Live Births

Importance

Birth defects affect approximately 1 in 33 children. Some birth defects are known to be strongly associated with childhood cancer (eg, trisomy 21 and acute leukemia). However, comprehensive evaluations of childhood cancer risk in those with birth defects have been limited in previous studies by insufficient sample sizes.

Objectives

To identify specific birth defect-childhood cancer (BD-CC) associations and characterize cancer risk in children by increasing number of nonchromosomal birth defects.

Design, Setting, and Participants

This multistate, population-based registry linkage study pooled statewide data on births, birth defects, and cancer from Texas, Arkansas, Michigan, and North Carolina on 10 181 074 children born from January 1, 1992, to December 31, 2013. Children were followed up to 18 years of age for a diagnosis of cancer. Data were retrieved between September 26, 2016, and September 21, 2017, and data analysis was performed from September 2, 2017, to March 21, 2019.

Exposures

Birth defects diagnoses (chromosomal anomalies and nonchromosomal birth defects) recorded by statewide, population-based birth defects registries.

Main Outcomes and Measures

Cancer diagnosis before age 18 years, as recorded in state cancer registries. Cox regression models were used to generate hazard ratios (HRs) and 95% CIs to evaluate BD-CC associations and the association between number of nonchromosomal defects and cancer risk.

Results

Compared with children without any birth defects, children with chromosomal anomalies were 11.6 (95% CI, 10.4-12.9) times more likely to be diagnosed with cancer, whereas children with nonchromosomal birth defects were 2.5 (95% CI, 2.4-2.6) times more likely to be diagnosed with cancer before 18 years of age. An increasing number of nonchromosomal birth defects was associated with a corresponding increase in the risk of cancer. Children with 4 or more major birth defects were 5.9 (95% CI, 5.3-6.4) times more likely to be diagnosed with cancer compared with those without a birth defect. In the analysis of 72 specific BD-CC patterns, 40 HRs were statistically significant (adjusted P < .05) after accounting for multiple comparisons. Cancers most frequently associated with nonchromosomal defects were hepatoblastoma and neuroblastoma.

Conclusions and Relevance

Several significant and novel associations were observed between specific birth defects and cancers. Among children with nonchromosomal birth defects, the number of major birth defects diagnosed was significantly and directly associated with cancer risk. These findings could inform clinical treatment for children with birth defects and may elucidate mechanisms that lead to these complex outcomes.

Abstract 5054: Are co-occurring structural birth defects associated with risk of acute lymphoblastic leukemia among children with Down syndrome

Background: Children with Down syndrome (DS) have a 15- to 20-fold increased risk of developing acute leukemia (ALL). While children with DS typically also present with multiple co-occurring major and minor structural birth defects, very little is known about whether the number and type of these co-occurring birth defects in children with DS are associated with risk of ALL.

Methods: The Genetic Overlap Between Anomalies and Cancer in Kids (GOBACK) Study included linking data from population-based birth defects and cancer registries in Texas for the years 1999-2013. We performed a case-control analysis of ALL risk in participants diagnosed with DS. We evaluated the risk of ALL according to the presence of major birth defects in eight organ systems, as well as by the number of birth defects.

Results: We identified 7,684 children with DS (controls) and 81 children with DS-ALL (cases) from among 5.7 million live births. There was a high burden of co-occurring birth defects in both the DS and DS-ALL groups, with 97% compared to 98% being diagnosed with at least one co-occurring birth defect (p = 0.39), respectively, and 68% compared to 71% being diagnosed with at least one major birth defect (p = 0.33). Similar to what has been reported among the general population of ALL patients, children with DS and ALL had a significantly higher mean birthweight (3088 vs 2891 g, p &lt;0.001) than children with DS overall, and were born to older parents (mean maternal age 33.7 vs. 31.7 yrs, p = 0.01; mean paternal age 36.6 vs. 33.8 yrs, p = 0.02). Although there were trends towards increased prevalences of major birth defects overall and in most organ systems among the DS-ALL group, none reached statistical significance. Similarly, we identified a non-significantly greater mean number of total birth defects in the DS-ALL group (p = 0.2). Neither number of total birth defects nor number of major birth defects were associated with ALL in multivariable Cox regression models.

Conclusions: In this population-based assessment, we did not find strong evidence that co-occurring structural birth defects were related to ALL risk among children with DS. However, the small numbers of children with DS-ALL make it difficult to draw definitive conclusions.

Citation Format: Jeremy M. Schraw, Tiffany M. Chambers, John P. Woodhouse, Peter H. Langlois, Mark A. Canfield, Angela E. Scheuerle, Michael E. Scheurer, Sharon E. Plon, Karen R. Rabin, Philip J. Lupo. Are co-occurring structural birth defects associated with risk of acute lymphoblastic leukemia among children with Down syndrome [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5054.

Weight trends in a multiethnic cohort of pediatric acute lymphoblastic leukemia survivors: A longitudinal analysis

BACKGROUND

As survival rates for childhood acute lymphoblastic leukemia (ALL) continue to improve, there is growing concern over the chronic health conditions that survivors face. Given that survivors of childhood ALL are at increased risk of cardiovascular complications and obesity, we sought to characterize BMI trends from diagnosis through early survivorship in a multi-ethnic, contemporary cohort of childhood ALL patients and determine if early weight change was predictive of long-term weight status.

METHODS

The study population consisted of ALL patients aged 2-15 years at diagnosis who were treated with chemotherapy alone at Texas Children's Hospital. Each patient had BMI z-scores collected at diagnosis, 30-days post-diagnosis, and annually for five years. Linear regression models were estimated to evaluate the association between: 1) BMI z-score change in the first 30 days and BMI z-scores at five-years post-diagnosis; and 2) BMI z-score change in the first year post-diagnosis and BMI z-scores at five-years post-diagnosis.

RESULTS

This retrospective cohort study included longitudinal data from 121 eligible patients. The mean BMI z-scores for the population increased significantly (p-value<0.001) from baseline (mean = 0.25) to 30 days post-diagnosis (mean = 1.17) before plateauing after one year post-diagnosis (mean = 0.99). Baseline BMI z-scores were statistically significant predictors to five year BMI z-scores (p <0.001). Independent of baseline BMI z-score and other clinical factors, the BMI z-score at one year post-diagnosis was significantly associated with BMI z-score at five-years post-diagnosis (β = 0.63, p <0.001), while BMI z-score at 30 days post-diagnosis was not (β = 0.10, p = 0.23).

CONCLUSION

Our results suggest that weight gain within the first year after diagnosis is more strongly associated with long-term BMI than early weight gain (within 30 days). If confirmed, this information may help identify a window of time during therapy when ALL patients would benefit most from weight management directed interventions.

Perinatal and familial risk factors for soft tissue sarcomas in childhood through young adulthood: A population-based assessment in 4 million live births

Perinatal factors have been associated with soft tissue sarcomas (STS) in case-control studies. However, (i) the contributions of factors including fetal growth remain unknown, ( ii) these factors have not been examined in cohort studies and (iii) few assessments have evaluated risk in specific STS subtypes. We sought to identify the role of perinatal and familial factors on the risk of STS in a large population-based birth cohort. We identified 4,023,436 individuals in the Swedish Birth Registry born during 1973-2012. Subjects were linked to the Swedish Cancer Registry, where incident STS cases were identified. We evaluated perinatal and familial factors obtained from Statistics Sweden, including fetal growth, gestational age, and presence of a congenital malformation. Poisson regression was used to estimate incidence rate ratios (IRRs) and 95% confidence intervals (CIs) for associations between perinatal factors and STS overall, as well as by common subtypes. There were 673 individuals diagnosed with STS in 77.5 million person-years of follow-up. Having a congenital malformation was associated with STS (IRR = 1.70, 95% CI: 1.23-2.35). This association was stronger (IRR = 2.90, 95% CI: 1.25-6.71) in recent years (2000-2012). Low fetal growth was also associated with STS during the same time period (IRR = 1.86, 95% CI: 1.05-3.29). Being born preterm was associated with rhabdomyosarcoma (IRR = 1.74, 95% CI: 1.08-2.79). In our cohort study, those with congenital malformations and other adverse birth outcomes were more likely to develop a STS compared to their unaffected contemporaries. These associations may point to disrupted developmental pathways and genetic factors influencing the risk of STS.

Hypospadias Risk from Maternal Residential Exposure to Heavy Metal Hazardous Air Pollutants

Objective: Investigate whether residential prenatal exposure to heavy metal hazardous air pollutants (HMHAPs) is associated with an increased risk of hypospadias. Methods: Data on non-syndromic hypospadias cases (n = 8981) and control patients delivered in Texas were obtained from the Texas Birth Defects Registry and matched 1:10 by birth year. Average exposure concentrations of HMHAPs were obtained from the 2005 U.S. Environmental Protection Agency National-Scale Air Toxics Assessment and categorized into quintiles. Odds ratios and 95% confidence intervals were estimated. STROBE reporting guidelines were followed. Results: We observed associations between hypospadias and prenatal HMHAP exposure. Manganese demonstrated significant increased risk of hypospadias at the medium, medium-high and high exposure quintiles; lead in the medium-high and high exposure quintiles. Cadmium, mercury and nickel demonstrated a significant inverted "U-shaped" association for exposures with significant associations in the medium and medium-high quintiles but not in the medium-low and high quintiles. Arsenic and chromium demonstrated a significant bivalent association for risk of hypospadias in a lower quintile as well as a higher quintile with non-significant intermediate quintiles. Conclusions: Using data from one of the world's largest active surveillance birth defects registries, we identified significant associations between hypospadias and HMHAP exposures. These results should be used in counseling for maternal demographic risk factors as well as avoidance of heavy metals and their sources.

Hypospadias risk is increased with maternal residential exposure to hormonally active hazardous air pollutants

BACKGROUND

With the increasing birth prevalence of hypospadias, there is growing concern for pollutant exposure interfering with normal penile development. We assess the association between hypospadias and hormonally active hazardous air pollutants (HAHAPs) through a nationwide database of hazardous air pollutants and the Texas Birth Defects Registry (TBDR).

METHODS

Using the TBDR, we identified 8,981 nonsyndromic isolated hypospadias cases from 1999 to 2008. Birth certificate controls were matched for birth year at a 10:1 ratio to cases. Estimated HAHAP concentrations from the 2005 U.S. EPA National-Scale Air Toxics Assessment were used to assign exposure based on maternal residence at birth. Exposure levels were categorized as quintiles based on the distribution in controls. Logistic regression was used to calculate the odds ratio (OR) and 95% confidence interval (CI) for each increasing exposure category of selected HAHAPs.

RESULTS

Of the 10 HAHAPs studied, seven were significantly associated with hypospadias risk. The HAHAP that was most strongly associated with hypospadias was phenol, which was associated with risk in all groups except the high exposure group. Cumulative HAHAP exposure demonstrated a modest increase in hypospadias risk (OR 1.15, 95% CI: 1.07-1.24, p < 0.001) in the medium and medium-high quintiles.

CONCLUSIONS

While maternal exposure to some HAHAPs was significantly associated with the risk of hypospadias in male offspring, the effects were modest, and no dose-response effects were observed. Future work should employ biomarkers of exposure to better delineate the relationship.

Intermittent or uneven daily administration of low-dose hydroxyurea is effective in treating children with sickle cell anemia in Angola

BACKGROUND

Although hydroxyurea is proven effective in treatment of sickle cell anemia (SCA) and is widely prescribed in high-income countries, due to questions about feasibility of treating large numbers of patients in resource-limited health systems, its use is limited in sub-Saharan Africa (SSA), where most children with SCA live. We assessed hematological response and toxicity of hydroxyurea treatment for SCA in Angola.

METHODS

Retrospective study of children with SCA (not selected for clinical severity) treated on a fixed dose of hydroxyurea for at least 6 months. Because only the 500 mg capsule was available, dose was averaged weekly. We evaluated toxicity events and magnitude of hydroxyurea-induced changes in blood counts and compared patients who received a uniform daily dose to those prescribed intermittent or uneven daily doses.

RESULTS

Only 13% of 303 patients received a uniform dose of hydroxyurea daily. Dose ranged from 16.5 to 22.8 mg/kg/day. Hydroxyurea increased HGB and mean cell volume values by 0.5 g/dL (P < 0.0001) and 8 fL (P < 0.0001), while ANC, PLT, and ARC decreased 1.1 × 10⁹ /L (P < 0.0001), 34 × 10⁹ /L (P = < 0.0001), and 19 × 10⁹ /L (P = 0.0008), respectively. There were no differences in magnitude of hydroxyurea-induced changes between patients prescribed intermittent or uneven doses and uniform daily doses, or between those treated in the lower and higher dose quartiles. Hematological toxicity events were mild and reversible.

CONCLUSION

Intermittent or uneven daily dosing of hydroxyurea is as effective as fixed daily doses in treating SCA. This strategy may enable treatment of additional children with SCA in SSA.

Epidemiology of anophthalmia and microphthalmia: Prevalence and patterns in Texas, 1999-2009

Anophthalmia and microphthalmia are a set of rare, yet severe, birth defects considered to be part of a spectrum of developmental ocular malformations ranging from smaller than average to completely absent eyes. Despite their clinical significance, little is known about the etiologies of these conditions. The goal of this study was to expand our understanding of the epidemiology of anophthalmia and microphthalmia. Data for this population-based assessment were obtained from the Texas Birth Defects Registry (TBDR) and Center for Health Statistics for the period 1999-2009. Descriptive analyses and estimates of birth prevalence and prevalence ratios (PR) were determined for this defect. There were 1,262 definite anophthalmia and microphthalmia patients identified in the TBDR, with an overall combined prevalence of 3.0 per 10,000 live births. More than half (55.7%) of the patients had at least one chromosome abnormality or syndrome. In addition, 92.4% of nonsyndromic patients (i.e., have no recorded chromosome abnormalities or syndromes) had at least one additional birth defect. After adjustment for multiple factors, the prevalence of nonsyndromic anophthalmia and microphthalmia was higher among mothers who had ≥2 previous fetal deaths (PR = 1.43, 95% confidence interval [CI]: 1.03-1.97) and among mothers with any reported diabetes (PR = 2.08, 95% CI: 1.49-2.90). Our results confirm that children with anophthalmia and microphthalmia frequently have genetic syndromes or are born with other major birth defects. Our findings add to the limited body of literature on anophthalmia and microphthalmia as well as help define subgroups of women who are more likely to have children with this malformation.

Abstract LB-161: A population-based assessment of cancer risk among children with non-chromosomal birth defects in 10 million live births

Purpose: While cancer risk is increased among children with chromosomal birth defects, less is known about associations between specific non-chromosomal structural birth defects and specific childhood cancers. To investigate these, we established a population-based retrospective cohort of &gt;10 million children by pooling statewide registry data from four U.S. states (Texas, Michigan, North Carolina, and Arkansas) for the period 1992-2013.

Methods: Individual level data from birth certificates, birth defects registries, and cancer registries were linked in each state; demographic and diagnostic variables were harmonized; and the data were pooled for the overall analysis. We used Cox proportional hazards models to evaluate associations between 60 birth defects and 31 childhood cancers when there were five or more comorbid cases. A hazard ratio (HR) and 95% confidence interval (CI) was calculated for each birth defect-childhood cancer (BD-CC) pairwise combination, adjusted for maternal age, infant sex, and state. The false discovery rate (FDR) was computed via the Benjamini-Hochberg procedure to account for multiple comparisons.

Results: We identified 517,548 children with non-chromosomal structural birth defects and 14,774 children with cancer. The risk of any cancer was increased among children with any non-chromosomal structural defect compared to children without any birth defect (HR=2.6, 95% CI 2.4-2.7). Of 2,511 potential BD-CC combinations, we tested 606 where there were ≥5 comorbid cases and identified 496 BD-CC associations with significantly elevated HRs at a 5% FDR. No significant inverse associations were identified for any BD-CC combination. Notably, hepatoblastoma, astrocytoma, ependymoma, and extracranial germ cell tumors were each strongly associated with several birth defects. For example, the risk of hepatoblastoma was increased among children with atrial septal defects (HR=12.5, 95% CI 7.9-19.7) and craniosynostosis (HR=15.4, 95% CI 7.6-31.3). Astrocytoma and ependymoma were associated with central nervous system (CNS) defects (HR=6.7, 95% CI 4.6-9.8 and HR=7.4, 95%CI 3.5-15.7, respectively). Elevated risk of extracranial germ cell tumors was observed among children with CNS defects (HR=22.5, 95% CI 10.9-46.4) and obstructive genitourinary defects (HR=32.4, 95% CI 16.2-64.6).

Conclusions: By pooling registry data across four U.S. states, we were able to evaluate specific BD-CC patterns and report several novel associations. Our findings suggest that children with non-chromosomal birth defects have a significantly elevated risk of several childhood cancers. These findings may inform research into the etiologies of childhood cancer, as well as new cancer surveillance protocols for children with non-chromosomal birth defects. This work was supported by the Cancer Prevention Research Institute of Texas.

Citation Format: Jeremy M. Schraw, Tania A. Desrosiers, Wendy N. Nembhard, Glenn Copeland, Robert E. Meyer, Austin L. Brown, Tiffany M. Chambers, Heather E. Danysh, Saumya Sisoudiya, Chunqiao Luo, Amir Mian, Michael E. Scheurer, Sharon E. Plon, Philip J. Lupo. A population-based assessment of cancer risk among children with non-chromosomal birth defects in 10 million live births [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-161.

Interaction between anthelmintic treatment and vaccine responses in ponies naturally infected with cyathostomins

Anthelmintics and vaccines are commonly given concurrently in routine equine management, but it is unknown to what extent an interaction between the two exists. Cyathostomins can modulate the local immune response by stimulating a type 2 helper T cell (Th2) response. In addition, anti-inflammatory effects of ivermectin have been found in rodent models. It is unknown whether these anti-inflammatory effects affect the acute phase response elicited by commonly used vaccines. This study evaluated how the acute phase inflammatory response, leukocyte expression of pro-inflammatory cytokines, and vaccine-specific titers induced by simultaneous injection of three vaccines (West Nile Virus, Equine Herpes Rhinopneumonitis, and Keyhole Limpet Hemocyanin) were modulated by concurrent administration of ivermectin or pyrantel pamoate in ponies naturally infected with cyathostomins. Mixed-breed yearling ponies were blocked by gender and fecal strongyle egg count, then randomly assigned to three treatment groups: ivermectin (n=8), pyrantel pamoate (n=8), and control (n=7). All ponies received vaccinations intramuscularly on days 0 and 29, and anthelmintics were administered on the same days. Whole blood, serum and plasma samples were collected one, three and 14 days after each vaccination. Samples were analyzed for concentrations of acute phase reactants (haptoglobin, serum amyloid A, fibrinogen and iron), mRNA expression levels of cytokines (interleukin (IL)-1β, IL-4, IL-10, tumor necrosis factor (TNF)-α and interferon (IFN)-γ) in leukocytes, and vaccine-specific antibody titers. A marked acute-phase response was noted following both vaccinations. In contrast, the pattern of change in cytokine expression was less pronounced and more variable. Statistical differences were observed between groups for haptoglobin, fibrinogen, IL-1β, IL-4, and IL-10, but differences were generally small and none of the vaccine titers were different between the groups. Taken together, the study found some signs of modulation of immunologic or inflammatory responses to the administered vaccines, when anthelmintics were administered concurrently, but these are unlikely to have practical implications for vaccination routines.

Influenza A viruses with truncated NS1 as modified live virus vaccines: pilot studies of safety and efficacy in horses

REASONS FOR PERFORMING STUDY

Three previously described NS1 mutant equine influenza viruses encoding carboxy-terminally truncated NS1 proteins are impaired in their ability to inhibit type I IFN production in vitro and are replication attenuated, and thus are candidates for use as a modified live influenza virus vaccine in the horse.

HYPOTHESIS

One or more of these mutant viruses is safe when administered to horses, and recipient horses when challenged with wild-type influenza have reduced physiological and virological correlates of disease.

METHODS

Vaccination and challenge studies were done in horses, with measurement of pyrexia, clinical signs, virus shedding and systemic proinflammatory cytokines.

RESULTS

Aerosol or intranasal inoculation of horses with the viruses produced no adverse effects. Seronegative horses inoculated with the NS1-73 and NS1-126 viruses, but not the NS1-99 virus, shed detectable virus and generated significant levels of antibodies. Following challenge with wild-type influenza, horses vaccinated with NS1-126 virus did not develop fever (>38.5 degrees C), had significantly fewer clinical signs of illness and significantly reduced quantities of virus excreted for a shorter duration post challenge compared to unvaccinated controls. Mean levels of proinflammatory cytokines IL-1beta and IL-6 were significantly higher in control animals, and were positively correlated with peak viral shedding and pyrexia on Day +2 post challenge.

CONCLUSION AND CLINICAL RELEVANCE

These data suggest that the recombinant NS1 viruses are safe and effective as modified live virus vaccines against equine influenza. This type of reverse genetics-based vaccine can be easily updated by exchanging viral surface antigens to combat the problem of antigenic drift in influenza viruses.

Cultures of equine respiratory epithelial cells and organ explants as tools for the study of equine influenza virus infection

Equine nasal turbinate epithelial cells and tracheal rafts were maintained with sustained viability in culture. Both types of culture supported productive replication of equine influenza virus (equine-2, subtype H3N8) and cell death occurred through apoptosis following viral infection. Thus, primary respiratory epithelial cell and organ cultures of equine origin may be valuable as alternatives to the intact animal for studying the virus-host interaction of equine respiratory viruses including influenza.

A new modified live equine influenza virus vaccine: phenotypic stability, restricted spread and efficacy against heterologous virus challenge

Flu Avert IN vaccine is a new, live attenuated virus vaccine for equine influenza. We tested this vaccine in vivo to ascertain 1) its safety and stability when subjected to serial horse to horse passage, 2) whether it spread spontaneously from horse to horse and 3) its ability to protect against heterologous equine influenza challenge viruses of epidemiological relevance. For the stability study, the vaccine was administered to 5 ponies. Nasal swabs were collected and pooled fluids administered directly to 4 successive groups of naïve ponies by intranasal inoculation. Viruses isolated from the last group retained the vaccine's full attenuation phenotype, with no reversion to the wild-type virus phenotype or production of clinical influenza disease. The vaccine virus spread spontaneously to only 1 of 13 nonvaccinated horses/ponies when these were comingled with 39 vaccinates in the same field. For the heterologous protection study, a challenge model system was utilised in which vaccinated or naïve control horses and ponies were exposed to the challenge virus by inhalation of virus-containing aerosols. Challenge viruses included influenza A/equine-2/Kentucky/98, a recent representative of the 'American' lineage of equine-2 influenza viruses; and A/equine-2/Saskatoon/90, representative of the 'Eurasian' lineage. Clinical signs among challenged animals were recorded daily using a standardised scoring protocol. With both challenge viruses, control animals reliably contracted clinical signs of influenza, whereas vaccinated animals were reliably protected from clinical disease. These results demonstrate that Flu Avert IN vaccine is safe and phenotypically stable, has low spontaneous transmissibility and is effective in protecting horses against challenge viruses representative of those in circulation worldwide.

Diverged evolution of recent equine-2 influenza (H3N8) viruses in the Western Hemisphere

We reported previously that equine-2 influenza A virus (H3N8) had evolved into two genetically and antigenically distinct "Eurasian" and "American" lineages. Phylogenetic analysis, using the HA1 gene of more recent American isolates, indicated a further divergence of these viruses into three evolution lineages: A South American lineage, a Kentucky lineage, and a Florida lineage. These multiple evolution pathways were not due to geographic barriers, as viruses from different lineages co-circulated. For the Kentucky lineage, the evolution rate was estimated to be 0.89 amino acid substitutions per year, which agreed with the previously estimated rate of 0.8. For the South American lineage, the evolution rate was estimated to be only 0.27 amino acid substitutions per year. This low evolution rate was probably due to a unique alternating Ser138 to Ala138 substitutions at antigenic site A. For the Kentucky lineage, there was a preference for sequential nonsynonymous substitutions at antigenic site B, which was also a "hot spot" for amino acid substitutions. Convalescent sera had minimal cross-reactivity to viruses of different lineages, indicating antigenic distinctions among these viruses. In contrast to human H3N2 viruses, our results suggested that the evolution of equine-2 influenza virus resembled the multiple evolution pathways of influenza B virus.

The involvement of a stress-activated pathway in equine influenza virus-mediated apoptosis

We have shown elsewhere that equine-2 influenza virus (EIV; subtype H3N8) induced pronounced cell death in infected cells through apoptosis as demonstrated by DNA fragmentation assay and a combined TUNEL and immunostaining scheme. In this study, we investigated the mechanism of EIV-mediated cytotoxicity on a permissive mammalian epithelial cell line, Madin-Darby canine kidney (MDCK) cells. EIV infection increased the cellular levels of oxidative stress and c-Jun/AP-1 protein (which is known to be affected by oxidative stress), as well as its DNA binding activity. Increased production of TGF-beta1, an inducer of c-Jun N-terminal kinase or stress-activated protein kinase (JNK/SAPK) activation, was also detected in EIV-infected MDCK cells. It has been reported that TGF-beta may initiate a signaling cascade leading to JNK/SAPK activation. Addition of c-Jun antisense oligodeoxynucleotide, antioxidant N-acetyl-cysteine (NAC), JNK/SAPK inhibitor carvedilol, or TGF-beta-neutralizing antibody effectively blocked c-Jun/AP-1 upregulation and TGF-beta1 production mediated by EIV infection. These treatments also attenuated EIV-induced cytopathogenic effects (CPE) and apoptosis. Our results suggest that a stress-activated pathway is involved in apoptosis mediated by EIV infection. It is likely that EIV infection turns on the JNK/SAPK cascade, which modulates the activity of apoptosis-promoting regulatory factor c-Jun/AP-1 and epithelial growth inhibitory cytokine TGF-beta.

Derivation and characterization of a live attenuated equine influenza vaccine virus

OBJECTIVE

To develop and characterize a cold-adapted live attenuated equine-2 influenza virus effective as an intranasal vaccine.

ANIMALS

8 ponies approximately 18 months of age.

PROCEDURES

A wild-type equine-2 virus, A/Equine/Kentucky/1/91 (H3N8), was serially passaged in embryonated chicken eggs at temperatures gradually reduced in a stepwise manner from 34 C to 30 C to 28 C to 26 C. At different passages, infected allantoic fluids were tested for the ability of progeny virus to replicate in Madin-Darby canine kidney (MDCK) cells at 34 C and 39.5 C. Virus clones that replicated at 26 C in eggs and at 34 C in MDCK cells, but not at 39.5 C in MDCK cells, were tested for stability of the cold-adapted, temperature-sensitive (ts), and protein synthesis phenotypes. A stable clone, P821, was evaluated for safety, ability to replicate, and immunogenicity after intranasal administration in ponies.

RESULTS

Randomly selected clones from the 49th passage were all ts with plaquing efficiencies of < 10(-6) (ratio of 39.5 C:34 C) and retained this phenotype after 5 serial passages at 34 C in either embryonated eggs or MDCK cells. The clone selected as the vaccine candidate (P821) had the desired degree of attenuation. Administered intranasally to seronegative ponies, the virus caused no adverse reactions or overt signs of clinical disease, replicated in the upper portion of the respiratory tract, and induced a strong serum antibody response.

CONCLUSION AND CLINICAL RELEVANCE

A candidate live attenuated influenza vaccine virus was derived by cold-adaptation of a wild-type equine-2 influenza virus, A/Equine/Kentucky/1/91, in embryonated eggs.

Safety, efficacy, and immunogenicity of a modified-live equine influenza virus vaccine in ponies after induction of exercise-induced immunosuppression

OBJECTIVE

To determine safety, efficacy, and immunogenicity of an intranasal cold-adapted modified-live equine influenza virus vaccine administered to ponies following induction of exercise-induced immunosuppression.

DESIGN

Prospective study.

ANIMALS

Fifteen 9- to 15-month old ponies that had not had influenza.

PROCEDURE

Five ponies were vaccinated after 5 days of strenuous exercise on a high-speed treadmill, 5 were vaccinated without undergoing exercise, and 5 were not vaccinated or exercised and served as controls. Three months later, all ponies were challenged by nebulization of homologous equine influenza virus. Clinical and hematologic responses and viral shedding were monitored, and serum and nasal secretions were collected for determination of influenza-virus-specific antibody isotype responses.

RESULTS

Exercise caused immunosuppression, as indicated by depression of lymphocyte proliferation in response to pokeweed mitogen. Vaccination did not result in adverse clinical effects, and none of the vaccinated ponies developed clinical signs of infection following challenge exposure. In contrast, challenge exposure caused marked clinical signs of respiratory tract disease in 4 control ponies. Vaccinated and control ponies shed virus after challenge exposure. Antibody responses to vaccination were restricted to serum IgGa and IgGb responses in both vaccination groups. After challenge exposure, ponies in all groups generated serum IgGa and IgGb and nasal IgA responses. Patterns of serum hemagglutination inhibition titers were similar to patterns of IgGa and IgGb responses.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that administration of this MLV vaccine to ponies with exercise-induced immunosuppression was safe and that administration of a single dose to ponies provided clinical protection 3 months later.

Sialic acid species as a determinant of the host range of influenza A viruses

The distribution of sialic acid (SA) species varies among animal species, but the biological role of this variation is largely unknown. Influenza viruses differ in their ability to recognize SA-galactose (Gal) linkages, depending on the animal hosts from which they are isolated. For example, human viruses preferentially recognize SA linked to Gal by the alpha2,6(SAalpha2,6Gal) linkage, while equine viruses favor SAalpha2,3Gal. However, whether a difference in relative abundance of specific SA species (N-acetylneuraminic acid [NeuAc] and N-glycolylneuraminic acid [NeuGc]) among different animals affects the replicative potential of influenza viruses is uncertain. We therefore examined the requirement for the hemagglutinin (HA) for support of viral replication in horses, using viruses whose HAs differ in receptor specificity. A virus with an HA recognizing NeuAcalpha2,6Gal but not NeuAcalpha2,3Gal or NeuGcalpha2,3Gal failed to replicate in horses, while one with an HA recognizing the NeuGcalpha2,3Gal moiety replicated in horses. Furthermore, biochemical and immunohistochemical analyses and a lectin-binding assay demonstrated the abundance of the NeuGcalpha2,3Gal moiety in epithelial cells of horse trachea, indicating that recognition of this moiety is critical for viral replication in horses. Thus, these results provide evidence of a biological effect of different SA species in different animals.

Comparison of the phenotypes of Streptococcus zooepidemicus isolated from tonsils of healthy horses and specimens obtained from foals and donkeys with pneumonia

OBJECTIVE

To determine whether streptococcal pneumonia is caused by strains of Streptococcus zooepidemicus similar to those obtained from the tonsils of healthy horses.

SAMPLE POPULATION

5 tonsils from healthy horses, 8 tracheal washes and 6 lung specimens from foals with pneumonia, and 5 nasopharyngeal swab specimens from donkeys with acute bronchopneumonia.

PROCEDURE

Variable M-like protectively immunogenic SzP proteins of 5 isolates of S. zooepidemicus from each tonsil and clinical specimen were compared, using immunoblots. The SzP gene of 13 isolates representative of various SzP immunoblot phenotypes from 1 healthy horse and 9 horses and donkeys with pneumonia were sequenced and compared. Cell-associated hyaluronic acid concentration and resistance to phagocytosis of some isolates were measured.

RESULTS

Tonsils of each healthy horse were colonized by several SzP phenotypes similar to those of foals or donkeys with pneumonia. In contrast, multiple isolates from animals with pneumonia had the same SzP phenotype, indicating infection by a single strain or clone. Analysis of the SzP sequence confirmed that differences in immunoblot phenotype were associated with sequence differences and that several SzP genotypes were in healthy horses and animals with pneumonia. Isolates with high concentrations of cell-associated hyaluronic acid were more resistant to phagocytosis.

CONCLUSIONS AND CLINICAL RELEVANCE

An SzP-specific immunoblot is a useful, sensitive measure of diversity among strains of S. zooepidemicus. Single strains with SzP phenotypes similar to those found in tonsils of healthy horses cause pneumonia. Because of the diversity of SzP phenotype and genotype among isolates from animals with pneumonia, SzP phenotype is not an important determinant of invasiveness or epizootic capabilities.

Pharmacokinetics and therapeutic efficacy of rimantadine in horses experimentally infected with influenza virus A2

OBJECTIVE

To determine pharmacokinetics of single and multiple doses of rimantadine hydrochloride in horses and to evaluate prophylactic efficacy of rimantadine in influenza virus-infected horses.

ANIMALS

5 clinically normal horses and 8 horses seronegative to influenza A.

PROCEDURE

Horses were given rimantadine (7 mg/kg of body weight, i.v., once; 15 mg/kg, p.o., once; 30 mg/kg, p.o., once; and 30 mg/kg, p.o., q 12 h for 4 days) to determine disposition kinetics. Efficacy in induced infections was determined in horses seronegative to influenza virus A2. Rimantadine was administered (30 mg/kg, p.o., q 12 h for 7 days) beginning 12 hours before challenge-exposure to the virus.

RESULTS

Estimated mean peak plasma concentration of rimantadine after i.v. administration was 2.0 micrograms/ml, volume of distribution (mean +/- SD) at steady-state (Vdss) was 7.1 +/- 1.7 L/kg, plasma clearance after i.v. administration was 51 +/- 7 ml/min/kg, and beta-phase half-life was 2.0 +/- 0.4 hours. Oral administration of 15 mg of rimantadine/kg yielded peak plasma concentrations of < 50 ng/ml after 3 hours; a single oral administration of 30 mg/kg yielded mean peak plasma concentrations of 500 ng/ml with mean bioavailability (F) of 25%, beta-phase half-life of 2.2 +/- 0.3 hours, and clearance of 340 +/- 255 ml/min/kg. Multiple doses of rimantadine provided steady-state concentrations in plasma with peak and trough concentrations (mean +/- SEM) of 811 +/- 97 and 161 +/- 12 ng/ml, respectively. Rimantadine used prophylactically for induced influenza virus A2 infection was associated with significant decreases in rectal temperature and lung sounds.

CONCLUSIONS AND CLINICAL RELEVANCE

Oral administration of rimantadine to horses can safely ameliorate clinical signs of influenza virus infection.

Amantadine and equine influenza: pharmacology, pharmacokinetics and neurological effects in the horse

Amantadine is an antiviral agent effective against influenza A viruses. We investigated 1) the antiviral efficacy, 2) analytical detection, 3) bioavailability and disposition, 4) pharmacokinetic modelling and 5) adverse reactions of amantadine in the horse. In vitro, amantadine and its derivative rimantadine suppressed the replication of recent isolates of equine-2 influenza virus with effective doses (EDs) of less than 30 ng/ml. Rimantadine was more effective than amantadine against most viral isolates; we suggest a minimum plasma concentration of 300 ng/ml of amantadine for therapeutic efficacy. In vivo an i.v. dose of amantadine 15 mg/kg bwt produced mild, transient CNS signs which were no longer apparent after 30 min. Amantadine administered at a dose of 15 mg/kg bwt was established as the maximum safe single i.v. dose. However, if repeated i.v. administration of amantadine is required no more than 10 mg/kg bwt t.i.d. should be used. The maximal safe plasma concentration of amantadine was not evaluated but is probably greater than 2000 ng/ml and possibly greater than 4000 ng/ml. On the other hand, horses with lower seizure thresholds, or those on medications that lower seizure thresholds, may be at increased risk of amantadine-induced seizures, which show few premonitory signs and are rapidly fatal. After i.v. administration of amantadine 10 mg/kg bwt, the disposition kinetics were well fitted by a 2-compartment open model. The estimated peak plasma concentration after this dose was about 4500 ng/ml, the volume of distribution at steady-state (Vdss) was (mean +/- s.d.) 4.9 +/- 1.9 l/kg bwt and the beta phase half-life was 1.83 +/- 0.87 h. Computer projections of plasma amantadine concentrations after i.v. administration of amantadine at a dose of 10 mg/kg bwt t.i.d. at 8 h intervals suggest peak plasma concentrations of 4000-5000 ng/ml and troughs of less than 300 ng/ml will be achieved. Amantadine administered orally at 10 mg/kg bwt and 20 mg/kg bwt showed mean oral bioavailability of about 40-60% and a plasma half life of 3.4 +/- 1.4 h; however, there was substantial inter-animal variation in bioavailability. Projections based on the kinetics observed in individual animals suggest that some animals readily maintain effective plasma concentrations of amantadine after oral administration of 20 mg/kg bwt t.i.d. On the other hand, animals in which amantadine is poorly bioavailable may require up to a 6-fold (120 mg/kg bwt) increase in the oral dose to achieve effective blood concentrations. Withholding food for 15 h did not reduce these inter-animal differences in bioavailability. Our results showed that simple dosing with oral amantadine will not yield effective plasma concentrations in all animals. While i.v. administration yielded more reproducible plasma concentrations, care should be taken to see that the seizure threshold is not exceeded. In acute situations, i.v. administration (5 mg/kg bwt) every 4 h should maintain safe and effective plasma and respiratory tract concentrations of amantadine.

Antigenic and genetic evolution of equine H3N8 influenza A viruses

Evolution of equine influenza a H3N8 viruses was examined by antigenic and genetic analysis of a collection isolates from around the world. It was noted that antigenic and genetic variants of equine H3N8 viruses cocirculate, and in particular that variants currently circulating in Europe and the USA are distinguishable from one another both in terms of antigenic reactivity and genetic structure of the HA1 portion of the haemagglutinin (HA) molecule. Whilst the divergent evolution of American and European isolates may be due to geographical isolation of the two gene pools, some mixing is believed to occur as 'American-like' viruses have been isolated during outbreaks of equine influenza in the UK. The cocirculation of two antigenically and genetically distinct lineages of equine influenza H3N8 viruses has serious implications for vaccine strain selection.

Genetic and antigenic analysis of the influenza virus responsible for the 1992 Hong Kong equine influenza epizootic

An outbreak of influenza occurred among thoroughbred racehorses in Hong Kong in November-December 1992, with morbidity of 37%. All horses involved had been vaccinated against equine-1 and equine-2 influenza viruses but not against the virus responsible for the 1989 equine influenza outbreak in northern China (influenza A/equine/Jilin/89, subtype H3N8). Therefore the source and nature of the virus causing the Hong Kong outbreak was investigated. Virus isolated from a horse infected during the outbreak was used for genetic analysis. All the viral gene segments were similar to those of equine-2 (H3N8) influenza viruses and unrelated to those of equine/Jilin/89 virus. The nucleotide sequence of the viral hemagglutinin gene showed high homology (99.4%) to that of influenza A/equine/Suffolk/89 (H3N8) virus which has circulated extensively in Europe. However, these viruses differed in their antigenic reactivity to a panel of monoclonal antibodies. Preliminary epizootiological information plus the concordance of amino acid sequence between hemagglutinins of the Hong Kong isolate and a contemporaneous equine-2 influenza virus isolate from the United Kingdom indicated that the probable source of the Hong Kong outbreak was horses recently imported from England or Ireland.

Rapid diagnosis of equine influenza by the Directigen FLU-A enzyme immunoassay

The Directigen FLU-A enzyme immunoassay was tested for its ability to detect equine-2 influenza viruses in nasopharyngeal fluids from horses and ponies. A total of 125 swabs from experimental infections and from different sources of natural infection in the USA and Hong Kong were examined. The assay results were compared with the results of standard virus culture in embryonated chicken eggs or Madin-Darby canine kidney cells, and with the serology of the horses sampled. In comparison with virus culture the enzyme immunoassay exhibited 83 per cent sensitivity, 78 per cent specificity, 70 per cent positive predictive value and 88 per cent negative predictive value. The test appeared to be more sensitive than haemagglutination for the detection of low levels of virus in embryonated egg cultures. It also detected equine-1 influenza virus in culture. The test is rapid (15 minutes), simple, and should be a convenient method for the rapid diagnosis and screening of horses for equine influenza infection.

Sequence specificity of furin, a proprotein-processing endoprotease, for the hemagglutinin of a virulent avian influenza virus

The virulence of avian influenza viruses correlates with the sensitivity of their hemagglutinin (HA) to cellular proteases. Furin, a proprotein-processing subtilisin-related endoprotease, is a leading candidate for the enzyme that cleaves the HA of virulent avian viruses. We therefore compared the specificity of furin with those of proteases in a variety of cultured cells and in a rat Golgi fraction, using the HA cleavage mutants of a virulent avian influenza virus, A/Turkey/Ireland/1378/85 (H5N8). The results indicated similar sequence specificities among the endoproteases when purified furin was used. In experiments with the vaccinia virus expression system, overexpressed furin cleaved mutant HAs that were not recognized by the endogenous proteases, resulting in an apparent broader specificity of furin. These findings authenticate the proposed role of furin as an HA-activating protease in vivo and caution against the use of expression vectors to study protease sequence specificity.

Diagnosis of equine influenza by the polymerase chain reaction

Influenza A is a common respiratory infection of horses, and rapid diagnosis is important for its detection and control. Sensitive detection of influenza currently requires viral culture and is not always feasible. The polymerase chain reaction (PCR) was used to detect DNA produced by reverse transcription of equine influenza in stored nasal secretions, vaccines, and allantoic fluids. Primers directed at a target of 212 bp on conserved segment 7 (matrix gene) of human influenza A/Bangkok/1/79(H3N2) produced amplification products of appropriate size with influenza A/Equine/Prague/1/56 (H7N7), A/Equine/Miami/63 (H3N8), A/Equine/Kentucky/79 (H3N8), and A/Equine/Kentucky/2/91 (H3N8) in infected frozen allantoic fluids and in frozen extracts of nasal swabs of 2 horses with naturally acquired influenza. The products bound a 32P-labeled hybridization probe to an inner region of the target. Control samples, including nasal secretions from a horse infected with herpesvirus, were negative. In a prospective study, 2 ponies inhaled aerosols of influenza A/Equine/Kentucky/2/91 (H3N8), and thereafter supernatants of nasal swabs in transport medium were obtained daily for 10 days for culture and PCR. Amplification products were evaluated by size and binding of a 32P-labeled probe and also by dot-blotting and binding of a biotin-labeled probe. Culture detected influenza more consistently than did PCR in the first 2 days of infection, but PCR detected virus more often later in infection. Gels were the most sensitive, but radiometric and biotin-labeled probes gave specific results and were consistently positive from days 3-6. PCR is suitable for detection of equine influenza in clinical samples.

Cross-reactivity of existing equine influenza vaccines with a new strain of equine influenza virus from China

A novel strain of equine influenza virus, influenza A/equine/Jilin (China)/1/89, has emerged which is genetically distinct from all earlier strains of equine influenza. It is therefore possible that the vaccines against equine influenza may be unable to protect horses against disease caused by this virus strain. In vitro serological assays established that there were low levels of immunological cross-reactivity between the new virus, the current vaccine strains and the strains of equine-2 influenza virus now in circulation.

Evolution and ecology of influenza A viruses

In this review we examine the hypothesis that aquatic birds are the primordial source of all influenza viruses in other species and study the ecological features that permit the perpetuation of influenza viruses in aquatic avian species. Phylogenetic analysis of the nucleotide sequence of influenza A virus RNA segments coding for the spike proteins (HA, NA, and M2) and the internal proteins (PB2, PB1, PA, NP, M, and NS) from a wide range of hosts, geographical regions, and influenza A virus subtypes support the following conclusions. (i) Two partly overlapping reservoirs of influenza A viruses exist in migrating waterfowl and shorebirds throughout the world. These species harbor influenza viruses of all the known HA and NA subtypes. (ii) Influenza viruses have evolved into a number of host-specific lineages that are exemplified by the NP gene and include equine Prague/56, recent equine strains, classical swine and human strains, H13 gull strains, and all other avian strains. Other genes show similar patterns, but with extensive evidence of genetic reassortment. Geographical as well as host-specific lineages are evident. (iii) All of the influenza A viruses of mammalian sources originated from the avian gene pool, and it is possible that influenza B viruses also arose from the same source. (iv) The different virus lineages are predominantly host specific, but there are periodic exchanges of influenza virus genes or whole viruses between species, giving rise to pandemics of disease in humans, lower animals, and birds. (v) The influenza viruses currently circulating in humans and pigs in North America originated by transmission of all genes from the avian reservoir prior to the 1918 Spanish influenza pandemic; some of the genes have subsequently been replaced by others from the influenza gene pool in birds. (vi) The influenza virus gene pool in aquatic birds of the world is probably perpetuated by low-level transmission within that species throughout the year. (vii) There is evidence that most new human pandemic strains and variants have originated in southern China. (viii) There is speculation that pigs may serve as the intermediate host in genetic exchange between influenza viruses in avian and humans, but experimental evidence is lacking. (ix) Once the ecological properties of influenza viruses are understood, it may be possible to interdict the introduction of new influenza viruses into humans.

Protection of chickens from lethal influenza virus infection by influenza A/chicken/Pennsylvania/1/83 virus: characterization of the protective effect

The influenza A/chicken/Pennsylvania/1/83 (H5N2) virus is the first known example of an influenza virus isolated from a natural infection which contained primarily defective interfering particles (T. M. Chambers and R. G. Webster, J. Virol. 61, 1517-1523, 1987). In chickens, coinoculation of this virus together with the closely related but highly virulent influenza A/chicken/Pennsylvania/1370/83 virus results in reduced mortality compared to virulent virus infection alone (Bean et al., J. Virol. 54, 151-160, 1985). The biological basis of this protective effect has not been established. Protective activity required greater than or equal to 100-fold excess input of protecting virus over virulent virus, functioned effectively during the first generations of virulent virus multiplication, and also functioned against an antigenically heterologous (H7N7) virulent influenza virus. Protection was correlated with the complete inhibition of virulent virus spread to the brain of infected chickens. Plaque-purified chicken/Pennsylvania/1/83 virus depleted of defective interfering particles, and beta-propiolactone-inactivated virus, had no protective effect. These characteristics are consistent with the hypothesis that protection was the result of defective interfering particle-mediated interference with virulent virus multiplication within the respiratory tract of the chicken.

Influenza viral infection of swine in the United States 1988-1989

Swine are an animal reservoir for influenza viruses capable of causing disease in humans. A serological survey in 1988-1989 demonstrates that subtype H1 influenza viruses continue to circulate at high frequency among swine in the north-central U.S.A. (average 51% incidence). Subtype H3 viruses antigenically similar to current human H3 viruses are circulating at low frequency (average 1.1%), particularly in the southeast U.S.A.

Molecular characterization of a new hemagglutinin, subtype H14, of influenza A virus

Two influenza A viruses whose hemagglutinin (HA) did not react with any of the reference antisera for the 13 recognized HA subtypes were isolated from mallard ducks in the USSR. Antigenic analysis by hemagglutination inhibition and double immunodiffusion tests showed that the HAs of these viruses are similar to each other but distinct from the HAs of other influenza A viruses. Nucleotide sequence analysis showed that these HA genes differ from each other by only 21 nucleotides. However, they differ from all other HA subtypes at the amino acid level by at least 31% in HAI. Thus, we propose that the HAs of these viruses [A/Mallard/Gurjev/263/82 (H14N5) and A/Mallard/Gurjev/244/82 (H14N6) belong to a previously unrecognized subtype, and are designated H14. Unlike any other HAs of influenza viruses, the H14 HAs contained lysine at the cleavage site between HA1 and HA2 instead of arginine. Experimental infection of domestic poultry and ferrets with A/Mallard/Gurjev/263/82 (H14N5) showed that the virus is avirulent for these animals. Based on comparative sequence analysis of different HA genes, it is suggested that differences of 30% or more at the amino acid level in HA1 constitute separate subtypes. Phylogenetic analysis of representatives of each HA subtype showed that H14 is one of the most recently diverged lineages while H8 and H12 branched off early during the evolution of the HA subtypes. These latter two subtypes (H8 and H12) have been isolated very infrequently in recent years, suggesting that these old subtypes may be disappearing from the influenza reservoirs in nature.

Conditional expression of foreign genes by temperature-sensitive mutants of vaccinia virus

To assess the utility of two temperature-sensitive (ts) mutant vaccinia viruses as vectors for the conditional in vitro expression of recombinant foreign genes, we have studied the kinetics of expression of foreign genes incorporated into these viruses. At nonpermissive temperature, 40 degrees C, these viruses were defective either in DNA synthesis or in virus assembly. Foreign gene expression was affected by the nature of the ts lesion and by the nature of the vaccinia promoter positioned upstream from the foreign gene. With both vector viruses, a foreign gene controlled by the p7.5 early-late promoter was expressed at both 33 degrees and 40 degrees C. With the DNA synthesis-defective vector virus, foreign gene expression controlled by the p11 DNA synthesis-dependent late promoter was inhibited at 40 degrees C, but could be turned on by shift to 33 degrees C. This ts expression system provides an alternative to use of drugs that inhibit DNA synthesis as a means for experimental manipulation of gene expression. Both vector viruses can be used with existing vaccinia virus expression technology.

Antigenic and molecular characterization of subtype H13 hemagglutinin of influenza virus

Influenza A viruses with subtype H13 hemagglutinin display an unusual host range. Although common in shorebirds, they are very rare or absent in wild ducks; additionally, H13 viruses have been isolated from a whale. To study the molecular basis for this host range, we have determined the complete nucleotide sequences of the hemagglutinin genes of three H13 influenza viruses from different species or geographical areas: A/gull/Maryland/77, A/gull/Astrachan (USSR)/84, and A/pilot whale/Maine/84. Based on the deduced amino acid sequences, H13 hemagglutinin shares the basic structure of other type A hemagglutinin subtypes such as H3, but has clearly diverged from other completely sequenced subtypes. Unique features of H13 hemagglutinin include the occurrence, near the receptor binding pocket, of residues Arg/Lys-227 and Trp-229 (H3 numbering); the significance of these are unknown. The sequence of the HA1-HA2 cleavage site resembles those of avirulent avian influenza viruses. The whale H13 hemagglutinin is similar to those from gulls, supporting the hypothesis that influenza viruses from avian sources can enter marine mammal populations but are probably not permanently maintained there. Antigenic analysis using a panel of monoclonal antibodies suggests that, like other subtypes, H13 viruses are heterogeneous, with different antigenic variants predominating in the eastern versus the western hemispheres.

Protection of chickens from lethal influenza infection by vaccinia-expressed hemagglutinin

To study the immune response of the chicken to specific influenza proteins, we have constructed a recombinant vaccinia virus containing the hemagglutinin gene of influenza A/Turkey/Ireland/1378/83 (H5N8). In mammalian cell culture the hemagglutinin expressed by this recombinant virus was full-length, cleaved into HA1 and HA2 in the absence of trypsin, and transported to the cell surface, confirming that other virus products are not required for cleavage activation. Chickens inoculated through the wing web with the live recombinant virus produced extremely low levels of hemagglutination-inhibiting or infectivity-neutralizing antibody. However, they were protected from lethal H5 influenza virus challenge. Protection extended to the antigenically distinct virulent H5 viruses, Chicken/Pennsylvania/1370/83 and Chicken/Scotland/59. Chemically bursectomized vaccinated chickens were not protected, whereas normal chickens with very low antibody levels (less than 10) obtained by passive transfer were protected in a dose-dependent fashion. This indicates that despite the low antibody titers induced by vaccination, protection was mediated by antibody.

Is the gene pool of influenza viruses in shorebirds and gulls different from that in wild ducks?

Evidence is presented for a second major gene pool of influenza A viruses in nature. Shorebirds and gulls harbor influenza viruses when sampled in the spring and fall. Approximately half of the viruses isolated have the potential to infect ducks but the remainder do not. The hemagglutinin subtypes that are prevalent in wild ducks were rare or absent in shorebirds and gulls.

Intracellular localization of the viral polymerase proteins in cells infected with influenza virus and cells expressing PB1 protein from cloned cDNA

The biosynthesis, nuclear transport, and formation of a complex among the influenza polymerase proteins were studied in influenza virus-infected MDBK cells by using monospecific antisera. To obtain these monospecific antisera, portions of cloned cDNAs encoding the individual polymerase proteins (PB1, PB2, or PA) of A/WSN/33 influenza virus were expressed as fusion proteins in Escherichia coli, and the purified fusion proteins were injected into rabbits. Studies using indirect immunofluorescence showed that early in the infectious cycle (4 h postinfection) of influenza virus, PB1 and PB2 are present mainly in the nucleus, whereas PA is predominantly present in the cytoplasm of the virus-infected cells. Later, at 6 to 8 h postinfection, all three polymerase proteins are apparent both in the cytoplasm as well as the nucleus. Radiolabeling and immunoprecipitation analyses showed that the three polymerase proteins remain physically associated as a complex in either the presence or the absence of ribonucleoproteins. In the cytoplasm, the majority of the polymerase proteins remain unassociated, whereas in the nucleus they are present as a complex of three polymerase proteins. To determine whether a polymerase protein is transported into the nucleus individually, PB1 was expressed from the cloned cDNA by using the simian virus 40 late promoter expression vector. PB1 alone, in the absence of the other polymerase proteins or the nucleoprotein, accumulates in the nucleus. This suggests that the formation of a complex with other viral protein(s) is not required for either nuclear transport or nuclear accumulation of PB1 protein and that the PB1 protein may contain an intrinsic signal(s) for nuclear transport.

Defective interfering virus associated with A/Chicken/Pennsylvania/83 influenza virus

The A/Chicken/Pennsylvania/1/83 influenza virus, isolated from a respiratory infection of chickens, is an avirulent H5N2 virus containing subgenomic RNAs (W.J. Bean, Y. Kawaoka, J.M. Wood, J.E. Pearson, and R.G. Webster, J. Virol. 54:151-160, 1985). We show here that defective interfering particles are present in this virus population. The virus had a low ratio of plaque-forming to hemagglutinating units and produced interference with standard virus multiplication in infectious center reduction assays. Subgenomic RNAs were identified as internally deleted polymerase RNAs. We have confirmed that this virus protects chickens from lethal H5N2 influenza virus infection. This protective effect appeared to be due to the inhibition of virulent virus multiplication. Additionally, subgenomic RNAs derived from polymerase RNAs were detected in 5 of 18 RNA preparations from animal influenza virus isolates. Therefore, defective interfering particles are sometimes produced in natural influenza virus infections, not just under laboratory conditions. These particles may be capable of suppressing the pathogenic effect of virulent virus infections in nature.

Effect of human alpha A interferon on influenza virus replication in MDBK cells

To determine the molecular mechanism whereby interferon induces resistance to influenza virus, we began an investigation of influenza virus replication in MDBK cells treated with recombinant human alpha A interferon. Negative- and positive-strand virus-specific RNA accumulation was monitored by blot hybridization with cloned probes. Primary transcription (transcription of infecting viral negative strands by the virion-associated polymerase) was inhibited by interferon treatment of MDBK cells. At moderate levels of interferon treatment (10 U/ml), this inhibition was restricted to transcripts of polymerase genes, whereas at higher levels of interferon treatment (50 U/ml), accumulation of all primary transcripts was markedly inhibited. Secondary transcripts and viral negative strands did not accumulate to any significant extent in interferon-treated MDBK cells. These results suggest that interferon-induced mechanisms which inhibit influenza virus replication in MDBK cells act at the level of primary transcription.