Fræðigrein

Background: Sensitization to Dermatophagoides pteronyssinus (D. pteronyssinus) occurs in 9% of the Reykjavik population, despite the fact that no Der p 1 antigen has been found in the area. A recent study revealed that sensitized persons more often had a childhood history of work or holiday stay in rural areas than controls. As a follow up we studied the risk of exposure to mites in farmland dwellings.

Methods: In a survey of work-related lung disorders among farmers in the south and west of Iceland, 80 samples of house dust, representing 42 farms, were collected from bedroom mattresses and the floors in living rooms and examined for mites. Treatment of samples was identical with the method used earlier in the Reykjavik investigation (ECRHS II).

Results: In contrast to the Reykjavik results, dust from farm dwellings showed a large diversity of mites. Seventeen taxons were found, with Acarus siro and D. pteronyssinus in 13 and 8 farms respectively, but the samples did not show signs that any of the taxons actually had lived or reproduced where they were collected.

Conclusion: The finding of D. pteronyssinus in farmland dwellings provides a possible explanation of why some Reykjavik citizens might have developed sensitization to this mite, even though cross sensitization to other species of mites could give a false positive reaction to D. pteronyssinus in at least some of those cases. Our observations did not support the idea that the mites were living in the dwellings and an explanation for their occurrence must be sought in the outdoor environment.

 

 

TableI. Results on housedust samples. Comparison is with previous study from Reykjavik where only bedrooms were studied (in italics).

Origin of samples	Rural farmhouses Southern and Western iceland 2005		Urban Reykjavik 2001-26
Mite location	Bedroom	Livingroom	Bedroom
Number of samples	39	41	194
Positive samples (%)	17 (43.6)	21 (51.2)	13 (6.7)
gram dust/ m2	0.71	0.71	0.86
mites/gram	20.6	27.7	1.1
mites/ m2	13.8	11.3	1.3

 

 

Table II. Number of mites and positive skinprick tests. Comparison is with previous study on mites from Reykjavik where only bedrooms were studied (in italics). Comparison is with two previous studies on skinprick tests (in italics). 

	---------------Mites-----------			--------------Skinprick tests------------
Origin	Rural farmhouses Íceland 2005 A                 B		Urban Reykjavik 2001-26	Rural Iceland2005	Urban Reykjavik  1991-25	Rural Íceland 198315
Acarus siro	8	9	0	-	-	14
D. farinae	1	1	0	1	-	14
D. pteronyssinus	7	5	2	2	33	10
G. domesticus	0	2	0	-	-	-
L. destructor	1	2	0	5	17	39
Tarsonemus sp.	0	2	0	-	-	-
Bryobia cristata	0	2	0	-	-	-
Tyrophagus similis	1	1	0	-	-	18*
Other mites	7	9	11	-	-	-

A: bedroom, B: livingroom

* Randomly selected sample of 197 individuals. Only bedroom was examined.

**Randomly selected sample of 537 individuals

***Sample of 103 individuals with symptoms from eyes and respiratory tract when exposed to haydust

^*tested for the species Tyrophagus putrescentiae.

 

Fig 1. Distribution of HDM at the farms studied. No HDM were found on 31 farms, Dermatophagoides pteronyssinus was found on 8 farms and Dermatophagoides farinae at 2 farms.

 

 

Fig 2. The finding places for A. siro were close to the sea (insertation), and the numbers of this mite declined with increasing distance form the seashore.