Mycobacteria is not new to the Chesapeake Bay and poses no health risks if
simple precautions are followed when handling, transporting, preparing and
consuming striped bass (rockfish). Outlined below are frequently asked questions
regarding mycobacteria and striped bass.
MYCOBACTERIA AND STRIPED BASS (ROCKFISH)
What is fish mycobacteria?
Mycobacteriosis is an infectious disease caused by bacteria in the genus
mycobacterium. These species of “marine mycobacteria” such as
mycobacterium marinum and chelonae are ubiquitous in the environment.
Newly identified species such as mycobacterium chesapeaki and
schottsii have only been described from the Chesapeake Bay. At least 10
species of mycobacteria have been isolated from striped bass lesions.
How does mycobacteriosis affect fish?
Mycobacteriosis is a bacterial infection that results in inflammation, tissue
destruction and formation of scar tissue in one or more organs. Signs of
infection are first noted in internal organs such as the spleen and kidney.
Nodules (called granulomas) composed of inflammatory cells and fibrous
connective tissue form in response to the bacteria in an attempt to stop the
infection. An increase in the number and size of granulomas leads to the
formation of extensive scar tissue and eventual loss of normal tissue
architecture. This disease progresses slowly in fish and has been characterized
as a “wasting disease” due to loss of body mass and emaciation. It is not known
how many fish die or if any fish recover from this disease in the Chesapeake
Bay.
Are the signs of mycobacteriosis in fish always externally visible?
No. Mycobacteriosis in fish is generally first found in internal organs. In mild
cases of this disease signs of infection may only be evident microscopically. As
the disease progresses additional internal organs may show signs of disease. In
severe cases virtually all organs and tissue are affected including the skin and
muscle. Mycobacteria have been isolated from young-of-year striped bass but no
visible signs of disease have been found. Infected 1- and 2-year-old fish
typically exhibit mild to moderate signs of the bacteria. However 3- to
5-year-old fish have the highest incidence of mycobacteriosis, and occasionally
exhibit severe infections, including emaciation and scar tissue formation on the
skin. It is important to note that striped bass are susceptible to other viral,
bacterial and parasitic infections; therefore not all striped bass with lesions
on the skin have mycobacteriosis.
How many fish are affected ?
The Maryland Department of Natural Resources (DNR) and Maryland Department of
Agriculture's Animal Health Laboratory at College Park first diagnosed
mycobacteriosis in the Chesapeake Bay in 1997. This prompted a Bay-wide striped
bass health assessment survey that continues today.
Currently, DNR surveys indicate that as many as 60 percent of striped bass in
the Chesapeake Bay have this disease. This infection rate has more than doubled
since 1998 when this survey began. Fish are probably exposed to these bacteria
early in life with infection rates increasing with age: 11 percent in
1-year-olds and 60 percent in 3- to 5-year-olds. Differences in reported
prevalence of mycobacteriosis may be due to variation in diagnostic techniques
employed.
Is mycobacteriosis specific to a certain region of the Bay?
No differences in infection rates have been detected between males or females;
between the upper, middle and lower Chesapeake Bay; or between fish caught from
pound nets vs. those captured by hook and line.
Are certain species more prone to
mycobacteriosis?
Mycobacteriosis has been documented in more than 160 species of fresh and
saltwater fish worldwide. However, there is no evidence that mycobacteriosis is
common in any Chesapeake Bay species other than striped bass. In 2001 surveys
were conducted with white and yellow perch and so far no fish were found with
the disease. Additional species will be added to this survey in the future.
What is the DNR doing about
mycobacteriosis?
DNR, along with state and federal partners, initiated a health survey of striped
bass in 1998. This general health survey involved collections of striped bass
from the lower, middle and upper Chesapeake Bay including numerous tributaries,
and was designed to identify problems in the population. Complete examinations
were performed on these fish and samples were processed for microbiology
(pathogen identification), histopathology (visible signs of disease at the
cellular level), nutritional status and parasite load. Results indicated that
the disease of concern was mycobacteriosis and that the infection rates were
rising. In addition to mycobacteriosis, resident fish also exhibited ulcers or
areas of hemorrhage on the skin, termed "ulcerative dermatitis syndrome" or UDS.
Starting in 2003, DNR and its partners began a more detailed study of
mycobacteriosis in striped bass, involving younger age classes of resident fish
as well as migratory fish. Fish from all areas of the Bay are being examined.
Experiments are underway to determine how this disease is transmitted to fish.
In addition, fisheries managers are taking a close look at the population
structure to determine what population level affects may be evident. DNR and its
partners (NOAA, USGS, VIMS and UMD) are currently planning a conference to
discuss current state of knowledge and future research concerning
mycobacteriosis.
Chesapeake striped bass migrate from Maine to North Carolina and their catch is
controlled by very tight quotas in the Atlantic states. Population numbers
remain high, and to date, scientific analyses have not shown an increase in the
number of stripers dying of natural causes; any kind of disease would be
considered a natural cause. Fisheries managers in all the coastal states are
continually monitoring catches and collecting data that would detect an increase
in mortality associated with mycobacteriosis.
HUMAN HEALTH CONCERNS ASSOCIATED WITH MYCOBACTERIA
Can humans get mycobacteria?
Yes. mycobacteriosis is zoonotic, which means it can be transmitted to humans.
Mycobacteriosis is also called "fish handler's disease" because of cases
involving people associated with fish hatcheries, aquaculture facilities and the
aquarium industry.
What is fish handler's disease?
Fish handler's disease is the human form of mycobacteriosis. It is contracted
through direct contact with infected fish or water.
How are humans affected?
Infections in human are generally limited to the extremities such as fingertips
and feet, but may involve the joints, bones and lymph nodes. Individuals with
cuts or scrapes are at higher risk for infection. The most frequent symptom is
the formation of a persistent bump or nodule under the skin. Additional symptoms
may include the formation of ulcers, swelling of lymph nodes and joint pain.
This disease can be treated with antibiotics. A health care provider should be
contacted if any of the above symptoms develop following direct skin contact
with fresh or salt water or after handling or processing fish. If you have any
questions or general concerns, please contact a health care provider.
How can anglers and fish handlers protect themselves?
Individuals that handle striped bass should wear heavy gloves (made of leather
of heavy cotton) and boots to avoid puncture wounds from fish spines, and wash
hands thoroughly after handling or processing striped bass. Open cuts or scrapes
on hands and arms should be thoroughly cleansed and bandaged. Again, this
disease can be treated with antibiotics, and any persons with questions or
concerns should contact a physician.
FISH PREPARATION AND CONSUMPTION
Can I get mycobacteria from eating a “tainted” rockfish?
A recent check of the published medical studies on this kind of infection in
human beings shows that eating properly prepared and cooked rockfish has not
been associated with human mycobacterial illness. DHMH recommends that people
not consume any raw rockfish or any fish that appears diseased.
Should I be concerned about preparing rockfish?
No. Use common sense when preparing your fish fillet. Fish with open, reddened
lesions on the body or with signs of hemorrhage or darkened patches in the
fillets should be discarded. Fish that appear to be healthy and are properly
cooked are safe to eat. DHMH recommends that people not consume any raw rockfish
or any fish that appears diseased.
While handling an infected rockfish, especially if the skin is cut or scraped,
can lead to skin infections, simple hygiene precautions can prevent this.
Should I be concerned when handling raw fish?
When handling any type of fish, use a few practical and simple precautions:
- If cuts, scrapes or other open or inflamed areas of the skin are present,
cover hands and wrists with an impermeable barrier (like a rubber or vinyl
glove) to prevent any bacteria from getting into the soft tissue under the
skin where mycobacterium marinum organisms are known to cause infections.
- Dispose of any leftover fish parts after preparing raw fish. Wash off all
cutting boards, surfaces, knives and other utensils used to process raw fish
with warm soapy water and rinse thoroughly.
- Stop any infections early. If red, itchy or ulcerated bumps appear on the
skin -- especially on the hands and forearms -- after processing or handling
fish, contact a health care provider. Those with underlying medical problems,
including a weakened immune system, should also contact a health care
provider.
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