While I am not by any means a vet, I believe every owner should have some basic knowledge of common ailments, their symptoms, and any at-home-treatment that is possible. So this page lists some of that information, in case you ever have an animal with a sickness, and so you know what to watch for so you can catch it early and have the best likelihood of treating it.
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Metabolic Bone Disease (MBD)
This occurs when there is not enough vitamin D3 utilized by the lizard or not enough calcium is given. This special form of D3 must be attained through UVB rays, and will not function correctly if given through the food they eat or water they drink. The D3 is what allows the calcium to be utilized. Without this, the lizard starts taking calcium from stores it has, such as the bones. The bones then become brittle, and then they start to fracture and break. Symptoms of this include a weak and rubbery mouth, dragging the legs (broken bones) and paralyzation (spine broken). Other symptoms include tremors and shaking, turning in of the feet, and stunted growth. It is best if a vet steps in on this one. They will give calcium shots or liquid calcium, and some other treatments. On your part, get a good UVB bulb (see the lighting section), take your pet outside if it is above 70 for some sunlight, up the calcium dustings on his food, and if possible add some high calcium foods to his diet as well. It is really best for a reptile vet to look at a pet suspected of having this disease though.
Impaction occurs when something is lodged in the digestive tract and blocks everything up. This can be deadly if left untreated. Its causes are dangerous substrates, such as calci-sand, repti-sand,-repti-bark, gravels, etc. and prey items larger than the space between your Bearded Dragon's eyes. Impaction can also occur if the temperatures are below 95 degrees, in which case your Bearded Dragon may have trouble digesting. Symptoms include lethargy, dragging the back legs, and most obviously not having any bowel movements. At home treatments include giving natural laxatives like drops of olive oil and apples. Upping the temperature to the warmer side towards 110 degrees is helpful as well. Another good trick is frequent warm baths. While your Bearded Dragon is in the water, gently massage just above the tail on his body and to the right to get things moving. In extreme cases, surgery may be required.
Causes of this include too low of a humidity level and tail trauma. Often, Tail Rot occurs when multiple sheds are done incompletely or improperly. Gradually, these sheds layer one on top of the other until they cut off the circulation and live tissue in the tail. What is left is thick, dead, often black or dark-colored tissue that will gradually lose feeling in it and start to work its way up the tail. Part of the tail may even fall off. If the tail rot works its way all the way up to the body, it can infect the organs and kill your Bearded Dragon. A vet really needs to see this before it advances far. Amputation may be required in extreme cases to save your Bearded Dragon's life. In the time you are waiting for the appointment, though, you can give frequent baths with diluted Betadine and slowly brush the caked on old shed with a soft-bristled toothbrush. After the bath, apply aloe vera for moisture.
Mites are nasty little external parasites that feast on your Bearded Dragon's blood. They also reproduce like crazy. They tend to be unwittingly transported from one reptile to another. The first thing you want to do when you have mites is make sure the animal is in absolute quarantine. Don't even let things it has touched near the other animals. Treat the animal itself by washing in a bath of diluted Betadine and then going over all spikes and crevices with a Betadine-soaked cotton swab. Avoid contact with the eyes. Also treat the entire cage with a mite treatment you can get at pet stores, and then disinfect the whole thing. Then you'll have to do a the whole thing again in a couple of weeks, when the new eggs hatch. Mites are a pain to get rid of, you may have to repeat this process multiple times. However, it is necessary, as too many mites on your lizard can kill him.
There are many types of internal parasites that effect Bearded Dragons. Common symptoms are lethargy, not eating or pooping in their normal schedule, and extremely runny and smelly feces. Some types, like Pinworms, are often contracted when the Bearded Dragon eats infected insects, like crickets. Other internal parasites, like Coccidea, are always present in some levels but due to spikes in stress and other factors can reach infestation levels. Besides keeping your tank scrupulously clean, this is pretty much in the vet's hands. They will prescribe medicines to take care of them, based on counts and types of parasites present.
Respiratory Tract Infection
Respiratory Tract Infection is a bacterial infection in the lungs. It is caused by too cold temperatures (keeping in mind here that the temperatures should be 100-110 on the surface of the basking temperature and 70-85 degrees on the cool side). It is also caused by too high of a humidity (above 60%). Stress can exacerbate this condition as well. Symptoms of Respiratory Infections include gaping constantly, mucus coming out of the mouth or nostrils, and a clicking or rattling sound when breathing. All you can do is correct the husbandry issues that may have caused this, and make the overall temperature a bit warmer. Be sure to check the night time temperature too and make sure it is above 70. Then take your animal to a vet, who will probably treat with antibiotics and some other treatment options.
Yellow fungus is a contagious disease. It is thought to be caused by yeast infections in the digestive system, gotten from antibiotics, that then exits with the feces and infects the Bearded Dragon on the outside. Or it can be passed on from an infected dragon to an uninfected one. It is characterized by the appearance of yellow patches of fungus on your Bearded Dragon. Preventive measures include always using a probiotic when you are using an antibiotic. Once this disease is contracted, a vet is a must. They will probably give antifungal treatments.