Download Communicable Disease Report 2003

CHAPTER 5: DISEASES SPREAD BY INSECTS
Highlights
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In Peel, approximately one to six cases per 100,000 of malaria are reported each
year, with the exception of 1996 and 1997 which had a dramatic increase in
incidence (16.4 and 15.6 cases per 100,000 respectively). Ontario and Canada
experienced a similar increase, however, the increased incidence was much
higher in Peel compared to either Ontario or Canada25.
There were 37 confirmed cases and 20 probable cases of West Nile Virus (WNV)
reported in Peel for the first time in 2002. There were also 28 hospitalizations
and two deaths attributed to WNV in 2002.
INTRODUCTION
Diseases spread by insects are caused by bacteria, parasites and viruses. Blood feeding
insects such as fleas, mosquitoes, midges and sandflies transmit these diseases and
often act as a site where the infectious organism can multiply or complete part of its
lifecycle. Although some insect born diseases can be transmitted from person to person
or through blood, this is not their main mode of transmission. Many insect born diseases
are major health problems for developing countries. Malaria is estimated to infect over
300 million people a year, killing one million.26
Fortunately, many insect born diseases are so rare in Ontario that they are not required
to be reported. The reportable insect born diseases in Ontario are: viral hemorrhagic
fevers, lyme disease, malaria, plague, Q fever, west nile virus and yellow fever. In Peel
only two of these insect born diseases averaged more than five cases per year. The first
is the parasite Malaria, acquired in areas of the world where this disease occurs, from
the bite of an infected mosquito. The second, also spread by mosquitoes is a new
disease to Peel, West Nile Virus. West Nile Virus was acquired locally for the first time in
2002. The extent to which it will affect Peel residents in the future is unknown.
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MALARIA
Malaria remains one of the world’s most important and widespread fatal infectious
diseases. 27 It is caused by one of four species of parasite of the genus Plasmodium.27
The disease is transmitted to humans through a bite of an infected female Anopheles
mosquito. While rare, the parasite can also be transmitted by transfusion with infected
blood, shared needle use, or from a mother to her unborn child. 27
Symptoms of malaria are non-specific and include fever, chills, headache, nausea,
vomiting, muscle pain and malaise.27
Malaria is endemic (i.e., constantly present) in the tropical and subtropical parts of the
world. 27 Nearly all cases of malaria in Canada occur in people who lived or travelled to
areas where malaria is common.
Figure 5.1: Incidence of Malaria,
Region of Peel and Ontario, 1993-2002
25
NA: 2001 and 2002 Ontario data
not available.
Cases per 100,000
20
Note: Rates age-standardized
using 1991 (adjusted) Canadian
population.
15
Sources: Ontario Data from
RDIS, Ontario Ministry of Health
and Long-Term Care, as of
06/13/2003.
10
5
0
Peel
Ontario
Peel Cases
1993 1994 1995 1996 1997 1998 1999 2000 2001 2002
4.0
2.4
32
3.7
2.1
32
5.9
2.3
50
16.4
4.0
138
15.6
4.2
142
2.4
1.4
21
2.2
1.5
24
2.9
1.5
31
1.6
NA
18
1.7
NA
20
Peel Data from RDIS, Region of
Peel Health Department, as of
09/23/2003.
Statistics Canada, Population
Estimates and Projections
distributed by the Ontario Ministry
of Health and Long-Term Care.
Year
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WEST NILE VIRUS (WNV)
West Nile Virus (WNV) is a mosquito-borne virus. A 1999 outbreak of WNV in New York
City was the first documented transmission of WNV within North America. Since then
WNV has spread to 7 provinces and 44 states. It is a human, horse and bird pathogen
that can cause diseases of the nervous system such as encephalitis and meningitis, and
can result in death.
Cases of locally acquired WNV occurred for the first time in 2002, with a total of 37
confirmed cases and 20 probable cases in Peel. Among the 57 confirmed or probable
cases, 26% were aged 50 to 59 years, 23% were aged 60 to 69 years and 18% were
aged 70 to 79 years, showing that cases were more prevalent among older adults, but
not limited to them.
In 2002, 28 cases of WNV (among confirmed and probable cases) required
hospitalization including two deaths.
More detailed information on WNV is contained in the West Nile Virus in the Region of
Peel 2002 Report.
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