It is not unusual for asthma and rhinitis symptoms to worsen following specific infectious. Most of the time these infections are viral. The increase in symptoms, particularly asthma symptoms, may take months to completely resolve even with appropriate therapy. I raise this issue as I suspect that your patient’s change in symptoms is not related to the mice in the attic. Furthermore, unless your patient was tested and showed specific-IgE to mouse, I would not make any conclusions about the importance of the mice in the home.
Mouse antigen has been associated with asthma exacerbations as mouse proteins are an important indoor allergen. Mouse antigen is usually considered a greater problem in inner city housing and high density housing. However, 82% of a nationally representative US housing survey had detectable mouse allergen (Cohn RD, Arbes SJ Jr, Yin M, Jaramillo R, Zeldin DC. National prevalence and exposure risk for mouse allergen in US households. J Allergy Clin Immunol. 2004;113:1167e1171.) and 95% of inner-city homes had measurable levels in the dust (Cohn RD, Arbes SJ Jr, Yin M, Jaramillo R, Zeldin DC. National prevalence and exposure risk for mouse allergen in US households. J Allergy Clin Immunol. 2004;113:1167e1171.). The amount of mouse allergen varies among rooms of homes with the highest levels in rooms with visible mouse droppings or stains. As with most indoor allergens, the distribution is based both upon source and particle size, but the use of central heating and air conditioning has the potential to distribute the allergen widely within the building. Mouse antigen is carried on small and larger airborne particles, facilitating its transfer via air movement within a building (Phipatanakul W. Rodent allergens. Curr Allergy Asthma Rep. 2002;2:412e416; Gordon S, Kiernan LA, Nieuwenhuijsen MJ, Cook AD, Tee RD, Newman Taylor AJ. Measurement of exposure to mouse urinary proteins in an epidemiological study. Occup Environ Med. 1997;54:135e140).
Allergens in the attic would not be as likely to be introduce into the living space unless an air intake was located in the attic or there is a leak in the central system. If the house does not have central ventilation, I think there would be limited exposure unless there is use of an attic fan or the mice or also present in the living space but not recognized. The amount of allergen would be dependent on the number of mice within the home and the duration of time they have resided in the space.
The major mouse allergen is a urinary and skin follicle protein which is produced in larger quantities by male mice. The protein is termed a lipocalin, a fatty-acid binding protein, and resembles allergens from other mammals. In particular, mouse allergen cross reacts with some cat and dog allergens as well as rat allergen. The importance of this cross-reactivity for causing clinical symptoms is unknown. The mouse antigen can be measured in dust or air sampling but the practicality of this is limited. Mouse allergen is presumably stable as levels can be detected in homes without any evidence of mouse, suggesting that the allergen has been resident for an extended time.
Allergen abatement requires thorough cleaning and removal of debris that have had contact with the animals. The measures used are variable depending on the circumstance. The practice parameter devoted to rodent allergy provides extensive recommendations on measures that are likely to be helpful (Environmental assessment and exposure reduction of rodents: A Practice Parameter).
In summary, mouse allergen is a potential source of increased asthma symptoms in individuals who are allergic. There is a potential, though not highly probable, that the mice in the attic could contribute to your patient’s increased symptoms I suspect she is experiencing post infectious worsening of symptoms but the prevalence of mice in human habitats support a potential role of mouse allergy. I would suggest your patient be evaluated by her allergist/immunologist to determine if she is clinically allergic to mouse and, if sensitive, consider the abatement measures discussed in the practice parameter.
I hope this information is of help to you and your patient.
All my best.
Dennis K. Ledford, MD, FAAAAI