🦀 Common Blue Crab Diseases

Below are some of the most common diseases affecting blue crabs around the world.


Effects blood and nerve cells and can be fatal to crabs in 72 hours. Found in Chincoteague and Chesapeake bays.

Several species of Vibrio have been identified from blue crabs. In 1978 cholera outbreak in Louisiana was attributed to poor sanitary practices in home prepared blue crabs.


A type of fungus that infects the blue crab eggs.


A parasite that has been known to cause the pepper spot disease.

The haplosporidan hyperparasite Urosporidium crescens is responsible for the condition in blue crabs known as “buckshot” or “pepper” crabs.


A protozoa which infects muscle tissue. Found in the Gulf of Mexico and the Atlantic. Causes meat to be fluffy in texture.

Ameson michaelis is a microsporidan parasite of blue crabs commonly isolated from crabs in Gulf and Atlantic waters. The muscle tissue of heavily infected crabs has an opaque chalky appearance.


Also known as gray crab disease, Paramoeba Perniciosa is a protozoa that infects the crab’s tissues and blood and is widely found during the Springtime in the Atlantic and the Gulf regions.


A parasitic infestation which can be 100% fatal to young crabs and as much as 75% fatal to crabs in shedding pots.


A worm which infects almost 25% of sponge crabs in the Atlantic and the Gulf.

The parasite nemertean (Carcinonemertes carcinophila) infects gills and eggs of adult female blue crabs in high salinity regions while gills of male crabs are seldom infected. This parasite can be used as a spawning history indicator in blue crabs.


The branchiobdellid annelid Cambarincola vitreus also infects blue crabs from freshwater and low salinity habitats. These small worms (2-3 mm) inhabit the gill chambers and shell surfaces of blue crabs but apparently cause no harm to the crab.


The rhizocephalan barnacle (Loxothylacus texanus) is found only in the Gulf of Mexico. Cypris larvae infect juvenile crabs during early stages of the molting process. After a brief incubation period, an extensive “root” system develops within the crab, with an externa or sac protruding between the thorax and abdomen of the host. The externa contains male and female gonads and serves as a brood pouch for developing larvae. Rhizocephalan infection alters the secondary sex characteristics of the crab by causing the abdomen to appear as that of a mature female.


  • Leeches (Myzobdella lugubris) are common of blue crabs from low salinity waters.
  • Blue crabs are host to external and internal barnacles. External barnacles include Chelonibia patula and Balanus niveus that attach to the outer surface of the carapace and appendages. Barnacle fouling of mature female blue crabs is common; large numbers of heavily fouled, spent females occasionally litter beaches in the northern Gulf of Mexico. The gooseneck barnacle (Octolasmis muelleri) is found on gills and in gill chambers and may impede respiration.

The Primary Causes

Water temperature, ecological conditions, and salinity all effect outbreaks of various crab diseases. Many of these diseases are passed from crab to crab as they feed upon one another, mate and generally interact and some infected crabs can become blind or paralyzed. Host crab populations have been infected in the Bay, California, British Columbia, Alaska, Scotland and the across the Atlantic seaboard.