Co-infection with another virus: The husband's positive antigen test suggests a current dengue infection, while the wife's negative antigen test could indicate a different viral infection with similar symptoms, such as Zika or Chikungunya. The negative IgG and IgM tests in both could be due to early infection or a false negative result.

Early dengue infection in the wife: The wife might be in the early stages of dengue infection, where the antigen test is not yet positive, but symptoms are already present. Repeat testing might be necessary to confirm.
False negative antigen test in the wife: The antigen test can sometimes yield false negative results, especially if the test is performed too early or too late in the course of the infection.
Different serotypes of dengue: The husband and wife might be infected with different serotypes of the dengue virus, which could explain the discrepancy in test results.

Malaria: Although less likely, malaria can present with similar symptoms to dengue and is a potentially life-threatening condition if not treated promptly. It's essential to consider this diagnosis, especially if the couple has recently traveled to areas where malaria is endemic.
Leptospirosis: This bacterial infection can cause symptoms similar to dengue and is often associated with exposure to contaminated water. It's a critical diagnosis not to miss due to its potential severity and the need for prompt antibiotic treatment.

Other arboviral infections: Infections like Mayaro or O'nyong-nyong virus, although rare, could present with similar symptoms and should be considered in the differential diagnosis, especially if the couple has traveled to areas where these viruses are known to circulate.
Hemorrhagic fever: Viruses such as Lassa fever or Ebola, although extremely rare and typically associated with specific geographic locations, could present with severe symptoms similar to dengue hemorrhagic fever and must be considered in the differential diagnosis to ensure prompt and appropriate management.