About half the world’s population are at risk of vector-borne diseases.
A VECTOR is an organism that transmits infectious organisms – bacteria, viruses and parasites – from a host to humans and other animals.
The common vectors are blood-feeding arthropods, which are invertebrate animals with an external skeleton (exoskeleton), a segmented body, and jointed appendages. Vectors of infections in humans include mosquitoes, ticks, mites and fleas.
About half the world’s population are at risk of vector-borne diseases. Increased travel, migration and trade have aggravated the risk.
According to the World Health Organisa-tion, vector-borne diseases account for 17% of all infectious diseases worldwide.
Vector-borne diseases are difficult to predict, prevent or control. These diseases can lead to serious illness and death.
It is pertinent to note that although infectious diseases comprised 6.82% of admissions to the Health Ministry’s hospitals in 2012, they were the cause of 17.17% of deaths.
Common vector-borne diseases
The prevalent vector-borne diseases in Malaysia are dengue, malaria and Japanese encephalitis.
Dengue: Dengue is a viral infection, with four viral types. It is spread through the bite of a mosquito infected after it has bitten a person who has the dengue virus in his or her blood.
The infected person may or may not have symptoms. The mosquito transmits the infection when it bites a healthy person.
Dengue cannot be spread directly from one person to another.
The infected person gets a dengue infection or dengue haemorrhagic fever (DHF).
The symptoms in the former are self-limiting, while DHF is characterised by excessively permeable (“leaky”) small blood vessels (capillaries) that result in the leaking of blood into body cavities.
This may lead to circulatory failure, shock and death if the circulatory failure is inadequately corrected.
The associated changes in blood coagulation in DHF lead to bleeding tendencies that may aggravate the circulatory failure.
There is no specific medicine for dengue and DHF. Early diagnosis, painkillers (analgesics), rest, drinking plenty of fluids and consulting a doctor are the essentials of treatment.
Early diagnosis and adequate fluid replacement, which requires hospitalisation, are the treatment of DHF.
Malaria: Malaria is a parasitic infection, with four parasitic types. It is spread through the bite of a mosquito infected after it has bitten an infected person. The mosquito transmits the infection when it bites a healthy person.
Malaria is not contagious – one cannot get it from close contact with an infected person.
The malarial parasite is found in the red blood cells of an infected person. As such, it can also be transmitted through blood transfusion, organ transplant, or the shared use of needles or syringes contaminated with blood.
It may also be transmitted from a mother to her unborn infant before or during delivery (congenital malaria).
Malaria is characterised by fever and flu-like symptoms. It may cause anaemia and yellow discolouration of the eyes and skin (jaundice). If not treated promptly, it can cause kidney failure, fits, mental confusion, coma and death.
There are specific medicines for malaria. Early diagnosis, specific medicines, analgesics, rest, drinking plenty of fluids and consulting a doctor are the usual treatments. Complications would require hospitalisation and supportive care.
Japanese encephalitis: Japanese encephalitis (JE) virus infection is transmitted following a bite by an infected mosquito after it has bitten an infected vertebrate, mainly pigs and birds.
Most infected humans have no symptoms or mild symptoms. However, a small percentage of those infected develop inflammation of the brain (encephalitis), of which one in four cases are fatal.
There is no specific medicine for JE. Treatment is focused on supportive care and management of complications.
Chikungunya: Chikungunya viral infection is transmitted following a bite by an infected mosquito after it has bitten an infected person.
The mosquito is the same type as the one that transmits dengue.
Most infected persons recover within a week. Some may develop long-term severe joint pain. Deaths are rare.
The condition was unheard of in Malaysia until recent years, and its emergence has been attributed to international travel.
There is no specific medicine for Chikungunya infection. Treatment is focused on supportive care like analgesics and anti-pyretics.
Vector-borne diseases like dengue, malaria, JE and Chikungunya are preventable.
There is currently no vaccine for dengue, malaria and Chikungunya. However, there is much research on developing an effective vaccine for both dengue and malaria, with clinical trials being carried out.
There is a vaccine for JE and yellow fever.
The best preventive measure for mosquito-borne diseases is the elimination of their breeding places, i.e. stagnant places, especially in construction sites or containers that hold water.
Containers that collect rain water or store water have to be covered or discarded properly.
Sleeping in a room that has screened windows and doors, which keep mosquitoes from coming indoors, or with a mosquito bed net, reduces the likelihood of mosquito bites.
Wearing long-sleeved pyjamas and proper application of insect repellents also decrease the risk of mosquito bites.
The control of vector-borne diseases lies in prevention, with the public having a cardinal role to play.
Dr Milton Lum is a member of the board of Medical Defence Malaysia. This article is not intended to replace, dictate or define evaluation by a qualified doctor. The views expressed do not represent that of any organisation the writer is associated with.
Disclaimer: Nothing on this blog should be considered or used as a substitute for medical advice, diagnosis or treatment. Blog visitors with personal health or medical questions should consult their health care provider.