Common Diseases to Watch Out for During the Rainy Season

Rainy season During the rainy season, the weather is relatively cool and humid, creating favorable conditions for various pathogens to thrive. Knowing the diseases that accompany this season—including their transmission modes, causes, symptoms, and self-care—is essential for prevention and awareness. Common diseases that tend to spread in the rainy season can be categorized as follows:

1. Respiratory tract infections

Common respiratory infections are usually caused by viruses and bacteria, spreading mainly through secretions like mucus, saliva, and phlegm, via contact, coughing, or sneezing. Common diseases include:

• Common cold Caused by rhinoviruses, the common cold is milder than influenza. Most patients recover on their own with symptomatic treatment, without the need for antibiotics. Adequate rest, plenty of fluids, and monitoring for high fever are recommended.
• Influenza Caused by influenza viruses, patients experience high fever, muscle aches, and respiratory symptoms such as cough, runny nose, and sore throat. Symptoms are more severe than the common cold. Complications may include pneumonia, ear infections, bronchitis, sinusitis, and, if bacterial infection occurs, serious complications like encephalitis, pericarditis, or bloodstream infections, which can be life-threatening.
• Pneumonia Caused by infections in the upper respiratory tract from viruses or bacteria, pneumonia is often seen in individuals with weak health, chronic illnesses, and the elderly.

2. Mosquito-borne diseases

• Dengue fever This disease occurs year-round but surges in the rainy season due to increased standing water that breeds Aedes mosquitoes. Early symptoms include high fever up to 38–40°C lasting 2–7 days, flushed face, loss of appetite, and lethargy. Some patients develop red spots on the body, arms, and legs. Without treatment, severe cases may progress to critical stages with liver enlargement and bloody vomiting, which can be fatal.
• Zika fever Transmitted by Aedes mosquitoes, patients experience fever, muscle pain, headache, red eyes, and body rash. Zika infection during pregnancy may affect fetal brain development.
• Chikungunya fever or Chikungunya Also spread by Aedes mosquitoes, key symptoms include fever, muscle pain, and joint pain (especially wrists and ankles), sometimes accompanied by red eyes and body rash. There is currently no vaccine; treatment focuses on symptom relief.
• Japanese encephalitis Transmitted by Culex mosquitoes commonly found in agricultural and pig-farming areas, this disease infects the brain causing fever, headache, drowsiness, seizures, unconsciousness, and can be fatal. Survivors often suffer lasting brain damage. There is no specific treatment, but vaccination with a live attenuated vaccine is available and recommended.

3. Skin and wound infections

• Melioidosis or Melioidosis Caused by bacteria residing in soil, which remain dormant in dry conditions and surface during rain. Farmers exposed to soil are at risk. The bacteria enter the body via respiratory tract or wounds, especially in those with poor health or chronic diseases like diabetes and kidney disease, or habitual alcohol use. Symptoms can affect multiple systems including pneumonia, bloodstream infection, and skin infections. At-risk individuals with fever, breathlessness, or chills should inform their doctor about occupational risks and medical history for accurate diagnosis.
• Leptospirosis or Leptospirosis Transmitted by rodents and various mammals, the bacteria reside in their urinary systems. When animals urinate in water, people wading or working in flooded areas can be infected through skin contact. Symptoms include fever, muscle pain, and headache. Severe cases can cause acute kidney failure or inflammation of the liver and bile ducts, resulting in jaundice.

4. Other common rainy season diseases

Often caused by viruses, diseases like acute diarrhea, conjunctivitis, and hand, foot, and mouth disease also require caution.

Many infectious diseases can be prevented or lessened in severity by vaccination, such as influenza vaccine, dengue vaccine, pneumonia vaccine, and Japanese encephalitis vaccine. Vaccination not only promotes health but also reduces economic losses and mental stress for individuals and their families.

Additionally, maintaining good hygiene, eating a balanced diet, getting sufficient rest, and regular exercise strengthen immunity, helping to prevent illness or reduce disease severity if infection occurs.

Information courtesy of the Department of Internal Medicine, Phyathai Nawamin Hospital