El Tor is the name given to a particular strain of the bacterium "Vibrio cholerae", the causative agent of cholera. Also known as "V. cholera" biotype eltor, it has been the dominant strain in the seventh global pandemic. It is distinguished from the classic strain at a genetic level, although both are in the serogroup O1 and both contain Inaba, Ogawa and Hikojima serotypes. It is also distinguished from classic biotypes by the production of hemolysins.

In acute cases, a green diarrhea can be an early symptom.

The most typical symptom, in chronic cases, is the swelling of the wattles. It is more frequent in resistant local breeds. Rather than a general infection, localized infections are more characteristic. These often occur in the respiratory tract including the sinuses and pneumatoics bones, hock joints, sternal bursa, foot pads, peritoneal cavity and oviducts.

In acute cases, the most typical p.m. lesion is the petechiae observed in the epicardial fatty tissue. Necrotic foci on liver are usually found and general hyperemia is common. Due to the speed of infection and mortality, birds are in good body condition and do not exhibit the signs of prolonged illness.

The primary symptoms of cholera are profuse diarrhea and vomiting of clear fluid. These symptoms usually start suddenly, half a day to five days after ingestion of the bacteria. The diarrhea is frequently described as "rice water" in nature and may have a fishy odor. An untreated person with cholera may produce of diarrhea a day. Severe cholera, without treatment, kills about half of affected individuals. If the severe diarrhea is not treated, it can result in life-threatening dehydration and electrolyte imbalances. Estimates of the ratio of asymptomatic to symptomatic infections have ranged from 3 to 100. Cholera has been nicknamed the "blue death" because a person's skin may turn bluish-gray from extreme loss of fluids.

Fever is rare and should raise suspicion for secondary infection. Patients can be lethargic, and might have sunken eyes, dry mouth, cold clammy skin, or wrinkled hands and feet. Kussmaul breathing, a deep and labored breathing pattern, can occur because of acidosis from stool bicarbonate losses and lactic acidosis associated with poor perfusion. Blood pressure drops due to dehydration, peripheral pulse is rapid and thready, and urine output decreases with time. Muscle cramping and weakness, altered consciousness, seizures, or even coma due to electrolyte imbalances are common, especially in children.

Fowl cholera is also called avian cholera, avian pasteurellosis, avian hemorrhagic septicemia.

It is the most common pasteurellosis of poultry. As the causative agent is "Pasteurella multocida", it is considered as a zoonosis.

Adult birds and old chickens are more susceptible. In parental flocks, cocks are far more susceptible than hens.

Besides chickens, the disease also concerns turkeys, ducks, geese, raptors, and canaries. Turkeys are particularly sensitive, with mortality ranging to 65%.

The recognition of this pathological condition is of ever increasing importance for differential diagnosis with avian influenza.

Cholera is an infection of the small intestine by some strains of the bacterium "Vibrio cholerae". Symptoms may range from none, to mild, to severe. The classic symptom is large amounts of watery diarrhea that lasts a few days. Vomiting and muscle cramps may also occur. Diarrhea can be so severe that it leads within hours to severe dehydration and electrolyte imbalance. This may result in sunken eyes, cold skin, decreased skin elasticity, and wrinkling of the hands and feet. Dehydration can cause the skin to turn bluish. Symptoms start two hours to five days after exposure.

Cholera is caused by a number of types of "Vibrio cholerae", with some types producing more severe disease than others. It is spread mostly by unsafe water and unsafe food that has been contaminated with human feces containing the bacteria. Undercooked seafood is a common source. Humans are the only animal affected. Risk factors for the disease include poor sanitation, not enough clean drinking water, and poverty. There are concerns that rising sea levels will increase rates of disease. Cholera can be diagnosed by a stool test. A rapid dipstick test is available but is not as accurate.

Prevention methods against cholera include improved sanitation and access to clean water. Cholera vaccines that are given by mouth provide reasonable protection for about six months. They have the added benefit of protecting against another type of diarrhea caused by "E. coli". The primary treatment is oral rehydration therapy—the replacement of fluids with slightly sweet and salty solutions. Rice-based solutions are preferred. Zinc supplementation is useful in children. In severe cases, intravenous fluids, such as Ringer's lactate, may be required, and antibiotics may be beneficial. Testing to see which antibiotic the cholera is susceptible to can help guide the choice.

Cholera affects an estimated 3–5 million people worldwide and causes 28,800–130,000 deaths a year. Although it is classified as a pandemic as of 2010, it is rare in the developed world. Children are mostly affected. Cholera occurs as both outbreaks and chronically in certain areas. Areas with an ongoing risk of disease include Africa and south-east Asia. The risk of death among those affected is usually less than 5% but may be as high as 50%. No access to treatment results in a higher death rate. Descriptions of cholera are found as early as the 5th century BC in Sanskrit. The study of cholera in England by John Snow between 1849 and 1854 led to significant advances in the field of epidemiology.

The prodromal symptoms are fever, headache, and myalgia, which can be severe, lasting as long as 24 hours. After 1–5 days, typically, these are followed by diarrhea (as many as 10 watery, frequently bloody, bowel movements per day) or dysentery, cramps, abdominal pain, and fever as high as 40 °C (104 °F). In most people, the illness lasts for 2–10 days. It is classified as invasive/inflammatory diarrhea, also described as bloody diarrhea or dysentery.

There are other diseases showing similar symptoms. For instance, abdominal pain and tenderness may be very localized, mimicking acute appendicitis. Furthermore, "Helicobacter pylori" is closely related to Campylobacter and causes peptic ulcer disease.

Intestinal infectious diseases include a large number of infections of the bowels including: cholera, typhoid fever, paratyphoid fever, other types of salmonella infections, shigellosis, botulism, gastroenteritis, and amoebiasis among others.

Typhoid and paratyphoid resulted in 221,000 deaths in 2013 down from 259,000 deaths in 1990. Other diseases which result in diarrhea caused another 1.3 million additional deaths in 2013 down from 2.6 million deaths in 1990.

External abscesses are the most common form of pigeon fever seen in horses. Abscesses develop on the body, usually in the pectoral region and along the ventral midline of the abdomen. However, abscesses can also develop on other areas of the body such as the prepuce, mammary gland, triceps, limbs and head. The fatality rate for this form infection is very low. The abscess is often drained once it has matured.

This is the least common form of pigeon fever seen in horses. It is characterized by severe limb swelling and cellulitis in one or both hind limbs and can lead to lameness, fever, lethargy and loss of appetite. Antimicrobial and anti-inflammatory treatments are required to prevent further complications such as limb edema, prolonged or recurrent infection, lameness, weakness and weight loss.

Complications include toxic megacolon, dehydration and sepsis. Such complications generally occur in young children (< 1 year of age) and immunocompromised people. A chronic course of the disease is possible; this disease process is likely to develop without a distinct acute phase. Chronic campylobacteriosis features a long period of sub-febrile temperature and asthenia; eye damage, arthritis, endocarditis may develop if infection is untreated.

Occasional deaths occur in young, previously healthy individuals because of blood volume depletion (due to dehydration), and in persons who are elderly or immunocompromised.

Some individuals (1–2 in 100,000 cases) develop Guillain–Barré syndrome, in which the nerves that join the spinal cord and brain to the rest of the body are damaged, sometimes permanently. This occurs only with infection of "C. jejuni" and "C. upsaliensis".

A "vaccine-preventable disease" is an infectious disease for which an effective preventive vaccine exists. If a person acquires a vaccine-preventable disease and dies from it, the death is considered a vaccine-preventable death.

The most common and serious vaccine-preventable diseases tracked by the World Health Organization (WHO) are: diphtheria, "Haemophilus influenzae" serotype b infection, hepatitis B, measles, meningitis, mumps, pertussis, poliomyelitis, rubella, tetanus, tuberculosis, and yellow fever. The WHO reports licensed vaccines being available to prevent, or contribute to the prevention and control of, 25 vaccine-preventable infections.

The symptoms are like those associated with many other febrile diseases, but with emphasis on muscular pain and night sweats. The duration of the disease can vary from a few weeks to many months or even years.

In the first stage of the disease, sepsis occurs and leads to the classic triad of undulant fevers, sweating (often with characteristic foul moldy smell sometimes likened to wet hay), and migratory arthralgia and myalgia (joint and muscle pain). Blood tests characteristically reveal a low number of white blood cells and red blood cells, show some elevation of liver enzymes such as aspartate aminotransferase (AST) and alanine aminotransferase (ALT), and demonstrate positive Bengal Rose and Huddleston reactions. Gastrointestinal symptoms occur in 70% of cases and include nausea, vomiting, decreased appetite, unintentional weight loss, abdominal pain, constipation, diarrhea, an enlarged liver, liver inflammation, liver abscess, and an enlarged spleen.

This complex is, at least in Portugal, Israel, and Jordan, known as Malta fever. During episodes of Malta fever, melitococcemia (presence of brucellae in blood) can usually be demonstrated by means of blood culture in tryptose medium or Albini medium. If untreated, the disease can give origin to focalizations or become chronic. The focalizations of brucellosis occur usually in bones and joints and spondylodiscitis of the lumbar spine accompanied by sacroiliitis is very characteristic of this disease. Orchitis is also common in men.

Diagnosis of brucellosis relies on:

1. Demonstration of the agent: blood cultures in tryptose broth, bone marrow cultures. The growth of brucellae is extremely slow (they can take up to two months to grow) and the culture poses a risk to laboratory personnel due to high infectivity of brucellae.

2. Demonstration of antibodies against the agent either with the classic Huddleson, Wright, and/or Bengal Rose reactions, either with ELISA or the 2-mercaptoethanol assay for IgM antibodies associated with chronic disease

3. Histologic evidence of granulomatous hepatitis on hepatic biopsy

4. Radiologic alterations in infected vertebrae: the Pedro Pons sign (preferential erosion of the anterosuperior corner of lumbar vertebrae) and marked osteophytosis are suspicious of brucellic spondylitis.

The consequences of "Brucella" infection are highly variable and may include arthritis, spondylitis, thrombocytopenia, meningitis, uveitis, optic neuritis, endocarditis, and various neurological disorders collectively known as neurobrucellosis.

The most frequent clinical sign following "B. suis" infection is abortion in pregnant females, reduced milk production, and infertility. Cattle can also be transiently infected when they share pasture or facilities with infected pigs, and "B. suis" can be transmitted by cow’s milk.

Swine also develop orchitis (swelling of the testicles), lameness (movement disability), hind limb paralysis, or spondylitis (inflammation in joints).

Swine brucellosis is a zoonosis affecting pigs, caused by the bacterium "Brucella suis". The disease typically causes chronic inflammatory lesions in the reproductive organs of susceptible animals or orchitis, and may even affect joints and other organs. The most common symptom is abortion in pregnant susceptible sows at any stage of gestation. Other manifestations are temporary or permanent sterility, lameness, posterior paralysis, spondylitis, and abscess formation. It is transmitted mainly by ingestion of infected tissues or fluids, semen during breeding, and suckling infected animals.

Since brucellosis threatens the food supply and causes undulant fever, "Brucella suis" and other "Brucella" species ("B. melitensis, B. abortis, B. ovis, B. canis") are recognized as potential agricultural, civilian, and military bioterrorism agents.

The onset of TD usually occurs within the first week of travel, but may occur at any time while traveling, and even after returning home, depending on the incubation period of the infectious agent. Bacterial TD typically begins abruptly, but "Cryptosporidium" may incubate for seven days, and "Giardia" for 14 days or more, before symptoms develop. Typically, a traveler experiences four to five loose or watery bowel movements each day. Other commonly associated symptoms are abdominal cramping, bloating, fever, and malaise. Appetite may decrease significantly. Though unpleasant, most cases of TD are mild, and resolve in a few days without medical intervention.

Blood or mucus in the diarrhea, significant abdominal pain, or high fever suggests a more serious cause, such as cholera, characterized by a rapid onset of weakness and torrents of watery diarrhea with flecks of mucus (described as "rice water" stools). Medical care should be sought in such cases; dehydration is a serious consequence of cholera, and may trigger serious sequelae—including, in rare instances, death—as rapidly as 24 hours after onset if not addressed promptly.

In some cases, internal and external bleeding may occur. This typically begins five to seven days after the first symptoms. All infected people show some decreased blood clotting. Bleeding from mucous membranes or from sites of needle punctures has been reported in 40–50 percent of cases. This may cause vomiting blood, coughing up of blood, or blood in stool. Bleeding into the skin may create petechiae, purpura, ecchymoses or hematomas (especially around needle injection sites). Bleeding into the whites of the eyes may also occur. Heavy bleeding is uncommon; if it occurs, it is usually located within the gastrointestinal tract.

Recovery may begin between 7 and 14 days after first symptoms. Death, if it occurs, follows typically 6 to 16 days from first symptoms and is often due to low blood pressure from fluid loss. In general, bleeding often indicates a worse outcome, and blood loss may result in death. People are often in a coma near the end of life.

Those who survive often have ongoing muscular and joint pain, liver inflammation, decreased hearing, and may have continued tiredness, continued weakness, decreased appetite, and difficulty returning to pre-illness weight. Problems with vision may develop.

Additionally, survivors develop antibodies against Ebola that last at least 10 years, but it is unclear if they are immune to repeated infections.

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.

Diagnosis is made with isolation of "Pasteurella multocida" in a normally sterile site (blood, pus, or cerebrospinal fluid).

Brucellosis is a highly contagious zoonosis caused by ingestion of unpasteurized milk or undercooked meat from infected animals, or close contact with their secretions.

"Brucella" species are small, gram-negative, nonmotile, nonspore-forming, rod-shaped (coccobacilli) bacteria. They function as facultative intracellular parasites, causing chronic disease, which usually persists for life. Four species infect humans: "B. abortus", "B. canis", "B. melitensis", and "B. suis". "B. abortus" is less virulent than "B. melitensis" and is primarily a disease of cattle. "B. canis" affects dogs. "B. melitensis" is the most virulent and invasive species; it usually infects goats and occasionally sheep. "B. suis" is of intermediate virulence and chiefly infects pigs. Symptoms include profuse sweating and joint and muscle pain. Brucellosis has been recognized in animals and humans since the 20th century.

Approximately 33% of people with influenza are asymptomatic.

Symptoms of influenza can start quite suddenly one to two days after infection. Usually the first symptoms are chills or a chilly sensation, but fever is also common early in the infection, with body temperatures ranging from 38 to 39 °C (approximately 100 to 103 °F). Many people are so ill that they are confined to bed for several days, with aches and pains throughout their bodies, which are worse in their backs and legs. Symptoms of influenza may include:

- Fever and extreme coldness (chills shivering, shaking (rigor))

- Cough

- Nasal congestion

- Vomiting

- Runny nose

- Sneezing

- Body aches, especially joints and throat

- Fatigue

- Headache

- Irritated, watering eyes

- Reddened eyes, skin (especially face), mouth, throat and nose

- Petechial rash

- In children, gastrointestinal symptoms such as diarrhea and abdominal pain, (may be severe in children with influenza B)

It can be difficult to distinguish between the common cold and influenza in the early stages of these infections. Influenza is a mixture of symptoms of common cold and pneumonia, body ache, headache, and fatigue. Diarrhea is not normally a symptom of influenza in adults, although it has been seen in some human cases of the H5N1 "bird flu" and can be a symptom in children. The symptoms most reliably seen in influenza are shown in the adjacent table.

Since antiviral drugs are effective in treating influenza if given early (see treatment section, below), it can be important to identify cases early. Of the symptoms listed above, the combinations of fever with cough, sore throat and/or nasal congestion can improve diagnostic accuracy. Two decision analysis studies suggest that "during local outbreaks" of influenza, the prevalence will be over 70%, and thus patients with any of these combinations of symptoms may be treated with neuraminidase inhibitors without testing. Even in the absence of a local outbreak, treatment may be justified in the elderly during the influenza season as long as the prevalence is over 15%.

The available laboratory tests for influenza continue to improve. The United States Centers for Disease Control and Prevention (CDC) maintains an up-to-date summary of available laboratory tests. According to the CDC, rapid diagnostic tests have a sensitivity of 50–75% and specificity of 90–95% when compared with viral culture. These tests may be especially useful during the influenza season (prevalence=25%) but in the absence of a local outbreak, or peri-influenza season (prevalence=10%).

Occasionally, influenza can cause severe illness including primary viral pneumonia or secondary bacterial pneumonia. The obvious symptom is trouble breathing. In addition, if a child (or presumably an adult) seems to be getting better and then relapses with a high fever, that is a danger sign since this relapse can be bacterial pneumonia.

Necrotising hepatopancreatitis (NHP), is also known as Texas necrotizing hepatopancreatitis (TNHP), Texas Pond Mortality Syndrome (TPMS) and Peru necrotizing hepatopancreatitis (PNHP), is a lethal epizootic disease of farmed shrimp. It is not very well researched yet, but generally assumed to be caused by a bacterial infection.

NHP mainly affects the farmed shrimp species "Litopenaeus vannamei" (Pacific white shrimp) and "Litopenaeus stylirostris" (Western blue shrimp), but has also been reported in three other American species, namely "Farfantepenaeus aztecus", "Farfantepenaeus californiensis", and "Litopenaeus setiferus". The highest mortality rates occur in "L. vannamei", which is one of the two most frequently farmed species of shrimp. Untreated, the disease causes mortality rates of up to 90 percent within 30 days. A first outbreak of NHP had been reported in Texas in 1985; the disease then spread to shrimp aquacultures in South America, in 2009 to China and subsequently Southeast Asia, followed by massive outbreaks in that region in 2012-2013.

NHP is associated with a small, gram-negative, and highly pleomorphic "Rickettsia"-like bacterium that belongs to its own, new genus in the alpha proteobacteria. However, in early-2013 a novel strain of "Vibrio parahaemolyticus" was identified as a more likely causative agent, though involvement of a virus cannot be definitely ruled out yet.

The aetiological agent is the pathogenic agent Candidatus "Hepatobacter penaei", an obligate intracellular bacterium of the Order α-Proteobacteria.

Infected shrimps show gross signs including soft shells and flaccid bodies, black or darkened gills, dark edges of the pleopods, and uropods, and an atrophied hepatopancreas that is whitish instead of orange or tan as is usual.

Whichever of the two bacteria associated with NHP actually causes it, the pathogen seems to prefer high water temperatures (above ) and elevated levels of salinity (more than 20–38 ppt). Avoiding such conditions in shrimp ponds is thus an important disease control measure.

An El Tor infection is relatively mild, or at least rarely fatal, and patients are asymptomatic for about a week. El Tor is able to survive in the body longer than classical cholera vibrios. This characteristic allows carriers to infect a greater population of people. In fact, "V. cholerae" biotype eltor can be isolated from water sources in the absence of an outbreak of cases. In extreme cases, persons can become long-term carriers; for example, Cholera Dolores, who tested vibrio positive nine years after her primary infection. El Tor is transmitted by the fecal-oral route. This route is the consequence of infected persons defecating near a water source, and uninfected persons consuming contaminated water. In addition, the bacteria can be transmitted by consuming uncooked food fertilized with human feces. Treatment of a cholera infection consists of replenishing lost fluid and electrolytes by intravenous or oral solutions, and by antibiotics. El Tor outbreaks can be prevented by better standards of sanitation, filtering and boiling water, thoroughly cooking seafood, and washing vegetables and fruits before consumption.

Symptoms of upper respiratory cryptosporidiosis include:

- Inflammation of the nasal mucosa, sinuses, larynx, or trachea

- Nasal discharge

- Voice change (e.g., hoarseness)

Symptoms of lower respiratory cryptosporidiosis include:

- Cough

- Shortness of breath

- Fever

- Hypoxemia

Common signs and symptoms of intestinal cryptosporidiosis include:

- Moderate to severe watery diarrhea, sometimes contains mucus and rarely contains blood or leukocytes

- In very severe cases, diarrhea may be profuse and cholera-like with malabsorption and hypovolemia

- Low-grade fever

- Crampy abdominal pain

- Dehydration

- Weight loss

- Fatigue

- Nausea and vomiting – suggests upper GI tract involvement and may lead to respiratory cryptosporidiosis

- Epigastric or right upper quadrant tenderness

Less common or rare signs and symptoms include:

- Reactive arthritis (may affect the hands, knees, ankles, and feet)

- Jaundice – suggests hepatobiliary involvement

- Ascites – suggests pancreatic involvement