Fungal Infection in Dogs


Histoplasmosis Causes and Symptoms

Question: My five year old schnauzer was diagnosed in September with histoplasmosis. I was told if he could make it two weeks with taking itracanozol he might have a chance. It is now December and we are well on our way. His blood count has gone from 19 to 36, a metriculicite count (spelling?). Are still on the medicine twice a day. My question is in regard to how do I know when he is cured? He stays on a tether or a leash at all times. Can he be reinfected? We walk the same two miles every day and I am concerned he might have gotten this terrible stuff from our walks. We live in the city and are walking around city streets. I have tried to find out info regarding this disease on websites but have not had much luck.He gets a monthly check up with our local vet who has done a super job of getting us diagnosed and to the right people to help us. I am just curious about this disease and so are my neighbors who also have dogs that walk the same path.

Hope you can help me, Ann

Answer: Anne-

Histoplasmosis is a fungal infection. The organism is supposed to be found nearly worldwide, but infections with it are more common in the areas around the Missouri, Ohio and Mississippi rivers. It enters the body by being inhaled or ingested but most cases are reported to occur due to inhalation of the conidia (the infective form) of the Histoplasma capsulatum organism. Most dogs and cats that become infected with histoplasmosis probably have inapparent infections, or subclinical infections. The immune system of these pets kills the fungal organism before clinical disease can occur. When the immune system is not working properly, or just can't handle the infection, clinical signs appear about 12 to 16 days after the Histoplasma organisms are inhaled or ingested. Clinical signs usually involve either respiratory signs or digestive signs, since the organism infects these areas first. Then there is a spread to the lymph nodes and then almost anywhere in the body. The signs of the disease depend on where the infection spreads to. Signs like decreases in appetite, depression, fever, anemia, weight loss, breathing difficulties, lameness and eye problems can occur.

The anemia associated with this disease is normally nonregenerative, which means that there is not a production of new blood cells. Reticulocytes are immature red blood cells, which are released when the bone marrow is working properly in a situation in which there is anemia. So having reticulocytes in the blood in an anemic patient is a good thing. The hematocrit increasing from 19 to 36 is a good sign, too. The hematocrit is a measurement of the percentage of blood that is composed of red blood cells. Normal values for dogs vary some from laboratory to laboratory, but for most labs 32 to 50 is about normal. So your dog is no longer anemic at this time.

Histoplasma organisms likes to grow in areas in which there is contamination of the soil with bird droppings, or bat droppings, or where there is just a lot of bird droppings. If your dog likes to sniff around a potentially contaminated site, it would be good to discourage that. Sniffing around in animal burrows probably isn't a good thing, either.

It takes at least two months of treatment and usually more than that, to feel reasonably certain that histoplasmosis has been successfully treated. The recommendation is to treat for a month after it seems reasonably certain that the clinical disease is completely gone. That is a judgment call, so it is a good idea to monitor for weight loss, appetite, anemia, etc. at one to three month intervals for several months after stopping treatment.

It does sound like you are out of the woods at this point and that this is going to turn out OK. Your vet did do a good job to identify the disease and manage it well.

Mike Richards, DVM 12/27/2000

Fungal nose infection - Miconazole nitrate

Question: Dr. Richards,

I have a 5 year old cocker spaniel with a white scab on her black nose. The scab appeared approximately 6 months ago after we spread soil in our backyard for landscaping. My vet has done lab work and determined the scab is a result of a fungus. He prescribed miconazole nitrate lotion (1%) 3x's a day. The dog immediately licks off the medicine. The scab does not seem to be going away and I'm worried that the continued ingestion of the medicine could be toxic. Are there alternative treatments?

Thank you, Kim

Answer: Kim-

There are several topical agents that work well for dogs with ringworm infections (the most common skin fungi) that are localized to one or two spots. Miconazole is one of the most commonly recommended treatments and clotrimazole is the other one. These are available under a lot of different brand names. Lime sulfur dip and enilconazole shampoo are also helpful, but enilconazole is not available in the United States (it is available in Canada).

Topical treatment of ringworm does not always work, even when the problem is confined to one single spot. When this happens, griseofulvin and itraconazole (Sporonax Rx) are the most commonly recommended medications. It is usually necessary to treat for several weeks with itraconazole and for about two months with griseofulvin (Fulvicin Rx, others).

It might also be worth reconsidering the diagnosis if treatment continues not to work. Sometimes fungal infections of the skin occur because there is an underlying problem, such as an immune mediated disease (discoid lupus, phemphigus) and biopsy of the affected area might be necessary to find the underlying problem.

We have not seen problems when pets have ingested miconazole or clotrimazole even when we have been using it for some time but I am not sure that there are never problems. Mike Richards, DVM 12/4/2000


Question: Dear Dr. Mike,

My dog (Riah) appeared to have contracted blasto back in 11/99. It all started when she punctured her foot in the backyard and needed a couple of stiches in between her toes. The punture healed fine but she had developed a pocket on the back of her paw that kept getting bigger. After trying all sorts of antibiotics, that seemed to help, but never did the job, our vet went in and did exploratory surgery. He said there was some scar tissue and that he cleaned up the dead tissue and closed her paw up. Although her bloodwork never confirmed that she had blasto, our Dr. started her on Sporanox as a last resort. Since then her foot has gone back to it's normal size but it still hasn't completely healed. She has been on Sporanox for at least six months. Is the amount of time that has past normal for her injury? Or, do you think she may have something else? Any information you could provide would be extremely helpful. Thank you.

Sincerely, Paula

Answer: Paula-

Blastomycosis is normally acquired by inhalation of spores of this fungus, causing pneumonia and then spread to other areas of the body. However, there are reports of it occurring after injuries. Oddly enough, there are the same number of reports of this happening to veterinarians as there are occurrences in dogs, in the Veterinary Information Network ( -- a service for veterinarians only).

Usually itraconazle (Sporonax Rx) is given for about 2 months, or until there is no clinical evidence of the infection and then several more weeks. However, in almost all the reports of the blastomycosis from injuries, the itraconazole had to be given for six months or more and in one case (Marcellin-Little, et al, JAVMA 1996), the dog's leg was amputated to control the infection, although no other treatment was attempted due to the severity of the infection in the leg in that case. So I think that when this infection does occur due to an injury or as a primary skin infection, treatment must be necessary for a longer time, at least based on the reports that I can find (including the vets, who also required long term treatment).

It is supposed to be fairly easy to identify blastomycosis in a wound based on the presence of the yeast-like organism in the wound. But I don't practice in an area in which this disease is common, so I am basing this on what my books say and experience tells me that is sometimes different from what happens in real life.

Just based on the fact that blastomycosis from a wound is unusual, I think it is necessary to keep a high degree of suspicion that something else might be going on. Follow up X-rays to look for changes in the bone and soft tissue in the region might be a good idea or even consideration of another exploratory surgery, although I'm sure that everyone would like to avoid that, if possible. It might be possible to get a culture sample by aspiration of the wound and to also look for blastomycosis organisms in any aspirate that is obtained. If your vet is not comfortable looking for these (I wouldn't be) it is possible to send a smear from an aspirate to a clinical pathologist at one of the vet schools or at some laboratories.

Hope this helps some.

Mike Richards, DVM 9/20/2000


Q: Hi i am a vet tech and need info on Blastomycosis A.S.A.P. Pleas e-mail me anything you know. A client called because 3 dogs on her block had to be put dow because of Blasto. The owner would like to know what she should do to prevent her dog from getting it and how it's transferred. Thank you. Jennifer

A: Jennifer-

Blastomycosis is a fungal infection. It can affect both dogs and cats. Humans may also be infected by this organism. It is not a contagious illness, though. The fungus is not passed from an infected pet to an uninfected pet as occurs with viral illnesses and some bacterial illnesses. It is acquired from the environment. If more than one animal on your client's street have been infected with this organism it would be a good idea to see if there is some obvious source of infection involving disturbance of the soil, such as a construction site or a yard the dogs are digging in a lot. Most infections occur in dogs that live very close to a body of water and this disease is most common in the Southeast and the states around the Ohio and Mississippi rivers. It takes one to three months for signs of infection to occur after the organism has invaded a dog or cat's body.

Blastomycosis can cause respiratory signs such as difficulty breathing, tiring easily or coughing. It causes weight loss and depression pretty frequently. There may be lymph node enlargement and skin disease such as lumps in the skin or draining tracts in the skin. Lung X-rays are a good screening test for this condition because most dogs have radiographic evidence of fungal infection. Examination of any drainage from the lesions on the body may be helpful, too. Serum testing for antibodies to blastomycosis is also available.

If your client's dog runs free or lives in an outdoor kennel near the water, it is at a higher risk than if it is a housedog that is walked on a leash so that its opportunity to dig in inviting soil is restricted.

I will try to gather more information and put together a more detailed description of this condition for the web site but that may take a few days or so.

Mike Richards, DVM

Blasto - continued

Q: Thank you for the info. Is there anything the owner can do to treat the soil/yard? Does the animal ingest it (walking in soil and then licking feet) or does it penetrate their skin?


A: The systemic form of blastomycosis occurs after inhalation of the infective form (spores) of the fungus from a site of disturbed soil or decaying wood. If the spores penetrate the skin due to an injury or across a cut surface they can cause local skin infections.

I am not aware of a method of treating the environment for blastomycosis. I think that keeping the dog away from potential sources of infection is the only available option for limiting the chances of infection. Avoid areas of disturbed soil near water in areas where this fungus is common. This would include animal dens like groundhog holes, sniffing of animal feces because they can support fungal growth, sniffing of holes in trees or decaying stumps, staying away from road or building construction sites, rotting vegetation and other interesting decaying organic material. Walking a dog on a leash rather than allowing it to run free and keeping it inside if it likes to dig in the yard would both help to lower the possibility of infection.

Mike Richards, DVM Coccidioidiomycosis (Valley Fever)

Q: Dear Dr. Mike: Our dog was recently diagnosed with Coccidiomycosis (Valley Fever). It has attacked his bones, not his respiratory system. We have decided to try to treat the disease, as he is a much loved member of our family. I have a few questions. Is this disease contageous to other dogs or to humans? Will the disease affect his disposition (we have small children)? Are there other methods of treatment, besides medication that will help or speed up his recovery? Also, what are the chances of full recovery? His a large dog (about 70#), 4 years old, and in good physical condition outside this disease. Any answers or suggestions will be appreciated! Thanks, D.

A: I do not practice in an area in which coccidioidomycosis is a problem, so all the information I have on this condition is second hand. From what I can find the literature:

1) Coccidioidiomycosis is not spread from animal to animal, nor from human to human. It develops after inhaling the infective stage (arthrospores) of the fungus from a contaminated environment in almost all cases.

2) There can be central nervous system infection which seems like it definitely could lead to changes in personality but I have no way of knowing if or how frequently that occurs. I could find no reference to long term change in personality so I suspect this is not likely to be a problem.

3) It takes long-term therapy to rid the dog of this organism and some dogs may even require lifelong therapy but my impression is that most dogs can be cured or the infection at least controlled enough for them to do well.

4) You would have to ask your vet, who probably has experience treating this condition what other things he or she has found useful to help during the infection. Many times there are ancillary treatments that are helpful that vets who deal with a specific disease more frequently will know.

Mike Richards, DVM


Q: I have a golden lab I year old which has been diagnosed with a fungal infection in her nostril, suspected aspergillus. could you explain the infection and treatment for this problem.

A: Every time I have diagnosed Aspergillosis in a dog, I have been wrong. It does occur in them and it is sometimes a disease but it is also a common contaminant of cultures, many dogs have a positive titer and it doesn't always cause disease when it is present. German Shepherds are supposed to account for over 90% of the cases of this disease, apparently due to some sort of immune system problem. My best advice would be to make sure that this diagnosis is correct. I am pretty sure that the only way to be certain is a biopsy of the affected nasal passages. When we suspect this problem (and we do sometimes really suspect it), we send the dog or cat to a veterinary school with the capability of doing the necessary biopsies. However, we have the luxury of being within a reasonable travel distance of a veterinary school. So far, we have been suspicious mostly in older dogs or cats and almost every one of them turned out to have cancer affecting the nasal passages. Since your dog is young, this seems less likely and makes me think your vet is more likely to be correct in his or her diagnosis. Still, if it is reasonable to get biopsies (your vet may even have the equipment and expertise for this), I'd recommend it.

The major reason for being certain is that treatment is both difficult and expensive. Currently, the best treatment is thought to be clotrimazole (or itraconazole if it is available) instilled into the nasal cavity with a one hour contact time at the time of exploratory surgery or as a nasal flush through indwelling tubes for 10 days. This treatment is about 90% effective. Oral medications are effective in 50% or less of the cases of nasal aspergillosis according to the references I have.

Since the treatment is difficult, uncomfortable and somewhat expensive, you can see the need for a definite diagnosis prior to starting treatment.

Mike Richards, DVM

also see Canine Valley Fever


Michael Richards, D.V.M. co-owns a small animal general veterinary practice in rural tidewater Virginia. Dr. Richards graduated from Iowa State University's College of Veterinary Medicine in 1979, and has been in private practice ever since. Dr. Richards has been the director of the PetCare Forum...