Answer: Epstein-Barr virus

The Epstein–Barr virus is one of eight known human herpesvirus types in the herpes family, and is one of the most common viruses in humans. Infection with Epstein-Barr virus (EBV) is common and usually occurs in childhood or early adulthood.
EBV is the cause of infectious mononucleosis, an illness associated with symptoms and signs like:
fever,
fatigue,
swollen tonsils,
headache, and
sweats,
sore throat,
swollen lymph nodes in the neck, and
sometimes an enlarged spleen.

Although EBV can cause mononucleosis, not everyone infected with the virus will get mononucleosis. White blood cells called B cells are the primary targets of EBV infection.
Petechiae on the palate are characteristic of streptococcal pharyngitis but also can be seen in Epstein–Barr virus infection, Arcanobacterium haemolyticum pharyngitis, rubella, roseola, viral haemorrhagic fevers, thrombocytopenia, and palatal trauma.
Despite the fact that infectious mononucleosis is a self-limiting disease, it may cause serious and lethal complications. The mechanism of splenic rupture secondary to infectious mononucleosis has been controversial. It is commonly believed that it is caused by an increase in intra-abdominal pressure or contraction of the diaphragm with vigorous cough, vomiting and defecation, leading to a compression of the spleen. However, Patel et al. argue that it is primarily the result of an expanding subcapsular haematoma which subsequently tears the capsule and leads to hemoperitoneum. Traditionally, rupture of spleen is treated by splenectomy. The rationale is to prevent the chance of sudden death as an early complication of splenic rupture and the risk from blood transfusion.

Birds, with their broad geographic ranges and close association with humans, have historically played an important role as carriers of human disease and as reservoirs for drug-resistant bacteria.
The highest diversity of bacteria were found on birds in natural habitats. The most frequently reported bacteria were Escherichia coli, Salmonella enterica, and Campylobacter jejuni. Of the bacteria species reported, 54% have shown pathogenicity toward humans. Percentage-wise, more pathogens were found in tropical (vs. temperate) habitats and natural (vs. suburban, urban, or agricultural) habitats.

Campylobacter jejuni is usually the most common cause of community-acquired inflammatory enteritis.

The symptoms and severity of the gastroenteritis produced can vary.
Patients may have a history of ingestion of inadequately cooked poultry, unpasteurized milk, or untreated water. The incubation period is 1-7 days and is probably related to the dose of organisms ingested.
A brief prodrome of fever, headache, and myalgias lasting up to 24 hours is followed by crampy abdominal pain, fever as high as 40°C, and as many as 10 watery, frequently bloody, bowel movements per day. Fever, which develops in more than 90% of patients, maybe low or high grade and can persist for a week.
Patients with C jejuni infection who report vomiting, bloody diarrhoea, or both tend to have a long illness and require hospital admission.
Abdominal pain and tenderness may be localized. Pain in the right lower quadrant may mimic acute appendicitis (pseudo appendicitis).
Tenesmus occurs in approximately 25% of patients.

One of the most serious post-ERCP complications is cholangitis leading to subsequent septicaemia. Enteric bacteria enter the biliary tree by the hematogenous route or following endoscopic or radiologic manipulation. Improperly disinfected endoscopes and accessories may also introduce infection into the biliary tree. The most common organisms responsible for infection after ERCP are the Enterobacteriaceae (especially Escherichia coli and Klebsiella species), alpha-haemolytic streptococci, Pseudomonas aeruginosa, Enterococcus, and Staphylococcus epidermidis. In most patients with acute cholangitis, a single organism is isolated from blood cultures.

Acute cholangitis is a clinical syndrome characterized by fever, jaundice, and abdominal pain that develops as a result of stasis and infection in the biliary tract. It is also referred to as Charcot’s Triad. Cholangitis was first described by Charcot as a serious and life-threatening illness; however, it is now recognized that the severity can range from mild to life-threatening.

Risk factors for post-ERCP infection include the use of combined percutaneous and endoscopic procedures, stent placement in malignant strictures, the presence of jaundice, low case volume, and incomplete or failed biliary drainage. Patients who are immunocompromised are more likely to experience an infectious complication.

Prevention and/or reduction of the risk of post-ERCP infectious complications can be achieved by judicious use of preprocedural antibiotics and intraprocedural steps, such as minimizing or avoiding contrast injection in patients with known biliary obstruction or cholangitis, endoscopic decompression, including the placement of a biliary stent when complete drainage cannot be achieved, and prompt percutaneous drainage if endoscopic drainage is not possible or incomplete. Prophylactic preprocedural antibiotics should be given to patients with jaundice and suspected mechanical obstruction. In addition, patients with sclerosing cholangitis, pancreatic pseudocysts, and those who are immunocompromised should also receive preprocedural antibiotics

Hepatitis A is a viral liver disease that can cause mild to severe illness. The hepatitis A virus (HAV) is transmitted through ingestion of contaminated food and water or through direct contact with an infectious person.
The risk of hepatitis A infection is associated with a lack of safe water, and poor sanitation and hygiene (such as dirty hands). Unlike hepatitis B and C, hepatitis A does not cause chronic liver disease and is rarely fatal, but it can cause debilitating symptoms and fulminant hepatitis (acute liver failure), which is often fatal.
Prodrome
In the prodrome, patients may have mild flulike symptoms of anorexia, nausea and vomiting, fatigue, malaise, low-grade fever (usually < 39.5°C), myalgia, and mild headache. Smokers often lose their taste for tobacco, like persons presenting with appendicitis. Icteric phase
In the icteric phase, dark urine appears first (bilirubinuria). Pale stool soon follows, although this is not universal. Jaundice occurs in most (70%-85%) adults with acute HAV infection; it is less likely in children and is uncommon in infants. The degree of icterus also increases with age. Abdominal pain occurs in approximately 40% of patients. Itching (pruritus), although less common than jaundice, is generally accompanied by jaundice.

Arthralgias and skin rash, although also associated with acute HAV infection, are less frequent than the above symptoms. Rash more often occurs on the lower limbs and may have a vasculitic appearance.

Relapsing hepatitis A
Relapsing hepatitis A is an uncommon sequela of acute infection, is more common in elderly persons, and is characterized by a protracted course of symptoms of the disease and a relapse of symptoms and signs following apparent resolution.

Answer: Streptococcus pyogenes

Tonsillitis is inflammation of the pharyngeal tonsils. The inflammation usually extends to the adenoid and the lingual tonsils; therefore, the term pharyngitis may also be used. Most cases of bacterial tonsillitis are caused by group A beta-haemolytic Streptococcus pyogenes (GABHS).

Signs and symptoms
Tonsillitis

Individuals with acute tonsillitis present with the following:
Fever
Sore throat
Foul breath
Dysphagia (difficulty swallowing)
Odynophagia (painful swallowing)
Tender cervical lymph nodes

Airway obstruction may manifest as mouth breathing, snoring, sleep-disordered breathing, nocturnal breathing pauses, or sleep apnoea.

Peritonsillar abscess

Individuals with peritonsillar abscess (PTA) present with the following:
Severe throat pain
Fever
Drooling
Foul breath
Trismus (difficulty opening the mouth)
Altered voice quality (the hot-potato voice)

Treatment of acute tonsillitis is largely supportive and focuses on maintaining adequate hydration and caloric intake and controlling pain and fever.

Corticosteroids may shorten the duration of fever and pharyngitis in cases of infectious mononucleosis (MN). In severe cases of MN, corticosteroids or gamma globulin may be helpful. GABHS infection obligates antibiotic coverage.

Infection by Ascaris lumbricoides usually occurs after individuals have visited places like sub-Saharan Africa or the Far East. Unlike Ancylostoma duodenale infection, there is usually an evidence of both worms and eggs in the stool. The absence of pruritus makes Enterobius vermicularis less likely.

Ascariasis occurs due to infection with a roundworm Ascaris lumbricoides. It begins in the gut following ingestion, then penetrates the duodenal wall to migrate to the lungs, is coughed up and swallowed, and the cycle begins again.

Diagnosis is made by identification of worms or eggs within the faeces. Treatment is with mebendazole.

Streptococcus bovis (S. bovis) bacteria are associated with colorectal cancer and adenoma. S. bovis is currently named S. gallolyticus. 25-80% of patients with S. bovis/gallolyticus bacteraemia have concomitant colorectal tumours. Colonic neoplasia may arise years after the presentation of bacteraemia or infectious endocarditis of S. bovis/gallolyticus. The presence of S. bovis/gallolyticus bacteraemia and/or endocarditis is also related to the presence of villous or tubular-villous adenomas in the large intestine.

P24 antigen test is used as one of the main investigations in diagnosing HIV seroconversion illness.

Some people experience a short illness soon after they contract HIV. This is known as seroconversion illness, or primary or acute HIV infection. It is the period when someone with HIV is at their most infectious.

HIV seroconversion is symptomatic in 60%–80% of the patients and typically presents as a glandular fever-type illness. Increased symptomatic severity is associated with poorer long-term prognosis. It typically occurs 2–3 weeks after contracting the virus.

Signs and symptoms include:
1. Sore throat
2. Malaise, myalgia, and arthralgia
3. Diarrhoea
4. Maculopapular rash
5. Oral ulcers
6. Lymphadenopathy
7. Meningoencephalitis (rarely)

HIV PCR and p24 antigen test can confirm the diagnosis. The former is the most common and accurate test and consists of both a screening ELISA and a confirmatory western blot assay. P24 antigen test is also used as the mainstay of diagnosis and is usually positive from about 1 week to 3–4 weeks after an infection with HIV.

Bacteroides species are anaerobic bacteria that are predominant components of the bacterial florae of mucous membranes and are therefore a common cause of endogenous infections. Bacteroides infections can develop in all body sites, including the CNS, the head, the neck, the chest, the abdomen, the pelvis, the skin, and the soft tissues. Inadequate therapy against these anaerobic bacteria may lead to clinical failure.

These bacteria are resistant to penicillins, mostly through the production of beta-lactamase. Anaerobic bacteria can infect deep wounds, deep tissues, and internal organs where there is little oxygen. These infections are characterized by abscess formation, foul-smelling pus, and tissue destruction. Anaerobes outnumber aerobes by 1000:1 in the large intestine; thus, they play an important role in almost all intra-abdominal infections.

Secondary peritonitis and abdominal abscesses generally occur after entry of enteric organisms into the peritoneal cavity through perforation of the intestine or other viscus as a result of obstruction, infarction, or trauma.

Most visceral abscesses (e.g., hepatic), chronic cholecystitis, perforated and gangrenous appendicitis, postoperative wound infections and abscesses, diverticulitis, and any infection associated with faecal contamination of the abdominal cavity involve both aerobes and anaerobes.

Answer: Yersinia enterocolitica

Yersinia enterocolitica (see the image below) is a bacterial species in the family Enterobacteriaceae that most often causes enterocolitis, acute diarrhoea, terminal ileitis, mesenteric lymphadenitis, and pseudo appendicitis but, if it spreads systemically, can also result in fatal sepsis. Symptoms of Y enterocolitica infection typically include the following:

Diarrhoea – The most common clinical manifestation of this infection; diarrhoea may be bloody in severe cases

Low-grade fever

Abdominal pain – May localize to the right lower quadrant

Vomiting – Present in approximately 15-40% of cases

Mesenteric adenitis, mesenteric ileitis, and acute pseudo appendicitis
These manifestations are characterized by the following symptoms (although nausea, vomiting, diarrhoea, and aphthous ulcers of the mouth can also occur):

Fever

Abdominal pain

Tenderness of the right lower quadrant

Leucocytosis

Pseudo appendicitis syndrome is more common in older children and young adults. Patients with Y enterocolitica infection often undergo appendectomy; several Scandinavian studies suggested a prevalence rate of 3.8-5.6% for infection with Y enterocolitica in patients with suspected appendicitis.

Analysis of several common-source outbreaks in the United States found that 10% of 444 patients with symptomatic, undiagnosed Y enterocolitica infection underwent laparotomy for suspected appendicitis.

Human clinical Y enterocolitica infections ensue after ingestion of the microorganisms in contaminated food or water or by direct inoculation through blood transfusion.

Y enterocolitica is potentially transmitted by contaminated unpasteurized milk and milk products, raw pork, tofu, meats, oysters, and fish. Outbreaks have been associated with raw vegetables; the surface of vegetables can become contaminated with pathogenic microorganisms through contact with soil, irrigation water, fertilizers, equipment, humans, and animals.

Pasteurized milk and dairy products can also cause outbreaks because Yersinia can proliferate at refrigerated temperatures.

Animal reservoirs of Y enterocolitica include swine (principle reservoir), dogs, cats, cows, sheep, goats, rodents, foxes, porcupines, and birds.

Reports of person-to-person spread are conflicting and are generally not observed in large outbreaks. Transmission via blood products has occurred, however, and infection can be transmitted from mother to new-born infant. Faecal-oral transmission among humans has not been proven.