Lyme Disease: Given the symptoms of fever, headache, and chills in the summer in Massachusetts, and the fact that both husband and wife have it, Lyme disease is a strong candidate. It's a common tick-borne illness in the Northeast United States, and the summer season is a peak time for tick bites. The lack of GI symptoms also aligns with Lyme disease, as it typically presents with fever, headache, and a characteristic rash (erythema migrans), without prominent gastrointestinal symptoms.

Anaplasmosis: Another tick-borne illness that could explain the symptoms, especially given the geographic location and the fact that both individuals are affected, suggesting exposure to the same tick vector.
Babesiosis: A parasitic disease transmitted by ticks, which could cause fever, chills, and headache. It's more common in the Northeast and could affect both individuals if they were exposed to infected ticks.
Viral Illness (e.g., Enterovirus): Although the question specifies no GI symptoms, some viral illnesses can present primarily with fever, headache, and chills. The fact that both husband and wife are affected suggests a contagious cause, but this is less likely given the specific symptoms and location.

Rocky Mountain Spotted Fever (RMSF): Although less common in Massachusetts compared to other parts of the United States, RMSF is a tick-borne disease that can be deadly if not treated promptly. It presents with fever, headache, and can progress to a rash, making it a critical diagnosis not to miss.
Ehrlichiosis: Similar to Anaplasmosis, Ehrlichiosis is a tick-borne disease that can cause severe illness, including fever, headache, and in severe cases, life-threatening complications.

Powassan Virus Disease: A rare tick-borne viral disease that can cause fever, headache, and encephalitis. It's less common but should be considered in the differential diagnosis given the geographic location and symptoms.
Southern Tick-Associated Rash Illness (STARI): Although more commonly associated with a rash, STARI could be considered if the rash is not prominent or has resolved, leaving only systemic symptoms like fever and headache. However, it's less likely given the primary symptoms described.