Colorado State University, Universidad Autonoma de Yucatan, and Servicios de Salud de Yucatan conducted a study from March 2007 to February 2008 to determine abundance of Aedes aegypti and presence of dengue virus (DENV) in female mosquitoes in the homes of laboratory confirmed dengue patients in Merida, Yucatan, Mexico.

880 homes were examined for presence of Ae. aegypti with backpack aspiration, and pools of Ae. aegypti females from 335 homes were examined for presence of DENV by RT-PCR.

Examples of typical houses in Merida

Backpack aspiration

Aedes aegypti and Culex quinquefasciatus were most the most commonly collected mosquitoes over the 12-month study period.

Environment and species	Females			Males
	Total number collected	(% of total)	Range for individual homes	Total number collected	(% of total)	Range for individual homes
Indoors
Aedes aegypti	1,836	39.7	0-83	1,292	38.2	0-48
Culex quinquefasciatus	2,641	57.1	0-59	2,076	61.4	0-189
Ochlerotatus taeniorhynchus	147	3.2	0-11	14	0.4	0-5
Ochlerotatus trivitattus	3	<0.1	0-3	0	0
Total	4,627	100		3,382	100
Backyard/Patio
Aedes aegypti	102	35.0	0-21	108	29.2	0-32
Culex quinquefasciatus	135	46.2	0-14	237	64.0	0-115
Ochlerotatus taeniorhynchus	50	17.1	0-10	20	5.4	0-12
Ochlerotatus trivitattus	5	1.7	0-3	5	1.4	0-2
Total	292	100		370	100

Aedes aegypti and Culex quinquefasciatus were collected predominantly from bedrooms and living/dining rooms during indoor collections.

Room	Females			Males
	Number collected	(% of total)	Range for individual homes	Number collected	(% of total)	Range for individual homes
Aedes aegypti
Bedroom	1,107	60.3	0-40	670	51.9	0-48
Living/Dining room	337	18.4	0-11	296	22.9	0-30
Kitchen	137	7.5	0-7	110	8.5	0-28
Bathroom	121	6.6	0-7	61	4.7	0-11
Storage room	71	3.9	0-6	66	5.1	0-21
Other rooms	54	2.9	0-19	66	5.1	0-29
Laundry room	9	0.5	0-2	23	1.8	0-6
Total	1,836	100		1,292	100
Culex quinquefasciatus
Bedroom	1,388	52.6	0-35	716	34.5	0-83
Living/Dining room	436	16.2	0-39	262	12.6	0-26
Kitchen	287	10.9	0-51	259	12.5	0-67
Storage room	225	8.8	0-59	432	20.8	0-189
Bathroom	172	6.5	0-6	161	7.8	0-38
Other rooms	85	3.2	0-13	168	8.1	0-50
Laundry room	48	1.8	0-5	78	3.8	0-27
Total	2,641	100		2,076	100

Dengue virus (DENV) was detected from 34 pools of female Ae. aegypti collected from dengue patient premises.

Collection period	Total no. of mosquitoes tested	No. of pools tested (premises represented)	No. (%) of pools positive for DENV	Minimum DENV infection rate (%)a
March 2007	42	10 (10)	0 (0)	0
April 2007	14	5 (5)	0 (0)	0
May 2007	0	0	0 (0)	0
June 2007	11	5 (5)	0 (0)	0
July 2007	100	11 (11)	4 (36.4)	4.0
August 2007	234	22 (22)	2 (9.1)	0.9
September 2007	518	74 (74)	13 (17.6)	2.5
October 2007	543	105 (104)	7 (6.7)	1.3
November 2007	314	61 (61)	5 (8.2)	1.6
December 2007	126	32 (32)	3 (9.4)	2.4
January 2008	29	10 (10)	0 (0)	0
February 2008	7	1 (1)	0 (0)	0
Total	1,938	336 (335)	34 (10.1)	1.8

^a Based on the assumption of one infected mosquito per pool.

The seasonal patterns of abundance of Ae. aegypti and dengue cases in Merida largely followed the pattern of rainfall.

Collections of DENV-infected Ae. aegypti females commonly occurred 7-21 d after the onset of symptoms in the dengue patients (see table below). This demonstrates the usefulness of indoor application of insecticides in the homes of suspected dengue patients (by the home-owner with spray cans and/or by vector control by fogging) to prevent their homes from becoming sources for dispersal of DENV by persons visiting and being bitten by infected mosquitoes.

Dengue patient characteristics		Testing of female Ae. aegypti from patient�s premise for DENV
Date of onset of symptoms	DENV serotypea	Mos-quito pool ID	Date of mosquito collection	Days between onset of symptoms and mosquito collection	Rooms from which females were collectedb	No. of females pooled and tested	DENV serotypea
06-29-07	ND	91	07-13-07	14	B/P, L	2	DENV-1
07-16-07	ND	98	07-25-07	9	L, Bed, B/P, O	16	DENV-3
07-11-07	ND	101	07-30-07	19	B/P, Bed, O	7	DENV-1
07-10-07	ND	102	07-31-07	21	Bed, K, L	27	DENV-1
07-24-07	ND	117	08-08-07	15	L, O	13	DENV-1
08-08-07	ND	127	08-20-07	12	Bed, L	15	DENV-1
08-08-07	ND	151	09-03-07	26	L	2	DENV-2
08-22-07	ND	164	09-05-07	12	Bath, Bed, L, B/P	21	DENV-2
08-21-07	ND	165	09-05-07	15	Bed	12	DENV-1
09-03-07	DENV-2	174	09-07-07	4	B/P	9	DENV-2
09-02-07	DENV-1	176	09-07-07	5	Bed	18	DENV-1
09-08-07	ND	211	09-14-07	6	Bath, L	4	DENV-1
09-03-07	ND	232	09-18-07	15	Bed	2	DENV-1
09-12-07	DENV-1	247	09-20-07	8	Bed, L, O	11	DENV-1
09-06-07	ND	267	09-21-07	15	Bed	6	DENV-1
09-15-07	ND	297	09-27-07	12	Bed	7	DENV-1
09-07-07	ND	300	09-26-07	9	Bed, Bath, K	7	DENV-2
09-16-07	ND	305	09-27-07	11	Bed	10	DENV-1
09-18-07	ND	309	09-28-07	10	Bed	27	DENV-1
09-17-07	ND	367	10-05-07	18	Bed, L	7	DENV-2
09-23-07	ND	390	10-09-07	16	Bed, L	9	DENV-2
09-24-07	ND	411	10-10-07	16	Bed	9	DENV-1
10-08-07	ND	437	10-12-07	4	Bed, L	28	DENV-2
10-01-07	ND	449	10-15-07	15	K	3	DENV-1
09-28-07	ND	487	10-17-07	19	Bed, O	6	DENV-3
10-22-07	ND	592	10-29-07	7	Bed	5	DENV-1
10-22-07	ND	647	11-1-07	9	Bed, Bath	4	DENV-1
10-20-07	ND	668	11-7-07	18	Bed	4	DENV-1
10-29-07	ND	710	11-12-07	14	Bed	4	DENV-2
11-05-07	DENV-1	713	11-13-07	8	L	9	DENV-1
10-31-07	ND	812	11-21-07	21	Bed, L	3	DENV-1
11-07-07	ND	920	12-04-07	27	Bed, L	3	DENV-1
11-09-07	ND	982	12-06-07	27	K	3	DENV-1
12-09-07	DENV-1	1087	12-18-07	9	Bed	8	DENV-1

^a Dengue virus serotype was determined by RT-PCR; ND, not determined.
^b Bath, bathroom; Bed, bedroom; K, kitchen; L, living/dining room; O, other room; B/P, backyard/patio.

Adapted from Garcia-Rejon et al. 2008. Dengue virus-infected Aedes aegypti in the home environment. American Journal of Tropical Medicine and Hygiene 79: 940-950.