What is Coccidioides?

Coccidioides fungi are a type of soil-dwelling fungus that belong to the family Onygenaceae. They are known for their distinctive lifecycle and their ability to cause Valley Fever (coccidomycosis). Coccidioides fungi have a unique lifecycle that begins when the fungus grows as a filamentous mold in the soil. Under dry and dusty conditions, the fungus produces small, round structures called arthroconidia that can become airborne and be dispersed over large distances by wind. This dispersal mechanism allows Coccidioides fungi to colonize new areas and maintain their population in harsh environments.

Coccidioides Lifecycle

Soilborne
PhasePathogenic
Phase

Coccidioides Lifecycle

The lifecycle of Coccidioides fungi involves a soilborne phase where they exist as mycelium in the soil, and a pathogen phase where infectious arthroconidia, which are easily aerosolized, can be inhaled by hosts, leading to respiratory infection. The arthroconidia transform into spherules in the lungs, containing endospores that mature, rupture, and spread to cause dissemination of the infection in the host.

Soilborne

01 Septate Mycelium

Coccidioides fungi initially grow as septate mycelium in the soil. The mycelium consists of thread-like structures called hyphae that are divided by septa or crosswalls. These septa help to compartmentalize the mycelium and allow for efficient nutrient uptake from the environment. The septate mycelium of Coccidioides fungi grows in the soil and decomposes organic matter, playing a role in nutrient cycling and ecological processes.

Soilborne

02 Arthrospore Formation

When environmental conditions are favorable, such as during dry and windy periods, the septate mycelium of Coccidioides fungi undergoes a process called arthroconidiation. This process involves the formation of small, barrel-shaped arthroconidia. The arthroconidia are asexual spores that are released from the mycelium and can be easily aerosolized into the air or the surrounding environment. Arthroconidia are infectious and represent an important stage in the lifecycle of Coccidioides fungi, as they can potentially be inhaled by hosts and lead to respiratory infection.

Soilborne

03 Disarticulation

After the arthroconidia are formed, they are disarticulated or broken apart from the septate mycelium. This process allows the arthroconidia to be released into the air or the surrounding environment, where they can potentially come into contact with hosts. Disarticulation is a critical step that enables the arthroconidia to be dispersed and potentially transmitted to susceptible hosts, increasing the likelihood of respiratory infection.

Soilborne

04 Free Arthrospores

Once disarticulated, the arthroconidia become free arthrospores. These small, infectious spores are capable of dispersing in the air and may be inhaled by humans and other animals, leading to respiratory infection. The free arthrospores represent the infectious propagules of Coccidioides fungi and are responsible for the potential development of coccidioidomycosis or Valley fever, a respiratory infection caused by inhalation of the arthrospores.

Pathogenic

05 Inhalation

Inhalation of contaminated air is the primary route of infection for Coccidioides fungi, as they are typically found in soil and can become airborne when soil is disturbed, such as during construction, excavation, or other human activities. Once the arthrospores become airborne, they can be carried by air currents and inhaled into the respiratory system of humans or animals. Dogs may have increased susceptibility to inhalation of Coccidioides arthrospores due to their sniffing behavior, which can lead to direct inhalation of contaminated air from the ground or disturbed soil. Additionally, dogs may have a higher likelihood of digging or disturbing soil during activities such as play, hunting, or digging for food, which can increase their exposure to airborne arthrospores.

Pathogenic

06 Immature Spherules

After the inhalation of free arthrospores, Coccidioides fungi can establish an infection in the host's lungs. The arthrospores transform into larger structures called spherules, which are spherical structures containing endospores. These early spherules are referred to as immature spherules. They are typically found inside the host's lungs and are surrounded by host tissue.

Pathogenic

07 Mature Spherules

Pathogenic

08 Rupturing Spherules

As the endospores continue to develop inside the spherules, the spherules eventually rupture or burst open. This release of endospores from the ruptured spherules allows the endospores to be released into the surrounding tissue or bronchial tubes of the host's lungs. The rupturing of the spherules is an important step in the dissemination of Coccidioides fungi within the host and the potential spread of infection to other organs or tissues.

Pathogenic

09 Free Endospores

Once the spherules rupture, the endospores are released into the host's tissue or bronchial tubes. These free endospores can then potentially form new immature spherules and repeat the cycle of maturation, endosporulation, and rupture, allowing for further dissemination of the infection. Free endospores are the infectious propagules of Coccidioides fungi that can potentially establish new infections in different parts of the host's body or be spread to other hosts.