Hello, as a licensed veterinarian I am happy to assist you!
To answer your question, no, hantavirus does not infect our pets (dogs or cats), though Fuji could get other pathogens from rodents such as parasites or bacterial overgrowths if he eats them so I would still discourage this (these would all cause GI signs- vomiting and/or diarrhea).
The signs you note are most suspicious of allergies- especially if these signs are more severe/noticeable during certain times of year. Dogs can get seasonal allergies just like us and it tends to cause itchy skin, itchy and watery (and sometimes red) eyes, and can cause mild upper respiratory congestion (like a runny nose).
You were on the right track with the antihistamine, but often people don't give enough and often more treatments than that are needed. Here is what I recommend trying:
- Zyrtec (cetirizine) or claritin (loratidine): these are 24-hour antihistamines that work well in some dogs. Antihistamines have variable results in different dogs so I usually recommend people try at least 2 or 3 before considering antihistamines unhelpful. The doses for these are as follows:
Zyrtec: 1mg/kg body weight once per day
Claritin: 0.5 mg/kg body weight once per day
*If you provide Fuji's weight I am happy to calculate his doses*
**Pick one, try it for a minimum of 2 weeks. If it does not help, try the other**
- Fatty acid supplementation: fatty acids help with overall coat and skin health as well as with skin inflammation. For therapeutic effects, dose at 40mg/kg body weight EPA once per day. **Note, you have to dose based on the EPA amount NOT total EFA (you may have to check the back or side of the container for this information)
*If you provide Fuji's weight I am happy to calculate his dose*
- If he has any brown staining of his legs where he is chewing, he may have caused a fungal infection, which will keep him itchy there. It therefore may be necessary to use an anti fungal wash to clear that. There are many options available online or at pets stores- simply wash the affected area daily for a minimum of 2 weeks. Discourage his chewing/licking
of the area or he can keep re-infecting the area (an e-collar may be necessary in the beginning)
With all that said, some dogs will need more aggressive treatments, especially if their allergies are more moderate to severe. These treatments include "immunotherapy" (allergy shots), which just like in people can be administered after intradermal or blood allergy testing, or immune-suppressing medications such as steroids (for short-term relief to allow healing), or a medication called cyclosporin (better for long-term use). Therefore, if my above suggestions don't do the trick, I recommend Fuji see his vet for evaluation and discussion of these prescription treatments.
Lastly, dogs can also have allergies to their food (typically to the protein source) which can cause similar signs (though in my experience not the respiratory signs), so this may be something to discuss with your vet as well.
Thank you for your question- I hope you find this information useful! Please feel free to respond with additional questions. Once you are satisfied with my answer, please remember to rate my answer so I receive credit for my time.
All the best to you and Fuji,