During the summer, cats can be susceptible to several diseases and health issues due to the heat, increased outdoor activity, and exposure to other animals. Here are some common diseases and conditions to be aware of:

1. Heatstroke: Cats can overheat in high temperatures, especially if they are left in hot environments without adequate shade, water, or ventilation. Symptoms include panting, drooling, lethargy, vomiting, and collapse.
2. Flea and Tick Infestations: Warm weather increases the activity of fleas and ticks, which can cause itching, skin infections, and transmit diseases like Lyme disease and bartonellosis.
3. Heartworm Disease: Mosquitoes, which are more prevalent in summer, can transmit heartworm larvae to cats. Although more common in dogs, heartworm can also affect cats, leading to respiratory and cardiovascular issues.
4. Upper Respiratory Infections: Cats can catch colds and other respiratory infections more easily if they are exposed to other animals in shelters, boarding facilities, or during outdoor activities.
5. Allergies: Pollen and other allergens are more prevalent in the summer, which can cause cats to suffer from allergic reactions, leading to skin irritation, itching, and respiratory issues.
6. Dehydration: Cats can become dehydrated if they do not drink enough water in hot weather. This can lead to urinary tract issues and kidney problems.
7. Sunburn: Cats with light-colored or thin fur are at risk of sunburn, especially on their ears, nose, and other exposed areas. This can lead to skin damage and increase the risk of skin cancer.

To keep your cat healthy during the summer, ensure they have access to plenty of fresh water, keep them indoors during the hottest parts of the day, use flea and tick preventatives, and monitor them for any signs of illness or distress.