Cat bites are usually considered as minor injuries but can result in serious infection. Not all infections that can be obtained from exposure to a cat are transmitted through a cat bite, like plague.

Cat bites are bites inflicted upon humans, other cats, and other animals by the domestic cat. () Though uncommon, sometimes cat bites can lead to complications and very rarely, death.

Orf is an exanthemous disease caused by a parapox virus and occurring primarily in sheep and goats. It is also known as contagious pustular dermatitis, infectious labial dermatitis, ecthyma contagiosum, thistle disease and scabby mouth. "Orf virus" is zoonotic—it can also infect humans.

Orf is a zoonotic disease, meaning humans can contract this disorder through direct contact with infected sheep and goats or with fomites carrying the orf virus. It causes a purulent-appearing papule locally and generally no systemic symptoms. Infected locations can include the finger, hand, arm, face and even the penis (caused by infection either from the hand during urination or from bestiality). Consequently, it is important to observe good personal hygiene and to wear gloves when treating infected animals. The papule may persist for 7 to 10 weeks and spontaneously resolves. It is an uncommon condition and may be difficult to diagnose.

While orf is usually a benign self-limiting illness, it can be very progressive and even life-threatening in the immune-compromised host. One percent topical cidofovir has been successfully used in a few patients with progressive disease. Serious damage may be inflicted on the eye if it is infected by orf, even among healthy individuals. The virus can survive in the soil for at least six months.

Cat-scratch disease commonly presents as tender, swollen lymph nodes near the site of the inoculating bite or scratch or on the neck, and is usually limited to one side. This condition is referred to as regional lymphadenopathy and occurs 1–3 weeks after inoculation. Lymphadenopathy in CSD most commonly occurs in the arms, neck, or jaw, but may also occur near the groin or around the ear. A vesicle or an erythematous papule may form at the site of initial infection. Most patients also develop systemic symptoms such as malaise, decreased appetite, and aches. Other associated complaints include headache, chills, muscular pains, joint pains, arthritis, backache, and abdominal pain. It may take 7 to 14 days, or as long as two months, for symptoms to appear. Most cases are benign and self-limiting, but lymphadenopathy may persist for several months after other symptoms disappear. The disease usually resolves spontaneously, with or without treatment, in one month.

In rare situations, CSD can lead to the development of serious neurologic or cardiac sequelae such as meningoencephalitis, encephalopathy, seizures, or endocarditis. Endocarditis associated with "Bartonella" infection has a particularly high mortality. Parinaud's oculoglandular syndrome is the most common ocular manifestation of CSD, and is a granulomatous conjunctivitis with concurrent swelling of the lymph node near the ear. Optic neuritis or neuroretinitis is one of the atypical presentations.

Immunocompromised patients are susceptible to other conditions associated with "B. henselae" and "B. quintana", such as bacillary angiomatosis or bacillary peliosis. Bacillary angiomatosis is primarily a vascular skin lesion that may extend to bone or be present in other areas of the body. In the typical scenario, the patient has HIV or another cause of severe immune dysfunction. Bacillary peliosis is caused by "B. henselae" that most often affects patients with HIV and other conditions causing severe immune compromise. The liver and spleen are primarily affected, with findings of blood-filled cystic spaces on pathology. In 2015 a Toledo, Ohio woman lost eyesight in an eye after a cat licked it.

Feline zoonosis are the viral, bacterial, fungal, protozoan, nematode and arthropod infections that can be transmitted to humans from the domesticated cat, "Felis catus". Some of these are diseases are reemerging and newly emerging infections or infestations caused by zoonotic pathogens transmitted by cats. In some instances, the cat can display symptoms of infection (these may differ from the symptoms in humans) and sometimes the cat remains asymptomatic. There can be serious illnesses and clinical manifestations in people who become infected. This is dependent on the immune status and age of the person. Those who live in close association with cats are more prone to these infections. But those that do not keep cats as pets are also able to acquire these infections because of the transmission can be from cat feces and the parasites that leave their bodies.

People can acquire cat-associated infections through bites, scratches or other direct contact of the skin or mucous membranes with the cat. This includes 'kissing' or letting the animal lick the mouth or nose. Mucous membranes are easily infected when the pathogen is in the mouth of the cat. Pathogens can also infect people when there is contact with animal saliva, urine and other body fluids or secretions, When fecal material is unintentionally ingested, infection can occur. Feline zooinosis can be acquired by a person by inhalation of aerosols or droplets coughed up by the cat.

In the United States, forty percent of homes have at least one cat. Some contagious infections such as campylobacteriosis and salmonellosis cause visible symptoms of the disease in cats. Other infections, such as cat scratch disease and toxoplasmosis, have no visible symptoms and are carried by apparently healthy cats.

Cytauxzoon felis is a protozoal organism transmitted to domestic cats by tick bites, and whose natural reservoir host is the bobcat. "C. felis" has been found in other wild felid species such as Florida bobcat, eastern bobcat, Texas cougar, and a white tiger in captivity. "C. felis" infection is limited to the family felidae which means that "C. felis" poses no zoonotic (transmission to humans) risk or agricultural (transmission to farm animals) risk. Until recently it was believed that after infection with "C. felis", pet cats almost always died. As awareness of "C. felis" has increased it has been found that treatment is not always futile. More cats have been shown to survive the infection than was previously thought. New treatments offer as much as 60% survival rate.

Cat-scratch disease (CSD) is a common and usually benign infectious disease caused by the bacterium "Bartonella henselae". It is most commonly found in children following a scratch or bite from a cat within about one to two weeks.

Zoonoses are infectious diseases of animals (usually vertebrates) that can naturally be transmitted to humans.

Major modern diseases such as Ebola virus disease and salmonellosis are zoonoses. HIV was a zoonotic disease transmitted to humans in the early part of the 20th century, though it has now evolved to a separate human-only disease. Most strains of influenza that infect humans are human diseases, although many strains of swine and bird flu are zoonoses; these viruses occasionally recombine with human strains of the flu and can cause pandemics such as the 1918 Spanish flu or the 2009 swine flu. "Taenia solium" infection is one of the neglected tropical diseases with public health and veterinary concern in endemic regions. Zoonoses can be caused by a range of disease pathogens such as viruses, bacteria, fungi and parasites; of 1,415 pathogens known to infect humans, 61% were zoonotic. Most human diseases originated in animals; however, only diseases that routinely involve animal to human transmission, like rabies, are considered direct zoonosis.

Zoonoses have different modes of transmission. In direct zoonosis the disease is directly transmitted from animals to humans through media such as air (influenza) or through bites and saliva (rabies). In contrast, transmission can also occur via an intermediate species (referred to as a vector), which carry the disease pathogen without getting infected. When humans infect animals, it is called reverse zoonosis or anthroponosis. The term is from Greek: ζῷον "zoon" "animal" and νόσος "nosos" "sickness".

Cryptosporidiosis is a parasitic disease that is transmitted through contaminated food or water from an infected person or animal. Cryptosporidiosis in cats is rare, but they can carry the protozoan without showing any signs of illness. Cryptosporidiosis can cause profuse, watery diarrhea with cramping, abdominal pain, and nausea in people. Illness in people is usually self-limiting and lasts only 2–4 days, but can become severe in people with weakened immune systems. Cryptosporidiosis (Cryptosporidium spp.) Cats transmit the protozoan through their feces. The symptoms in people weight loss and chronic diarrhea in high-risk patients. More than one species of this genus can be acquired by people. Dogs can also transmit this parasite.

Most infected cats have been healthy before a very sudden onset of severe disease. The course of clinical disease is often swift with clinical signs of lethargy and inappetence within 5 to 20 days after the tick bite. Cats develop a high fever, but the temperature may become low before death. Other clinical findings can be: dehydration, icterus (jaundice), enlarged liver and spleen, lymphadenopathy, pale mucus membranes, respiratory distress, tachycardia or bradycardia, and tick infestation (although ticks are not often found on infected cats since cats typically groom ticks off their fur). Signs of disease seen on blood work include hemolytic anemia, thrombocytopenia, increased or decreased white blood cell numbers, icterus, and elevated liver enzymes. Death usually follows the onset of clinical signs within a few days. However, more recent studies show not all cats develop clinical signs after infection, and some cats survive the infection.

Zoonotic transmission can occur in any context in which there is companionistic (pets), economic (farming, etc.), predatory (hunting, butchering or consuming wild game) or research contact with or consumption of animals, animal products, or animal derivatives (vaccines, etc.).

Cat flu is the common name for a feline upper respiratory tract disease. While feline upper respiratory disease can be caused by several different pathogens, there are few symptoms that they have in common.

While Avian Flu can also infect cats, Cat flu is generally a misnomer, since it usually does not refer to an infection by an influenza virus. Instead, it is a syndrome, a term referring to the fact that patients display a number of symptoms that can be caused by one or more of the following infectious agents (pathogens):

1. Feline herpes virus causing feline viral rhinotracheitis (cat common cold, this is the disease that is closely similar to cat flu)

2. Feline calicivirus—(cat respiratory disease)

3. "Bordetella bronchiseptica"—(cat kennel cough)

4. "Chlamydophila felis"—(chlamydia)

In South Africa the term cat flu is also used to refer to Canine Parvo Virus. This is misleading, as transmission of the Canine Parvo Virus rarely involves cats.

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease recently discovered in northeast and central China. SFTS has fatality rates ranging from 12% to as high as 30% in some areas. The major clinical symptoms of SFTS are fever, vomiting, diarrhea, multiple organ failure, thrombocytopenia (low platelet count), leucopenia (low white blood cell count), and elevated liver enzyme levels.

"B. henselae" and "B. quintana" can cause bacillary angiomatosis, a vascular proliferative disease involving mainly the skin, and other organs. The disease was first described in human immunodificiency virus (HIV) patients and organ transplant recipients. Severe, progressive and disseminated disease may occur in HIV patients. Differential diagnoses include Kaposi´s sarcoma, pyogenic granuloma, hemangioma, "verruga Peruana", and subcutanous tumors. Lesions can affect bone marrow, liver, spleen, or lymph nodes.

Dry FIP will also present with lack of appetite, fever, jaundice, diarrhea, and weight loss, but there will not be an accumulation of fluid. Typically a cat with dry FIP will show ocular or neurological signs. For example, the cat may develop difficulty in standing up or walking, becoming functionally paralyzed over time. Loss of vision is another possible outcome of the disease.

"B. henselae" is the etiologic agent for peliosis hepatis, which is defined as a vascular proliferation of sinusoid hepatic capillaries resulting in blood-filled spaces in the liver in HIV patients and organ transplant recipients. Peliosis hepatis can be associated with peliosis of the spleen, as well as bacillary angiomatosis of the skin in HIV patients.

The hallmark clinical sign of effusive FIP is the accumulation of fluid within the abdomen or chest, which can cause breathing difficulties. Other symptoms include lack of appetite, fever, weight loss, jaundice, and diarrhea.

Cutaneous BA is characterised by the presence of lesions on or under the skin. Appearing in numbers from one to hundreds, these lesions may take several forms:

- papules or nodules which are red, globular and non-blanching, with a vascular appearance

- purplish nodules sufficiently similar to Kaposi's sarcoma that a biopsy may be required to verify which of the two it is

- a purplish lichenoid plaque

- a subcutaneous nodule which may have ulceration, similar to a bacterial abscess

While cutaneous BA is the most common form, it can also affect several other parts of the body, such as the brain, bone, bone marrow, lymph nodes, gastrointestinal tract, respiratory tract, spleen, and liver. Symptoms vary depending on which parts of the body are affected; for example, those whose livers are affected may have an enlarged liver and fever, while those with osseous BA experience intense pain in the affected area.

Pulicosis (also known as "flea bites") is a skin condition caused by several species of fleas, including the cat flea ("Ctenocephalides felis") and dog flea ("Ctenocephalides canis"). This condition can range from mild irritation to severe irritation. In some cases, 48 to 72 hours after being bitten, a more severe rash-like irritation may begin to spread across the body. Symptoms include swelling of the bitten area, erythema, ulcers of the mouth and throat, restlessness, and soreness of the areolae. In extreme cases, within 1 week after being bitten, the condition may spread through the lymph nodes and begin affecting the central nervous system. Permanent nerve damage can occur.

If they receive an excessive number of bites, pets can also develop flea allergy dermatitis, which can potentially be fatal if no actions are taken. However, dogs and cats are not the only ones that are at risk. Humans can suffer from flea bites and, depending on a variety of factors, the bites can cause much pain and discomfort.

Bacillary angiomatosis (BA) is a form of angiomatosis associated with bacteria of the "Bartonella" genus.

Cats with Avian Influenza exhibit symptoms that can result in death. They are one of the few species that can get Avian Influenza. The specific virus that they get is H5N1, which is a subtype of Avian Influenza. In order to get the virus, cats need to be in contact with waterfowl, poultry, or uncooked poultry that are infected. Two of the main organs that the virus affects are the lungs and liver.

The several forms of the infection are:

- Skin/subcutaneous tissue disease is a septic phlegmon that develops classically in the hand and forearm after a cat bite. Inflammatory signs are very rapid to develop; in 1 or 2 hours, edema, severe pain, and serosanguineous exudate appear. Fever, moderate or very high, can be seen, along with vomiting, headache, and diarrhea. Lymphangitis is common. Complications are possible, in the form of septic arthritis, osteitis, or evolution to chronicity.

- Sepsis is very rare, but can be as fulminant as septicaemic plague, with high fever, rigors, and vomiting, followed by shock and coagulopathy.

- Pneumonia disease is also rare and appears in patients with some chronic pulmonary pathology. It usually presents as bilateral consolidating pneumonia, sometimes very severe.

- Zoonosis, pasteurellosis can be transmitted to humans through cats.

Other locations are possible, such as septic arthritis, meningitis, and acute endocarditis, but are very rare.

Pork–cat syndrome is an allergy to pork, usually post adolescence, that is caused by exposure to cats. Although first described in 1994, it was first documented in the U.S. by Scott Commins and Thomas Platts-Mills during their research on alpha-gal allergy.

It is called "pork–cat syndrome" because "almost all people with the condition are cat owners, and many have multiple cats. Some develop an allergic response to cat serum albumin (protein made by a cat’s liver) that cross-reacts with albumin in pork when someone consumes it, and can lead to severe or even fatal allergic reactions when pork is consumed."

Acute toxoplasmosis is often asymptomatic in healthy adults. However, symptoms may manifest and are often influenza-like: swollen lymph nodes, headaches, fever, and fatigue, or muscle aches and pains that last for a month or more. Rarely will a human with a fully functioning immune system develop severe symptoms following infection. People with weakened immune systems are likely to experience headache, confusion, poor coordination, seizures, lung problems that may resemble tuberculosis or Pneumocystis jiroveci pneumonia (a common opportunistic infection that occurs in people with AIDS), or blurred vision caused by severe inflammation of the retina (ocular toxoplasmosis) Young children and immunocompromised people, such as those with HIV/AIDS, those taking certain types of chemotherapy, or those who have recently received an organ transplant, may develop severe toxoplasmosis. This can cause damage to the brain (encephalitis) or the eyes (necrotizing retinochoroiditis). Infants infected via placental transmission may be born with either of these problems, or with nasal malformations, although these complications are rare in newborns. The toxoplasmic trophozoites causing acute toxoplasmosis are referred to as tachyzoites, and are typically found in bodily fluids.

Swollen lymph nodes are commonly found in the neck or under the chin, followed by the armpits and the groin. Swelling may occur at different times after the initial infection, persist, and recur for various times independently of antiparasitic treatment. It is usually found at single sites in adults, but in children, multiple sites may be more common. Enlarged lymph nodes will resolve within one to two months in 60% of cases. However, a quarter of those affected take two to four months to return to normal, and 8% take four to six months. A substantial number (6%) do not return to normal until much later.