Research Proposal A Study on the Threshold of Triatoma dimidiata Domestic Infestation Rate: For the regional elimination of Chagas disease in the Central America

August 15, 2008

Japan International

Cooperation Agency World Health Organization

Pan-American Health Organization

Secretariat of Health, Republic of Honduras

Ministry of Public Health and Social Welfare

Republic of El Salvador

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Table of Contents

1. Introduction………………………………….....……………………………………………… 2 2. Objectives of study…………………....................…..………………………………………..… 3

2.1 Objectives………………………........................………………………..…………….…… 3 2.2 Hypotheses ……........................………………..………………………...………………… 3

3. Data collection methods………………………………………………….…………......…..… 3

3.1 Target areas and individuals…………………………………………….…………….…… 3 3.1.1 Target area selection………………………………………………..……………..… 3 3.1.2 Target individual selection………………..………………………..………………… 3 3.1.3 Establishment of a cohort clusters…………………………….…..………………… 4

3.2. Study period………………………………………………………...…..…………….…… 4

3.2.1 Primaly data collection frequency and period…..………………………………… 4 3.2.2 Secondary data collection:………...........………………..…...…………………… 4 3.2.3 YEAR3, May 2010……………………………………………..……..……………… 4

3.3. Type of data to be collected…………………………………….....……………………… 5

3.3.1 Serological test……………………………….…………........……………………… 6 3.3.2 Entomological test……………………………………………….…..................…… 6

3.4 Ethics………………………………………………………….…...………………………… 7

4. Data analysis plan……………….………………………………...…………………………… 8

4.1 Outline of analytical approach……..........................................................................… 8 4.2 [Step 1] Association between infestation rate and seroprevalence……..................… 8 4.3 [Step 2] Relationship between correlation coefficient and age…............................... 9

5. Limitation of the study………......….…………………………………………………..……… 9 6.Research committee…….........…….…………………………………………………..……… 10 References……………………………...…………..………………………………………….…… 11 Tables & Figures Table 1 Timeline of the study Figure 1 Association between infestation rate and seroprevalence Figure 2 Relationship between correlation coefficients (Spearman ρ) and age

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1. Introduction

Today, Neglected Tropical Diseases (NTDs) are a symptom of poverty and disadvantages (WHO 2006). Chagas disease, one of the 14 NTDs adopted by WHO, is the most closely associated with poverty (Paz-Bailey et al. 2002) as it has been more prevalent among those living in poor housing structures made from mud-blocks. It is also the world’s fourth most critical parasitic disease after malaria, schistosomiasis and intestinal worms (World Bank 1993). To address the disease, the Central American countries have been sharing the common goal of elimination of transmission of Chagas disease by 2010, since the joint launch of the Initiative of the Central American Countries for the Control of Chagas Disease (IPCA) in 1998. One of the three specific targets of the initiative is to control Triatoma dimidiata (T. dimidiata), a major vector of Chagas disease (WHO 2002).

Although the control of T. dimidiata has recently made a significant progress in each country, it is not clear to what extent and how further domestic infestation rates need to be reduced and maintained in itsendemic areas. The domestic infestation rate of T. dimidiata has been reduced: from 16.3% in 2003 to 0.7% in 2006 in the western endemic areas of El Salvador (JICA 2007); from 31.1% in 2004 to 11.5% in 2006 in the western endemic areas of Honduras (JICA 2007); and from 10.3% in 2000 to 2.7% in 2005 in Guatemala (Hashimoto 2005). However, it would be useful to find out at what level the domestic infestation rate of T. dimidiata should be controlled during the period of the MSPAS/SH-JICA Chagas Disease Control Projects (phase II) period, as they are aimed at establishing self-reliant surveillance and response system. Note that it is reality that the target threshold for the domestic infestation rate of T. infestans in some parts of Brazil (=5%) has been applied to that of T. dimidiata in Central America (PAHO 2005) without scientific justifications. Yet, 5% should be respected as the tentative target threshold till the rigorous one is identified in a scientific manner, because it is commonly accepted as the empirical in the Central American countries.

Several earlier studies reported that T. dimidiata is a less effective vector than R. prolixus (Paz-Bailey et al. 2002; Ponce et al. 1995). This is possibly because T. dimidiata defecates more slowly when feeding and, when infected, its faeces is less likely to contain Trypanosoma cruzi than R. prolixus (Coura 1988). However, T. dimidiata, an indigenous species in Central America, is difficult to control because it infests not only housing structures but also peri-domestic and silvatic habitats (WHO 2002). The control target therefore, is not complete elimination (such as control of R. prolixus) but instead to reduce domestic infestation rates to the levels below which transmission would become unlikely.

To identify possible thresholds, below which the domestic infestation rate of T. dimidiata should be controlled as a better replacement for 5% in a scientific manner will be conducive to efficient achievement of the IPCA target by saving resources and costs to be invested1 (e.g. insecticide procured, human resources for sprayers, households’ opportunity cost for preparation for being sprayed). Thus, this study is crucial to controlling T. dimidiata in its endemic areas of the Central American countries.

1 Presentation of the threshold will help save the resources to be invested for achievement of the IPCA goal.

Nevertheless, note that this does not suggest the presence of bugs such as T. dimidiata be admitted and acceptable in each household. Continuous efforts should be made so as for no single bug to be finally identified, regardless of being infected by T. cruzi.

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2. Objectives of the study

2.1 Objectives: The objective of the study is to verify the possible thresholds below which the domestic infestation rate of T. dimidiata should be controlled for more efficient vectorial transmission of Chagas disease in Central America. To achieve this objective, both spatial and temporal relationships between entomological and serological indicators willl be examined.

2.2 Hypotheses

Hypothesis 1: A threshold below which the domestic infestation rate of T. dimidiata should be controlled in its endemic areas exists and is identifiable. Hypothesis 2: Seroprevalence is in proportion to the length of time spent in infested housing structures, which is reflected and approximated by individuals’ age.

3. Data collection methods

It is proposed that the data collection for the study be designed in the following manner.

3.1 Target areas and individuals

3.1.1 Target area selection: An adequate number of localities are selected per department with MSPAS/SH-JICA intervention, e.g. three localities: 21 (=7x3) in El Salvador 2 ; 24 (=8x3) in Honduras3; and in total 45 (=21+24). This arbitrary number of localities per department should be adjusted, according to the number of children under 15 years of age residing in those localities the locality list to ensure the adequate number of cohort clusters (see 3.1.3). There are four major criteria for locality selection. First, localities free of R. prolixus are selected. Second, those localities ideally should have various infestation rates of T. dimidiata, to ensure the diversity that enables a possible threshold to be identified (e.g. 10%, 20%, 30%, 40%, etc.). Third, similarly those localities should have various seroprevalence among children under 15 years of age, to ensure the diversity that enables a possible threshold to be identified (e.g. 0.5%, 1%, 1.5%, etc.). Fourth, the localities to be selected should ideally have infrequent migration, to avoid significant reduction of the cohort size (see 3.1.3). Fifth, a locality or cluster should have more than 40 households. (Considering that an average of three children under 15 years live in each household, a total children in 40 household will be 120. This criterion allows us to have at least 100 children under 15 years in each locality or cluster.)

3.1.2 Target individual selection: All the children over 6 month years of age and under 15 years of age are selected in each cluster (i.e. census in selected clusters).4 To examine this hypothesis, this study also attempts to estimate the extent to which the current infestation rate of T. dimidiata is associated with seroprevalence by age(-group) by applying Spearman’s correlation coefficients (non-parametric method).

2 Since there are seven target localities for the SH-JICA Project in El Salvador, it is suggested that 21 localities (= 7x3)

be covered by the study 3 Since there are eight target localities for the MSPAS-JICA Project in Honduras, it is suggested that 24 localities (= 8x3)

be covered by the study. 4 In El Salvador, all the children under 16 years of age in target localities are targeted for serological test.

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3.2. Study period

3.2.1 Primaly data collection frequency and period: Data collection will take place twice; first between July and November in 2008, and second between July and November and 2010. Each country will decide the exact data collection periods, considering the operational schedules for dengue fever control activities.

3.2.2 Secondary data collection: In parallel to this primary data collection in the target areas of El Salvador and Honduras, it is desirable to collect similar datasets available and accessible in neighbouring countries such as Guatemala. This will enrich the robustness of data and subsequently help ensure more universal threshold applicable across the T. dimidiata prevalent countries.

3.2.3 Timeline of the study: The following table presents the timeline of the major milestone tasks and responsibility to be taken by each stakeholder (see Table 1).

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3.3 Type of data to be collected

In principle, only the data necessary for achieving the study objectives should be collected. In other words, those data without analysis plan should be dropped off, to efficiently use the study resources and relieve possible burdens of interviewee households (Aiga 2006). In view of this, the types of the data to be collected include:

(1) Serological data (seroprevalence per age group at time of testing) => individual-based data; (2) Entomological data (domestic and peri-domestic infestation rate of T. dimidiata % at time of

survey and past data from existing dataset) => cluster-based data; (3) Socio-demographic data (birth, death, migration, household composition) =>

individual/household-based data; and (4) Environmental data (coordinates, altitude, past spraying intervention) => cluster-based

data.

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3.3.1 Serological test: It is crucial to employ high quality of serological test which are sensitive enough to detect seropositivity of Chagas disease. Key point is to ensure the human resources with adequate technical skills who are available commonly in El Salvador and Honduras. A combination of ELISA IgG and Stat-Pak tests are employed for serological tests. The details on the techniques required for the ELISA IgG test are presented in Annex 1. The most resourceful expert on serological tests is Dr. Carlos Ponce of the SoH, Honduras. It is essential to match between serological, entomological, and other data so as to enable finally all these datasets to be integrated into one datafile.

3.3.2 Parasitological test: If person suspected of being acute cases of Chagas disease during the serological test, the presence of parasite in the blood will be tested (Annex 2), and in case of being positive, that result will be included as a result of the survey. 3.3.3 Entomological test5: Of the following two methods, “One-hour person-minutes method” should be employed as a common requirement for both El Salvador and Honduras (Annex 3). In accordance with local situation and the government’s decision, “verbal investigation”, another method, can be additionally employed for smoother implementation of “One-hour person-minutes method”. (i) 60 person-minutes method: A pair of two trained investigators searches for the bugs in both intra-domestic (indoor) and peri-domestic (outdoor) by spraying flush-out insecticide sensitive to T. dimidiata,6 (Annex 4). First, the pair attempts to search a T. dimidiata bug by spending max 20 person-minutes (i.e. 10 minutes per investigator)7 in the bedroom where each child under 15 years of age sleeps. Once any T. dimidiata bug is detected in the bedroom, the house will be judged to be domestically infested. Second, after finishing searching bugs indoor, the pair moves to small-scaled man-made facilities located in the peri-dometic areas (e.g. poultry house, animal shed, kitchen, latrine, bathroom) to determine whether the house is peri-domesitcally infected. Max 10 person-minutes (5 minutes per investigator) should be spent. Once any T. dimidiata bug is detected in the peri-domestic area, the house will be judged to be peri-domestically infested.8 According to the Honduran National Chagas Programme policy, bug(s) should be sent to the local health facility when T. dimidiata is found by inhabitants after the process of the 30 person-minutes method. This is important from the public health viewpoint to ensure sustainability of community-self-reliant monitoring system, although the data reported will not be analyzed for this study.

5 “A4-white paper method”, another method for detecting bug, (Schofield et al. 1986; Monroy C et al. 1998) is not

recommended for this study, because it is less effective. The method involves investment of significant resources but is not sensitive enough to T. dimidiata.

6 Acqua Resilina (Bayer). Composition: (i) 10.8% permelthrin; and (ii) 0.18% broallethrin. 7 Once a bug is detected in a bedroom before 20 person-minutes have passed, the pair of investigators can finish

searching bugs indoor and move outdoor in search for bugs in the peri-domestic area. 8 Once a bug is detected in the peri-domestic area before 10 person-minutes have passed, the pair of investigators can

finish searching bugs.

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4. Data analysis plan

To assess age-specific relationship between seroprevalence and domestic/peri-domestic infestation rates of T. dimidiata, it is important to ensure the number and diversity of the plots of these two variables (see Figure 1) are adequate. Ideally, there should be 50-70 plots (i.e. 50-70 clusters)9 with a variety of infestation rates and seroprevalance rates. Moreover, it is essential to ensure the weight of each plot is standardized to a reasonable extent. Therefore, a cluster composed of approximately 100 (±20) children under 15 years of age is established.10 For instance, a locality with 800 children under 15 years of age is divided into eight clusters which will create eight plots. Those children should be consistently contacted when baseline end-point data collections are conducted. This cohort construction enables more accurate measurement of the intervention impact to be feasible. However, note that some of those initially contacted during baseline data collection may be lost to follow-up (e.g. emigration into other area, death). This information should be fully recorded to ensure the cohort size. Similarly, there should be some under 15 years of age who may immigrate into and be newly born in the target clusters. Those children should be included in the dataset, although they are not part of cohort because they have not participated in the study during the baseline data collection period. Nevertheless, it is crucial to include those when calculating seroprevalence and infestation rate since this study is aimed at developing practical tools which must have already considered demographic vitality such as migrations, deaths, and births.

We propose the data analysis for the study be conducted in the following manner. For data entry, either Epi-Info or Excel is recommended. Once the data are fully entered and cleaned up, then it will be exported to SPSS for analysis purpose.

4.1 Outline of analytical approach

To achieve the objectives, a series of analyses are composed of two steps: (i) [Step 1] to assess the association between domestic infestation rate of T. dimidiata and seroprevalence among each age group of selected populations; and (ii) [Step 2] to identify a possible threshold below which the infestation rate of T. dimidiata needs to be controlled for ensuring an elimination of or a significant lower prevalence of Chagas disease caused primarily by T. dimidiata.

4.2 [Step 1] Association between infestation rate and seroprevalence:

First, the mean of seroprevalence of each cluster is plotted against its infestation rate of T. dimidiata (see Figure 1) by age or by age group. Only when either non-parametric correlation coefficient (Spearman ρ) is significant (p<0.05) or R2 is great enough (e.g. >0.25), should a regression line be drawn. Then, its intersection with horizontal axis, if there is, would be a possible threshold which ensures adequately low seroprevalence (≈ 0%).11

9 The number of cohort clusters required should be adjusted, according to logistic feasibility, and resource availability.

There are five major selection criteria for the localities. 10 Clusters should be set according to geographic context of each locality (e.g. block, hamlet, etc.) 11 More than 1 regression line could be drawn per age group. When it is revealed that T. dimidiata has different levels

of force of infection (FOI) according to their sub-species and environmental factors, it is necessary to classify the plots with the same spatial conditions into one group, calculate correlation coefficient for each group, and then draw a regression line, if correlation coefficient is significant (e.g. p <0.05) and great enough (|ρ| >0.30 or R2>0.30).

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Figure 1 Association between infestation rate and seroprevalence

Infestation rate of T. dimidiata

Ser

opre

vale

nce

(%)

ki: Infestation rate threshold

[Example] 2 years of age Spearman ρ = 0.71 p-value = 0.048 *

R2 = 0.305 Significant correlation

[Example] 1 year of age

Spearman ρ = 0.85 p-value = 0.032 *

R2 = 0.588 Significant correlation

coefficient

. . . . . . . .

[Example] 14 years of age Spearman ρ = 0.23

p-value = 0.868 R2 = 0.152

Not significant correlation coefficient

El Salvador

Honduras

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4.3 [Step 2] Relationship between correlation coefficient and age

To assess and identify valid age groups among which the current infestation rate of T. dimidiata can represent the effective risks to being infected, age-specific non-parametric correlation coefficients (Spearman ρ) between infestation rate and seroprevalence are plotted against age (see Figure 2). Most likely limited age groups (e.g. up to 2 years of age) will produce significant correlation coefficient (p<0.05). This implies an infestation rate adequately is reflected as a risk factor on seroprevalence only among the age groups. In other words, the seropositive of other age groups most likely had been infected either many years ago or prior to migrating into the locality.

Figure 2 Relationship between correlation coefficients (Spearman ρ) and age

5. Limitations of the study

There are several possible limitations in this study as follows.

(1) There are a number of sub-species of T. dimidiata and their natural infection rates significantly vary (Dorn et al. 2007; Schofield CJ. 2000). Therefore, a threshold to be identified may be specific to El Salvador and Honduras and cannot be applied to other T. dimidiata-prevalent countries or areas. Moreover, the validity of the threshold even for El Salvador and Honduras will need further triangulation and fine-tuning.

(2) This study does not examine the natural infection rate of faeces of T. dimidiata. Therefore, there will be a certain limitation in ensuring the validity of threshold. Again, further studies will be necessary.

p < 0.05

p ≥ 0.05

Age (year)

Spea

rman

ρ

1 year of age

2 years of age

3 years of age

14 years of age

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6. Ethics

An informed consent to participate in the study is obtained in written form from individuals at every data collection point (i.e. baseline and end-point). In the case of children under fifteen years of age, consent should be obtained from their parents (Annex 5). In addition, an ethical approval is obtained from the authority responsible for health researches in both El Salvador and Honduras. All the houses found to be infested by T. dimidiata will be sprayed with appropriate insecticide and that all the children found to seropositive be treated. All the children being suspected of being acute cases will receive parasitological diagnosis for confirmation.

There are two main justifications for exclusion of those 15 years of age and older. First, it is ethically difficult to justify the inclusion of those 15 years of age and older because currently there is no effective and officially recommended therapy against Chagas disease for that age group. Second, some of them would most likely have been infected significantly longer years ago. For this reason, it is highly questionable that the current infestation rate of T. dimidiata can represent the risks which actually have caused infection on them.

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7. Research committee

It was agreed to organize a research committee to maintain momentum and quality assurance of this study. The members and their roles are described as follows:

Ministry of Public Health and Social Welfare (MSPAS), El Salvador Dr Hector Manuel Ramos Hernandez (National Programme of Chagas, MSPAS, San

Salvador) Dr Mario Vicente Serpas Montoya (Health Surveillance Direction, MSPAS, San Salvador) Mr. Eduardo Romero (National Programme of Chagas, MSPAS, San Salvador)

Secretariat of Health (SH), Honduras

Dr Concepcion Zuniga Valeriano (National Programme of Chagas & Leishmaniasis, SH, Tegucigalpa)

Dr Carlos Ponce (National Laboratory of Chagas & Leishmaniasis, SH, Tegucigalpa) Japan International Cooperation Agency (JICA)

Dr Hirotsugu Aiga (Dept of Human Development, JICA, HQ, Tokyo) Dr Jun Nakagawa (Chagas Disease Control Project II, JICA, San Salvador) Ms Emi Sasagawa (Chagas Disease Control Project II, JICA, San Salvador) Dr Ken Hashimoto (Chagas Disease Control Project II, JICA, Tegucigalpa) Mr Jiro Nakamura (Chagas Disease Control Project II, JICA, Tegucigalpa)

World Health Organization (WHO)

Dr Jean Jannin (IDM/NTD, WHO, Geneva) Dr Pedro Albajar Vinas (IDM/NTD, WHO, Geneva) Dr Kazuyo Ichimori (VEM/NTD, WHO, Geneva)

Pan-American Health Organization (PAHO)

Dr Roberto Salvatella (Regional Coordinator for Chagas, PAHO Uruguay) Dr Enrique Gil (Transmissible Diseases, PAHO, Guatemala)

European Community Latin American network for research on Triatominae (ECLAT)

Dr Chris Schofield (ECLAT, London)

Responsibilities of Committee Member:

(1) MoH Joint data collection and analysis with JICA; (2) JICA Joint data collection and analysis with MoH, coordination and financial assistance; (3) WHO Technical advice; (4) PAHO Technical advice; and (5) ECLAT Technical advice.

Note; In Honduras, CIDA (Canadian International Development Agency) are prepared to provide technical and financial assistance to this study.

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8. Timeline of the study

Step # Tasks Responsible party

Proposed timing Status

Step 1

Prepare 1st draft technical proposal and share it with the Research Committee members

JICA HQ fm: 1st Apr 2008 to: 11th Apr 2008

Done

Step 2

Revise 1st draft technical proposal and prepare the final draft

JICA HQ fm: 1st Apr 2008 to: 30th Apr 2008

Done

Step 3

Design draft data collection tools JICA Project (Honduras) fm: 1st Apr 2008 to: 30th Apr 2008

Done

Step 4

Adjust the final draft technical proposal to data collection tools and finalize it

JICA HQ fm: 1st May 2008 to: 20th May 2008

Step 5

Adjust the draft data collection tools to the final draft technical proposal and finalize them

JICA Project (Honduras) fm: 1st May 2008 to: 20th May 2008

Step 6

Prepare financial proposals (cost estimation)

JICA Project (El Salvador) JICA Project (Honduras)

fm: 1st May 2008 to: 30th Jun 2008

Step 7

Obtain approval by ethical committee of El Salvador and Honduras

MSPAS/ SH fm: 20th May 2008 to: 31th Jul 2008

Step 8

Define the human and financial resources

MSPAS/ JICA Project (El Salvador) SH/ JICA Project (Honduras) JICA El Salvador Office JICA Honduras Office JICA HQ

fm: 1st May 2008 to: 31st Jul 2008

Step 9

Implement primary data collection at the field

MSPAS/ JICA Project (El Salvador) SH/ JICA Project (Honduras)

fm: Jul 2008 to: Nov 2008

Step 10

Analyse the collected data MSPAS/ JICA Project (El Salvador) SH/ JICA Project (Honduras) JICA HQ

fm: Dec 2008 to: Feb 2009

Step 11 Write a progress report and final report

MSPAS/ JICA Project (El Salvador) SH/ JICA Project (Honduras)

2009

Step 12

Coordinate the committee to write a first paper

JICA HQ 2009

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References

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Hashimoto K. (2005). Informe Final: Prevención y Control de la Enfermedad de Chagas en la República de Guatemala. Guatemala City: PAHO.

Hashimoto K, Trampe R, Cordón-Rosales C, Kawabata M. (2006) Impact of multiple residual spraying of pyrethroid insecticides against Triatoma dimidiata (Reduviiade; Triatominae), the principal vector of Chagas disease in Jutiapa, Guatemala. American Journal of Tropical Medicine and Hygiene. 75 (2):226-230.

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