Macau's warm, humid climate supports mosquitoes every month of the year. Here is what every dog owner should know about heartworm transmission, the slow onset of disease, and why prevention is far safer than treatment.
Heartworm disease (dirofilariasis) is a serious, potentially fatal condition for dogs and, less commonly, cats. It is transmitted by mosquitoes, and in Macau there is no real 'off season' — the warm, humid climate supports mosquito activity every month of the year. This guide explains how heartworm is transmitted locally, why Macau dogs are genuinely at risk, what signs to watch for, and why a once-a-month or annual preventive is far safer and cheaper than treating an established infection.
How heartworm actually works
When a mosquito bites an infected animal, it picks up microscopic heartworm larvae (microfilariae). Inside the mosquito, the larvae mature over about two weeks into the infective stage. When that mosquito bites your dog, the larvae are deposited on the skin and migrate into the body, eventually reaching the heart and pulmonary arteries where they grow into adult worms up to 30cm long. The whole process takes 6 to 7 months. Because of this slow timeline, the disease is usually advanced by the time symptoms appear.
Why Macau is genuinely a year-round risk
In cooler climates, heartworm prevention is typically given seasonally from spring through autumn. Macau does not have that luxury: average monthly temperatures stay above 17°C even in January, and humidity remains high enough to support active mosquito populations year-round. Local studies of canine heartworm prevalence in southern China consistently show positive rates, and we do see positive cases in our clinic. The implication is simple: dogs in Macau should be on continuous, year-round heartworm prevention — not seasonal.
Signs to watch for, and why they appear so late
Early heartworm infection produces no symptoms at all, which is exactly what makes prevention so important. As the disease progresses over months to years, dogs may develop a soft, persistent cough, exercise intolerance, weight loss, and a swollen belly from fluid accumulation. By the time these signs are visible, significant heart and lung damage has usually already occurred. Treatment of established heartworm disease involves a long course of injections (melarsomine), strict exercise restriction for months, and carries real risks. Prevention is dramatically safer, simpler and less expensive than treatment.
What prevention looks like in practice
We recommend year-round heartworm prevention for all dogs in Macau, regardless of whether they 'go outside much'. The most common options are: a monthly oral chew (e.g. milbemycin-based products, often combined with intestinal worm protection), a monthly topical spot-on, or an annual injection (moxidectin) that your vet administers. Puppies should start prevention by 8 weeks of age. Adult dogs that have never been on prevention need a quick blood test first to confirm they are not already infected, then start prevention immediately. Cats are also at risk, though they are less commonly affected; we can discuss feline prevention during a consultation.
Getting started at Royal Veterinary Center
If your dog has not been on heartworm prevention, or if you are unsure of their status, book a wellness consultation. We will perform a 4DX snap test (a single blood drop that screens for heartworm antigen plus three tick-borne diseases common in the region), discuss the best prevention option for your dog's age and lifestyle, and get them started on the same day. Prevention given consistently is one of the most cost-effective and impactful things you can do for your dog's long-term health in Macau.
Key Takeaways
- Heartworm is transmitted by mosquitoes, and Macau supports mosquitoes year-round.
- Symptoms appear only after months of silent damage — by then, treatment is risky and expensive.
- Year-round monthly or annual prevention is recommended for all dogs in Macau, without a seasonal break.
- Puppies should start prevention by 8 weeks of age.
- A single 4DX blood test confirms your dog's status and lets us start prevention the same day.