The burden of vector-borne infections in the Middlesex-London region was relatively low between 2005 and 2018. However, as potential vectors like mosquitoes and ticks adapt to changing environments, the risk areas where they are prevalent may change, which may impact disease rates. Ongoing public health efforts are needed to monitor emerging trends in vector-borne infections, to inform activities aimed at reducing the risk of these diseases to the public.
|Annual variation of vector-borne infections||West Nile virus|
Between 2005 and 2018, the number of vector-borne infections reported among Middlesex-London residents was low, at fewer than 100 cases in total. However, there was marked annual variation for both Lyme disease and West Nile virus infections, with no infections reported in some years. The number of Lyme disease infections was highest at 15 cases reported in 2017, and West Nile virus infections peaked in 2018 at 12 reported cases (Figure 9.5.1).
View more information about Lyme disease.
The rate of Lyme disease infections among Middlesex-London residents was highest among those 40-49 years of age, at 3.7/100,000. There were no significant differences among any of the age groups, with the exception of the rate among those in their 20s, which was significantly lower than the rate among those in their 40s (Figure 9.5.2).
Although low, the rate of Lyme disease infections among Middlesex-London residents significantly increased from 0.2/100,000 in 2005 to 2.2/100,000 in 2018. The Ontario rate also significantly increased over the same time frame. Across the 14-year time period, the local rate was lower than the provincial rate in all but two years, and from 2016 to 2018 the difference was significant (Figure 9.5.3).
View more information about West Nile virus.
Among Middlesex-London residents, the rate of West Nile virus infections was greatest among those 50-59 years of age, at 1.4/100,000. However, there were no significant differences among any age groups (data not shown).
Between 2005 and 2018 the rate of West Nile virus infections among Middlesex-London residents was low and ranged between no cases and 2.4/100,000, with the highest rate observed in 2018. Across the 14-year time period, the local rate was similar to the rate for Ontario as a whole, although the Middlesex-London rate was significantly lower than the provincial rate in 2016 and 2017 (Figure 9.5.4).
As of 2009, the provincial case definition for Lyme disease was updated. Analyses of data from 2009 to 2018 included both confirmed and probable cases, whereas only confirmed cases were included in the data from 2005 to 2008. This was done to ensure comparability across the entire time period of interest, since some cases that would have been considered confirmed prior to 2009 were reported as probable from 2009 onwards.
Since 2002, provincial and national analyses of West Nile virus infections have included both confirmed and probable cases. The analyses shown here align to the provincial and national reporting standards and include infections that meet either the provincial confirmed or probable case definition.
As climates change, the habitats of ticks and mosquitoes potentially carrying vector-borne pathogens are changing and expanding.1,2 For example, the tick that carries Lyme disease is now endemic in multiple regions of Ontario.3 Expansion of the risk areas for these vector-borne infections may account for part of the corresponding increases in the rate of reported cases of Lyme and West Nile Virus infections, both locally and across the province.
1. Clow KM, Leighton PA, Ogden NH, Lindsay LR, Michel P, Pearl, Jardine CM. Northward range expansion of Ixodes scapularis evident over a short timescale in Ontario, Canada. PLoS One [Internet]. 2017 Dec [cited 2019 May 31];12(12):e0189393. Available from: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0189393
2. Wijayasri S, Nelder MP, Russell CB, Johnson KO, Johnson S, Badiani T, Sider D.
West Nile virus illness in Ontario, Canada: 2017. Can Commun Dis Rep [Internet]. 2019 Jan 3 [cited 2019 May 31];45(1):32-7. Available from: https://doi.org/10.14745/ccdr.v45i01a04
3. Ontario Agency for Health Protection and Promotion (Pubic Health Ontario). Ontario lyme disease map 2019: estimated risk areas [Internet]. Toronto (ON): Public Health Ontario; 2019 Apr [cited 2019 May 31]. 5 p. Available from: https://www.publichealthontario.ca/-/media/documents/lyme-disease-risk-a...
Last modified on: July 26, 2019
Vector-borne infections are diseases that are spread from an infected person or animal to another person through intermediaries, such as ticks or mosquitoes, that carry the pathogen causing illness.