Food Hygiene and Fecal Contamination on the Household Compound are Associated with Increased Pediatric Diarrhea in Urban Bangladesh (CHoBI7 Program)

In this prospective cohort study, we explored individual- and household-level risk factors associated with diarrheal diseases among 251 children younger than 5 years in slum areas of urban Dhaka, Bangladesh. During the 3-month study period, diarrhea surveillance was conducted monthly, and spot checks of the household compound were performed at baseline to assess the presence of feces (animal or human) in the household compound and in cooking and food storage areas, and to assess whether cooked food was covered and refrigerated. We also collected caregiver reports on child mouthing behaviors. Children living in households with feces within 10 steps of cooking and food storage areas (odds ratio [OR], 8.43; 95% CI, 1.01-70.18), those with visible feces found on the ground of the household compound (OR, 4.05; 95% CI, 1.24-13.22), and those in households found to keep cooked food uncovered and without refrigeration (OR, 6.16; 95% CI, 1.11-34.25) during spot checks had a significantly greater odds of diarrhea. There was no significant association between pediatric diarrhea and caregiver-reported child mouthing behaviors or presence of animals in the cooking area. These study findings demonstrate that presence of visible feces in the household compound and near cooking and food storage areas, and poor household food hygiene practices, were significant risk factors for diarrheal disease among young children in Dhaka, Bangladesh. Health communication programs are needed to target these exposure pathways to fecal pathogens.

Reduced Diarrhea Prevalence and Improvements in Handwashing with Soap and Stored Drinking Water Quality Associated with Diarrheal Disease Awareness Measured by Interactive Voice Response Messages in the CHoBI7 Mobile Health Program

The Cholera-Hospital-Based-Intervention-for-7-Days (CHoBI7) mobile health program promotes water, sanitation, and hygiene (WASH) behaviors through interactive voice response (IVR), voice, and text messages to reduce diarrheal diseases in Bangladesh. The objective of this study was to investigate the relationship between responses to CHoBI7 WASH IVR quiz messages and subsequent diarrhea and WASH behaviors. Fourteen CHoBI7 IVR quiz messages on handwashing with soap and treatment of stored water were sent to 517 households with 1,777 participants during the 12-month program period. IVR message responses were classified as correct answer, incorrect answer, no response (did not press 1 or 2), and failed (did not answer the phone). Diarrhea prevalence was assessed through self-reported monthly clinical surveillance visits. Handwashing with soap was assessed by a 5-hour structured observation, and stored water quality was defined by Escherichia coli concentration. Households that responded correctly to a CHoBI7 IVR quiz message had significantly lower odds of diarrhea for all age groups (adults and children) at the subsequent visit 1 month later (odds ratio [OR], 0.73; 95% CI, 0.54-0.98), and significantly greater odds of handwashing with soap after stool-related events (OR, 2.48; 95% CI, 1.12-5.49) and E. coli levels < 100 colony forming units (CFU)/100 mL (World Health Organization high-risk cutoff) in the stored household water (OR, 2.04; 95% CI, 1.25-3.33) compared with households that did not answer CHoBI7 IVR quiz calls. Correct responses to CHoBI7 IVR quizzes were associated with decreased diarrhea prevalence and improved stored drinking water quality and handwashing with soap behaviors at the subsequent visits. These findings suggest engagement in the CHoBI7 mobile health (mHealth) program and awareness of diarrheal disease prevention can reduce diarrhea and facilitate changes in WASH behaviors.

Formative Research for the Development of the CHoBI7 Cholera Rapid Response Program for Cholera Hotspots in Bangladesh

Cholera is a severe form of acute watery diarrhea that if left untreated can result in death. Globally, there are 2.9 million cholera cases annually. Individuals living in close proximity to cholera cases are at a higher risk for developing cholera compared to the general population. Targeted water, sanitation, and hygiene (WASH) interventions have the potential to reduce cholera transmission in cholera hotspots around cholera cases. The objective of this study was to expand the scope of the Cholera-Hospital-Based-Intervention-for-7-Days (CHoBI7) program, focused on cholera patient households, for delivery in cholera hotspots in urban slums in Dhaka, Bangladesh. Thirty-one semi-structured interviews were conducted in cholera hotspots around cholera patients, and three intervention planning workshops were conducted to inform modifications needed to the CHoBI7 program. After exploratory interviews, a two-phase, iterative pilot study was conducted for 9 months to test the developed CHoBI7 Cholera Rapid Response program among 180 participants to further inform modifications to intervention content and delivery. Findings from pilot participant interviews highlighted the need to adapt intervention content for delivery at the compound-rather than household-level, given an environment with multiple households sharing a water source, toilets, and kitchen facilities. This was addressed by conducting a "ring session" for intervention delivery in cholera hotspots for households to discuss how to improve their shared facilities together and encourage a compound-level commitment to promoted WASH behaviors and placement of soapy water bottles in shared spaces. Based on the low number of soapy water bottles observed in communal spaces during the first iteration of the pilot, we also added context-specific examples using the narratives of families in mobile messages to encourage WASH behavioral recommendations. Formative research identified important considerations for the modifications needed to tailor the CHoBI7 program for delivery in cholera hotspots in urban Bangladesh.

Fecal Sampling of Soil, Food, Hand, and Surface Samples from Households in Urban Slums of Dhaka, Bangladesh: An Evidence-Based Development of Baby Water, Sanitation, and Hygiene Interventions

The aim of this study was to identify the exposure pathways of fecal pathogens for a pediatric population living in the urban slums of Bangladesh. A total of 252 soil, food, surface, and hand rinse samples were collected from the pilot households with children less than 5 years of age. All samples were analyzed using the IDEXX Quanti-Tray System (Colilert-18) to enumerate fecal indicator bacteria Escherichia coli. Escherichia coli was detected in all soil samples collected from children play spaces (N = 46), 35% of objects and surfaces children frequently put in their mouths, and 31% of child food samples. Thirty-three percent of hand samples from the child and 46% of hand samples from the caregiver had detectable E. coli. These findings showed high fecal contamination of soil, food, and on hands and surfaces in households with young children and demonstrate the need for interventions reducing these exposure pathways for susceptible pediatric populations.

Low Fruit and Vegetable Consumption Associated with Linear Growth Faltering among Children in Urban Bangladesh

The objective of this study was to examine the association between dietary diversity and child growth among children 6 to 23 months of age in urban slums of Bangladesh. This prospective cohort study enrolled 192 participants 6 to 23 months of age in Dhaka, Bangladesh. A total of 170 children with follow-up anthropometric data were included in the analysis. To collect dietary intake information for children 6 to 23 months of age, consumption of five or more of the following eight minimum dietary diversity food groups was recorded using 24-hour dietary recall at enrollment provided by the child's caregiver: 1) breast milk; 2) grains, roots, and tubers; 3) legumes and nuts; 4) dairy products; 5) flesh foods; 6) eggs; 7) vitamin A-rich fruits and vegetables; and 8) other fruits and vegetables. Height and weight were measured at baseline and at a 12-month follow-up. Fifty-five percent of children (106 of 192) consumed five or more of the eight minimum dietary diversity food groups during their first visit to assess dietary intake. Eighty-two percent of children (157 of 192) had a report of consuming an animal source of food (e.g., eggs, diary, flesh foods) in the past 24 hours, 85% (164 of 192) consumed any source of protein (e.g., eggs, diary, flesh foods, nuts, and legumes), and 65% of children (125 of 192) were reported to consume any fruits and vegetables. Child consumption of fruits and vegetables was associated positively with change in length-for-age z-scores from baseline to the 12-month follow-up (coefficient, 0.86; 95% CI, 0.03-1.68). Inadequate fruit and vegetable consumption was associated with linear growth faltering among the young children residing in urban Dhaka, Bangladesh. These findings demonstrate the need for effective interventions to increase fruit and vegetable consumption in this susceptible pediatric population.

Diarrhea Prevalence and Child Growth Faltering Are Associated with Subsequent Adverse Child Developmental Outcomes in Bangladesh (CHoBI7 Program)

Millions of young children annually are not meeting their developmental potential in low- and middle-income countries. Previous studies have shown that diarrheal diseases during early life are associated with subsequent malnutrition. This prospective cohort study of 576 children under 5 years was conducted in urban Dhaka, Bangladesh, to investigate the association between diarrhea prevalence, child growth, and child cognitive developmental outcomes. Height and weight were measured at baseline and a 12-month follow-up. Diarrhea prevalence was assessed through monthly surveillance visits. Developmental outcomes were assessed by communication, fine motor, gross motor, personal social, problem-solving, and combined developmental scores measured by the Extended Ages and Stages Questionnaire (EASQ) at the 12-month follow-up visit. To assess the association between diarrhea prevalence, child growth, and child cognitive developmental outcomes, linear regression models were fit using generalized estimating equations to account for clustering at the household level and to approximate 95% CIs. Diarrhea prevalence was negatively associated with change in height-for-age (HAZ) Z-scores from baseline to the 12-month follow-up (coefficient -0.85 [95% CI: -1.42, -0.28]). Diarrhea prevalence was a significant predictor of combined EASQ Z-scores with and without baseline stunting included in the model (-0.89 [95% CI: -1.67, -0.09] [baseline stunting included]) and (-0.88 [95% CI: -1.69, -0.07]). Change in HAZ from baseline to the 12-month follow-up was positively associated with follow-up combined EASQ Z-scores (0.28 [95% CI: 0.15, 0.42]). High diarrhea prevalence and linear growth faltering were associated with negative cognitive developmental outcomes among children residing in urban Dhaka, Bangladesh. Furthermore, high diarrhea prevalence was associated with negative child cognitive developmental outcomes with stunting included in the model, suggesting an effect of diarrhea on cognition independent of stunting.

Child Mouthing of Soil and Contaminated Fomites and Unimproved Sanitation are Associated with Subsequent Poor Child Developmental Outcomes in Urban Bangladesh (CHoBI7 Program)

OBJECTIVE

To evaluate the relationship between mouthing of soil and living in unsanitary conditions and child cognitive development in urban Bangladesh.

STUDY DESIGN

This prospective cohort study of 224 children under 5 years of age was conducted in urban Dhaka, Bangladesh. Developmental outcomes were assessed by communication, fine motor, gross motor, personal social, problem solving, and combined developmental scores measured by the Extended Ages and Stages Questionnaire (EASQ) at a 12-month follow-up visit.

RESULTS

Children who had caregiver reports of puting soil in their mouths at the majority of surveillance visits had significantly lower combined EASQ Z scores (coefficient, -0.53; 95% CI, -0.83 to -0.22) at the 12-month follow-up visit. Children who had caregiver reports of putting visibly dirty objects in their mouths at the majority of visits had significantly lower combined EASQ Z scores (-0.50; 95% CI, -0.79 to -0.22). Children in households with unimproved sanitation had significantly lower combined EASQ Z scores (-0.63; 95% CI, -1.11 to -0.16).

CONCLUSIONS

Children found to frequently put soil and visibly dirty objects in their mouths, and those who resided in households using unimproved sanitation, had lower subsequent cognitive developmental outcomes. These findings demonstrate the importance of interventions targeting child mouthing behaviors and sanitation infrastructure to decrease exposure to fecal pathogens and improve child cognitive developmental outcomes.

Fecal Contamination on the Household Compound and in Water Sources are Associated with Subsequent Diarrhea in Young Children in Urban Bangladesh (CHoBI7 Program)

We investigated the environmental and individual-level risk factors for diarrheal disease among young children in slum areas of Dhaka, Bangladesh. A prospective cohort study was conducted among 884 children under 5 years of age. Caregiver reports were collected on sociodemographic factors and hygiene behaviors. Diarrhea surveillance data was collected monthly based on caregiver-reported diarrhea for children in the past 2 weeks during the 12-month study period. Unannounced spot checks of the household compound were performed at 1, 3, 6, 9, and 12 months after enrollment to check for the presence of feces (animal or human) and the presence of animals in the child's sleeping space, to assess child and caregiver hands for the presence of dirt, and to collect samples of the household's source and stored drinking water. Children with feces found on the household compound during spot checks had a significantly higher odds of diarrhea (odds ratio: 1.71; 95% confidence interval: 1.23-2.38). Children residing in households with > 100 colony forming units/100 mL Escherichia coli in source drinking water had a significantly higher odds of diarrhea (OR: 1.43; 95% CI: 1.06-1.92). The presence of feces on the household compound and source drinking water with > 100 colony forming units/100 mL E. coli were significant risk factors for diarrheal disease for children < 5 years of age in slum areas of Dhaka, Bangladesh. These findings demonstrate the urgent need for comprehensive interventions to reduce fecal contamination on the household compound to protect the health of susceptible pediatric populations.

Psychosocial Factors Mediating the Effect of the CHoBI7 Mobile Health Program on Handwashing With Soap and Household Stored Water Quality: A Randomized Controlled Trial

Household members of diarrhea patients are at higher risk of developing diarrheal diseases (>100 times for cholera) than the general population during the 7 days after the diarrhea patient is admitted at a health facility. There is growing evidence demonstrating that theory-driven water, sanitation, and hygiene (WASH) interventions are likely to yield greater behavior change than those based on health education alone. The Cholera Hospital-Based Intervention for 7-Days (CHoBI7) mobile health (mHealth) program is a theory-driven WASH intervention initially delivered to a diarrhea patient by a health promoter during a health facility visit and reinforced through weekly voice and text messages. In the recent randomized controlled trial (RCT) of the CHoBI7-mHealth program in Bangladesh, this intervention significantly reduced diarrheal disease and stunting, and increased handwashing with soap and stored drinking water quality over the 12-month program period. The aim of this study was to assess the underlying mechanism of change of this intervention. Handwashing with soap was measured by 5-hour structured observation. Stored drinking water quality was assessed by the presence of Escherichia coli during unannounced spot checks. Psychosocial factors were measured among 1,468 participants in the CHoBI7-mHealth RCT. Perceived susceptibility, response efficacy, self-efficacy, dirt reactivity, and diarrhea knowledge were mediators of the CHoBI7-mHealth program's effect on stored drinking water quality at the 1-week follow-up. Self-efficacy, response efficacy, and diarrhea knowledge were mediators of the intervention's effect on handwashing with soap habit maintenance and stored drinking water quality at the 12-month follow-up. This study demonstrates how theory-driven approaches for intervention design can facilitate WASH behavior change.

Formative Research for the Design of a Baby Water, Sanitation, and Hygiene Mobile Health Program in Bangladesh (CHoBI7 Mobile Health Program)

Poor food hygiene practices, child feces not being disposed of in a latrine, child mouthing of contaminated fomites, and poor hand hygiene of caregivers have been associated with diarrheal diseases, environmental enteropathy, and impaired growth in young children. Mobile health (mHealth) programs present a low-cost approach to delivering water, sanitation, and hygiene (WASH) programs. We conducted a theory-driven and evidence-based approach to formative research and intervention development to design and pilot test a Baby WASH mHealth program targeting food hygiene, child mouthing, and child feces disposal behaviors in urban Dhaka, Bangladesh. Formative research activities included 31 semi-structured interviews, five group discussions, six mHealth workshops, and a three-phase iterative pilot study among 102 households. Findings from semi-structured interviews and group discussions indicate that caregivers of young children have relatively high awareness of the need for safer food hygiene, child mouthing, and child feces disposal practices, but are limited by existing household responsibilities and restricted access to enabling technology that would facilitate practicing recommended behaviors. The piloted Baby WASH mHealth program was well-received by households. This study presents a theory-driven and evidence-based approach for intervention development that can be implemented for the development of future WASH mHealth programs in low-resource settings.

Diarrhoeal disease knowledge among diarrhoea patient housholds: findings from the randomised controlled trial of the Cholera-Hospital-Based-Intervention-for-7-days (CHoBI7) mobile health program

OBJECTIVE

The objective of this study was to evaluate the impact of the Cholera-Hospital-Based-Intervention-for-7-days (CHoBI7) handwashing with soap and water treatment mobile health (mHealth) program on diarrhoeal disease knowledge among diarrhoea patients and their household members in urban Dhaka, Bangladesh.

METHODS

A cluster-randomised controlled trial of the CHoBI7 mHealth program was conducted among diarrhoea patient households in Dhaka, Bangladesh. Patients were randomised to three arms: standard recommendation on oral rehydration solution use; health facility delivery of CHoBI7 plus mHealth (weekly voice and text messages) (no home visits); and health facility delivery of CHoBI7 plus two home visits and mHealth. An open-ended questionnaire was administered to 1468 participants 12 years of age or older on diarrhoeal disease transmission and prevention. These items were combined to form a diarrhoeal disease knowledge score measured at baseline and at a 1 week, 6 month and 12 month follow-up.

RESULTS

At baseline, when participants were asked to report three ways diarrhoeal diseases were spread 37% (546/1468) of participants reported by water, 13% (187/1468) by lack of handwashing and 4% (53/1468) by food not being covered properly. At baseline when asked to name three ways diarrhoeal diseases could be prevented, 35% (515/1468) of participants reported safe water, and 16% (228/1468) reported handwashing with soap. At the 12-month follow-up, the overall diarrhoeal disease knowledge score was significantly higher in the mHealth with no home visits arm (score coefficient: 0.69, 95% Confidence Interval: 0.36, 1.01, P < 0.0001) and the mHealth with two home visits arm (score coefficient: 1.18, 95% CI: 0.87, 1.49, P < 0.0001) compared with the standard recommendation arm.

CONCLUSION

The CHoBI7 mHealth program significantly increased knowledge of diarrhoeal disease transmission and prevention among diarrhoea patients and their household members 12 months after in-person visits for program delivery were conducted.

Process evaluation for the delivery of a water, sanitation and hygiene mobile health program: findings from the randomised controlled trial of the CHoBI7 mobile health program

OBJECTIVE

The Cholera-Hospital-Based Intervention for 7-days (CHoBI7) mobile health (mHealth) program delivers mobile messages to diarrhoea patient households promoting water treatment and handwashing with soap. The randomised controlled trial (RCT) of the CHoBI7 mHealth program demonstrated this intervention was effective in significantly reducing diarrhoea and stunting amoung young children. The objective of this study was to assess the implementation of the CHoBI7 mHealth program in delivering mHealth messages during this RCT.

METHODS

517 diarrhoea patient households with 1777 participants received weekly text, voice and interactive voice response (IVR) messages from the CHoBI7 mHealth program over the 12-month program period. The program process evaluation indicators were the following: the percentage of CHoBI7 mHealth messages received and fully listened to by program households (program fidelity and dose), and household members reporting receiving and sharing an mHealth message from the program in the past two weeks (program reach).

RESULTS

Ninety two percent of text messages were received by program households. Eighty three percent of voice and 86% of IVR messages sent were fully listened to by at least one household member. Eighty one percent of IVR quiz responses from households were answered correctly. Program households reported receiving a CHoBI7 mHealth message in the past two weeks at 79% of monthly household visits during the 12-month program. Seventy seven percent of participants reported sharing a program message with a spouse, 55% with a neighbour and 49% with a child during the program period.

CONCLUSION

There was high fidelity, dose and reach of mobile messages delivered for the CHoBI7 mHealth program. This study presents an approach for process evaluation that can be implemented to evaluate future mHealth programs.

Effect of a water, sanitation and hygiene program on handwashing with soap among household members of diarrhoea patients in healthcare facilities in Bangladesh: a cluster-randomised controlled trial of the CHoBI7 mobile health program

OBJECTIVE

The Cholera-Hospital-Based-Intervention-for-7-days (CHoBI7) is a water treatment and handwashing with soap intervention for diarrhoea patients and their household members which is initially delivered in a healthcare facility setting. This study evaluated the effectiveness of CHoBI7 program delivery in increasing handwashing with soap in a healthcare facility setting among diarrhoea patients and their household members.

METHODS

A randomised controlled trial of the CHoBI7 program was conducted among 404 diarrhoea patients and their accompanying household members in healthcare facilities in Dhaka, Bangladesh. The 'Standard Message' Arm received the standard message given in Bangladesh to diarrhoea patients on the use of oral rehydration solution. The 'Health Facility Visit + Soapy Water' Arm received the standard message, the CHoBI7 communication module delivered bedside to the patient; and a soapy water bottle in the healthcare facility. The 'Health Facility Visit + Handwashing Station' Arm received this same intervention plus a small plastic handwashing station. Within 24 h of intervention delivery, three-hour structured observation of handwashing practices at stool/vomit- and food-related events (key events) was conducted in healthcare facilities of diarrhoea patients and their accompanying household members.

RESULTS

Compared to the Standard Message Arm, there was significantly more handwashing with soap at key events in both the Health Facility Visit + Soapy Water Arm (51% vs. 25 %) (Odds Ratio: 3.02; (95% Confidence Interval (CI): 1.41, 6.45) and the Health Facility Visit + Handwashing Station Arm (58% vs. 25%) OR: 4.12; (95% CI: 1.86, 9.14).

CONCLUSION

These findings demonstrate that delivery of the CHoBI7 communication module and provision of a soapy water bottle to diarrhoea patients and their accompanying household members presents a promising approach to increase handwashing with soap among this high risk population in a healthcare facility setting in Bangladesh.

Prospective cohort study of child mouthing of faeces and fomites in Dhaka, Bangladesh (CHoBI7 Program)

OBJECTIVE

To characterise childhood mouthing and handling behaviours and to assess the association between hand-to-object and object-to-mouth contacts and diarrhoea prevalence in young children in urban Dhaka, Bangladesh.

METHODS

A prospective cohort study was conducted among 494 children under 5 years of age in Dhaka, Bangladesh. This study was nested within the randomised controlled trial of the Cholera Hospital-Based Intervention for 7 Days (CHoBI7) mobile health (mHealth) program. The CHoBI7 mHealth program focuses on promoting handwashing with soap and water treatment to diarrhoea patients and their household members through mobile messages and a single in person visit. Mouthing and handling of faeces and fomites among young children was measured by five-hour structured observation and caregiver reports. Diarrhoea surveillance data was collected monthly for 12 months.

RESULTS

Fifty five percent of caregivers reported that their child put a visibly dirty fomite (object or soil) in their mouth in the past week. Caregivers reported that 50% of children had mouthed visibly dirty objects, 26% had mouthed dirt, and 2% had mouthed faeces. Forty five percent of children were observed mouthing a visibly dirty fomite during structured observation, 40% of children were observed mouthing a visibly dirty object, 10% were observed mouthing soil, and one child (0.2%) was observed mouthing faeces. Mouthing of visibly dirty fomites was highest for children 12-18 months of age with 69% of these children having caregiver reports and 54% having observed events. Children with caregiver reports of mouthing faeces had a significantly higher odds of diarrhoea over the subsequent month (Odds Ratio: 4.54; 95% Confidence Interval: 1.06, 19.48).

CONCLUSION

These findings demonstrate that mouthing of contaminated fomites among young children is frequent in urban environments in Bangladesh, and that mouthing faeces is associated with a significantly higher odds of diarrhoea. Interventions are urgently needed to protect young children from faecal pathogens in their play spaces.

Genetic relatedness of Vibrio cholerae isolates within and between households during outbreaks in Dhaka, Bangladesh

Background

Household contacts of cholera patients have a 100 times higher risk of developing a cholera infection than the general population. To compare the genetic relatedness of clinical and water source Vibrio cholerae isolates from cholera patients’ households across three outbreaks, we analyzed these isolates using whole-genome-sequencing (WGS) and multilocus variable-number tandem-repeat analysis (MLVA).

Results

The WGS analyses revealed that 80% of households had source water isolates that were more closely related to clinical isolates from the same household than to any other isolates. While in another 20% of households an isolate from a person was more closely related to clinical isolates from another household than to source water isolates from their own household. The mean pairwise differences in single nucleotide-variant (SNV) counts for isolates from the same household were significantly lower than those for different households (2.4 vs. 7.7 p < 0.0001), and isolates from the same outbreak had significantly fewer mean pairwise differences compared to isolates from different outbreaks (mean: 6.2 vs. 8.0, p < 0.0001). Based on MLVA in outbreak 1, we observed that the majority of households had clinical isolates with MLVA genotypes related to other clinical isolates and unrelated to water source isolates from the same household. While in outbreak 3, there were different MLVA genotypes between households, however within the majority of households, the clinical and water source isolates had the same MLVA genotypes. The beginning of outbreak 2 resembled outbreak 1 and the latter part resembled outbreak 3. We validated our use of MLVA by comparing it to WGS. Isolates with the identical MLVA genotype had significantly fewer mean pairwise SNV differences than those isolates with different MLVA genotypes (mean: 4.8 vs. 7.7, p < 0.0001). Furthermore, consistent with WGS results, the number of pairwise differences in the five MLVA loci for isolates within the same household was significantly lower than isolates from different households (mean: 1.6 vs. 3.0, p < 0.0001).

Conclusion

These results suggest that transmission patterns for cholera are a combination of person-to-person and water-to-person cholera transmission with the proportions of the two modes varying within and between outbreaks.

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4254-9) contains supplementary material, which is available to authorized users.