Rocky Mountain spotted fever can be a very severe illness and patients often require hospitalization. Because "R. rickettsii" infects the cells lining blood vessels throughout the body, severe manifestations of this disease may involve the respiratory system, central nervous system, gastrointestinal system, or kidneys.

Long-term health problems following acute Rocky Mountain spotted fever infection include partial paralysis of the lower extremities, gangrene requiring amputation of fingers, toes, or arms or legs, hearing loss, loss of bowel or bladder control, movement disorders, and language disorders. These complications are most frequent in persons recovering from severe, life-threatening disease, often following lengthy hospitalizations

"Rickettsia africae" is a gram-negative, obligate intracellular, pleomorphic bacterium. It belongs to the "Rickettsia" genus, which includes many bacterial species that are transmitted to humans by arthropods.

Prevention of ATBF centers around protecting oneself from tick bites by wearing long pants and shirt, and using insecticides like DEET on the skin. Travelers to rural areas in Africa and the West Indies should be aware that they may come in contact with ATBF tick vectors. Infection is more likely to occur in people who are traveling to rural areas or plan to spend time participating in outdoor activities. Extra caution should be taken in November - April, when "Amblyomma" ticks are more active. Inspection of the body, clothing, gear, and any pets after time outdoors can help to identify and remove ticks early.

There are only between 500 and 2500 cases of Rocky Mountain spotted fever reported in the United States per year, and in only about 20% can the tick be found.

Host factors associated with severe or fatal Rocky Mountain spotted fever include advanced age, male sex, African or Caribbean background, chronic alcohol abuse, and glucose-6-phosphate dehydrogenase (G6PD) deficiency. Deficiency of G6PD is a genetic condition affecting about 12 percent of the Afro-American male population. Deficiency in this enzyme is associated with a high proportion of severe cases of Rocky Mountain spotted fever. This is a rare clinical complication that is often fatal within five days of the onset of the disease.

In the early 1940´s, outbreaks were described in the Mexican states of Sinaloa, Sonora, Durango, and Coahuila driven by dogs and Rhipicephalus sanguineus sensu lato, the brown dog tick. Over the ensuing 100 years case fatality rates were 30%–80%. In 2015, there was an abrupt rise in Sonora cases with 80 fatal cases. From 2003 to 2016, cases increased to 1394 with 247 deaths.

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.

It is estimated that seven to ten million people are infected by leptospirosis annually. One million cases of severe leptospirosis occur annually, with 58,900 deaths. Annual rates of infection vary from 0.02 per 100,000 in temperate climates to 10 to 100 per 100,000 in tropical climates. This leads to a lower number of registered cases than likely exists.

The number of new cases of leptospirosis is difficult to estimate since many cases of the disease go unreported. There are many reasons for this, but the biggest issue is separating the disease from other similar conditions. Laboratory testing is lacking in many areas.

In context of global epidemiology, the socioeconomic status of many of the world’s population is closely tied to malnutrition; subsequent lack of micronutrients may lead to increased risk of infection and death due to leptospirosis infection. Micronutrients such as iron, calcium, and magnesium represent important areas of future research.

Outbreaks that occurred after the 1940's have happened mostly in the late summer seasons, which happens to be the driest part of the year. The people at the highest risk for leptospirosis are young people whose age ranges from 5-16 years old, and can also range to young adults.

The amount of cases increase during the rainy season in the tropics and during the late summer or early fall in Western countries. This happens because leptospires survive best in fresh water, damp alkaline soil, vegetation, and mud with temperatures higher that 22° C. This also leads to increased risk of exposure to populations during flood conditions, and leptospire concentrations to peak in isolated pools during drought. There is no evidence of leptospirosis having any effect on sexual and age-related differences. However, a major risk factor for development of the disease is occupational exposure, a disproportionate number of working-aged males are affected. There have been reported outbreaks where more than 40% of people are younger than 15. “Active surveillance measures have detected leptospire antibodies in as many as 30% of children in some urban American populations.” Potential reasons for such cases include children playing with suspected vectors such as dogs or indiscriminate contact with water.

The most common way the disease is spread is via arthropod vectors. Ticks involved include "Amblyomma", "Dermacentor", "Haemaphysalis", and "Ixodes". Rodents, rabbits, and hares often serve as reservoir hosts, but waterborne infection accounts for 5 to 10% of all tularemia in the US. Tularemia can also be transmitted by biting flies, particularly the deer fly "Chrysops discalis". Individual flies can remain infectious for 14 days and ticks for over two years.Tularemia may also be spread by direct contact with contaminated animals or material, by ingestion of poorly cooked flesh of infected animals or contaminated water, or by inhalation of contaminated dust.

Several species of rickettsia bacteria cause anaplasmosis in ruminants:

- Cattle:

- "Anaplasma marginale" - found worldwide.

- "Anaplasma centrale" - found mainly in South America, Africa and the Middle East.

- Sheep and goats:

- "Anaplasma ovis" - found worldwide.

Scrub typhus is transmitted by some species of trombiculid mites ("chiggers", particularly "Leptotrombidium deliense"), which are found in areas of heavy scrub vegetation. The bite of this mite leaves a characteristic black eschar that is useful to the doctor for making the diagnosis.

Scrub typhus is endemic to a part of the world known as the tsutsugamushi triangle (after "O. tsutsugamushi"). This extends from northern Japan and far-eastern Russia in the north, to the territories around the Solomon Sea into northern Australia in the south, and to Pakistan and Afghanistan in the west. It may also be endemic in parts of South America, too.

The precise incidence of the disease is unknown, as diagnostic facilities are not available in much of its large native range which spans vast regions of equatorial jungle to the subtropics. In rural Thailand and Laos, murine and scrub typhus account for around a quarter of all adults presenting to hospital with fever and negative blood cultures. The incidence in Japan has fallen over the past few decades, probably due to land development driving decreasing exposure, and many prefectures report fewer than 50 cases per year.

It affects females more than males in Korea, but not in Japan, and which may be because sex-differentiated cultural roles have women tending garden plots more often, thus being exposed to vegetation inhabited by chiggers.

The incidence is increasing in the southern part of the Indian subcontinent and in northern areas around Darjeeling.

One study using the medicinal plant "Peganum harmala" showed it to have a lifesaving effect on cattle infected with East Coast fever.

The classical treatment with tetracyclines (1970–1990) cannot provide efficiency more than 50%.

Since the early 1990s, buparvaquone is used in bovine theileriosis with remarkable results (90 to 98% recovery).

Other than the buparvaquones, other chemotherapeutic options are the parvaquones, e.g. Clexon. Halofuginone lactate has also been shown to have an 80.5% efficacy against "Theirelia parva parva" infections. The ultimate factor that causes death is pulmonary edema.

In May 2010, a vaccine to protect cattle against East Coast fever reportedly had been approved and registered by the governments of Kenya, Malawi and Tanzania. This consists of cryopreserved sporozoites from crushed ticks, but it is expensive and can cause disease.

Control of the disease relies on control of ticks of domestic animals, particularly disease-resistant ticks. This is a major concern in tropical countries with large livestock populations, especially in the endemic area. Pesticides (acaricides) are applied in dipping baths or spray races, and cattle breeds with good ability to acquire immune resistance to the vector ticks are used.

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 bacteria can penetrate into the body through damaged skin, mucous membranes, and inhalation. Humans are most often infected by tick/deer fly bite or through handling an infected animal. Ingesting infected water, soil, or food can also cause infection. Hunters are at a higher risk for this disease because of the potential of inhaling the bacteria during the skinning process. It has been contracted from inhaling particles from an infected rabbit ground up in a lawnmower (see below). Tularemia is not spread directly from person to person. Humans can also be infected through bioterrorism attempts.

Francisella tularensis can live both within and outside the cells of the animal it infections, meaning it is a facultative intracellular bacterium. It primarily infects macrophages, a type of white blood cell, thus is able to evade the immune system. The course of disease involves the spread of the organism to multiple organ systems, including the lungs, liver, spleen, and lymphatic system. The course of disease is different depending on the route of exposure. Mortality in untreated (before the antibiotic era) patients has been as high as 50% in the pneumoniac and typhoidal forms of the disease, which however account for less than 10% of cases.

Ehrlichiosis (; also known as canine rickettsiosis, canine hemorrhagic fever, canine typhus, tracker dog disease, and tropical canine pancytopenia is a tick-borne disease of dogs usually caused by the organism "Ehrlichia canis". "Ehrlichia canis" is the pathogen of animals. Humans can become infected by "E. canis" and other species after tick exposure. German Shepherd Dogs are thought to be susceptible to a particularly severe form of the disease, other breeds generally have milder clinical signs. Cats can also be infected.

East Coast fever (theileriosis) is an animal disease in Africa caused by the protozoan parasite "Theileria parva". It excludes diseases caused by other "Theileria"

AHSV was first recorded south of the Sahara Desert in the mid-1600s with the introduction of horses to southern Africa. The virus is considered endemic to the equatorial, eastern, and southern regions of Africa. Several outbreaks have occurred in Equidaes throughout Africa and elsewhere. AHS is known to be endemic in Sub-Saharan Africa, and has spread to Morocco, the Middle East, India, and Pakistan. More recently, outbreaks have been reported in the Iberian Peninsula. AHS has never been reported in the Americas, eastern Asia or Australasia. Epidemiology is dependent on host-vector interaction, where cyclic disease outbreaks coincide with high numbers of competent vectors. The most important vector for AHS in endemic areas is the biting midge "Culicoides imicola", which prefers warm, humid conditions. Larvae do not carry the virus and long, cold winters are sufficient to break epidemics in non-endemic areas.

There is currently no treatment for AHS.

Control of an outbreak in an endemic region involves quarantine, vector control and vaccination. To prevent this disease, the affected horses are usually slaughtered, and the uninfected horses are vaccinated against the virus. Three vaccines currently exist, which include a polyvalent vaccine, a monovalent vaccine, and a monovalent inactivated vaccine. This disease can also be prevented by destroying the insect vector habitats using insecticides.

Vaccines against anaplasmosis are available. Carrier animals should be eliminated from flocks. Tick control may also be useful although it can be difficult to implement.

The degree of pathogenicity depends on what species the host is, the virulence of the "Trypanosoma evansi" strain, and the dose received by the host. Many species such as dogs, horses and rats, have been shown to have immunological reactions to the infection, such as anemia due to decrease in erythrocytes and hemoglobin. Although not fully understood at this point in time, some theories believe that the erythrocytes could acquire trypaonosomal antigen, resulting in a negative immunological reaction.

Animals that have been infected show loss of appetite, weight loss, anaemia, odema, fever, salivations, lacrimation, and abortion. The proteases that are released during infection of T.evansi might degrade the host tissue proteins and are a huge force in the pathogenesis. That is why scientists are looking at immune targeting of these proteases to protect the infected host.

Scrub typhus or bush typhus is a form of typhus caused by the intracellular parasite "Orientia tsutsugamushi", a Gram-negative α-proteobacterium of family Rickettsiaceae first isolated and identified in 1930 in Japan.

Although the disease is similar in presentation to other forms of typhus, its pathogen is no longer included in genus "Rickettsia" with the typhus bacteria proper, but in "Orientia". The disease is thus frequently classified separately from the other typhi.

A vaccine is available, called "Chinese Live Attenuated EIA vaccine", developed in China and widely used there since 1983. Another attenuated live virus vaccine is in development in the United States.

Reuse of syringes and needles is a risk factor for transfer of the disease. Currently in the United States, all horses that test positive must be reported to federal authorities by the testing laboratory. EIA-positive horses are infected for life. Options for the horse include sending the horse to a recognized research facility, branding the horse and quarantining it at least 200 yards from other horses for the rest of its life, and euthanizing the horse. Very few quarantine facilities exist, which usually leads to the option of euthanizing the horse. The Florida Research Institute for Equine Nurturing, Development and Safety (a.k.a. F.R.I.E.N.D.S.) is one of the largest such quarantine facilities and is located in south Florida.

The horse industry and the veterinary industry strongly suggest that the risks posed by infected horses, even if they are not showing any clinical signs, are enough of a reason to impose such stringent rules. The precise impacts of the disease on the horse industry are unknown.

A vaccine is in the process of being developed, but is not yet licensed. There is a fear that when a vaccine is licensed, financial constraints will make the vaccination an unrealistic factor for many countries that are suffering from high rates of melioidosis.

Yellow fever is common in tropical and subtropical areas of South America and Africa. Worldwide, about 600 million people live in endemic areas. The WHO estimates 200,000 cases of disease and 30,000 deaths a year occur; the number of officially reported cases is far lower.

Person-to-person transmission is exceedingly unusual; and patients with melioidosis should not be considered contagious. Lab workers should handle "B. pseudomallei" under BSL-3 isolation conditions, as laboratory-acquired melioidosis has been described.

In endemic areas, people (rice-paddy farmers in particular) are warned to avoid contact with soil, mud, and surface water where possible. Case clusters have been described following flooding and cyclones and probably relate to exposure. Other case clusters have related to contamination of drinking water supplies. Populations at risk include patients with diabetes mellitus, chronic renal failure, chronic lung disease, or an immune deficiency of any kind. The effectiveness of measures to reduce exposure to the causative organism have not been established. A vaccine is not yet available.

As of 2017 there is no commercially available vaccine. A vaccine has been in development for scrub typhus known as the scrub typhus vaccine.

They are usually spread by eating or drinking food or water contaminated with the feces of an infected person. They may occur when a person who prepares food is infected. Risk factors include poor sanitation as is found among poor crowded populations. Occasionally they may be transmitted by sex. Humans are the only animal infected.