In general, specific laboratory tests are not available to rapidly diagnose tick-borne diseases. Due to their seriousness, antibiotic treatment is often justified based on clinical presentation alone.

Tick-borne diseases, which afflict humans and other animals, are caused by infectious agents transmitted by tick bites. Tick-borne illnesses are caused by infection with a variety of pathogens, including rickettsia and other types of bacteria, viruses, and protozoa. Because individual ticks can harbor more than one disease-causing agent, patients can be infected with more than one pathogen at the same time, compounding the difficulty in diagnosis and treatment. As of 2016, 16 tick-borne diseases of humans are known (four discovered since 2013).

As the incidence of tick-borne illnesses increases and the geographic areas in which they are found expand, health workers increasingly must be able to distinguish the diverse, and often overlapping, clinical presentations of these diseases.

An estimated 60% of people infected with the fungi responsible for coccidioidomycosis have minimal to no symptoms, while 40% will have a range of possible clinical symptoms. Of those who do develop symptoms, the primary infection is most often respiratory, with symptoms resembling bronchitis or pneumonia that resolve over a matter of a few weeks. In endemic regions, coccidioidomycosis is responsible for 20% of cases of community-acquired pneumonia. Notable coccidioidomycosis signs and symptoms include a profound feeling of tiredness, fever, cough, headaches, rash, muscle pain, and joint pain. Fatigue can persist for many months after initial infection. The classic triad of coccidioidomycosis known as "desert rheumatism" includes the combination of fever, joint pains, and erythema nodosum.

Nearly 3% to 5% of infected individuals do not recover from the initial acute infection and develop a chronic infection. This can take the form of chronic lung infection or widespread disseminated infection (affecting the tissues lining the brain, soft tissues, joints, and bone). Chronic infection is responsible for most of the morbidity and mortality. Chronic fibrocavitary disease is manifested by cough, sputum, fevers, night sweats and weight loss. Osteomyelitis, including involvement of the spine, and meningitis which may occur months to years after initial infection. Severe lung disease may develop in HIV-infected persons.

An emerging infectious disease (EID) is an infectious disease whose incidence has increased in the past 20 years and could increase in the near future. Emerging infections account for at least 12% of all human pathogens. EIDs are caused by newly identified species or strains (e.g. Severe acute respiratory syndrome, HIV/AIDS) that may have evolved from a known infection (e.g. influenza) or spread to a new population (e.g. West Nile fever) or to an area undergoing ecologic transformation (e.g. Lyme disease), or be "reemerging" infections, like drug resistant tuberculosis. Nosocomial (hospital-acquired) infections, such as methicillin-resistant Staphylococcus aureus are emerging in hospitals, and extremely problematic in that they are resistant to many antibiotics. Of growing concern are adverse synergistic interactions between emerging diseases and other infectious and non-infectious conditions leading to the development of novel syndemics. Many emerging diseases are zoonotic - an animal reservoir incubates the organism, with only occasional transmission into human populations.

Human granulocytic anaplasmosis (HGA) is a tick-borne, infectious disease caused by "Anaplasma phagocytophilum", an obligate intracellular bacterium that is typically transmitted to humans by ticks of the "Ixodes ricinus" species complex, including "Ixodes scapularis" and "Ixodes pacificus" in North America. These ticks also transmit Lyme disease and other tick borne diseases.

The bacteria infect white blood cells called neutrophils, causing changes in gene expression that prolong the life of these otherwise short-lived cells.

After "Coccidioides" infection, coccidioidomycosis begins with Valley fever, which is its initial acute form. Valley fever may progress to the chronic form and then to disseminated coccidioidomycosis. Therefore, "Coccidioidomycosis" may be divided into the following types:

In the subgroup of patients where an inoculating event was noted, the mean incubation period of acute melioidosis was 9 days (range 1–21 days). Patients with latent melioidosis may be symptom-free for decades; the longest period between presumed exposure and clinical presentation is 62 years. The potential for prolonged incubation was recognized in US servicemen involved in the Vietnam War, and was referred to as the "Vietnam time-bomb". A wide spectrum of severity exists; in chronic presentations, symptoms may last months, but fulminant infection, particularly associated with near-drowning, may present with severe symptoms over hours.

Symptoms usually appear 2 to 4 weeks after exposure. There are four general types of infection including localized, pulmonary, blood-borne, or disseminated throughout the body. The type and location of the infection usually determines which symptoms appear first as well as which symptoms are more prominent.

Patients with melioidosis usually present with fever. Pain or other symptoms may be suggestive of a clinical focus, which is found in around 75% of patients. Such symptoms include cough or pleuritic chest pain suggestive of pneumonia, bone or joint pain suggestive of osteomyelitis or septic arthritis, or cellulitis. Intra-abdominal infection (including liver and/or splenic abscesses, or prostatic abscesses) do not usually present with focal pain, and imaging of these organs using ultrasound or computed tomography should be performed routinely. In one series of 214 patients, 27.6% had abscesses in the liver or spleen (95% confidence interval, 22.0% to 33.9%). "B. pseudomallei" abscesses may have a characteristic "honeycomb" or "swiss cheese" architecture (hypoechoic, multiseptate, multiloculate) on CT.

Regional variations in disease presentation are seen: parotid abscesses characteristically occur in Thai children, but this presentation has been described only once in Australia. Conversely, prostatic abscesses are found in up to 20% of Australian males, but are rarely described elsewhere. An encephalomyelitis syndrome is recognised in northern Australia.

Patients with melioidosis usually have risk factors for disease, such as diabetes, thalassemia, hazardous alcohol use, or renal disease, and frequently give a history of occupational or recreational exposure to mud or pooled surface water. However, otherwise healthy patients, including children, may also get melioidosis.

In up to 25% of patients, no focus of infection is found and the diagnosis is usually made on blood cultures or throat swab. Melioidosis is said to be able to affect any organ in the body except the heart valves (endocarditis). Although meningitis has been described secondary to ruptured brain abscesses, primary meningitis has not been described. Less common manifestations include intravascular infection, lymph node abscesses (1.2–2.2%), pyopericardium and myocarditis, mediastinal infection, and thyroid and scrotal abscesses and ocular infection.

Melioidosis is an infectious disease caused by a Gram-negative bacterium, "Burkholderia pseudomallei", found in soil and water. It is of public health importance in endemic areas, particularly in northeast Thailand, Vietnam, and northern Australia. It exists in acute and chronic forms. Signs and symptoms may include pain in chest, bones, or joints; cough; skin infections, lung nodules, and pneumonia.

"B. pseudomallei" was previously classed as part of the "Pseudomonas" genus; until 1992, it was known as "Pseudomonas pseudomallei". It is phylogenetically related closely to "Burkholderia mallei" which causes glanders, an infection primarily of horses, donkeys, and mules. The name melioidosis is derived from the Greek "melis" (μηλις) meaning "a distemper of asses" with the suffixes -oid meaning "similar to" and -osis meaning "a condition", that is, a condition similar to glanders.

Signs and symptoms may include:

- fever

- severe headache

- muscle aches (myalgia)

- chills and shaking, similar to the symptoms of influenza

- nausea

- vomiting

- loss of appetite

- unintentional weight loss

- abdominal pain

- cough

- diarrhea,

- aching joints

- sensitivity to light

- weakness

- fatigue

- change in mental status (extreme confusion, memory loss, inability to comprehend environment- interaction, reading, etc.)

- temporary loss of basic motor skills

Symptoms may be minor, as evidenced by surveillance studies in high-risk areas. Gastrointestinal tract symptoms occur in less than half of patients and a skin rash is seen in less than 10% of patients. It is also characterized by a low number of platelets, a low number of white blood cells, and elevated serum transaminase levels in the majority of infected patients. Even though people of any age can get HGA, it is usually more severe in the aging or immune-compromised. Some severe complications may include respiratory failure, kidney failure, and secondary infections.

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.

Symptoms of illness are specific to the type of viral infection and vary on severity, based on the individuals infected.

Symptoms vary on severity, from mild unnoticeable symptoms to more common symptoms like fever, rash, headache, achy muscle and joints, and conjunctivitis. Symptoms can last several days to weeks, but death resulting from this infection is rare.

Waterborne diseases are conditions caused by pathogenic micro-organisms that are transmitted in water. Disease can be spread while bathing, washing or drinking water, or by eating food exposed to infected water. Various forms of waterborne diarrheal disease are the most prominent examples, and affect children in developing countries most dramatically.

According to the World Health Organization, waterborne diseases account for an estimated 3.6% of the total DALY (disability- adjusted life year) global burden of disease, and cause about 1.5 million human deaths annually. The World Health Organization estimates that 58% of that burden, or 842,000 deaths per year, is attributable to a lack of safe drinking water supply, sanitation and hygiene (summarized as WASH).

Changes are mild at first; slight behavioural changes and an increase in chewing movements may occur. Ataxia and neurological signs then develop, and affected sheep struggle to keep up with the flock.

Some sheep scratch excessively and show patches of wool loss and lesions on the skin. Scratching sheep over the rump area may lead to a nibbling reflex, which is characteristic for the condition.

Signs of a chronic systemic disease appear later, with weight loss, anorexia, lethargy, and death.

"Post mortem" examination is important for the diagnosis of scrapie. Histology of tissues shows accumulation of prions in the central nervous system, and immunohistochemical staining and ELISA can also be used to demonstrate the protein.

Colorado tick fever (CTF) (also called mountain tick fever, American tick fever, and American mountain tick fever) is a viral infection (Coltivirus) transmitted from the bite of an infected Rocky Mountain wood tick ("Dermacentor andersoni"). It should not be confused with the bacterial tick-borne infection, Rocky Mountain spotted fever.

The type species of the genus "Coltivirus", Colorado tick fever virus (CTFV) infects haemopoietic cells, particularly erythrocytes, which explains how the virus is transmitted by ticks and also accounts for the incidence of transmission by blood transfusion.

Scrapie is a fatal, degenerative disease that affects the nervous systems of sheep and goats. It is one of several transmissible spongiform encephalopathies (TSEs), which are related to bovine spongiform encephalopathy (BSE or "mad cow disease") and chronic wasting disease of deer. Like other spongiform encephalopathies, scrapie is caused by a prion. Scrapie has been known since 1732, and does not appear to be transmissible to humans.

The name scrapie is derived from one of the clinical signs of the condition, wherein affected animals will compulsively scrape off their fleeces against rocks, trees, or fences. The disease apparently causes an itching sensation in the animals. Other clinical signs include excessive lip smacking, altered gaits, and convulsive collapse.

Scrapie is infectious and transmissible among conspecifics, so one of the most common ways to contain it (since it is incurable) is to quarantine and destroy those affected. However, scrapie tends to persist in flocks and can also arise apparently spontaneously in flocks that have not previously had cases of the disease. The mechanism of transmission between animals and other aspects of the biology of the disease are only poorly understood, and these are active areas of research. Recent studies suggest prions may be spread through urine and persist in the environment for decades.

Scrapie usually affects sheep around three to five years of age. The potential for transmission at birth and from contact with placental tissues is apparent. No evidence indicates scrapie is infectious to humans.

A list of the more common and well-known diseases associated with infectious pathogens is provided and is not intended to be a complete listing.

A combination of clinical signs, symptoms, and laboratory tests can confirm the likelihood of having CTF. Some tests include complement fixation to Colorado tick virus, immunofluorescence for Colorado tick fever, and some other common laboratory findings suggestive of CTF, including leucopenia, thrombocytopenia, and mildly elevated liver enzyme levels.

Detection of viral antibodies on red blood cells is possible.

Infections associated with diseases are those that are associated with possible infectious etiologies, that meet the requirements of Koch's postulates. Other methods of causation are described by the Bradford Hill criteria and Evidence-based medicine. Koch's postulates have been altered by some epidemiologists based upon sequence-based detection of distinctive pathogenic nucleic acid sequences in tissue samples. Using this method, absolute statements are not always possible regarding causation. Since this is true, higher amounts of distinctive pathogenic nucleic acid sequences would be in those exhibiting disease compared to controls since inoculating those without the pathogen is unethical. In addition, the DNA load should drop or become lower with the resolution of the disease. The distinctive pathogenic nucleic acid sequences load should also increase upon recurrence.

Other conditions are met to establish cause or association including studies in disease transmission. This means that there should be a high disease occurrence in those carrying an pathogen, evidence of a serologicalresponse to the pathogen, and the success of vaccination prevention. Direct visualization of the pathogen, the identification of different strains, immunological responses in the host, how the infection is spread and, the combination of these should all be taken into account to determine the probability that an infectious agent is the cause of the disease. A conclusive determination of a causal role of an infectious agent for in a particular disease using Koch's postulates is desired yet this might not be possible.

The leading cause of death worldwide is cardiovascular disease, but infectious diseases are the second leading cause of death worldwide and the leading cause of death in infants and children.

If symptoms of histoplasmosis infection occur, they will start within 3 to 17 days after exposure; the average is 12–14 days. Most affected individuals have clinically silent manifestations and show no apparent ill effects. The acute phase of histoplasmosis is characterized by non-specific respiratory symptoms, often cough or flu-like. Chest X-ray findings are normal in 40–70% of cases. Chronic histoplasmosis cases can resemble tuberculosis; disseminated histoplasmosis affects multiple organ systems and is fatal unless treated.

While histoplasmosis is the most common cause of mediastinitis, this remains a relatively rare disease. Severe infections can cause hepatosplenomegaly, lymphadenopathy, and adrenal enlargement. Lesions have a tendency to calcify as they heal.

Presumed ocular histoplasmosis syndrome (POHS) causes chorioretinitis, where the choroid and retina of the eyes are scarred, resulting in a loss of vision not unlike macular degeneration. Despite its name, the relationship to "Histoplasma" is controversial. Distinct from POHS, acute ocular histoplasmosis may rarely occur in immunodeficiency.

Sporotrichosis can be diagnosed in domestic and wild mammals. In veterinary medicine it is most frequently seen in cats and horses. Cats have a particularly severe form of cutaneous sporotrichosis and also can serve as a source of zoonotic infection to persons who handle them and are exposed to exudate from skin lesions.

The virus can infect the brain (encephalitis), the meninges (meningitis) or both (meningoencephalitis).

In general, mortality is 1% to 2%, with deaths occurring 5 to 7 days after the onset of neurologic signs.

In dogs, the disease also manifests as a neurological disorder with signs varying from tremors to seizures and death.

In ruminants, neurological disease is also present, and animals may refuse to eat, appear lethargic, and also develop respiratory signs.

A bloodborne disease is a disease that can be spread through contamination by blood and other body fluids. Bloodborne pathogens are microorganisms such as viruses or bacteria. The most common examples are HIV, hepatitis B and viral hemorrhagic fevers.

Diseases that are not usually transmitted directly by blood contact, but rather by insect or other vector, are more usefully classified as "vector-borne disease", even though the causative agent can be found in blood. Vector-borne diseases include West Nile virus and malaria.

Many bloodborne diseases can also be contracted by other means, including high-risk sexual behavior or intravenous drug use. These diseases have also been identified in sports medicine.

Since it is difficult to determine what pathogens any given sample of blood contains, and some bloodborne diseases are lethal, standard medical practice regards all blood (and any body fluid) as potentially infectious. "Blood and Body Fluid precautions" are a type of infection control practice that seeks to minimize this sort of disease transmission.

Tick-borne encephalitis (TBE) is a viral infectious disease involving the central nervous system. The disease most often manifests as meningitis, encephalitis, or meningoencephalitis. Although TBE is most commonly recognized as a neurological disorder, mild fever can also occur. Long-lasting or permanent neuropsychiatric consequences are observed in 10 to 20% of infected patients.

The number of reported cases has been increasing in most countries.

The tick-borne encephalitis virus is known to infect a range of hosts including ruminants, birds, rodents, carnivores, horses, and humans. The disease can also be spread from animals to humans, with ruminants and dogs providing the principal source of infection for humans.

TBE, like Lyme disease, is one of the many tick-borne diseases.

Most people who are infected develop sickness between five and 15 days after they are bitten. The symptoms may include a sudden fever, chills, headaches, muscle or joint aches, and nausea. A rash may also occur. These symptoms usually continue for two to 9 days, then disappear. This cycle may continue for several weeks if the person is not treated.