गौंवंश ब्रुसेलोसिस: भारत में संक्रामक गर्भपात की व्यापकता
Brucellosis is one of the most common but often neglected zoonotic diseases in the India. The disease occurs worldwide, but in some countries, the disease is often underreported and there is little or no control, which leads to major health, economic and livelihood burdens. Despite its brutal impact on economic loss, it is also associated with high morbidity, both for humans and animals in developing countries like India.
Brucellosis is a contagious, costly disease of ruminant (E.g. cattle, bison and cervids) animals that also affects humans. Although brucellosis can attack other animals, its main threat is to cattle, bison, cervids (E.g. elk and deer), and pigs. The disease is also known as contagious abortion or Bang's disease.
In humans, it's known as undulant fever because of the severe intermittent fever accompanying human infection or Malta fever because it was first recognized as a human disease on the island of Malta.
Transmission of bovine brucellosis is estimated to occur at an endemic equilibrium in India, with disease prevalence estimated to be 13.5%. Equilibrium dynamics were used to estimate the transmission rate of 0.1156 per year.
The disease is caused by bacteria of the genus Brucella which consist twelve species of Brucella have been identified so far. In cattle, the infection is predominantly caused by B. abortus, less frequently by B. melitensis and occasionally by B. suis. In adult female cattle, infection confined in the reproductive tract and produces placentitis followed by abortion, causing production losses.
Most of the infected animals abort only once in their lifetime, but may remain infected their whole life. The disease remains asymptomatic in non-pregnant female cattle and after the first abortion. Adult male cattle may develop orchitis, and brucellosis may cause infertility in both sexes. Hygromas can occur in leg joints are also a common finding of brucellosis in our countries.
Bovine brucellosis is an important disease of livestock specially in bovine that has significant animal health, public health, and international trade consequences. Detrimental effects of this disease are infection in animals, decreased milk production, weight loss, loss of young, infertility and lameness. this disease not only cause formidable threat to livestock, but also spread rapidly and be transmitted to humans makes it all the more serious.
Incubation period of disease
- Acute or sub-acute disease follows an incubation period which can vary from 1 week to 6 or more months.
- Bison, and other animals is quite variable ranging from about 2 weeks to 1 year and even longer in certain instances.
- When abortion is the first sign observed, the minimum incubation period is usually about 30 days.
- Some animals abort before developing a positive reaction to the diagnostic test.
- Generally, infected animals that do not abort develop a positive reaction to the diagnostic test within 30 to 60 days after infection, although some may not develop a positive reaction for several months to over a year.
- The length of the incubation period may be influenced by many factors are virulence of the infecting strain, size of the inoculum, route of infection and resistance of the host.
Signs of Brucellosis
There is no fruitful technique to detect infected animals by their appearance. The clearest signs in pregnant animals are abortion or birth of weak calves. Milk production may be decreased from changes in the normal lactation period caused by abortions and delayed conceptions. Abortion not found in all infected cows, but those that do usually abort between the fifth and seventh month of pregnancy.
Calves from infected cattle may have dormant infections, i.e. infections that are not diagnosed until they become pregnant, abort or give birth. Even though their calves may appear healthy, infected cows continue to harbour and discharge infectious organisms and should be regarded as threatening sources of the disease.
Other signs of brucellosis include an apparent lowering of fertility with poor conception rates, retained foetal membrane afterbirths with resulting uterine infections, and (occasionally) enlarged, arthritic joints.
Spread of Brucellosis
Brucellosis is frequently transmitted to prone animals by direct contact with infected animals or with an environment that has been contaminated with discharges from infected animals. Aborted foetuses, placental membranes or fluids, and other vaginal discharges are the instant source of Brucella organisms which may leads to spread of infection.
Cows may lick those materials or the genital area of other cows or ingest feed or water contaminated with the disease-causing organisms. Despite occasional exceptions, brucellosis is mainly spread from one herd to another by an infected or exposed animal.
This mode of transmission occurs when a herd owner buys or replace cattle that are infected or have been exposed to infected animals, animal tissues or animal discharges prior to purchase. The disease may also be unrolled when wild animals or animals from an infected herd mingle with brucellosis-free herds.
Brucellosis control and prevention
No treatment is available, which makes detection and prevention essential. Brucellosis is a notifiable disease. Because of this most countries have strict regulations in place to control brucellosis, however it is still a threat. Testing herds regularly and culling has been an effective way of eradicating the disease in individual herds before. Quarantines are placed on infected herds and good sanitation and biosecurity will protect uninfected herds.
Proper herd management strategies can also aid in the avoidance of the disease. These include: Maintaining closed herds, recording individual animal identification and maintaining accurate records, isolating and testing purchased additions as well as cattle re-entering the herd and arranging diagnostic workups and necropsies for potentially or suspected brucellosis infected cattle.
In endemic areas vaccination is available. Mass vaccination is important for the control and eradication of disease in bovine, ovine and caprine but other complementary measures that may need consideration involves improved farm hygiene, restriction and control of trade and movement of animals, testing of animals and isolation and removal of infected animals.
Though the existing vaccine for bovine brucellosis, the B. abortus strain 19 (S19), and the vaccine for ovine and caprine brucellosis, the B. melitensis strain Rev 1, have some undesirable traits. Given the complexity of the epidemiology of brucellosis involving various animal species, the effective control will include a long-lasting and carefully controlled and monitored effort.
In some area’s wild populations of buffalo, bison or cattle can carry the disease and infect domestic animals if they come into contact. Vaccination is not a guarantee but can increase resistance to infection. There is also no vaccine for humans, and high rates of initial treatment failure and relapse rates make clinical management particularly difficult.
Hence, prevention of human brucellosis depends on management of the animal reservoir. Disease management for brucellosis may best take the form of test-and-slaughter, abortion notification, and vaccination.
Economic impact, loss and cost of bovine brucellosis
There is a dearth of comprehensive economic studies which reveals bovine brucellosis causes huge losses to the dairy sector. It is also noticed that terms such as economic impact can include direct (e.g. reduced milk yield, increased mortality) and indirect (e.g. vaccination, culling) costs.Direct impacts may further be categorised as visible symptoms (e.g. abortion, repeat breeding), invisible symptoms (e.g. lower fertility), additional costs (e.g. treatment, vaccination) and revenue forgone (e.g. distress selling).
Loss may mainly consist only those parameters that reduce benefits (e.g. reduced milk yield, reduced weight gain, reduced fertility, increased replacement cost, increased mortality etc.) while cost would include amounts spent for treatment and control (e.g. biosecurity, vaccination, movement control, disease surveillance, research etc.) of the disease.
Most economic evaluates have not taken into consideration the loss caused by distress selling, feeding and management loss of pregnant animals in the event of abortion, person-days loss for treating animals, cost of antiseptic and detergents, cost of transportation related to treatment, cost of diagnosis etc. Because of lack of uniformity in perspective to measurement of economic impact/cost/loss, and the reality that these are highly context specific, the estimates have also varied widely.
Conclusion
Brucellosis is an important zoonosis worldwide. In livestock, it frequently causes chronic disease with reproductive failures that contribute to production losses, and in humans, it causes an often-chronic febrile illness that is frequently underdiagnosed in many countries, including India.
India has one of the largest ruminant populations in the world, and brucellosis is endemic in our country for both animals and humans. Control of brucellosis in India is even more difficult because of animal’s movement for different reasons, and high socio-religious sentiments towards rearing of dairy animals which does not allow slaughtering of animal.
Therefore, in India’s context strengthening disease reporting system, including diagnostic capabilities and surveillance in livestock, wildlife and human. Vaccination, improved cleanliness and hygiene, better management, adoption of quarantine measure, restriction in movement of animals, adoption of more artificial insemination and customised health education programme on brucellosis may be helpful in reducing brucellosis cases.
Authors:
Dr. Anjali1, Dr. Gururaj VK1, Dr. Madhuri Patel2, Dr. Vandita Mishra3
1 Division of Physiology and Climatology, 2Division of Pharmacology, 3Division of Livestock Product Technology
ICAR-Indian Veterinary Research Institute, Izzatnagar-243122, India
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