Overview
This is an experimental exploratory descriptive study, targeted at defining national guidelines, and a standardised rodents surveillance protocol, in addition to conducting an operational comprehensive rodent surveillance training and setup a standardised surveillance within the urban disadvantaged community of Over-the-Hill, Nassau, The Bahamas (25° 4'11.40"N 77°20'4.87"W).
To do this, we simultaneously conducted parallel but integrated activities, specifically: (i) developed a standardised surveillance protocol adapted to the local environment, (ii) conducted 8 days of theoretical and practical rodent surveillance training (7th – 14th June 2022), and (iii) 3 months of pilot rodent surveillance after the training (June – August 2022), respectively (see details of the three activities under “guidelines preparation“, “preparation of course materials” and “pilot surveillance study” below). Reports of the “Rodent Control Assessment Workshop” and “Environmental Health Advisor for The Bahamas Hurricane Dorian Response” conducted in April-May 2019 and October 2019 were instrumental in developing this training. The reports highlighted the strengths and weaknesses of the Department of Environmental Health Services (DEHS), which is the arm of the Ministry of Environment and Natural Resources that drives the management of rodent population in The Bahamas. These reports revealed that rodent surveillance in The Bahamas is based on a “top-down” approach that lacks data standardisation across monitored areas, subsequently impacting the accurate definition of rodent infestation, damage level and pathogens spillover in the given area. From there, we developed a situational analysis, identified an explicit guidelines for rodent surveillance, as well as a multi-sectoral integrated rodent surveillance protocol that was used during the training and pilot surveillance program (see below, the course preparation, design and surveillance for details).
(i) Guidelines Preparation
Before the training session per se, we developed a site-specific integrated pest management (IPM) guideline for rodent surveillance with likely interventions in The Bahamas (Annex II). Briefly, we carefully explained the phases of IPM as applicable to The Bahamas. In particular, basic biology and ecology of rodents; the planning phase consisting of: identification of rodent-associated problems and areas to be surveyed based on previous study results & direct or indirect reports of rodent sightings/activities, the definition of activities and resources required for the programs; methods of rodent infestation surveillance essentially based on modified exterior and interior Centers for Diseases Control and Prevention (CDC) survey form38, and including direct and indirect observation of rodent signs, a survey using community perception/sightings, track plates, bait consumption, chew cards and rodent trapping; definition of rodent threshold levels which establish the level of acceptable rodent infestation in and around the household; possible interventions such as sanitation improvement, habitat management, diversionary feeding, exclusion, scaring and usage of repellents, chemical control, mechanical and biological control; evaluation of results, notably the assessment of the effectiveness of the intervention; and plans for the continuity of the actions likewise adherence to bio-safety measures.
(ii) Course Preparation, Design and Surveillance
The rodent surveillance training team consisted of multidisciplinary professionals drawn up from four institutions, namely: the DEHS, PAHO, WHO and Instituto de Saude Coletiva, Universidade Federal da Bahia who collaboratively worked to execute the rodent surveillance training and the post-training pilot surveillance. These four institutions regularly organised weekly meetings for 8-weeks before the training to plan and to shape the training program. Specifically, they extensively studied the previous reports and the findings of Awoniyi et al.30 that characterised the unsatisfactory top-down method used for evaluating rodent infestation in urban communities of the Bahamas that principally relied on the reports of less than or equal to four hours rodent sightings per day, and the ineptness of the rodent control method (chemical application) used across the disadvantaged community to develop innovative surveillance and likely control strategies. These baseline reports guided identification of the relevant items to be included in the training module, the type of rodent surveillance and format, teaching method, study area-sample size, materials and documents to be used, appropriate training period and the profession/number of the audience (trainers) and community members to be invited and engaged. Following the request of the DEHS representatives and subsequent evaluation during the teams’ weekly meetings, it was agreed that the training should focus on the following topics: basic rodent biology; the economic impact of rodents on agriculture, health and household properties; rodent survey methods (track plate, rodent trapping and exterior & interior household survey); definition of the study area; geographical identification of households/sampling points; dataflow; interpretation of data and community collaborative mapping; and rodent management (in the framework of an Integrated Pest Management approach) which were delivered by seasoned experts during the rodent surveillance training. It was believed that the wide panel of the training components would inspire the standardisation of rodent surveillance, maintenance of accurate and unified data and provision of essential information during rodent management intervention that would be specifically adapted in The Bahamas.
(iii) Preparation of Course Materials (theoretical and practical)
Course procedure
The training course described techniques that are available to assist DEHS staff, ministry of agriculture and marine resources, ministry of health and other local communities/multi-sectoral bodies that are interested in rodent-related studies in setting up rodent surveillance, gathering information about local rodent infestation and evaluating possible socio-environmental conditions that could influence rodent infestation in the environment. For this purpose, the training was structured in two components: theoretical and practical. During the theoretical component of the rodent surveillance training, revised topics requested by the DEHS representatives were discussed.
As a baseline material, we modified previous manuals such as the CDC for exterior and interior rodent survey38, the track plate protocol from Hacker et al.40, the snap trap protocol from Woodman et al.39 and the “Levantamento Rapido de Indices para Aedes aegypti – LIRAa” protocol by Brasil55 to develop specific protocols that remedy the flaws identified in the previous protocol and suitable to The Bahamas condition. These Bahamas-specific protocols are described in detail under “preparation of protocols” and included the following components: definition of sampling size; preparation of maps; preparation of databases; approaching residents;household survey protocol, track plate and snap trap protocols as well as a road map for community collaborative engagement. The protocols were also used to train the course participants about different rodent survey techniques such as exterior and interior household rodent inspection, track plate and snap trap application.
Briefly, the household survey protocol provided means of obtaining information about rodent infestations and environmental factors influencing rodent proliferation in the study areas. The track plate (TP) and snap trap (ST) protocols provided the proxy for infestation level, providing information such as the distribution and approximate abundance of rodents in the environment which are fundamental information required for environmental management40. Likewise, considering that community participation in collaborative mapping is a proven instrument for collating information about local problems, residents’ perception and likely social solutions58, these were additionally used to identify high-risk locations for rodent infestation in addition to the experimental findings.
(iv) Preparation of protocols
Definition of sampling size
To select the blocks and the households to be inspected, we adapted the LIRAa protocol originally developed for Aedes aegypti55 in order to estimate the appropriate sample size for rodent surveillance activities. The blocks were sampled by a conditional stratified random selection where the selected blocks could not be neighbour. The study community was divided into strata to facilitate field logistic and household identifications. We then relied on a systematic random sampling technique to select one of every other household in the study areas for inspection to ensure an acceptable representation of the entire study community.
The sample size was obtained following the LIRAa guideline with the formula corrected for by the number of households in the area, as detailed here below:
a) Household sample size (n): n = 450 / (1+ 450/N) where N = number of properties in the area
The number of blocks to be inspected was evaluated using:
b) Average size of blocks (B): B = number of households/properties in the stratum/number of blocks of area = N / A
c) Number of blocks that will compose the sample: From the definition of the number of properties to be sampled, it was necessary to determine the “Q” number of blocks that will compose the sample.
Q = number of properties to be sampled/ average size of blocks / 2 = n / (B/2). The value “2” in the denominator corresponds to the sampling of 50% of the properties of the selected blocks.
All blocks and houses selected for the survey were numbered during the inspection to facilitate easy identification of the study area.
Preparation of maps and database
Following the proliferation of rodents in the study areas after the occurrence of Hurricane Dorian in 2019, 50% of the affected areas (7 areas) were selected for pilot rodent surveillance as defined by the sampling strategy above. A map of the study areas containing the randomly selected blocks from each area was produced using spatial analysis software QGis Version 3.22 (Fig. 3).
Additional maps containing the selected blocks from each study area were produced to assist the field teams in identifying the households to be visited and monitored during the fieldwork. Each area contained between 4 and 9 blocks depending on the size of the area. Figure 3 was also used during the community collaborative mapping to indicate possible rodent foci as identified by the residents.
To encourage data homogeneity and standardisation of results across study areas, we used web-based software called Research Electronic Data Capture (REDCap) to create a database for the project. The REDCap is a secured environment that can be used to store and export datasets into statistical programs such as SPSS, R, Stata, and Epiinfo, among other data analysis software (see Annex III for more details).
Approaching residents
We adapted the procedure of Pan-American Organization for Health59 to approach the residents upstream the field survey. Briefly, this protocol emphasised the need to: meet with the community leaders and seek their approval for conducting a rodent survey; explain the details of the experiment i.e. its objectives, methods and expected benefits to the community; explain the required level of support from the community/residents; politely introduce the team members to residents; ask the residents if they could join in the survey of their residences and appreciate their collaboration while seeking for the perfect opportunity to say goodbye after the inspection of their residences.
Household rodent survey
Households were surveyed to monitor and evaluate the severity of rodent infestation and causal conditions encouraging rodent infestation in the area, in a way to guide future rodent intervention programs. We slightly modified the CDC38 manual to develop a simple household inspection procedure that consisted of observed active rodent signs (e.g. faeces, trails, grease marks, gnawed materials and active burrows) and causal conditions (e.g. harbourage source-abandoned appliances, food source-improper waste disposal, animal feed, water source-leakages, stagnant water, e.t.c.). We recorded and saved information obtained for each of these variables in the web-based REDCap software using a structured rodent exterior and interior survey form (Annex IV). The presentation of the team members and the project to the residents was followed by the inspection of residents’ facilities upon their approval at each surveillance point. In the case of evident rodent signs during the exterior inspection, permission was sought to conduct an interior inspection while the residents were enjoined to join in the inspection, if possible. Moving objects during the survey exercise was discouraged, while stores, kitchens and perimeters of the walls were thoroughly checked for any rodent signs (observed active rodent signs).
Ethical clearance to conduct household rodent surveillance and trapping was granted by the Ministry of Environment and Natural Resources, Department of Environmental Health Services’ ethics committee. Participation in the household survey was entirely voluntary.
Track Plates (TP) & Snap Traps (ST)
The protocols that have been extensively described and previously validated by Hacker et al.40 and Woodman et al.39 were simplified and used for TP & ST training, respectively. The TP is capable of evaluating the distribution and activities of rats (but not their abundance or density), especially when carried out for two consecutive nights. A 0.2 x 0.2 m acetate sheet (TP) was painted with weather-resistant lampblack that dried off in less than 5 minutes using a paint roller. The TP is capable of capturing different types of marks that are left by rats such as paw prints, tail marks and scratches. These marks were recorded and evaluated as positive signs of rodent infestation. The ST is useful for either the management of rodent populations or determining species richness and relative abundance. The field officers were encouraged to conduct at least one-two days of pre-baiting before the trapping proper, this has shown to increase rodent trapping success and prevent neophobia among the rodent community40,54,55,58-60. Before trap placement, field officers obtained trapping permit or approval where necessary; checked the functionality of the traps; placed traps in areas with no or low livestock activities (to prevent the killing of non-target species); marked all trapping points on the map; placed traps in areas with active rodent signs (i.e. rodent runs, trails, burrows etc); placed traps at noon and checked them at dawn while discarding carcasses according to the procedure for discarding biological waste.
Community collaborative meeting and mapping
The community conversation approach was planned and implemented based on years of study and experiences in vulnerable urban communities of Salvador, Brazil61-63. Residents belonging to different socioeconomic and education levels, age classes and genders, residing in the blocks of the study areas and who participated in the household rodent survey were deemed eligible and invited to the community meeting.
Members of the research team carried out visits, and invited residents who live within the study community, and presented the objectives of the project and the organizations involved in the study. The team also confirmed residents’ availability and communicated details (i.e. venue, day and time) of the meeting to the invitees. In total, 11 influential participants were invited to the community meeting and collaborative mapping, with the intention of communicating the project initiative to other community members.
The meeting started with a brief self-introduction of both the participating community members and the research team. Subsequently, the purpose and outline of the program (Annex V-Part I) were presented to the participants. The dialogue mainly focused on subjects such as living in the community, perception and exposure to risk factors, collaborative mapping, actions to reduce risk, thus allowing participants to broadly express their minds even beyond the pre-conceived items contained in the training document. The conversation with the community members lasted for about two hours, and the key opinions expressed by the participants were recorded and evaluated during the expert meeting in an attempt to guide a holistic site-specific rodent surveillance program in The Bahamas.
Also, during the community meeting, participants were engaged in collaborative mapping (the process by which a group of residents aggregate self-generated contents that are entered on the map to improve the gaps identified in official maps58) that was targeted at identifying the places with increased rodent presence; accumulated garbage; abandoned properties; accumulated rubble; and overgrown vegetation (Annex V-Part II). It is believed that this map would contribute to the definition of priority areas that require attention during intervention, and to promote future sustainable and culturally appropriate interventions based on community participation58.
(v) Pilot Surveillance Study
Pilot community (Over-the-Hill)
The study community (Fig 3) has been previously described partly in Awoniyi et al.30. The disadvantaged low-income community of Over-the-Hill was founded by the freed African slaves in the 1800s and represented their core socio-cultural and educational activities post-slavery era. Over-the-Hill is bordered by School Lane to the north, Collins Wall to the east, Nassau Street to the west and Wulff Road to the south. However, the community that once produced the most accomplished and noteworthy Bahamians in modern history, has experienced a pitiful level of deterioration in recent years and is now a hotspot of violent and crime activities and poverty64. Over-the-Hill is the most marginalised and poorest community in The Bahamas. The community is now epitomised by dilapidated buildings with no electricity and potable water access, overgrown properties, abandoned vehicles and furniture, haphazard dumping of refuse, records of regular rodent sightings, and unemployment where only 5 out of every 100 employment-age residents are often gainfully employed with formal jobs64. The current study community was chosen based on previous records of high rat sightings30.
Surveillance
Seven hundred and thirteen points were randomly selected across 23 blocks as suggested in the definition of the sampling size for the cross-sectional survey. We excluded two hundred and fifty-six of the points due to inaccessibility or missing data, thereby leaving us with four hundred and fifty-seven points. We used the household rodent survey form to extensively inspect the 457 points for three months (June - August 2022). We also conducted a night rodent trapping in these points. Prior to the inspection, we followed the recommendations of how to approach the residents and carefully inspected designated households (as contained in the map) for active rodent signs. Following the surveillance exercise, all data obtained from the field were uploaded into the earlier created REDCap account for subsequent analyses.
Analyses
To evaluate the socio-environmental variables associated with rodent proliferation in Over-the-Hill, we used a generalized linear model (GLM) with a logistic link and binomially distributed error structure. Our response variable at each sampling point was coded as 1 if there was at least one active sign of rodent infestation (that is, report of rodent sightings, runs, burrows, presence of faecal material, or presence of gnawed material), and coded as 0 if none of these rodent active signs was noted.
Before testing for the effect of socio-environmental variables on rodent infestation (using active rodent signs as a proxy), we controlled for environmental variables that could influence rodent infestation. We first used separate GLMs to test for the relationships between the response variable and each of the following explanatory variables: premise type; presence of garbage, presence of water & food; the number of dwelling units; closeness to sewer, presence of unapproved refuse storage, privy closet, dilapidated fence and structural deficiencies; households with pipe or wiring gaps, presence of overgrown vegetation; the number of domestic animals; and harbourage access i.e. presence of construction materials. Variables with p-values of ≤ 0.15 from the single factor models were included in a provisional multi-factor model since opting for the more conventional level of 0.05 at this stage could fail to identify all the important variables65. A mixed forward and backward stepwise model selection approach was used to determine the final model using the Akaike Information Criterion (AIC). We chose the most parsimonious model with ΔAIC < 2 compared to the minimum as the final model66.
All analyses were performed in R version 4.3.067, using the lme4 “nAGQ = 9”68 and MuMIn “v1.43.17”69 (Barton, 2020) packages.
Table 1: Summary of the generalized linear model showing the variables that were associated with rodent proliferation in The Bahamas
|
Signs of household rodent infestation
|
Predictors
|
Odds Ratios
|
CI
|
P
|
(Intercept)
|
0.09
|
0.04 – 0.19
|
<0.001
|
Area [2]
|
0.55
|
0.20 – 1.50
|
0.192
|
Area [3]
|
0.36
|
0.13 – 1.00
|
0.047
|
Area [4]
|
0.27
|
0.08 – 0.84
|
0.021
|
Area [5]
|
0.71
|
0.34 – 2.91
|
0.532
|
Area [6]
|
0.99
|
0.31 – 2.64
|
0.855
|
Area [7]
|
0.07
|
0.02 – 0.28
|
<0.001
|
Residence with unapproved refuse storage [Yes]
|
2.29
|
1.22 – 4.27
|
0.008
|
Residence with exposed garbage [Yes]
|
2.31
|
1.20 – 4.45
|
0.016
|
Residence with source of animal food [Yes]
|
2.30
|
1.11 – 4.17
|
0.021
|
Residence with other sources of food [Yes]
|
1.76
|
0.89 – 3.53
|
0.096
|
Residence with bulk wastes [Yes]
|
2.06
|
1.00 – 4.21
|
0.045
|
Residence with construction materials [Yes]
|
2.06
|
1.04 – 4.07
|
0.047
|
Residence with structural deficiencies [Yes]
|
3.09
|
1.52 – 6.25
|
0.001
|
Observations
|
457
|
R2 Tjur
|
0.358
|