Brucella (Brucella) is a Gram-negative, non-motile bacterium without pods, catalase and oxidase positive, absolutely aerobic, nitrate reducing, intracellularly parasitic, and can survive in many species of livestock. There are six species of the genus Brucella: Brucella marcescens (sheep type Brucella), Brucella abortus (bovine type Brucella), Brucella swine and Brucella dog, Brucella lindemuthianum, Brucella sheep. Among those causing human disease are Brucella abortus in sheep, cattle, pigs, and dogs. on December 19, 2010, 28 students and faculty members of Tohoku Agricultural University participated in a live animal experimentation course on sheep, resulting in 28 people contracting severe Brucella abortus infections. on September 5, 2011, the matter came to light.
Discovery history
Brucellosis caused by Brucella infection is a zoonotic systemic infectious disease, also known as Mediterranean flaccid fever, Maltese fever, and wave fever. Brucella is the most pathogenic in sheep, and it has been documented in Arabic that sheep have aborted due to infection with this bacterium.
In 1886, the Scottish pathologist and microbiologist David Bruce
Bruce, a Scottish pathologist and microbiologist, first identified and isolated the bacterium from the spleen of a soldier who died of Maltese fever while working as a military doctor in the Mediterranean island of Malta. Scholars later named the bacterium Brucella in his honor.
In the mid-1950s, Brucella became the first bacterium to be tried by the U.S. military in the development of biological weapons because it was easy to manufacture and did not cause uncontrollable outbreaks. The U.S. experimental germ warfare program focused on three types of Brucella: Brucella porcine; Brucella bovis; and Brucella goat. Near the end of World War II, Brucella porcine was the first to be developed. When the U.S. Army Air Corps wanted to have a biological warfare capability, the Chemical Corps loaded the M114 bomblet with B. burgdorferi, a bomblet that spread anthrax when it exploded during World War II. But in operational tests of the M114 bomb load, the U.S. Army found that the bacteria had poor stability and a short shelf life. The U.S. Army Air Corps therefore kept it in reserve as a temporary combat capability.
Between 1971 and 1972, President Richard Nixon ended the very powerful germ warfare by destroying all Brucella and other remaining biological weapons in U.S. arsenals.
In 1985, the World Health Organization (WHO) Expert Committee on Brucellosis, divided the genus Brucella into 6 species and 19 types.
The year 2011 was feared to be the most “eventful” year for Brucella.
From March to May 2011, 27 students and one teacher from the School of Animal Medicine of Northeastern Agricultural University were diagnosed with brucellosis one after another due to the use of unquarantined goats in dissection experiments.
In June 2011, the Center for Disease Control and Prevention in Zhenhai District, Ningbo, Zhejiang Province, also found two slaughterhouse staff infected with Brucellosis when blood samples were taken from staff at two dairy farms and one slaughterhouse under its jurisdiction. In the second half of the year, the famous Feihe Dairy was also caught in a “brucellosis crisis”, with hundreds of cows and dozens of employees infected.
Bacterial typing
Brucella spp. are divided into 6 species and 19 types, namely Brucella spp. for sheep (3 types), Brucella spp. for cattle (8 types), Brucella spp. for pigs (5 types), Brucella spp. for sheep (1 type), Brucella spp. for desert forest rats (1 type) and Brucella spp. for dogs (1 type). The four species that cause disease in humans are pigs, cattle, sheep, and dogs, and can directly infect humans through diet and injured skin and mucous membranes. The most pathogenic species of Brucella is the sheep species that made its “debut” in Malta.
Brucellosis has now been classified as a Class B infectious disease in the “Prevention and Control of Infectious Diseases Law of the People’s Republic of China,” which is the same class of infectious diseases as the more familiar SARS, swine flu, anthrax, AIDS, rabies, and hepatitis B. The CDC also considers it to be a biochemical weapon and defines it as a “Class B bioterrorism agent”.
Bacterial characteristics
Immune defenses help Brucella to multiply
When Brucella enters the body through skin wounds or mucous membranes, phagocytes in nearby capillaries are the first to burrow out and meet the enemy. As long as the immune function is normal, any unknown foreign organism that invades the body will be blocked by the immune army. If the phagocytes fail to destroy the germs, they will “drift” along with the “remnants” of Brucella to the lymphatic fluid to join the phagocytes stationed there and swallow the germs into the “abdomen”. in the “belly”.
The phagocytes secrete digestive enzymes to completely destroy the enemy “germs”. However, Brucella is an intracellular parasitic bacterium that adapts to the intracellular environment. If the body does not have antibodies that specifically deal with it, it can stay inside the cell more easily than non-intracellular parasitic bacteria and, being inside a normal cell, is protected from specific antibodies and other antimicrobial substances in the body fluids. In this way, the phagocytosis of phagocytes has the effect of protecting against Brucella instead. At this point, the lymph node becomes a local primary lesion, and some strong bacteria take up residence within the phagocyte, carrying out metabolic and reproductive activities in a big way, gradually dismantling the phagocyte from within.
Batches of Brucella reenter the lymphatic and blood circulation, resulting in a bacteraemia with “no systemic symptoms of toxicity but detectable presence of bacteria in the blood. In the blood, an army of phagocytic cells comes to fight against Brucella again, and the battlefield expands throughout the body with the blood flow.
Subsequently, these engulfed brucellae concentrate in the liver, spleen and bone marrow and begin to multiply, becoming multiple foci. When the size of the enemy “bacteria” becomes bigger and bigger, the phagocytic cells are overwhelmed, the brucella metabolizes and multiplies in the blood outside the cells, thus causing sepsis and intermittent fever for a long time, which is called “wave fever” and “flaccid fever”. This is the origin of the name “wave fever” and “flaccid fever”.
In addition to macrophages being broken, Brucella can also die. However, the cell walls of this bacterium are laden with endotoxin, a lipid substance that is harmful to the host. When the brucella is destroyed, the endotoxin leaches out with the broken body and enters the body fluids, giving the body a final, one-time poisoning, just like a death spontaneous explosion. Once the living Brucella takes control of the situation in the body, the patient begins to experience systemic symptoms, such as night sweats, loss of appetite, swollen lymph nodes at the liver and spleen, pain in muscles and large joints throughout the body, painful weakness of the bones, led by the spine, etc.
Survival conditions
The virus survives for weeks to months in mild conditions, in fur, water and dry soil. The virus is not tolerant to high temperature, high humidity and light: it can be killed in 7-9 minutes in dry heat at 100 degrees Celsius, and the sterilization time in wet heat at 80 degrees Celsius is only about 6 minutes; by direct sunlight alone, Brucella can live up to 4 hours. Pasteurization and ultra-high temperature sterilization methods are sufficient to effectively kill all brucella in milk. As long as the milk or milk powder is qualified, it is no longer possible for Brucella to be present.
Mode of Infection
Pathogenesis
The bacterium invades the body from the skin or mucous membranes, reaches the lymph nodes with the lymph fluid and is engulfed by phagocytes. If the phagocytes fail to kill the bacteria, the bacteria grow and multiply intracellularly, forming a local primary lesion. This stage has been referred to by some as the lymphogenic migratory stage, which is equivalent to the incubation period. Bacterial proliferation within the phagocyte leads to rupture of the phagocyte and subsequent entry of a large number of bacteria into the lymphatic fluid and blood circulation to form bacteraemia.
In the bloodstream bacteria are in turn engulfed by phagocytes in the bloodstream and carried with the bloodstream throughout the body, multiplying in the mononuclear-phagocyte system in the liver, spleen, lymph nodes, and bone marrow to form multiple foci. When the bacteria released from the foci exceed the phagocytic capacity, they grow and multiply in the extracellular blood stream and present clinically significant sepsis. Under the action of various factors in the body, some are destroyed and die, releasing endotoxin and other components of the bacteria, resulting in clinical manifestations of not only bacteremia, sepsis, but also toxemia.
In the early stage of the disease, the macrophages, T cells and humoral immune function of the body are normal, and they work together to remove the bacteria and heal. If the bacteria are not completely eliminated, the bacteria, metabolites and endotoxins repeatedly stimulate the body locally or enter the blood stream, resulting in T-lymphocyte sensitization. This causes all tissues and organs of the body, and the reticuloendothelial system to undergo metabolic changes due to the repeated stimulation of bacteria, bacterial metabolites and endotoxins into the blood stream, which increases sensitivity. This leads to metaplastic inflammation characterized by mononuclear cell infiltration and the formation of chronic lesions such as granulomas and fibrous tissue hyperplasia. Recent studies suggest that type I, II, III, and IV metaplasia may all play a role in the pathogenesis of brucellosis.
Endotoxin can cause pathological damage, if the body immune function is normal, through the cellular immunity and humoral immunity to clear the germs and get cured. If the immune function is not sound. If the immune function is not sound or the infected bacteria are large and virulent, some bacteria can escape from immunity and be phagocytosed to form new foci of infection in various tissues and organs, which is called multiple foci stage. After a certain period of time, bacteria from the infected foci grow and multiply into the blood again, leading to disease recurrence. The histopathological damage is extensive. The clinical manifestations are also diversified. This repeatedly becomes a chronic infection.
Transmission routes
Brucella abortus is generally parasitic in cattle, sheep, dogs, pigs and other animals that are closely related to humans. The pathogen is transmitted through infected animals (zoonoses), their excreta and contaminated food. Brucella can be found in animals such as sheep, goats, pigs, cattle and dogs. Humans are usually infected by contact with the secretions of infected animals or by eating contaminated meat or dairy products, but human-to-human transmission is rare. The symptoms are similar to those of influenza.
The disease is usually contracted by contact with the secretions of infected animals, or by eating meat and dairy products made from these animals that have not been adequately sterilized. Human-to-human transmission is relatively rare, and transmission is limited to several routes such as breastfeeding, sexual intercourse, and organ transplantation. Such transmission characteristics make the distribution of brucellosis in China characterized by a clear geography – mostly in Inner Mongolia, northeast and northwest.
The prevalence of brucellosis is closely related to animal husbandry. A cow infected with Brucella and not promptly cleaned and vaccinated, brucellosis can quickly break out in livestock populations, which in turn increases the chances of people being infected. Herders, employees working on the front lines of the ranching and dairy industry, experimenters doing related research, and others who are in regular contact with livestock or Brucella itself are more likely to be infected.
For the general public – especially city dwellers – the overall risk is much lower, but drinking unsterilized dairy products or even raw milk in pursuit of so-called “originality” is paving a “brucella lane to the city”.
Diagnosis
Generally speaking, the diagnosis and treatment are very important in the acute phase about one month after the onset of fever. After blood tests confirm the diagnosis, patients often need to take antibiotics for at least 3 weeks. Even if the symptoms disappear during this period, it is important not to “abandon” the treatment, otherwise it will be more difficult to deal with a relapse. Most cases heal in a few weeks to a few months if treated properly and in a timely manner. If you miss the “opportunity” to make the disease chronic, you will have to face a long and repeated course of the disease and unbearable pain, and may also develop complications such as arthritis, and the most serious is the loss of work capacity, female miscarriage or infertility.
The disease is accompanied by fever, joint pain, night sweats, which are more typical early symptoms of brucellosis and are also the basic features of the common cold, but the difference is that this suspected “cold” lingers, and there is a greater possibility of misdiagnosis or neglect in the early stage of the disease.
Detection standards
Brucella antigen skin test shows typical hypersensitivity in sensitive patients, and the chronic phase of the disease reveals an increase in circulating immune complexes and autoantibodies, indicating that humoral immunity is also involved in the pathological damage during the chronic phase.
In untreated patients, serum antibodies are first elevated in IgM, followed by IgG, and then IgA, which rises at low levels and decreases after about a year. Thereafter, IgG may rapidly rebound whenever the disease is repeatedly exacerbated. In the chronic phase, IgG circulating immune complexes were elevated in 53.13% of patients and IgM circulating immune complexes were elevated in 28.13% of patients.
Animal experiments with bovine brucella immunized rabbits, extracted IgM, IggG, respectively, for bactericidal test, proved that IgM, IgG has strong bactericidal activity. After infecting guinea pigs with strong virulent sheep strain bacteria, purified IgG and IgM can play a protective role. However, it is also believed that serum antibodies do not correlate with protective immunity and can only be used as a marker of disease activity, such as Hodgkin’s disease and high incidence of brucellosis in patients with lymphoma.
Pathological changes
The pathological changes of the disease are extensive, the damaged tissues are not only liver, spleen, bone marrow, lymph nodes, but also involve bone, joints, blood vessels, nerves, endocrine and reproductive system; not only interstitial cells, but also parenchymal cells of organs are damaged. The most significant lesions are those of the monocyte-phagocyte system.
The main pathological changes of the lesions are.
(1) exudative degenerative necrotic changes are mainly seen in the liver, spleen, lymph nodes, heart and kidney, with plasmacytic inflammatory exudation interspersed with a little cellular necrosis.
②Proliferative changes of lymphatic and monocyte-phagocyte proliferation, especially in the early stage of the disease. It is often diffuse and later often accompanied by fibroblast proliferation.
(iii) Granuloma formation is seen in the foci of granulomas composed of epithelioid cells, macrophages, lymphocytes, and plasma cells. The granuloma further undergoes fibrosis and eventually results in sclerosis of tissues and organs.
The three pathological changes can alternate and develop sequentially from the acute to the chronic phase. In the liver, for example, plasmacytic inflammation with parenchymal cell degeneration and necrosis is seen in the acute phase, followed by proliferative inflammation, formation of epithelioid granulomas in the liver lobules, and then fibrous tissue proliferation, resulting in mixed or atrophic cirrhosis.
Clinical manifestations
Human
The clinical symptoms of the disease are similar to those of influenza, mainly manifesting as prolonged fever, excessive sweating, arthralgia and hepatosplenomegaly. The disease does not heal on its own or turn into a chronic disease. On physical examination, patients with brucellosis may also see enlarged lymph nodes in certain areas (department, armpit, groin, etc.), enlarged liver and spleen, etc. Other symptoms such as malaise, loss of appetite and mental lethargy are similar to the flu, and the incubation period of the disease is 2 weeks to 6 months.
Brucellosis, early onset is accompanied by moderate fever, which worsens at night during acute attacks. Liver enlargement, splenomegaly or lymph node enlargement are characteristic of this period, and intermittent fever with fluctuating temperature is characteristic of Brucella marcescens and Brucella porcineis infections.
Brucellosis, in its advanced stages, may present with incapacity, bedriddenness, neurological or psychiatric symptoms. 1/3 of patients have hypothalamic-pituitary-adrenal system hypofunction, resulting in the loss of immune stabilization of the organism, which may also contribute to the chronicity of the disease.
Brucellosis causes a chronic disease with a variety of clinical symptoms that may lead to lesions in several organs or organ systems, bones or joints, and granulomas with histological features may be observed in infected tissues. Bacterial endocarditis will be life-threatening if left untreated.
1. The first symptom that appears after the onset of brucellosis is a fever with a body temperature of up to 38-40 degrees, and the fever pattern varies widely from person to person. Some people’s body temperature is not too high, fluctuating between 37-38 degrees, lasting a long time, in a long-term low-grade fever; some people’s body temperature is wavy, that is, high fever for a few days, the body temperature down for a few days, and then start high, repeatedly, so the disease is also known as wave fever. There are also people with high and low body temperature, with big changes in the morning and evening, with dangerous conditions, with flaccid fever and so on. At present, there are mainly more people with prolonged hypothermia.
Another characteristic is that the patient sweats a lot, especially at the beginning of the disease, and sweats more at night, and the sweat is sticky, mostly in the head and chest, etc.
3. Patients also often have bone and joint pain and swelling. Male patients tend to have swollen testicles (single case), female patients may have menstrual irregularities, miscarriage,
Female patients may have irregular menstruation, miscarriage, excessive leucorrhea, etc. The onset of the disease is not obvious at the beginning, but the bone and joint symptoms appear gradually when the body temperature decreases. Pain or impaired bone and joint movement is mostly found in the large joints. For example, lumbar, sacral, hip, shoulder, elbow, knee and other joints. It is often misdiagnosed as rheumatic disease.
Animals
Cattle: The most notable symptom in cows is abortion, which often occurs in the 6th-8th week. The discharge is grayish-white at the time of abortion and discharges a dirty gray or brownish-red foul-smelling discharge after abortion, which disappears after 1-2 weeks. The fetus of early abortion has mostly died before delivery, and the calves produced later are weak and not easily viable. If a cow that has been aborted aborts again, it is generally later than the first abortion, and it is easy to cause the retention of fetal clothing, leading to uterine inflammation and long-term sterility. If the abortion does not occur, the sick cow recovers quickly and can conceive again, but may abort again later.
It is common for bulls to have testicular inflammation, where the testicles are swollen and painful and hard to touch. Brucellosis can also cause arthritis, commonly lameness in the knee and wrist joints. Sometimes there are mild signs of mastitis.
Sheep: The onset of symptoms is similar to but less pronounced than in cattle. Abortions in ewes occur in the 3rd-4th months. Testicular inflammation and epididymitis occur in rams. Other symptoms may include mastitis, bronchitis, arthritis and lameness due to synovial bursitis.
Pigs: Abortion mostly occurs at the full term of gestation, i.e., premature birth. Early abortion is often not easily detected because the sow often eats the fetus along with the fetal coat. Retention of fetal clothes after abortion is rare, and uterine secretion disappears within 8 days. In a few cases, the retention of fetal coat causes uterine inflammation and sterility. Boars commonly suffer from orchitis and epididymitis, with generalized fever and local pain and reluctance to breed. Less common symptoms include subcutaneous abscess, arthritis and tenosynovitis in affected pigs, and hind limb paralysis may occur if there are lesions in the vertebrae.
Distribution range
Brucella mainly invades in human body
(1) Motor system: joint and muscle pain. Knee, lumbar, shoulder, hip, elbow and other joint pains occur.
(2) Nervous system: It can cause damage to nerve stem nerve roots, resulting in neuralgia. Low back pain, hip pain, leg pain, etc. appear.
(3) Respiratory system: some patients develop cough due to interstitial pneumonia.
(4) Digestive system: Individual patients in the acute stage develop gastrointestinal symptoms such as yellow urine, yellow sclera, discomfort in the liver area, and loss of appetite due to more severe liver damage.
(5) Genitourinary system: male patients present with testicular pain and small abdominal pain due to orchitis or epididymitis. In the chronic stage, spermatorrhea may occur, resulting in impotence, seminal emission, and hypogonadism. Female patients may present with breast pain, lumbago, small abdominal pain, irregular menstruation, amenorrhea or excessive bleeding, excessive leucorrhea, decreased libido, premature labor, miscarriage, and stillbirth. Nephrolithiasis, nephromonephritis, and cystitis may also occur.
Treatment measures
(1) Tetracycline antibiotics and treatment with streptomycin: tetracycline 2 grams per day, divided into four oral doses, 21 days as a course of treatment, can be repeated 1-2 courses of treatment, the course of treatment interval of 5-7 days. The first course of treatment with streptomycin. Adults are given 1 gram per day, twice intramuscularly. Because of the many side effects, it is necessary to weigh the advantages and disadvantages when using it.
(2) Rifampin, and treated with doxycycline: rifampin 600-900 mg per day in two oral doses for adults, and oral doxycycline 200 mg every morning for 6 weeks.
(3) Sulfanilamide treatment: cotrimoxazole adults take 2 tablets orally each time, 3 times a day for 2 weeks, and then 2 times a day. 3 weeks is a course of treatment, can be treated for 2-3 courses, the interval between courses of 5-7 days. There is a certain recurrence rate after treatment with such drugs.
(4) Symptomatic treatment: In addition to antibiotic treatment, symptomatic treatment should be used. Such as insomnia can take sedatives, joint pain, headache, etc. can take analgesics, high fever can be supplemented with physical cooling or take antipyretic drugs, etc.
There is no specific drug treatment for chronic brucellosis. Because the symptoms of chronic patients are complex, different people have different performance. Some have mainly allergic symptoms, some have mainly endocrine disorders, and some are immunocompromised. Doctors should provide appropriate treatment according to different situations.
Preventive measures
1, strengthen quarantine advocate self-breeding, do not buy livestock from overseas. Newly purchased livestock must be isolated for one month and quarantined twice for brucella, and only after confirming their health can they be combined with the herd. Before breeding every year, the male breeding animals must also be quarantined and confirmed to be healthy before breeding. The sick animals detected should be kept in strict isolation, fixed grazing place and watering field, and contact with healthy animals is strictly prohibited.
2. Regular immunization is required for livestock in areas where brucellosis is common, and regular preventive injection is required every year. On the basis of eliminating sick animals after quarantine, do basic immunization in the first year, strengthen immunization in the second year and consolidate immunization in the third year, so as to achieve the purpose of purifying the herd.
3, strict disinfection of sick animals contaminated barns, sports fields, feeding troughs and all kinds of feeding utensils, etc., disinfection with 5% Kliorin or Lysol solution, 10-20% lime milk, 2% sodium hydroxide solution, etc. The aborted fetus, fetal clothes, amniotic fluid and secretions from the birth canal should be properly disinfected. The skin of sick animals, soaked in 3-5% Lysol for 24 hours before use. The milk should be disinfected by boiling and the manure should be fermented.
4, sick animals to deal with sick animals to cull is appropriate. Those who really need treatment can be carried out under isolation conditions. For abortions accompanied by endometritis or fetal clothing, after stripping the sick animals, use 0.1% potassium permanganate solution, 0.02% furacilin solution, etc. to wash the vagina and uterus. The serious cases can be treated with antibacterial and sulfonamide drugs.
5, breeding healthy young animals more than 50% of the hidden sick animals, in good isolation conditions, artificial fertilization with the semen of healthy male animals, so as to breed healthy young animals. After the young animals are born and fed colostrum, they are isolated and fed sterilized milk and healthy milk.
6, WHO also reminds consumers that milk and milk products that have not been processed and sterilized have a large and uncertain health risk and should not be consumed as much as possible. Water should be boiled and drunk, meat should be cooked and eaten, and buy qualified dairy products.