انت هنا الان : شبكة جامعة بابل > موقع الكلية > نظام التعليم الالكتروني > مشاهدة المحاضرة

الامراض المشتركة-Brucellosis/كلية الطب البيطري

الكلية كلية الطب     القسم  الاحياء المجهرية     المرحلة 3
أستاذ المادة حبيب صاحب نهر المزيداوي       4/29/2011 8:19:15 PM

Brucellosis:

Etiological agent = Brucella spp.
Brucella are small, gram (-ve) coccobacilli. They are facultative intracellular pathogens that survive and replicate in white blood cells. Their virulence is associated with the organism s LPS.
Historically, brucellosis was one of the major public health concerns (along with bovine tuberculosis) for the veterinary profession. In the U.S., the veterinary community can be duly proud of its role in reducing the incidence of human and animal disease caused by Brucella and Mycobacterium bovis through test and slaughter and, in the case of brucellosis, vaccination programs. Because of these efforts, there are now only about 100 cases of human brucellosis per year in the U.S., and many of these are imported. But in developing countries, several hundred thousand cases of human brucellosis still occur each year, due to the continued presence of substantial animal reservoirs of the organisms.
• In proximity to the U.S., brucellosis remains one of the most important animal diseases in Latin America. In 1998, there were ~6,500 cases of brucellosis in humans in Mexico alone. Brucellosis is also widespread in portions of the Middle East.

Brucellosis in humans:
Brucellosis, also known as "undulant fever", "Malta fever" or "Mediterranean fever," is primarily a disease of those whose occupations bring them into direct contact with domestic animals. (Brucella suis infection has also been documented in feral swine hunters.)
The severity of human disease varies, depending largely upon the infecting strain:
• B. melitensis infection causes the most severe disease, followed by B. suis > B. abortus > B. canis. 
B. melitensis and B. suis are more resistant to bacteriolytic factors in serum. 
- Of regional concern, there were 6,500 cases of human brucellosis in Mexico in 1998, many of which were attributable to B. melitensis.
• B. ovis is not known to be zoonotic.

Modes of transmission:
• Transmission via unpasteurized milk and contaminated cheese was, historically, a serious problem. However, where pasteurization is practiced, such transmission is rare today - the exception being an on-going risk of infection from consumption of soft cheese products.
• Infection today occurs most commonly by contact with placental tissues or vaginal secretions from infected animals (and to a lesser degree because of contact with blood or urine). 
- Contact with secretions from both domestic and exotic animals can pose risks, e.g. 5 zookeepers in Japan developed brucellosis in 2001 after attending the delivery of a baby moose.
• There is limited evidence of person-to-person transmission of Brucella spp.-- Venereal transmission has been reported between a laboratory worker and his spouse, and B. melitensis abscesses in a woman s breast may serve as a source of infection for her infant.
• Brucellosis is also a disease of concern as a bioterrorist weapon.
Clinical symptoms of brucellosis in humans:
The incubation period is generally 1-2 months, after which the onset of illness may be acute or insidious. Thereafter, symptoms may include:
• an intermittent, "undulating" fever
• headaches, chills, depression, profound weakness
• arthralgia, myalgia
• weight loss
• orchitis/epididymitis in men and spontaneous abortion in pregnant woman 
- Brucellosis lasts for days to months, and can be quite debilitating, although the case fatality rate is very low (except in cases of B. melitensis endocarditis). 
- Chronic sequelae may include sacroiliitis, hepatic disease, endocarditis, colitis and meningitis.
Diagnosis is based on isolation of the organism and/or serology.
A combination of doxycycline (100mg BID) (or in children, substitute with trimethoprim-sulfamethoxazole to prevent dental staining) and rifampcin (600-900mg/day) for 6 weeks is the treatment of choice.
Brucellosis in animals:
Brucellosis in animals is generally typified by late-term abortions and inflammatory lesions in the male reproductive tract.

In cattle:
• Brucella abortus is the strain that most commonly infects cattle. 
B. suis and B. melitensis infections can occur if cattle are in contact with infected pigs or goats. 
- Less severe disease occurs when cattle are infected with these stains.
• Infection most commonly occurs via ingestion, but B. abortus can also be transmitted venereally.
• Adult cows are more susceptible than young stock.

 In cows: Bacteremia and colonization of the mammary gland and supramammary lymph nodes lead to suppurative placentitis, necrosis of cotyledons and abortion. 
- Erythritol in the placenta may enhance the growth of Brucella spp. 
- Abortion generally occurs after the 5th month of gestation; the fetus is usually autolyzed.
• In bulls: seminal vesiculitis and/or orchitis 
- Occasionally lameness and mastitis may occur as herd problems.

In pigs:
• Brucella suis is the most common strain isolated from pigs. 
B. abortus infections can occur if pigs are in contact with infected cattle.
• Infection occurs by ingestion or via venereal transmission.
• In sows: abortion and other reproductive disorders
• In boars: orchitis 
- Less commonly, arthritis, spondylitis or abscesses in various organs can occur in pigs of either sex.

In sheep and goats:
• Brucella melitensis is the classical strain of Brucella affecting female sheep and goats. 
B. abortus and B. suis infections can occur if small ruminants are in contact with infected cattle or pigs. 
- Infection with B. melitensis is acquired primarily by ingestion. 
- Clinical signs include late term abortion or birth of weak lambs and kids, and mastitis (particularly in goats).
• Brucella ovis is almost exclusively a concern in rams, causing epididymitis. It only very rarely causes abortion in ewes.

In dogs:
• Brucella canis is the most common strain of Brucella infecting dogs. 
B. abortus, B. suis and B. melitensis infections occur occasionally when dogs eat placentas from farm animals.
• Brucella canis is most commonly transmitted venereally.
• In bitches: abortions at 40-60 days of gestation
• In stud dogs: epididymitis/orchitis and scrotal dermatitis, sometimes progressing to complete scrotal necrosis
• Brucellosis is also an important rule-out for diskospondylitis in dogs of either sex. 
• treatment = neutering and aminoglycosides + minocycline or doxycycline
In cats:
• Cats are relatively resistant to Brucella infections.
In horses:
• Brucella abortus (less commonly B. suis) is one cause of the bursitis conditions called "fistulous withers" and "poll evil".

In other species:
• Bison, elk, reindeer and caribou can be infected with Brucella spp., but their role in transmission of the infections to livestock remains under debate. 
- There is one suspected human case of brucellosis linked to the use of deer and elk urine as a scenting agent during hunting!
• Most recently, Brucella spp. (different from those in land mammals) were isolated from dolphins, seals and an otter. Experimentally, at least one of the marine mammal species can infect and cause abortion in cattle, and marine mammal species have also been isolated from human beings.

Control of brucellosis:
The United States has maintained a federal program for the eradication of brucellosis from domestic livestock for many years. The country is very near its goal of being brucellosis-free. (In fact, we reached a point of having no cattle herds quarantined for brucellosis for the first time in 2001, although there have been additional cases detected again since that time.) The specific approach to control in each state depends upon the state s eradication status, but in general:

Swine brucellosis: Brucella suis is controlled through serologic testing and inspection at slaughter, with trace-back investigations to the farm of origin of any suspect pigs at slaughter. Pigs are not vaccinated against brucellosis.

Bovine brucellosis: Brucella abortus is controlled through a program that combines vaccination of calves, periodic testing of farm bulk milk samples for anti-Brucella antibodies and serologic testing and inspection at slaughter.

 Vaccination: 
 RB51 vaccine: the newer live-attenuated vaccine strain that is used today - This is a "rough" variant of B. abortus that lacks the O-side chain on its LPS. 
 Vaccination should occur during calfhood (4-12 months for RB51) so as to minimize the induction of antibodies that might be interpreted as evidence of actual infection. (This is much less of a problem with RB51 than it was with Str. 19 because of the lack of the O-chain on RB51.)
? Vaccination was mandatory in the past when the incidence of brucellosis was greater. Today, the most common reason for vaccination is that vaccinated animals command a higher value at sale. However, some countries will not accept vaccinated animals for export. Vaccinated cattle are identified by:

(R) ear tattoo ("RV/last number of the year of vaccination," with RV standing for RB51 vaccinated) 
- Orange (R) ear tag 
- Vaccination should not be conducted in pregnant animals because of the risk of vaccine-induced abortion. 
- Strain 19 vaccine: the original (since 1941) "smooth" but attenuated live vaccine strain, Str. 19 vaccine will induce brucellosis in humans who are inadvertently "stuck." If this happens, you should receive 3 weeks of doxycycline and rifampcin antibiotics prophylactically. The potential for human disease due to RB51 remains unclear, but prophylaxis with doxycycline for 21 days is prudent and recommended until further information is available. (Rifampcin need not be included since RB51 is rifampcin-resistant.) 
- Milk ring test (MRT) ("Brucella ring test"=BRT): Dairy herds are screened every 6 months by testing a bulk tank milk sample for antibodies against Brucella. 
-If the BRT is positive, all cows on the farm are tested individually (card test, plate or tube agglutination tests) and any (+) "reactor" animals are slaughtered. 
 Animals are also Brucella blood tested at slaughter. A positive test results will lead to a trace back and testing of other cattle at the farm of origin.
(Diagnosis of B. melitensis and B. ovis is usually accomplished by bacterial isolation, or demonstration of the organism in tissue or by serology.)
(Diagnosis of B. canis is by serology. AGID is more specific and sensitive than agglutination tests for B. canis.)


المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .