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  • Writer's pictureDr, Vijayshree Patil

MONSOON ILLNESSES : Vector Borne Illnesses

What is a vector?

Vectors are living organisms that can transmit infectious pathogens between humans, or from animals to humans. Many of these vectors are bloodsucking insects, like mosquitoes, ticks, etc, which ingest disease-producing microorganisms during a blood meal from an infected host (human or animal) and later transmit it into a new host, after the diseases causing organism has replicated. Often, once a vector becomes infectious, they are capable of transmitting the pathogen for the rest of their life during each subsequent bite/blood meal.

Vector-borne diseases are human illnesses caused by parasites, viruses and bacteria that are transmitted by vectors.

In this blog we will talk about the common vector borne illnesses seen in our country especially during the monsoon and make up the majority of diseases seen during this time.

The aim of this blog is to educate you about these diseases, their transmission, clinical features and prevention strategies so that you can either prevent contraction of the disease or recognise the symptoms early on so you can seek prompt medical help.



Caused by:  Plasmodium parasites. There are 5 parasite species that cause malaria in humans, and 2 of these species – P. falciparum and P. vivax – pose the greatest threat.

Vector : The parasites are spread to people through the bites of infected female Anopheles mosquitoes, called "malaria vectors.”

Clinical symptoms:

Malaria can present in two clinical ways :

Uncomplicated Malaria: Symptoms of uncomplicated malaria include an initial stage with sensations of cold with chills or shivering, followed by the second stage of headaches, fever, and vomiting, followed by a return to normalcy (in temperature) with sweating, fatigue, or tiredness. Sometimes seizures may occur in younger individuals

Severe Malaria: Symptoms of severe malaria include fever and shivers/chills, impaired consciousness, respiratory distress and deep breathing, multiple convulsions, signs of anaemia and abnormal bleeding, evidence of vital organ dysfunction, and clinical jaundice.

Treatment :

Anti malarial medicines which are very effective in treating the disease. There is also a vaccine available for preventing malaria.


Caused by : Dengue virus

Vector : Aedes aegypti mosquito

Clinical features:

Dengue fever (more common)

Dengue should be suspected when a high fever (40°C/104°F) is accompanied by 2 of the following symptoms during the febrile phase:

• severe headache

• pain behind the eyes

• muscle and joint pains

• nausea

• vomiting

• swollen glands

• rash.

Severe dengue

A patient enters what is called the critical phase normally about 3-7 days after illness onset. It is at this time, when the fever is dropping (below 38°C/100°F) in the patient, that warning signs associated with severe dengue can manifest. Severe dengue is a potentially fatal complication, due to plasma leaking, fluid accumulation, respiratory distress, severe bleeding, or organ impairment.

Warning signs that doctors should look for include:

• severe abdominal pain

• persistent vomiting

• rapid breathing

• bleeding gums

• fatigue

• restlessness

• blood in vomit.

If patients manifest these symptoms during the critical phase, close observation for the next 24–48 hours is essential so that proper medical care can be provided, to avoid complications and risk of death.

Treatment :

Since it is a viral disease, we treat the patients symptomatically.

Hydrations, anti pyretics and keep a close watch on any bleeding and the platelet count which tends to fall in this disease.

There is no vaccine for dengue.


This term chikungunya means ‘to walk bent’ and the main symptoms experienced by the patients include fever and joint pain.

Caused by : Chikangunya virus

Vector : Aedes aegypti mosquito

Clinical features :

Some of the most common symptoms include high fever (40 °C or 104 °F) that lasts for two days and abruptly ends, viral rashes on the trunk or limbs, joint pain affecting multiple joints, headache, loss of appetite, etc.

Treatment :

It is treated symptomatically with anti pyretics to bring down the fever, hydration and prevention of complications.

There is no vaccine for the prevention of chikangunya.


Since they are transmitted by mosquitoes, prevention includes all measure necessary to prevent them.

• Aedes aegypti mosquito (dengue, chikangunya) breeds in small pools of collected water like in flower pots, garbage containers, gutters, water coolers, etc. Do not allow water to collect in these spots.

• Anopheles mosquito (malaria) breeds in fresh/ salt water pools, marshy land, any slow moving water body. Anti larvicidal spraying (usually done by the govt authorities)

• Vigilance around these areas.

• Wear appropriate Clothing  - cover your arms and legs. Preferably light coloured clothes.

• Using mosquito repellant creams, coils etc.

• Medicated or non medicated Mosquito nets while sleeping.

• Barriers (nets) at windows and doors.


Caused by: Bacteria - spirocheates leptospira

Vector : Rats (through their urine).

Leptospirosis is an infection in rodents. Rodents are implicated most often in human cases. The infection in man is contracted through skin abrasions and the mucosa of the nose, mouth and eyes. Exposure through water contaminated by urine from infected animals is the most common route of infection.

Outdoor and agricultural workers (rice-paddy and sugarcane workers for example) are particularly at risk but it is also a recreational hazard to those who swim or wade in contaminated waters especially, in case of flooding because the floods cause rodents to move into the city.

Clinical features:

Headache, fever, myalgia (muscular pain), jaundice, conjunctival suffusion, bleeding tendencies, oliguria (decreased urine output), and pulmonary manifestations like cough, breathlessness, and hemoptysis (bleeding while coughing).

Severe disease can present with jaundice, kidney dysfunction, and bleeding.

Treatment :

Antibiotics. Although, Treatment is always easier when caught early.  Severe disease can be fatal.


Disease spreads through urine of rats which can enter your body through breaks in your skin, cuts or open wounds especially on your feet when exposed to contaminated water like in floods.

Hygiene is essential in prevention. Wash your exposed feet or hands immediately. Do not leave any cuts / wounds open.

Tend to any fever immediately after any such exposure.

Be alert during the Monsoon season. Do not take any symptoms lightly. Seek appropriate, timely medical help.

Stay safe stay healthy.


Dr Vijayshree Patil

Anaesthesiologist and Critical Care Specialist

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