Eosinopenia is a form of agranulocytosis where the number of eosinophil granulocytes is lower than expected. Leukocytosis with eosinopenia can be a predictor of bacterial infection. It can be induced by stress reactions, Cushing's syndrome, or the use of steroids. Pathological causes include burns and acute infections.

Agranulocytosis may be asymptomatic, or may clinically present with sudden fever, rigors and sore throat. Infection of any organ may be rapidly progressive (e.g., pneumonia, urinary tract infection). Septicemia may also progress rapidly.

Agranulocytosis, also known as agranulosis or granulopenia, is an acute condition involving a severe and dangerous leukopenia (lowered white blood cell count), most commonly of neutrophils causing a neutropenia in the circulating blood. It is a severe lack of one major class of infection-fighting white blood cells. People with this condition are at very high risk of serious infections due to their suppressed immune system.

In agranulocytosis, the concentration of granulocytes (a major class of white blood cells that includes neutrophils, basophils, and eosinophils) drops below 500 cells/mm³ of blood.

Many signs are associated with PPID, but only a subset of these are displayed in any single horse. Some horses may present with chronic laminitis without other overt signs of the disease.

- Hypertrichosis (hirsutisim) produces a long, thick, wavy coat that often has delayed shedding or fails to shed completely, and may lighten in color. Hirsutism has been suggested to be pathognomonic for PPID, with up to 95% of horses having PPID.

- Laminitis

- Increased drinking and increased urination

- Pot-bellied appearance

- Weight loss

- Redistribution of fat, leading to bulging supraorbital fat pad, a "cresty" neck, and fat over the tail head or in the sheath of males

- Lethargy

- Behavioral changes, often an increased docility

- Muscle wasting, especially along the top line

- Increased sweating, or less commonly, decreased sweating

- Increased appetite

- Decreased sensitivity to pain

- Recurrent infections due to immune impairment

- Rarely neurologic signs such as narcolepsy, blindness, or seizures

- Suspensary ligament degeneration

Complete blood counts and serum chemistry profiles may be normal in affected horses. Persistent hyperglycemia and glucosuria are very commonly seen. Hyperlipidemia may be present, especially in ponies. Other abnormalities associated with the disease include mild anemia, neurophilia, lymphopenia, eosinopenia, and increased liver enzymes.

Classically, the course of untreated typhoid fever is divided into four distinct stages, each lasting about a week. Over the course of these stages, the patient becomes exhausted and emaciated.

- In the first week, the body temperature rises slowly, and fever fluctuations are seen with relative bradycardia (Faget sign), malaise, headache, and cough. A bloody nose (epistaxis) is seen in a quarter of cases, and abdominal pain is also possible. A decrease in the number of circulating white blood cells (leukopenia) occurs with eosinopenia and relative lymphocytosis; blood cultures are positive for "Salmonella" Typhi or "S. paratyphi". The Widal test is usually negative in the first week.

- In the second week, the person is often too tired to get up, with high fever in plateau around and bradycardia (sphygmothermic dissociation or Faget sign), classically with a dicrotic pulse wave. Delirium is frequent, often calm, but sometimes agitated. This delirium gives to typhoid the nickname of "nervous fever". Rose spots appear on the lower chest and abdomen in around a third of patients. Rhonchi are heard in lung bases.

- The abdomen is distended and painful in the right lower quadrant, where borborygmi can be heard. Diarrhea can occur in this stage: six to eight stools in a day, green, comparable to pea soup, with a characteristic smell. However, constipation is also frequent. The spleen and liver are enlarged (hepatosplenomegaly) and tender, and liver transaminases are elevated. The Widal test is strongly positive, with antiO and antiH antibodies. Blood cultures are sometimes still positive at this stage.

- (The major symptom of this fever is that the fever usually rises in the afternoon up to the first and second week.)

- In the third week of typhoid fever, a number of complications can occur:

- Intestinal haemorrhage due to bleeding in congested Peyer's patches; this can be very serious, but is usually not fatal.

- Intestinal perforation in the distal ileum: this is a very serious complication and is frequently fatal. It may occur without alarming symptoms until septicaemia or diffuse peritonitis sets in.

- Encephalitis

- Respiratory diseases such as pneumonia and acute bronchitis

- Neuropsychiatric symptoms (described as "muttering delirium" or "coma vigil"), with picking at bedclothes or imaginary objects.

- Metastatic abscesses, cholecystitis, endocarditis, and osteitis

- The fever is still very high and oscillates very little over 24 hours. Dehydration ensues, and the patient is delirious (typhoid state). One-third of affected individuals develop a macular rash on the trunk.

- Platelet count goes down slowly and risk of bleeding rises.

- By the end of third week, the fever starts subsiding

Typhoid fever, also known simply as typhoid, is a bacterial infection due to "Salmonella" typhi that causes symptoms. Symptoms may vary from mild to severe and usually begin six to thirty days after exposure. Often there is a gradual onset of a high fever over several days. Weakness, abdominal pain, constipation, and headaches also commonly occur. Diarrhea is uncommon and vomiting is not usually severe. Some people develop a skin rash with rose colored spots. In severe cases there may be confusion. Without treatment, symptoms may last weeks or months. Other people may carry the bacterium without being affected; however, they are still able to spread the disease to others. Typhoid fever is a type of enteric fever along with paratyphoid fever.

The cause is the bacterium "Salmonella" typhi, also known as "Salmonella enterica" serotype Typhi, growing in the intestines and blood. Typhoid is spread by eating or drinking food or water contaminated with the feces of an infected person. Risk factors include poor sanitation and poor hygiene. Those who travel to the developing world are also at risk and only humans can be infected. Diagnosis is by either culturing the bacteria or detecting the bacterium's DNA in the blood, stool, or bone marrow. Culturing the bacterium can be difficult. Bone marrow testing is the most accurate. Symptoms are similar to that of many other infectious diseases. Typhus is a different disease.

A typhoid vaccine can prevent about 30% to 70% of cases during the first two years. The vaccine may have some effect for up to seven years. It is recommended for those at high risk or people traveling to areas where the disease is common. Other efforts to prevent the disease include providing clean drinking water, better sanitation, and better handwashing. Until it has been confirmed that an individual's infection is cleared, the individual should not prepare food for others. Treatment of disease is with antibiotics such as azithromycin, fluoroquinolones or third generation cephalosporins. Resistance to these antibiotics has been developing, which has made treatment of the disease more difficult.

In 2015, there were 12.5 million new cases worldwide. The disease is most common in India. Children are most commonly affected. Rates of disease decreased in the developed world in the 1940s as a result of improved sanitation and use of antibiotics to treat the disease. Each year in the United States, about 400 cases are reported and it is estimated that the disease occurs in about 6,000 people. In 2015, it resulted in about 149,000 deaths worldwide – down from 181,000 in 1990 (about 0.3% of the global total). The risk of death may be as high as 20% without treatment. With treatment, it is between 1 and 4%. The name typhoid means "resembling typhus" due to the similarity in symptoms.