Brucella Antigen (Brucellosis), Diagnosis of Brucella Infection

Definition
Three members of the genus brucella produce an uncommon febrile disease known as Brucellosis (Undulant fever).
Undulant fever is found as:
- Brucella suis is pig-associated.
- Brucella melitensis is goat-associated.
- Brucella canis is dog-associated.
- Brucella abortus is cattle-associated.
Sample
- It is done on the serum of the patient.
- The serum is taken in the first week of illness and later in the 3 to 4 weeks.
- Brucella can be cultured from the blood, sputum, bone marrow, CSF, tissue, lymph node, and urine.
Indications:
- The patient with a fever of unknown origin.
- The patient with a suspected history of contact with cattle.
- The patient with signs and symptoms of Brucella infection.
Pathophysiology
Microbiology:
- Brucellosis is caused by the Brucella abortus, B.suis, B. melitensis, or B.canis.
- Brucella is a slow-growing aerobic gram-negative coccobacillus.
- Short, slender, pleomorphic, gram-negative bacilli (coccobacillus).
- Brucella is an oxidase-positive urease variable.
- Brucella is nonmotile.
- These are non-sporing.
- Culture media:
- Enriched medium such as glucose serum or liver infusion broth or agar.
- Small transparent colonies develop after several days, incubation at 37 °C in aerobic conditions.
- CO2 is needed for the growth of B. abortus.
- Enriched medium such as glucose serum or liver infusion broth or agar.
- There is growth in selective buffered charcoal yeast extract and Thayer-Martin medium.
- Brucella canis is very rare and is due to exposure to dogs.
The characteristic feature of Brucella organism:
Characteristic features | B. abortus | B. melitensis | B. sius |
Infection in | Cattle | Goat and sheep | Swine |
Biotypes of Brucella | 8 | 3 | 4 |
Production of H2S | positive | negative | positive |
Growth need for CO2 | positive | negative | negative |
Growth in | |||
Basic fuchsin | positive | positive | negative |
Thionine | negative | positive | positive |
Methyl violet | positive | positive | negative |
Lysis by phage Tb | positive | negative | negative |
Antibody Titer positive | >1:320 | >1:320 | >1:320 |
- Mode of spread:
- It is by ingestion of contaminated milk products, especially goat milk.
- When sheep, goats, cows, or camels are infected with these bacteria, their milk is also contaminated.
- These names are based on infected animals.
- Brucella is mostly spread by unpasteurized milk or raw dairy products.
- Direct puncture of the skin of butchers and farmers. These bacteria can enter through the skin and mucous membranes.
- Brucella can spread through inhalation.
- Brucella can penetrate the skin, conjunctiva, lungs, and GI Tract.
- Penetration is followed by the lymphatics spread.
- There is a facultative intracellular growth in the macrophages.
- It also involves the organs.
Type of Brucella:
- There are the following types of Brucella:
- Brucella abortus source is from cattle and has moderate pathogenicity.
- Brucella melitensis source is sheep, and these are highly pathogenic.
- Brucella Canis source is from dogs and has moderate pathogenicity.
- Brucella Sui’s source is from pigs, and these are highly pathogenic.
Antigenic structure:
- Three species share two antigens A and M.
- B. melitensis contains an excess of M antigen.
- B. abortus and suis contain an excess of A antigen.
- Monospecific antisera can be prepared and are used for identification.
Sign and symptoms:
-
- This may be the acute or insidious onset of the symptoms.
- This is a multisystem disease characterized by the acute or insidious onset of signs and symptoms.
- There may be fever, chills, and night sweating.
- The fever peak is in the evening and slowly returns to normal by morning.
- Undulant fever because of a slow rise in temperature during the day, declining at night.
- There is undue fatigue.
- There is anorexia, weight loss.
- There may be a headache and arthralgia. 25% of the patients develop single joint arthralgia.
- There may be a pain in muscles, joints, or back. Myalgia may be the first symptom.
- Sometimes there is lymphadenopathy. But most lymph nodes are not enlarged.
- 20% of the patients may show splenomegaly.
- Some patients may develop pneumonia.
- If not treated, then these patients may have:
- Arthritis.
- Recurrent fever.
- Swelling of the scrotal area and testes.
- Depression.
- Chronic fatigue.
- May develop endocarditis.
- Splenomegaly and hepatomegaly are common findings.
- Spondylitis is also common.
- These symptoms may last months to years, but the outcome is not fatal.
Complications:
- The patient may develop endocarditis.
- There may be arthritis and osteomyelitis.
- The infection of the testes gives rise to epididymal orchitis.
- CNS involvement may lead to meningitis or encephalitis.
- Inflammation of the liver and spleen leads to splenomegaly and hepatomegaly.
- Relapses occur within the first year in about 10% of the cases.
Prevention of Brucellosis:
- Please avoid the following:
- Use of unpasteurized milk and dairy products (cheese, ice cream).
- When handling animals, use preventive measures like gloves, etc.
Brucella diagnosis:
- WBC count is usually normal or decreased.
- There is mild anemia.
- There is relative lymphocytosis.
- Liver function tests are abnormal.
- B. melitensis infection is more severe, giving more raised AST, ALT, and LDH, and may give rise to thrombocytopenia.
- By serological test detecting the Brucella antibodies.
- By culture of:
- Blood culture. This is positive in 30% to 40% of the cases.
- Blood culture for B abortus needs 10% CO2.
- Blood culture must be kept for at least 4 weeks.
- About 70% are positive.
- Bone marrow.
- Bone marrow culture may be positive when blood culture and serologic tests are negative.
- Bone marrow culture has more positivity.
- CSF.
- Sputum.
- Food specimen.
- Biopsy and culture of affected tissue and organs.
- Blood culture. This is positive in 30% to 40% of the cases.
- By immunofluorescent demonstration of the organism in the clinical specimens.
- A skin test with brucellergin is available, but a positive result only indicates exposure to the organism and does not prove active disease.
- Serology values: Test results >1:80 are suspicious for brucellosis. The serologic tests become positive during the second to the third week of illness.
- 90% of the patients have a titer of ≥1:160.
- The rising titer is diagnostic.
- False-negative results are rare.
- In chronic localized brucellosis, the titer may be negative or ≤1:200.
- These tests remain for a long time positive after the infection is cured.
- EIA is the method of choice to detect specific IgM and IgG antibodies.
- Failure of the decline in the titer indicates an incomplete cure.
- With a high titer, multiple blood cultures are positive.
- Source 1
- This is the detection of the presence of antibodies against the Brucella antigen.
- Highly suggestive of active infection = > 1: 320
- Significan level = >1:160
- Borderline cases 1: 160
- Source 2
- A rising titer ≥ 1:160 suggests infection, either past or present.
- A single titer 1:160 or 1:320 may be suggestive if there are clinical S/S of brucellosis.
- It can prevent the prozone phenomenon by diluting the serum ≥1: 1280.
- Antibody level decreases in 3 months or with antibiotics, but it will persist at a low level for years, especially in chronic infection.
- Antibody titer may last for 1 to 2 years after the recovery.
- Skin test: Brucellergen (these are killed bacteria) are injected into the skin. After 24 to 48 hours, it shows >5 mm reaction.
- Definitive diagnosis needs the isolation of the organism by blood culture or the tissue sample.
- Real-time PCR is more specific.
Treatment
- These bacteria are sensitive to tetracycline, combined with streptomycin. This combination is the choice of treatment.
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