Heartworm Spreads Beyond Traditional Hotspots

Heartworm disease is actively spreading into new territories across the United States, as indicated by a recent nationwide map based on 2025 data. Veterinarians are issuing a strong warning to dog owners, highlighting that the risk is no longer confined to traditional hotspots.

Texas has emerged as the state with the highest incidence of heartworm, closely followed by Louisiana and Arkansas. However, concerning increases are also being reported in states like California, Colorado, and Wisconsin, where infection rates have risen significantly. This geographic expansion is attributed to multiple factors.

Expanding mosquito populations, particularly species like the Asian tiger mosquito, and warmer, more humid climates contribute to a longer transmission season. Increased dog mobility through relocations and rescue transports also plays a role in spreading the disease. Despite these risks, many infections stem from missed or delayed doses of preventative medication rather than product failure.

Experts stress that heartworm is preventable and that year-round prevention is recommended for all dogs nationwide, even those primarily indoors. Consistent administration of medication is vital for eliminating immature worms before they mature. Prevention is considerably less expensive and less stressful for pets than treatment, which can involve extensive testing, veterinary visits, and restricted activity for months.