Diseases and Parasites of Minks

JOHN R. GORHAM.

THE BOTULISM bacterium, Clostridium botulinum, produces a potent toxin in contaminated meat. Such meat, fed to minks, can kill them in 18 to 96 hours. Almost immediately the animals suffer muscular incoordination and stiffness. Paralysis of the front or hind legs follows. The muscles used in breathing become paralyzed by the toxin, and the minks die.

The carcasses of sick horses and spoiled feed that has had a chance to become warm for a time should never be used.

The treatment of minks affected with botulism often is to no avail. Prompt recognition by the rancher will give the veterinarian a better chance to save the minks that have not eaten enough of the poisoned food to show symptoms. The owner should throw away immediately all the contaminated, frozen, stored food and the uneaten ration in the pens.

Antitoxin that contains toxin-neutralizing antibodies against the three common types of toxins, designated A, B, and C, should be administered to every mink on the ranch as soon as possible.

For prevention, a toxoid preventive inoculation offers fair promise of being helpful. The first work on botulism toxoids for minks was done in Sweden. Following the disastrous outbreaks of botulism in this country when spoiled whale meat was fed, research workers in Utah and Wisconsin and at the Department of Agriculture Fur Animal Disease Station developed an experimental toxoid, which is available commercially. It is emphasized, however, that care in management and selection of feed is the best insurance for preventing this malady.

ANTHRAX is a fatal disease of minks caused by the bacterium Bacillus anthraces. Minks die within a few days after eating meat from an anthrax-infected cow, pig, or horse. The animals show few if any signs of sickness before death.

An autopsy discloses that the spleen is enlarged, blue black, and easily torn. Because other disease conditions in minks seem to be similar to anthrax, a diagnosis can only be made on bacteriological examination in a laboratory. The surest prevention is to avoid feeding meat from sick animals.

Penicillin injections have been given to affected minks with good results.

People may become infected by handling pelts removed from minks that died from anthrax. Because the spores the resistant stage of the bacterium survive the tanning process, dead animals should be burned and not pelted. Premises once contaminated remain infected.

ABSCESSES caused by Micrococcus and Streptococcus and by Klebsiella ozaenae are common in minks. Often slivers of bone or barbed grasses injure the animal and carry the bacteria into the skin or lining of the mouth. Pus accumulates, and an abscess, or boil, is formed.

When the abscess feels hot and swollen and is fluctuating to the touch, one should make a vertical incision long enough to drain away the pus with a sharp, sterile blade. The cavity should be washed out with a mild disinfectant, such as dilute hydrogen peroxide, and dusted with sulfa powder, such as sulfathiazole or sulfanilamide. A veterinarian can demonstrate this simple technique. In all cases, an injection of 100,000 to 200,000 units of penicillin should be given.

STREPTOCOCCUS organisms the small bacteria which, when viewed under the microscope, occur in chains like a string of beads may cause other troubles. Ranchers may notice that the top and sides of the head, nose, and upper neck region of some of their minks have suddenly become swollen. This condition is called cephalic cellulitis. The minks are sluggish and refuse food. If they are not given an inoculation of penicillin at this time, death will ensue.

These types of bacteria may also cause fatal septicemia (blood poisoning) in young minks. The symptoms are not apparent, and the animals are found dead in their nest boxes. Penicillin is the antibiotic most frequently recommended for treating streptococcal infections.

Pseudomonas aeruginosa causes a rare but deadly disease in minks. This bacterium is introduced into the herd through contaminated drinking water. Most minks are sick only an hour or two before they die they may look healthy in the evening but are found dead the next morning. Pneumonia is the most significant finding at autopsy.

Streptomycin and polymyxin are the antibiotics of choice. As these drugs are highly toxic to minks, information as to the dosage and manner of treatment should be obtained from a veterinarian.

PASTEURELLA MULTOCIDA is found in cases of mink pneumonia. The disease often appears in the spring and fall when the weather is damp and the temperature is subject to rapid change. The nest boxes should be constructed so that they can be kept dry and well ventilated. Minks can stand freezing temperatures, but they cannot tolerate wet nest hay and boxes.

Rapid, shallow breathing, as evidenced by a heaving of the flanks, is the most important clinical sign of the malady.

For treatment, injections of penicillin, Aureomycin, or Terramycin can be given. Treatment is not always successful because the animal is often too far gone by the time it looks ill.

GANGRENE occasionally develops in wounds and after contaminated tissue vaccines have been injected. Various bacteria have been isolated Clostridium, Streptococcus, Micrococcus, and Actinomyces.

Animals that have been given contaminated vaccine drag the inoculated leg. Gas bubbles form in the muscle and a foul discharge is noted later.

The broad-spectrum antibiotics, such as Aureomycin and Terramycin, are used for treatment.

PLEURITIS, or inflammation of the lining membranes of the chest cavity, often causes death. When the ribs are cut and the chest cavity is opened, a large amount of thick, grayish-yellow pus is seen. The lungs are compressed and covered with adhesions.

Many bacteria have been isolated from this pus, including Streptococcus and Micrococcus species, coliforms, Norcardia species, Actinomyces necrophorous, and organisms like pleuropneumonia.

Animals sick with pleuritis are rarely treated, because they usually are found dead with no signs of illness.

ENTERITIS, an inflammatory condition of the small and large intestine, is commonly observed on mink ranches in the United States and Canada.

Spoiled food, corrosive chemicals, and a specific virus can cause it. Many bacteria have been suspected, but the actual cause in many instances is unknown. The disease is more apt to develop in the summer months.

Affected minks often have a big appetite. Beneath their pen is seen a large accumulation of black, tarry, or grayish-white droppings. Usually only a few minks on the ranch are affected.

When the whole herd is involved, prompt veterinary assistance is required, because sulfa drugs or high levels of antibiotics will have to be added to the rations.

WHEN DISTEMPER is mentioned, mink ranchers everywhere have cause for alarm, for it is very serious in minks throughout the United States. Although almost all of the minks get the disease in any given outbreak, some animals do not show any symptoms. The number of deaths may vary from one outbreak to another. The loss may be as high as 90 percent in young mink, but the average loss in older mink is 30 to 40 percent. Kittens as young as 3 weeks may be infected. Outbreaks can occur at any time.

The incubation period the interval between the time the virus first enters the mink and the appearance of disease is about 9 to 14 days.

The first sign of the disease is swollen, watery eyelids. The lids become crusty and stick together in 2 or 3 days. The minks may have an excellent appetite at this time.

Next the feet may swell the so-called "snowshoe" foot. Small, brownish, granular scabs can be seen on the surfaces of the pads. The minks may die at this time or appear to recover, but these "recovered" individuals may later die of what the rancher calls the "screaming fits." In this type of distemper, the virus has invaded the brain, causing the minks to froth at the mouth, chew violently on the wire netting, roll about the pen, and scream sharply. These convulsive seizures may last a short or a long time. The mink usually dies after one or two attacks.

The virus is spread from animal to animal through the air. In the normal breathing process, minks that show distemper (as well as the apparently healthy carriers) emit millions of small, virus-containing droplets into the air. The virus also is found in the saliva, nasal secretions, and skin scurf shortly before and during an attack. A mink may also shed virus into the air after the signs disappear.

Distemper can be transmitted among mink by indirect means, such as contaminated mitts and food pans.

A diagnosis often can be made by observing affected animals, but sometimes laboratory tests are necessary.

Microscopic slides can be made of tissue from the bladder and trachea (windpipe) and stained with special dyes. Distemper leaves rather characteristic marks, called inclusion bodies, in those tissues. They are small stained "dots," or specks, which represent distemper virus.

The surest way to obtain a diagnosis is to remove the spleen from the suspected distemper-infected mink, grind it in a liquid suspension, and inject it into a ferret. If the spleen from the animal in question contains active virus, the ferret, which is almost 100-percent susceptible to the virus, will become infected.

Every precaution must be made to keep distemper away from the ranch. New breeding stock or minks returned from fur shows should be quarantined for 2 months, as they may carry the virus into the herd.

Infected dogs are a dangerous source of distemper virus for minks.

Two general types of distemper vaccine are on the market the killed-virus vaccines and the living modified-virus vaccines.

The killed-virus vaccines, prepared from a spleen containing virulent virus of an animal dead of the disease and treated with formalin to inactivate the virus, have some disadvantages. Animals inoculated with them develop immunity rather slowly. The immunity seems to leave the animal, and so revaccination is necessary.

Living-virus vaccines, which are made by growing the virus in chicken embryos, have been more successful in controlling outbreaks.