A Comparative Study on the Efficacy of

N-N-diethyl-m-toluamide, Picaridin,

and Citronella as Repellents Against

Aedes Aegypti

• January to August 2012– Dengue Fever: 7321 cases– Dengue Hemorrhagic Fever: 4181

cases

• January to August 2013– Dengue Fever: 2494 cases– Dengue Hemorrhagic Fever: 1552

cases

Recent large clinical trial conducted in Thailand yielded only 30% effectivity of the dengue vaccine, 40% short of it’s expected outcome.

Celgosivir (6-O-butanoyl castanospermine), which misfolds the dengue NS1 protein is still in the initial stages of clinical trials.

Most Feasible Prevention

Insect Repellents

• DEET (N, N diethyl-meta-toluamide)– GOLD STANDARD– Blocks insect olfactory receptors– Toxic effects:

• impaired cognitive function• Insomnia•mood distrubances,•severe epidermal reactions

Insect Repellents

•Non-DEET containing–Picaridin–Citronella

PICARIDIN

• (2-(2-hydroxyethyl)-1-piperidinecarboxylic acid 1-methylpropyl ester)

• used in Europe, Australia, Latin America and Asia as an alternative to DEET

• Unknown exact mechanism of action but repellency is comparable to that of DEET

• included in the list of effective repellents by the CDC

CITRONELLA

• plant-based insect repellent• product from the steam distillation of

freshly cut or partially dried grasses• unkown exact mechanism of action

but acts mainly as a feeding depressant

• US Environmental Protection Agency classifies citronella’s dermal toxicity as Category III or only slight toxicity if improperly used

General Objective

–To compare the efficacy of different variants of insect repellents (DEET containing versus non-DEET containing versus plant-based) against mosquito landing and bites

Specific Objectives

1. To determine the LANDING frequency (mosquitoes landed on the subject, but not necessarily bit) for each variant of insect repellent

2. To compare the MEAN LANDING frequency of the insect repellents

3. To determine the BITING frequency for each variant of insect repellent

Specific Objectives

• 4. To compare the MEAN BITING frequency for the insect repellents

• 5. To determine which of the insect repellent variant provides the best protection against mosquito bites

• 6. To observe adverse events/reaction, if there is any, upon application/usage of the insect repellents

Materials and Methods

• STUDY DESIGN– Double blind randomized controlled

trial

• Proposal reviewed and approved by IRB

• SETTING

• STUDY POPULATION– any male or female– aged 18-50 years old– without pre-existing co-morbidities

and allergies

Aedes Aegypti Mosquitoes

• SAMPLE SIZE– 9 (WHO and RITM protocol)

Repellents Tested

• A: N-N-diethyl-meta-toluamide (DEET) 25%

• B: Picaridin 10%• C: Citronella

• Informed consents were secured.• Subjects were randomly allocated

to three groups.

• Eight trials• Test mosquitoes replaced for

each trial• Each trial ran for 5 minutes• Repellent was not reapplied prior

to the next trial

• Adverse Reactions were recorded– Rashes– Pain– Discomfort– Difficulty of Breathing

Events

• LANDING FREQUENCY: number of mosquitoes that LANDED on the test limb instantaneously

• BITING FREQUENCY: number of mosquitoes that landed on the test limb and are able to BITE the test limb, may be evidenced by the appearance of a rash/papule on the test limb

Statistical Analysis

• One-Way Analysis of Variance– To prove that at least two of the

means are significantly different

• Tukey’s Test– To compare specific pairwise

differences

Results

Landing FrequenciesTRIA

L1 2 3 4 5 6 7 8 MEAN TOTA

L

DEET

A 2 8 0 0 3 6 10 8 4.625 6.43

B 0 0 0 0 2 3 5 6 2.000

C 0 0 3 8 29 0 23 38 12.625

PICARIDIN

A 5 17 40 13 31 28 35 32 25.125 47.12

B 22 32 40 43 48 70 58 74 48.375

C 24 66 57 47 75 92 86 96 67.875

CITRONELLA

A 30 69 127 90 135 105 167 132 106.88 65.33

B 32 44 53 52 80 77 113 98 68.625

C 6 12 13 23 25 16 26 43 20.500

Hourly Landing Frequency

Biting FrequenciesTRIA

L1 2 3 4 5 6 7 8 MEAN TOTA

L

DEET

A 0 0 0 0 0 0 0 0 0 0.292

B 0 0 0 0 0 0 0 0 0

C 0 0 0 0 6 0 0 1 0.875

PICARIDIN

A 0 0 1 0 1 2 1 2 0.875 1.333

B 0 0 0 0 0 0 1 1 0.250

C 24 66 57 47 75 92 86 96 67.875

CITRONELLA

A 0 41 30 27 50 105 167 132 69.000 32.04

B 0 7 12 13 26 23 30 32 17.875

C 0 9 11 11 13 7 13 10 9.250

Hourly Biting Frequency

One Way ANOVA (Landing)

• Critical Value (F): 5.14• Computed Test Statistic: 20.255

• Decision: Reject Null Hypothesis

SOURCE Degrees of Freedom

Sum of Squares

Mean Squares

F

Treatment 2 14131.266 5977.288 20.255

Error 6 1770.613 295.102

Total 8 15901.879

One Way ANOVA (Biting)

• Critical Value (F): 5.14• Computed Test Statistic: 0.729

• Decision: Do not Reject Null Hypothesis

SOURCE Degrees of Freedom

Sum of Squares

Mean Squares

F

Treatment 2 1133.444 395.297 0.729

Error 6 3251.901 541.984

Total 8 4385.345

Tukey’s Test (Landing)

• D min: 24.850

SET-UP A B C

6.417 47.125 65.333

A 6.417 40.708 58.916

B 47.125 18.208

C 65.333

• NO allergic reactions noted

Discussion

• DEET, the gold standard, provided the best protection against mosquito bites based on landing and biting frequency

• Picaridin and citronella subjects acquired more landing and bites

-Consistent with studies done by Fradin and Beeyer -DEET is still the most effective mosquito repellent in the market.

Discussion

• INCREASE in the number of landing and bites as the trials progressed (waning of repellency)

Discussion

• One Way ANOVA for LANDING frequency: mean landing frequencies are SIGNIFICANTLY DIFFERENT from one another.

• One Way ANOVA for BITING frequency: mean biting frequencies are NOT SIGNIFICANTLY DIFFERENT from one another.

Discussion

• Less number of bites compared to landing in general

• Raw data: DEET subjects had the LEAST NUMBER of bites (best protection among the three)

Discussion

• Tukey’s test: In general, mean landing frequencies are SIGNIFICANTLY DIFFERENT

Discussion

• Consolidating raw data and statistical analysis– DEET is SUPERIOR to Picaridin and

Citronella in repellency, based on LANDING and BITING frequency

Conclusion

• DEET is SUPERIOR to Picardin and Citronella based on LANDING and BITING frequency raw data

• One Way Analysis of Variance: MEAN LANDING frequencies are SIGNIFICANTLY DIFFERENT, MEAN BITING frequencies are NOT SIGNIFICANTLY DIFFERENT

• Tukey’s Test: In general, MEAN LANDING frequencies are SIGNIFICANTLY DIFFERENT

• DEET provides the BEST PROTECTION against Aedes Aegypti

Limitations and Recommendations

• Minimum required sample size employed, larger sample size needed for a more conclusive study

• Only the landing and biting frequency were measured. Toxicity is another important parameter

• Future studies: recommendations on the safe levels of insect repellents