These are the 5 possible diseases that we deduce the elderly man may be contracted with.

5 possible diseases:

Hantavirus
Leptospirosis
Murine Typhus
Rat-bite fever
Typhoid Fever

REASONS

Hantavirus pulmonary syndrome (HPS)
- a deadly disease transmitted by infected rodents through urine, droppings, or saliva
- symptoms like fever, chills, malaise, fatigue match with those symptoms that the patient had (1)





--> Transmission electron micrograph of the Sin Nombre Hantavirus (1)



Leptospirosis
- Transmitted through contact with water, food, or soil containing urine from infected animals like dogs, rats and mice. This may happen by swallowing contaminated food or water or through skin contact. (2)
- Symptoms like high fever, chills, rash, muscle aches, match with those symptoms that the patient had (2)
- Since he had a habit of feeding stray dogs and cat that might be infected with Leptospira, hence he might be infected through their urine and feces.







--> Scanning electron microscope of a number of Leptospira sp. bacteria atop a 0.1 µm polycarbonate filter(2)

Murine Typhus
- Transmitted through exposure to rat fleas or rat feces, or exposure to other animals such as cats and rats (3)
- Symptoms like extremely high fever, dull red rash, severe muscle pain, chills, match with those symptoms that the patient had (3)
- Might result in mild kidney failure which causes excessive urination at night, which explains why his mattress was soiled with urine.




--> Rickettsia typhi (Bacteria) (6)




Rat-bite fever
- Caused by bacteria, transmitted from rodent to human via the rodent's urine or mucous secretions (4)
- Symptoms like moderate fever, chills, a diffuse red rash, match with those symptoms that the patient had (4)
- Mostly found in Asia (4)

(7)

Typhoid Fever
- Caused by the bacterium Salmonella typhi, transmitted by ingestion of food or water contaminated with feces from an infected person (5)
- Symptoms like high fever, weakness, and rash of flat, rose-colored spots, match with those symptoms that the patient had (5)
- Might result in gastroenteritis, diarrhea, which explains the human excreta present on his mattress

--> Salmonella typhi bacteria (5)

References:
1. http://en.wikipedia.org/wiki/Main_Page > Hantavirus
2. http://en.wikipedia.org/wiki/Main_Page > Leptospirosis
3. http://www.nlm.nih.gov/medlineplus/ency/article/001363.htm > encyclopedia > article001363
4. http://en.wikipedia.org/wiki/Main_Page > Rat-bite_fever
5. http://en.wikipedia.org/wiki/Main_Page > Typhoid_fever
6. http://www.cdc.gov/ > Report > Fatal Rat-Bite Fever
7. http://www.genomenewsnetwork.org/ > Bacteria