Ehrlichiosis is a nationally notifiable disease in the United States. There have been cases reported in every month of the year, but most cases are reported during April–September. These months are also the peak months for tick activity in the United States.

From 2008-2012, the average yearly incidence of ehrlichiosis was 3.2 cases per million persons. This is more than twice the estimated incidence for the years 2000-2007. The incidence rate increases with age, with the ages of 60–69 years being the highest age-specific years. Children of less than 10 years and adults aged 70 years and older, have the highest case-fatality rates. There is a documented higher risk of death among persons who are immunosuppressed.

Doxycycline and minocycline are the medications of choice. For people allergic to antibiotics of the tetracycline class, rifampin is an alternative. Early clinical experience suggested that chloramphenicol may also be effective, however, in vitro susceptibility testing revealed resistance.

The prognosis is good for dogs with acute ehrlichiosis. For dogs that have reached the chronic stage of the disease, the prognosis is guarded. When bone marrow suppression occurs and there are low levels of blood cells, the animal may not respond to treatment.

"A. phagocytophilum" is transmitted to humans by "Ixodes" ticks. These ticks are found in the US, Europe, and Asia. In the US, "I. scapularis" is the tick vector in the East and Midwest states, and "I. pacificus" in the Pacific Northwest. In Europe, the "I. ricinus" is the main tick vector, and "I. persulcatus" is the currently known tick vector in Asia.

The major mammalian reservoir for "A. phagocytophilum" in the eastern United States is the white-footed mouse, "Peromyscus leucopus". Although white-tailed deer and other small mammals harbor "A. phagocytophilum", evidence suggests that they are not a reservoir for the strains that cause HGA. A tick that has a blood meal from an infected reservoir becomes infected themselves. If an infected tick then latches onto a human the disease is then transmitted to the human host and "A." "phagocytophilum" symptoms can arise.

"Anaplasma phagocytophilum" shares its tick vector with other human pathogens, and about 10% of patients with HGA show serologic evidence of coinfection with Lyme disease, babesiosis, or tick-borne meningoencephalitis.

Tick control is the most effective method of prevention, but tetracycline at a lower dose can be given daily for 200 days during the tick season in endemic regions.

Humans contract the disease after a bite by an infected tick of the species "Amblyomma americanum".

Those with an underlying immunodeficiency (such as HIV) appear to be at greater risk of contracting the disease. Compared to HME, ewingii ehrlichiosis has a decreased incidence of complications.

Like "Anaplasma phagocytophilum", the causative agent of human granulocytic ehrlichiosis, Ehrlichia ewingii infects neutrophils. Infection with "E. ewingii" may delay neutrophil apoptosis.

From the first reported case in 1994 until 2010, HGA's rates of incidence have exponentially increased. This is likely because HGA is found where there are ticks that carry and transmit Lyme disease, also known as Borrelia burgdorferi, and babesiosis, which is found in the northeastern and midwestern parts of the United States, which has seemingly increased in the past couple of decades. Before 2000, there were less than 300 cases reported per year. In 2000, there were only 350 reported cases. From 2009-2010, HGA experienced a 52% increase in the number of cases reported.

Ehrlichiosis ewingii infection is an infectious disease caused by an intracellular bacteria, "Ehrlichia ewingii". The infection is transmitted to humans by the tick, "Amblyomma americanum". This tick can also transmit "Ehrlichia chaffeensis", the bacteria that causes human monocytic ehrlichiosis (HME).

Human monocytotropic ehrlichiosis (HME) is a form of ehrlichiosis associated with "Ehrlichia chaffeensis". This bacterium is an obligate intracellular pathogen affecting monocytes and macrophages.

If ehrlichiosis is suspected, treatment should not be delayed while waiting for a definitive laboratory confirmation, as prompt doxycycline therapy has been associated with improved outcomes. Doxycycline is the treatment of choice.

Presentation during early pregnancy can complicate treatment.Rifampin has been used in pregnancy and in patients allergic to doxycycline.

While a vaccine is available for PHF, it does not cover all strains of the bacterium, and recent vaccine failures seem to be on the rise. Additionally, the vaccine usually produces a very weak immune response, which may only lessen the severity of the disease rather than prevent it. The vaccine is administered twice a year, in early spring and in early summer, with the first one inoculation given before the mayflies emerge and the second administered as a booster.

Some veterinarians have started making recommendations for farm management to try to prevent this disease:

- Maintaining riparian barriers along bodies of water may encourage aquatic insects to stay near their places of origin

- Turning off outside lights around the barn will prevent insects from being attracted

- Cleaning water buckets and feed areas frequently and keeping food covered will reduce the chance that the horse will accidentally ingest infected insects

The U.S. Centers for Disease Control and Prevention (CDC) publishes a journal "Emerging Infectious Diseases" that identifies the following factors contributing to disease emergence:

- Microbial adaption; e.g. genetic drift and genetic shift in Influenza A

- Changing human susceptibility; e.g. mass immunocompromisation with HIV/AIDS

- Climate and weather; e.g. diseases with zoonotic vectors such as West Nile Disease (transmitted by mosquitoes) are moving further from the tropics as the climate warms

- Change in human demographics and trade; e.g. rapid travel enabled SARS to rapidly propagate around the globe

- Economic development; e.g. use of antibiotics to increase meat yield of farmed cows leads to antibiotic resistance

- Breakdown of public health; e.g. the current situation in Zimbabwe

- Poverty and social inequality; e.g. tuberculosis is primarily a problem in low-income areas

- War and famine

- Bioterrorism; e.g. 2001 Anthrax attacks

- Dam and irrigation system construction; e.g. malaria and other mosquito borne diseases

The mortality rate of the virus largely depends on the immune status of the infected dogs. Puppies experience the highest mortality rate, where complications such as pneumonia and encephalitis are more common. In older dogs that develop distemper encephalomyelitis, vestibular disease may present. Around 15% of canine inflammatory central nervous system diseases are a result of CDV.

Methicillin-resistant Staphylococcus aureus (MRSA) evolved from Methicillin-susceptible Staphylococcus aureus (MSSA) otherwise known as common "S. aureus". Many people are natural carriers of "S. aureus", without being affected in any way. MSSA was treatable with the antibiotic methicillin until it acquired the gene for antibiotic resistance. Though genetic mapping of various strains of MRSA, scientists have found that MSSA acquired the mecA gene in the 1960s, which accounts for its pathogenicity, before this it had a predominantly commensal relationship with humans. It is theorized that when this "S. aureus" strain that had acquired the mecA gene was introduced into hospitals, it came into contact with other hospital bacteria that had already been exposed to high levels of antibiotics. When exposed to such high levels of antibiotics, the hospital bacteria suddenly found themselves in an environment that had a high level of selection for antibiotic resistance, and thus resistance to multiple antibiotics formed within these hospital populations. When "S. aureus" came into contact with these populations, the multiple genes that code for antibiotic resistance to different drugs were then acquired by MRSA, making it nearly impossible to control. It is thought that MSSA acquired the resistance gene through the horizontal gene transfer, a method in which genetic information can be passed within a generation, and spread rapidly through its own population as was illustrated in multiple studies. Horizontal gene transfer speeds the process of genetic transfer since there is no need to wait an entire generation time for gene to be passed on. Since most antibiotics do not work on MRSA, physicians have to turn to alternative methods based in Darwinian medicine. However prevention is the most preferred method of avoiding antibiotic resistance. By reducing unnecessary antibiotic use in human and animal populations, antibiotics resistance can be slowed.

"N. risticii" responds well to tetracycline antibiotics. Mild cases may be treated with oral doxycycline, while severe cases are usually treated with intravenous oxytetracycline.

Supportive care for severe cases is aimed at minimizing the effects of endotoxemia and preventing laminitis. This may include intravenous fluids and electrolytes to counteract the diarrhea; NSAIDs such as Banamine (flunixin meglumine); intravenous dimethyl sulfoxide; administration of products such as Biosponge or activated charcoal via nasogastric tube to bind endotoxins; polymyxin B or plasma for endotoxemia; supportive shoeing; low doses of intramuscular acepromazine; and pentoxifylline.

The prevalence of canine distemper in the community has decreased dramatically due to the availability of vaccinations. However, the disease continues to spread among unvaccinated populations, such as those in animal shelters and pet stores. This provides a great threat to both the rural and urban communities throughout the United States, affecting both shelter and domestic canines. Despite the effectiveness of the vaccination, outbreaks of this disease continue to occur nationally. In April 2011, the Arizona Humane Society released a valley-wide pet health alert throughout Phoenix, Arizona.

Outbreaks of canine distemper continue to occur throughout the United States and elsewhere, and are caused by many factors. These factors include the overpopulation of dogs and the irresponsibility of pet owners. The overpopulation of dogs is a national problem that organizations such as the Humane Society and ASPCA face every day. This problem is even greater within areas such as Arizona, owing to the vast amount of rural land. An unaccountable number of strays that lack vaccinations reside in these areas and are therefore more susceptible to diseases such as canine distemper. These strays act as a host for the virus, spreading it throughout the surrounding area, including urban areas. Puppies and dogs that have not received their shots can then be infected if in a place where many dogs interact, such as a dog park.

A canine vector-borne disease (CVBD) is one of "a group of globally distributed and rapidly spreading illnesses that are caused by a range of pathogens transmitted by arthropods including ticks, fleas, mosquitoes and phlebotomine sandflies." CVBDs are important in the fields of veterinary medicine, animal welfare, and public health. Some CVBDs are of zoonotic concern.

Many CVBD infect humans as well as companion animals. Some CVBD are fatal; most can only be controlled, not cured. Therefore, infection should be avoided by preventing arthropod vectors from feeding on the blood of their preferred hosts. While it is well known that arthropods transmit bacteria and protozoa during blood feeds, viruses are also becoming recognized as another group of transmitted pathogens of both animals and humans.

Some "canine vector-borne pathogens of major zoonotic concern" are distributed worldwide, while others are localized by continent. Listed by vector, some such pathogens and their associated diseases are the following:

- Phlebotomine sandflies (Psychodidae): "Leishmania amazonensis", "L. colombiensis", and "L. infantum" cause visceral leishmaniasis (see also canine leishmaniasis). "L. braziliensis" causes mucocutaneous leishmaniasis. "L. tropica" causes cutaneous leishmaniasis. "L. peruviana" and "L. major" cause localized cutaneous leishmaniasis.

- Triatomine bugs (Reduviidae): "Trypanosoma cruzi" causes trypanosomiasis (Chagas disease).

- Ticks (Ixodidae): "Babesia canis" subspecies ("Babesia canis canis", "B. canis vogeli", "B. canis rossi", and "B. canis gibsoni" cause babesiosis. "Ehrlichia canis" and "E. chaffeensis" cause monocytic ehrlichiosis. "Anaplasma phagocytophilum" causes granulocytic anaplasmosis. "Borrelia burgdorferi" causes Lyme disease. "Rickettsia rickettsii" causes Rocky Mountain spotted fever. "Rickettsia conorii" causes Mediterranean spotted fever.

- Mosquitoes (Culicidae): "Dirofilaria immitis" and "D. repens" cause dirofilariasis.

No human vaccine is currently available for any tick-borne disease, except for tick-borne encephalitis. Individuals should therefore take precautions when entering tick-infested areas, particularly in the spring and summer months. Preventive measures include avoiding trails that are overgrown with bushy vegetation, wearing light-coloured clothes that allow one to see the ticks more easily, and wearing long pants and closed-toe shoes. Tick repellents containing DEET (N,N, diethyl-m-toluamide) are only marginally effective and can be applied to skin or clothing. Rarely, severe reactions can occur in some people who use DEET-containing products. Young children may be especially vulnerable to these adverse effects. Permethrin, which can only be applied to clothing, is much more effective in preventing tick bites. Permethrin is not a repellent but rather an insecticide; it causes ticks to curl up and fall off the protected clothing.

Traditionally, canine transmission is directly from sandfly to dog. Cases in the United States have proven "L. infantum" transmission from dog to dog by direct contamination with blood and secretions, as well as transplacentally from an infected bitch to her pups. This mode of transmission seems to be unique to the "L. infantum" Mon1 strain found in the United States. Although "in utero" transmission is likely the predominant method of disease spread amount the "L. infantum" Mon1 strain, it is still a viable parasite (has not lost virulence factors associated with sandfly-uptake) which can be transmitted via sandfly bite. A Brazilian study of 63 puppies from 18 "L. donovani"-infected parents found no evidence of congential or transplacental infection.

Removal of the embedded tick usually results in resolution of symptoms within several hours to days. If the tick is not removed, the toxin can be fatal, with reported mortality rates of 10–12 percent, usually due to respiratory paralysis. The tick is best removed by grasping the tick as close to the skin as possible and pulling in a firm steady manner.

Unlike the other species of ticks, the toxin of Ixodes holocyclus (Australian Paralysis Tick) will not resolve itself and will be fatal if medical assistance is not immediately sought after pulling the tick off of the animal. Contrary to popular belief, if the head detaches from the body while being pulled off, leaving the head will not inject more venom. The head may cause a skin irritation but it will not inject any more venom. Once the tick is removed, place it in a clear bag [preferably ziplock] so the vet can identify it.

Water and food can worsen the results of the animal as the venom can prevent the animal from swallowing properly. If you find an Australian Paralysis Tick on your animal, immediately remove the tick and seek veterinary assistance even if you do not think the tick has been on the animal long enough to inject venom.

Coccidiosis is a significant disease for chickens, especially affecting the young chicks. It can be fatal or leave the bird with compromised digestion. There are chick feed mixes that contain a coccidiostat to manage exposure levels and control disease. In an outbreak, coccidiocidal medications are given. Examples are toltrazuril (Baycox) or amprolium. After multiple infections, surviving chickens become resistant to the coccidia.

In areas where the known vector is a sandfly, deltamethrin collars worn by the dogs has been proven to be 86% effective. The sandfly is most active at dusk and dawn; keeping dogs indoors during those peak times will help minimize exposure.

Unfortunately, there is no one answer for leishmaniasis prevention, nor will one vaccine cover multiple species. "Different virulence factors have been identified for distinct "Leishmania" species, and there are profound differences in the immune mechanisms that mediate susceptibility/resistance to infection and in the pathology associated with disease."

In 2003, Fort Dodge Wyeth released the Leshmune vaccine in Brazil for "L. donovani" (also referred to as "kala-azar" in Brazil). Studies indicated up to 87% protection. Most common side effects from the vaccine have been noted as anorexia and local swelling.

The president of the Brazil Regional Council of Veterinary Medicine, Marcia Villa, warned since vaccinated dogs develop antibodies, they can be difficult to distinguish from asymptomatic, infected dogs.

Studies also indicate the Leshmune vaccine may be reliable in treating "L. chagasi", and a possible treatment for dogs already infected with "L. donovani".

"Bartonella quintana" is transmitted by contamination of a skin abrasion or louse-bite wound with the faeces of an infected body louse ("Pediculus humanus corporis"). There have also been reports of an infected louse bite passing on the infection.

Tetracycline-group antibiotics (doxycycline, tetracycline) are commonly used. Chloramphenicol is an alternative medication recommended under circumstances that render use of tetracycline derivates undesirable, such as severe liver malfunction, kidney deficiency, in children under nine years and in pregnant women. The drug is administered for seven to ten days.

The treatment for bacillary angiomatosis is erythromycin given for three to four months.

The most common medications used to treat coccidian infections are in the sulfonamide antibiotic family.

Depending on the pathogen and the condition of the animal, untreated coccidiosis may clear of its own accord, or become severe and damaging, and sometimes cause death.