Mastitis, Biology


The term mastitis refers to the inflammation of udder and is characterized by physical and chemical changes in the milk which include discolouration, presence of clots and a large number of leucocytes. An affected cow loses about 15 to 100 % of its production. The incidence is similar among buffaloes and goats kept for milk production. The bacterial contamination of milk may render it unsuitable for human consumption, or interfere with manufacturing processes and in some cases spread the infection to humans. Sore throat, tuberculosis and brucellosis may spread to humans in this way.

The most common bacteria and fungi associated with the disease are various species of streptococci like Str. agalactiae, Str. uberis, Str. dysgalactiae and a few others. In India Staphylococcus aureus induced mastitis in cattle assumes equal importance. Sporadic cases of bovine mastitis are due to Pseudomonas aeruginosa and Escherichia coli. Rarely Mycobacterium, Mycoplasma and Bacillus cereus are also associated with mastitis. Even common bacteria like coliforms are reported to be causing mastitis. The disease in milking buffaloes is caused by the same bacteria as in cattle. Mycotic agents like Candida parapsiolsis, Aspergillus spp., Candida tropicalis, Candida guillermondii, Candida krusei, Cryptococcus neoformans, Rhodotroula glutins, Penicillium sp. have been isolated from cases of bovine mastitis.

Transmission: Except in the case of tuberculosis where the infection of the udder
is haematogenous, the infection in mastitis occurs via the teat canal. The organisms are derived from the contaminated environment, from the skin of udder and teat, and milking equipment where they remain viable for many weeks. Sometimes the milker’s are the source of infection. Normally, the udder tissue, the milk cistern, and milk within the udder and cistern are sterile. Where predisposing factors are present the organisms are able to pass along the teat canal and enter udder to set up infection.

The predisposing factors may be;
(a)  Age: The older the animal, the greater the likelihood of the infection.
(b)  State of lactation: Infection is more likely at the beginning and end of lactation. (c)  Milk yield: High yielder appear to be more often infected.
(d)  Hereditary factors: Crossbred cows are more prone to infection than the country cows.
(e)  Trauma: Injury to teat and udder allow the micro-organisms to invade the organism.
(f)  Hygiene.
(g)  Unknown factors: There are certain undetermined factors which make it possible for one of the two apparently identical animals in the same environment to  contract mastitis while the other is completely healthy.

Symptoms: Streptococcal mastitis arises from the multiplication of organisms from the teat canal extending into the ducts and secreting tissues of the mammary gland. The condition may be chronic or acute depending upon the streptococcal species. Str. agalactiae causes a chronic disease. Milk secretion becomes scanty, thick and purulent. It contains fibrin and blood. The epithelial tissue of ducts becomes thick. Some ducts get occluded due to granulation of the tissue. When the disease progresses, areas of induration develop. The disease due to Str. uberis is clinically similar to that due to Str. agalactiae. Str. dysgalactiae causes acute mastitis characterized by hot, swollen, painful udder with purulent yellow secretion. Acute staphylococcal mastitis is characterized by sudden rise in body temperature, enlargement and hardening of affected quarter with cessation of milk secretion. The milk secretion becomes blood stained, and contains pus and shreds of necrotic tissue. If the animal survives the udder quarter will become functionless. Sometimes the affected quarter becomes dark in colour, cold, gangrenous and finally sloughs off. Fatal cases die of toxaemia. In chronic staphylococcal mastitis the udder is indurated, milk contains clots and leucocytic count increases. Summer mastitis is due to Corynebacterium pyogenes (now called as Areanobacterium pyogenes). The disease occurs most frequently in heifers and dry cows during summer months. The mastitis caused is acute in nature, and the affected quarter becomes enlarged and firm. The milk becomes purulent and gives an offensive smell. The gland may slough off. The animal will have fever and show signs of toxaemia. Mortality rate is very high. Among survivors the affected quarter may get permanently damaged.

Latent or sub clinical infection is common. The affected animals excrete the organisms in their milk regularly or intermittently and act as a source of great danger to healthy cows in a herd. There are no visible clinical signs. The animal, the udder and the drawn milk are apparently normal. This can only be identified by laboratory infection.

Diagnosis: The early detection of disease is very important because in early stages it is amenable to treatment. Physical examination of udder helps in detecting cases where changes have occurred. Laboratory procedures are of great value in examining milk samples for cells, bacteria and chemical changes, and for testing sensitivity of bacteria to specific drugs. Cell count and bacterial examination are usually performed on the same sample of milk. Because of the expense of laboratory examination of a large number of milk samples, indirect tests based on physical and chemical changes of milk have been developed. These indirect tests are of value as screening tests and should be supplemented by bacteriological examination. Indirect tests are now restricted to the determination of DNA which approximately determines the number of leucocytes. The California Mastitis Test (CMT) is most commonly used and has proved to be very efficient. After mixing milk and the reagent the result is read as traces 1, 2, 3 and negative depending upon the gel formation in the milk sample. The test is not reliable in the first week after calving or in the last stages of lactation when the test is always positive.
Treatment: The degree of response to treatment depends on the type of causative agent and the speed with which the treatment is commenced. It is always preferable to conduct a quick in vitro drug sensitivity test before starting the treatment. It is preferable to use such antibiotics which are normally not used for therapeutic purposes in man especially children so that resistance due to residual antibiotic in the milk may not pose a problem in man especially children. The treatment of staphylococcal mastitis is not always satisfactory and is less reliable than the treatment of streptococcal mastitis.Parenteral treatment is advisable in all cases of mastitis. Antibiotics and sulphonamides are used to control the reaction. Udder infusion with suitable drugs in a water-soluble ointment base are used. During the treatment, strict hygienic measures are necessary to avoid the introduction or organisms in the quarter. Cortisone and other allied compounds are used to facilitate the reduction of inflammation and convalescent time.

Mastitis caused by Streptococcus strains responds well to penicillin treatment. Treatment of all quarter with infusions of 100,000 units of penicillin after 5 successive evening milkings is effective. Vaccination with Str.agalactiae is in an experimental stage.A high proportion of staphylococci has become resistant to penicillin and streptomycin. Treatment using 3 infusions with 250 mg novobiocin per infusion or 400 mg tetracyclines or penicillin-nitrofurazone combination (100,000 units-150 mg) or penicillin-tylosin combination (100,000 units-240 mg), has been found to be satisfactory.  For  mastitis  due  to  E.coli  and  Cor y n e b a c te r i u m  p y o g e n e s (Areanobacterium pyogenes ) the drugs mentioned about may be used.

Lactating goats also suffer from mastitis in the same way as bovines. The treatment and control measures are the same as in the case of cows and buffaloes.

Control: Even with the most careful hygiene, mastitis sometimes persists in a dairy herd, but with every hygienic device the spread of infecting micro-organisms can be controlled. The following hygiene measures are recommended for preventing the spread of the disease;
(a)  Animals diagnosed positive should be milked at last.
(b)  Milkers should wash their hands before milking and should use well-washed white overalls.
(c)  A separate clean cloth for each cow is used for washing the udder with a disinfectant.
(d)  The first stream of milk from each quarter should not be allowed to drop on floor but collected in a separate container. Milkers should not wet their hands with first stream of milk.
(e)  Normal milk-room hygiene including washing of milk containers and equipment should be practised.

Posted Date: 9/17/2012 6:57:12 AM | Location : United States

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