Infectious Disease

Infectious diseases are caused by bacteria, viruses, or fungal organisms that are able to enter the body, multiply and cause infections. These types of infectious pathogens are usually controlled by our immune system which can specifically target the invading bacteria, virus, or fungal organisms and eliminate them so they do not cause disease. However, in some instances, the infection can bypass or overwhelm the immune system, or the infected individual’s immune system may be suppressed, predisposing them to infections. In these instances, the infection can overtake the body and cause significant disease, sepsis, and death. Learn more about infectious and zoonotic diseases at Penn Vet’s Institute for Infectious and Zoonotic Diseases.

Alexander Fleming’s seminal discovery of penicillin in 1928 led to the first antibiotic and revolutionized the treatment of bacterial infections. Likewise, more effective treatments for viral fungal and parasitic infections have been developed. However, over time and accelerated by inappropriate use of these antimicrobial agents, antimicrobial resistant (AMR) bacteria, viruses, fungi, and parasites have developed. AMR microbes are resistant to current medicines and are extremely challenging to treat and control their spread. As such, new therapies such as immunotherapies, are being sought to address antimicrobial resistance.
Infectious disease
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Cellular Therapies for the Treatment of Fungal Disease

Cellular therapies that target fungal diseases offer the opportunity to treat local and systemic infections. Reports of using immune cells known as “T cells” that are engineered to recognize fungal targets and activate when they encounter them suggest this may be beneficial in helping to control fungal infections.

Monoclonal Antibodies for Antibiotic Resistant Bacteria

Cellular therapies that target fungal diseases offer the opportunity to treat local and systemic infections. Reports of using immune cells known as “T cells” that are engineered to recognize fungal targets and activate when they encounter them suggest this may be beneficial in helping to control fungal infections.


  • What are the most common infectious diseases in dogs?

    Many of the common infectious diseases in dogs and cats are caused by viruses and these can be prevented by proper vaccination as puppies and kittens and at regular intervals as outlined by your veterinarian. Many infections are also easily cleared by the immune system of a normal healthy pet. But as animals age or develop other naturally occurring diseases they become more susceptible to infections which can become a chronic problem or a life-threatening one. Common types of infections seen in susceptible dogs and cats include skin infections (pyoderma), ear infections (otitis externa) and urinary tract infections (UTI). Some infections are caused by microbes that are resistant to the drugs we use to treat them (antimicrobials). Over- and inappropriate use of antibiotics contributes to the development of antibiotic resistant bacteria which can be extremely difficult to treat as commonly used antibiotics do not work against these organisms.

  • What are common drug resistance microbes in companion animals?

    There are several antimicrobial resistant bacteria of concern including methicillin-resistant Staphylococcus pseudintermedius (MRSP) and multidrug resistant (MDR) Gram-negative bacteria like E. coli and Pseudomonas aeruginosa. One type of MDR bacteria that are an emerging concern are carbapenem-resistant Enteorbacterale (CRE) which have recently been reported in pets and are considered an urgent health concern by the Centers for Disease Control and Prevention because they are often resistant to all antimicrobials. Dr. Stephen Cole at Penn Vet is actively investigating CRE in pets and his work. Antimicrobial resistant fungi are not common yet in companion animals but there is growing concern that they could be a major problem in the future. Other challenges included the development of resistance in parasites that cause infections in dogs and cats such as in Giardia and hookworms.

  • How is antimicrobial resistance diagnosed in pets?

    The most common test used to diagnose antimicrobial resistance is called “bacterial culture and antimicrobial susceptibility testing.” Veterinarians submit samples of the infection taken from the animal and submit that to a specialized laboratory. The laboratory grows the bacteria from that sample and test them across a suite of antimicrobials to determine which drugs are most likely to kill the bacteria. In some cases, these antimicrobials are ineffective in the laboratory which leads to a diagnosis of a multidrug resistant infection in the pet.

  • How are infections with drug resistant microbes treated in pets? 

    Currently, when bacteria are resistant to our commonly used veterinary antimicrobials, veterinarians must use antibiotics typically reserved for humans. This is troublesome because veterinarians aim to practice under the “One Health” concept and preserve the use of these drugs for people. Additionally, these drugs have not been studied extensively in animals and it can be difficult for veterinarians to know how to use them safely and effectively. Unfortunately, in extreme circumstances animals may need to be humanely euthanized to alleviate suffering from these challenging infections. New strategies for treatment would help to treat these resistant infections and prevent their spread to others.

  • Why are fungal infections so concerning?

    Fungi are normal in the environment around us, but systemic fungal diseases often occur in patients that are either immune suppressed or those that have defects in their immune system. Fungi are much more closely related to animals than bacteria which makes developing novel therapies more challenging. Local and systemic fungal diseases can be challenging to treat and better therapies are needed.

  • How can studying infections in pets help people?

    People and pets get very similar types of infections and similar challenges are faced during treatment. Pets can serve as a “naturally-occurring model” of infectious diseases which may more accurately reflect infections in people than laboratory models. By studying solutions to infectious diseases in pets, we can improve the health and welfare of both animals and people.