Occupations at risk include veterinarians, slaughterhouse workers, farmers, sailors on rivers, sewer maintenance workers, waste disposal facility workers, and people who work on derelict buildings. Slaughterhouse workers can contract the disease through contact with infected blood or body fluids. Rowers, kayakers and canoeists also sometimes contract the disease. It was once mostly work-related but is now often also related to adventure tourism and recreational activities.

Leptospirosis is transmitted by the urine of an infected animal and is contagious as long as the urine is still moist. Although "Leptospira" has been detected in reptiles and birds, only mammals are able to transmit the bacterium to humans and other animals. Rats, mice, and moles are important primary hosts—but a wide range of other mammals including dogs, deer, rabbits, hedgehogs, cows, sheep, swine, raccoons, opossums, skunks, and certain marine mammals carry and transmit the disease as secondary hosts. In Africa, the banded mongoose has been identified as a carrier of the pathogen, likely in addition to other African wildlife hosts. Dogs may lick the urine of an infected animal off the grass or soil, or drink from an infected puddle.

House-bound domestic dogs have contracted leptospirosis, apparently from licking the urine of infected mice in the house. The type of habitats most likely to carry infective bacteria includes muddy riverbanks, ditches, gullies, and muddy livestock rearing areas where there is a regular passage of wild or farm mammals. The incidence of leptospirosis correlates directly with the amount of rainfall, making it seasonal in temperate climates and year-round in tropical climates.

Leptospirosis also transmits via the semen of infected animals.

Humans become infected through contact with water, food, or soil that contains urine from these infected animals. This may happen by swallowing contaminated food or water or through skin contact. The disease is not known to spread between humans, and bacterial dissemination in convalescence is extremely rare in humans. Leptospirosis is common among water-sport enthusiasts in specific areas, as prolonged immersion in water promotes the entry of this bacterium. Surfers and whitewater paddlers are at especially high risk in areas that have been shown to contain these bacteria, and can contract the disease by swallowing contaminated water, splashing contaminated water into their eyes or nose, or exposing open wounds to infected water.

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.

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.

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.

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.

Currently, no vaccine against relapsing fever is available, but research continues. Developing a vaccine is very difficult because the spirochetes avoid the immune response of the infected person (or animal) through antigenic variation. Essentially, the pathogen stays one step ahead of antibodies by changing its surface proteins. These surface proteins, lipoproteins called variable major proteins, have only 30–70% of their amino acid sequences in common, which is sufficient to create a new antigenic "identity" for the organism. Antibodies in the blood that are binding to and clearing spirochetes expressing the old proteins do not recognize spirochetes expressing the new ones. Antigenic variation is common among pathogenic organisms. These include the agents of malaria, gonorrhea, and sleeping sickness. Important questions about antigenic variation are also relevant for such research areas as developing a vaccine against HIV and predicting the next influenza pandemic.

Along with "Rickettsia prowazekii" and "Bartonella quintana", "Borrelia recurrentis" is one of three pathogens of which the body louse ("Pediculus humanus humanus") is a vector. Louse-borne relapsing fever is more severe than the tick-borne variety.

Louse-borne relapsing fever occurs in epidemics amid poor living conditions, famine and war in the developing world. It is currently prevalent in Ethiopia and Sudan.

Mortality rate is 1% with treatment and 30–70% without treatment. Poor prognostic signs include severe jaundice, severe change in mental status, severe bleeding and a prolonged QT interval on ECG.

Lice that feed on infected humans acquire the "Borrelia" organisms that then multiply in the gut of the louse. When an infected louse feeds on an uninfected human, the organism gains access when the victim crushes the louse or scratches the area where the louse is feeding. "B. recurrentis" infects the person via mucous membranes and then invades the bloodstream. No non-human, animal reservoir exists.

Globally, 59,000 people die from rabies each year. This is the equivalent of one person dying every nine minutes, with half of the people who die from rabies being under the age of 15. The Pan American Health Organization (PAHO) and the Pan American Center of foot-and-mouth disease (PANAFTOSA) led a mission to eliminate dog-mediated rabies in the American region by 2015. These organizations are cognizant of the regional control of rabies. The PAHO and PANAFTOSA visited Haiti in early December, 2013, and the objectives of the mission were to assess the status of Haiti’s rabies program as delivered by the Haitian Ministry of Agriculture, Natural Resources and Rural Development (MARNDR) and the Ministry of Health (MSPP). The mission was to seek opportunities for collaboration between Haiti, Brazil, and the Centers for Disease Control and Prevention (CDC) in Haiti.

Even in 2017, rabies in Haiti is still identified as a national problem, even with PEP proposed.

In Haiti, few cases of human rabies are reported to health authorities. In 2016, a report of a woman who had been exposed to rabies three months prior and was showing symptoms went to the hospital where no treatment was administered to her. Even after being reported to both the CDC and the national Department of Epidemiology and Laboratory Research (DELR), as required by Haiti's surveillance program, the woman ended up passing away. This goes to show the lack of communication and effectiveness in caring for human subjects in Haiti, and the continued focus is on eliminating dog-mediated rabies altogether.

Human diploid cell culture rabies vaccine (HDCV) and purified chick embryo cell culture rabies vaccine (PCEC) are used to treat post-exposure immunization against a human rabies infection. Recommendations for treatment are given by governmental health care organizations and in health literature. Health care providers are encouraged to administer a regimen of four 1-mL doses of HDCV or PCEC vaccines. According to the CDC, these injections should be administered intramuscularly to persons who have not yet been vaccinated for rabies.

For those who are unvaccinated, the first of four doses is administered immediately after exposure to the rabies virus. Additional doses are given three, seven, and fourteen days after the first vaccination. Exposure usually means a bite from a rabid animal.

At an individual patient level, post-exposure prophylaxis (PEP) consists of local treatment of the wound, vaccination, and administration of immunoglobulin, if necessary [3]. At the program level, several components are critical, including: adequate and prompt recognition of the need for PEP by the public, if exposed, and by health officials, prompt and sufficient availability of high-quality PEP, and adequate follow-up of PEP use. Health officials' awareness of the need for PEP after a dog bite can only be achieved if the exposure is attended to immediately and communicated effectively.

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.

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.

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 disease was first reported in the town of in Buenos Aires province, Argentina in 1958, giving it one of the names by which it is known. Various theories about its nature were proposed: it was Weil's disease, leptospirosis, caused by chemical pollution. It was associated with fields containing stubble after the harvest, giving it another of its names.

The endemic area of AHF covers approximately 150,000 km², compromising the provinces of Buenos Aires, Córdoba, Santa Fe and La Pampa, with an estimated risk population of 5 million.

The vector, a small rodent known locally as "ratón maicero" ("maize mouse"; "Calomys musculinus"), suffers from chronic asymptomatic infection, and spreads the virus through its saliva and urine. Infection is produced through contact of skin or mucous membranes, or through inhalation of infected particles. It is found mostly in people who reside or work in rural areas; 80% of those infected are males between 15 and 60 years of age.

AHF is a grave acute disease which may progress to recovery or death in 1 to 2 weeks. The incubation time of the disease is between 10 and 12 days, after which the first symptoms appear: fever, headaches, weakness, loss of appetite and will. These intensify less than a week later, forcing the infected to lie down, and producing stronger symptoms such as vascular, renal, hematological and neurological alterations. This stage lasts about 3 weeks.

If untreated, the mortality of AHF reaches 15–30%. The specific treatment includes plasma of recovered patients, which, if started early, is extremely effective and reduces mortality to 1%.

Ribavirin also has shown some promise in treating arenaviral diseases.

The disease was first detected in the 1950s in the Junín Partido in Buenos Aires, after which its agent, the Junín virus, was named upon its identification in 1958. In the early years, about 1,000 cases per year were recorded, with a high mortality rate (more than 30%). The initial introduction of treatment serums in the 1970s reduced this lethality.

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.

Canine influenza (dog flu) is influenza occurring in canine animals. Canine influenza is caused by varieties of influenzavirus A, such as equine influenza virus H3N8, which in 2004 was discovered to cause disease in dogs. Because of the lack of previous exposure to this virus, dogs have no natural immunity to it. Therefore, the disease is rapidly transmitted between individual dogs. Canine influenza may be endemic in some regional dog populations of the United States. It is a disease with a high morbidity (incidence of symptoms) but a low incidence of death.

A newer form was identified in Asia during the 2000s and has since caused outbreaks in the US as well. It is a mutation of H3N2 that adapted from its avian influenza origins. Vaccines have been developed for both strains.

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.

Influenza A viruses are enveloped, negative sense, single-stranded RNA viruses. Genome analysis has shown that H3N8 was transferred from horses to dogs and then adapted to dogs through point mutations in the genes. The incubation period is two to five days, and viral shedding may occur for seven to ten days following the onset of symptoms. It does not induce a persistent carrier state.

"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.

Dogs will typically recover from kennel cough within a few weeks. However, secondary infections could lead to complications that could do more harm than the disease itself. Several opportunistic invaders have been recovered from the respiratory tracts of dogs with kennel cough, including Streptococcus, Pasteurella, Pseudomonas, and various coliforms. These bacteria have the potential to cause pneumonia or sepsis, which drastically increase the severity of the disease. These complications are evident in thoracic radiographic examinations. Findings will be mild in animals affected only by kennel cough, while those with complications may have evidence of segmental atelectasis and other severe side effects.

Viral infections such as canine parainfluenza or canine coronavirus are only shed for roughly 1 week following recovery; however, respiratory infections involving "Bordetella bronchiseptica" can be transmissible for several weeks longer. While there was early evidence to suggest that "B. bronchiseptica" could be shed for many months post-infection, a more recent report places detectable nasal and pharyngeal levels of "B. bronchiseptica" in 45.6% of all clinically healthy dogs. This has potentially expanded the vector from currently or recently infected dogs to half the dog population as carriers. To put the relative levels of shedding bacteria into perspective, a study analyzing the shedding kinetics of "B. bronchiseptica" presents the highest levels of bacterial shedding one week post-exposure, with an order of magnitude decrease in shedding observed every week. This projection places negligible levels of shedding to be expected 6 weeks post-exposure (or ~5 weeks post-onset of symptoms). Dogs which had been administered intranasal vaccine 4 weeks prior to virulent "B. bronchiseptica" challenge displayed little to no bacterial shedding within 3 weeks of exposure to the virulent strain.

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.

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.

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.