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Microbiology
Table of Contents
Unit 21 Overview: Skin and Eye Infections
21.1 Anatomy and Normal Microbiota of the Skin and Eyes
21.2 Bacterial Infections of the Skin and Eyes
21.3 Viral Infections of the Skin and Eyes
21.4 Mycoses of the Skin
21.5 Protozoan and Helminthic Infections of the Skin and Eyes

🦠microbiology review

21.5 Protozoan and Helminthic Infections of the Skin and Eyes

Citation:

Acanthamoeba and Loa loa are two parasites that can wreak havoc on our skin and eyes. Acanthamoeba, a free-living amoeba, lurks in water and soil, causing nasty eye infections in contact lens wearers. It can even lead to brain infections in some cases.

Loa loa, the African eye worm, is spread by deer fly bites in West and Central Africa. It causes itchy swellings and can be seen moving across the eye. Both parasites pose unique challenges in diagnosis and treatment, highlighting the importance of proper hygiene and awareness in prevention.

Protozoan and Helminthic Infections of the Skin and Eyes

Life cycle of Acanthamoeba

  • Acanthamoeba is a free-living amoeba found in various environments
    • Commonly present in soil, dust, air, freshwater sources (lakes, rivers), tap water, and contaminated contact lens solutions
  • Two stages in life cycle:
    • Trophozoite (active, feeding stage) moves and feeds on bacteria, algae, and organic matter
    • Cyst (dormant, resistant stage) can survive harsh environmental conditions (desiccation, extreme temperatures)
  • Trophozoites transform into cysts under unfavorable conditions and revert back to trophozoites when conditions improve
  • Cysts are resistant to chlorine and other disinfectants commonly used in water treatment

Transmission and effects of Acanthamoeba

  • Transmission occurs through direct contact with contaminated water, soil, or surfaces
    • Swimming in or exposure to contaminated water sources (pools, hot tubs, lakes)
    • Improper handling or storage of contact lenses and use of contaminated lens solution
  • Can cause severe eye infections, particularly Acanthamoeba keratitis
    • Strongly associated with contact lens wear, poor hygiene practices (inadequate lens cleaning), and corneal trauma (abrasions)
    • Symptoms include severe pain, redness, blurred vision, light sensitivity (photophobia), and excessive tearing
    • May lead to corneal ulceration, visual impairment, or blindness if left untreated or misdiagnosed
  • Acanthamoeba can also cause granulomatous amebic encephalitis (GAE) and skin lesions
    • GAE is rare but often fatal, primarily affecting immunocompromised individuals (HIV/AIDS, organ transplant recipients)
    • Skin lesions may appear as nodules, ulcerations, or erythematous plaques resembling fungal or bacterial infections
  • Pathogenesis involves the organism's ability to adhere to host cells and secrete proteases, contributing to tissue damage

Loiasis symptoms and diagnosis

  • Loiasis is caused by the filarial nematode Loa loa, also known as the African eye worm
  • Symptoms:
    • Calabar swellings: localized, itchy, and painless subcutaneous swellings typically on extremities (arms, legs)
    • Eye worm: adult worm visible moving across the surface of the eye (subconjunctival space) causing irritation and discomfort
    • Generalized itching, fatigue, muscle aches, and joint pain
  • Diagnosis:
    • Identification of microfilariae in blood smears, typically during the day due to diurnal periodicity of microfilariae
    • Observation of adult worms in the eye or subcutaneous tissues during physical examination
    • Serological tests (ELISA) to detect antibodies against Loa loa antigens
    • Eosinophilia (elevated eosinophil count) may be present in blood tests
  • Immunology plays a crucial role in the host response to Loa loa infection, influencing symptom severity and disease progression

Treatment options for loiasis

  • Diethylcarbamazine (DEC) is the drug of choice for microfilarial clearance
    • Administered orally in divided doses over 2-4 weeks
    • Requires careful monitoring due to potential severe adverse reactions (encephalopathy) in individuals with high microfilarial loads
  • Albendazole or ivermectin may be used as alternative treatments, particularly in areas co-endemic with onchocerciasis or lymphatic filariasis
  • Surgical removal of adult worms from the eye (subconjunctival space) may be necessary to alleviate symptoms and prevent complications
  • Supportive care and management of symptoms (antihistamines for itching, pain relief for swellings)

Acanthamoeba vs Loa loa infections

  • Modes of infection:
    • Acanthamoeba: direct contact with contaminated water, soil, or surfaces (swimming, contact lens wear)
    • Loa loa: transmitted through the bite of infected deer flies (Chrysops spp.) in endemic areas (West and Central Africa)
  • Health risks:
    • Acanthamoeba:
      1. Eye infections (Acanthamoeba keratitis), potentially leading to visual impairment or blindness if untreated
      2. Granulomatous amebic encephalitis (GAE) in immunocompromised individuals, often fatal
      3. Skin lesions (nodules, ulcerations, erythematous plaques) mimicking fungal or bacterial infections
    • Loa loa:
      1. Calabar swellings (localized, itchy, painless subcutaneous swellings) on extremities
      2. Eye worm (adult worm visible moving in subconjunctival space) causing irritation and discomfort
      3. Generalized itching, fatigue, muscle aches, and joint pain
      4. Potential for severe adverse reactions (encephalopathy) during treatment with DEC in individuals with high microfilarial loads

Epidemiology, Transmission, and Global Health Impact

  • Vector-borne transmission is crucial for the spread of Loa loa, while Acanthamoeba is primarily acquired through environmental exposure
  • Zoonotic infections are less common in these diseases, but understanding animal reservoirs is important for control strategies
  • Parasitology research focuses on improving diagnostic techniques and developing new treatment options for both infections
  • Global health efforts aim to reduce disease burden through improved sanitation, education, and access to healthcare in endemic regions

Key Terms to Review (30)

Chlorhexidine: Chlorhexidine is an antiseptic agent used to reduce bacteria on the skin and mucous membranes. It is commonly used in healthcare settings for disinfection and sterilization purposes.
Contact lenses: Contact lenses are thin, curved lenses placed directly on the surface of the eyes to correct vision or for cosmetic reasons. They can create a favorable environment for microbial growth if not properly maintained.
Corticosteroids: Corticosteroids are a class of steroid hormones that reduce inflammation and modulate immune responses. They are often used in treating skin and eye infections caused by protozoan and helminthic pathogens to alleviate symptoms.
Diethylcarbamazine: Diethylcarbamazine is an antihelminthic medication used to treat infections caused by certain parasitic worms, including those affecting the skin and eyes. It works by paralyzing and killing microfilariae and adult worms.
Granulomatous amoebic encephalitis (GAE): Granulomatous amoebic encephalitis (GAE) is a rare but severe brain infection caused by free-living amoebae, such as Acanthamoeba spp. and Balamuthia mandrillaris. It primarily affects immunocompromised individuals and leads to chronic inflammation of the brain.
Ivermectin: Ivermectin is an antiparasitic drug used to treat various helminthic infections. It works by binding to glutamate-gated chloride channels in the parasite's nerve and muscle cells, causing paralysis and death of the parasite.
Loiasis: Loiasis is a parasitic infection caused by the filarial nematode Loa loa, commonly known as the African eye worm. It primarily affects the skin and eyes of humans.
Polyhexamethylene biguanide: Polyhexamethylene biguanide (PHMB) is a polymeric antimicrobial agent used for its broad-spectrum activity against bacteria, fungi, and viruses. It is commonly employed in medical and cosmetic applications, including wound care and contact lens solutions.
Transmissible spongiform encephalopathy: Transmissible spongiform encephalopathy (TSE) is a group of progressive, fatal neurodegenerative diseases caused by prions. These diseases are characterized by brain tissue damage that leads to sponge-like holes in the brain.
Chrysops: Chrysops is a genus of flies, commonly known as deer flies, that are vectors for the transmission of certain protozoan and helminthic infections affecting the skin and eyes. These biting flies are found worldwide and are known for their aggressive feeding behavior and ability to transmit diseases to humans and animals.
Zoonotic Infections: Zoonotic infections are diseases that can be transmitted from animals to humans. These types of infections are caused by pathogens, such as viruses, bacteria, parasites, and fungi, that are able to cross the species barrier and infect both animal and human hosts.
Parasitology: Parasitology is the study of parasites, their hosts, and the relationship between them. It encompasses the investigation of protozoan and helminthic (worm) infections that can affect the skin and eyes, as outlined in the topics 21.5 Protozoan and Helminthic Infections of the Skin and Eyes.
Acanthamoeba: Acanthamoeba is a genus of free-living, opportunistic protozoan parasites that can infect the skin, eyes, and central nervous system in humans. These amoebae are ubiquitous in the environment and can cause serious infections, particularly in individuals with compromised immune systems.
Acanthamoeba keratitis: Acanthamoeba keratitis is a serious eye infection caused by a free-living, opportunistic protozoan parasite known as Acanthamoeba. It primarily affects the cornea, the clear, dome-shaped front part of the eye, and can lead to severe vision impairment or blindness if left untreated.
Microfilariae: Microfilariae are the larval stage of filarial nematodes, which are parasitic worms that can infect the skin and eyes. These microscopic, thread-like larvae are a crucial part of the life cycle of these parasites and are responsible for the transmission and spread of filarial infections.
Global Health: Global health is an area of study, research, and practice that places a priority on improving health and achieving health equity for all people worldwide. It encompasses the transnational approach to health issues that transcend national boundaries, with a focus on the socioeconomic, political, and environmental determinants of health.
Loiasis: Loiasis is a parasitic infection caused by the filarial worm Loa loa, which is transmitted by the biting midge flies of the genus Chrysops. This infection primarily affects the skin and eyes, leading to various clinical manifestations.
Calabar swellings: Calabar swellings are localized, transient, and non-pitting edematous swellings that occur in certain parasitic infections, particularly those caused by filarial nematodes. They are an important clinical manifestation in the context of protozoan and helminthic infections of the skin and eyes.
Diethylcarbamazine: Diethylcarbamazine is a medication primarily used to treat certain parasitic infections, particularly those caused by filarial worms, which can lead to skin and eye-related diseases. It is an important drug in the context of protozoan and helminthic infections affecting the skin and eyes.
Encephalopathy: Encephalopathy is a general term that refers to any disease or dysfunction of the brain, often characterized by altered mental state, impaired cognitive function, and neurological abnormalities. It can have various underlying causes, including infections, toxins, metabolic disorders, and structural brain damage.
Vector-Borne Transmission: Vector-borne transmission refers to the mode of disease transmission where pathogens are carried and transmitted by living organisms, known as vectors, to human hosts. This mode of transmission is particularly relevant in the context of protozoan and helminthic infections affecting the skin and eyes.
Loa loa: Loa loa, also known as the African eye worm, is a parasitic nematode that infects humans and can cause a range of skin and eye-related conditions. It is primarily found in certain regions of West and Central Africa and is transmitted through the bites of infected deerflies.
African Eye Worm: The African eye worm, also known as Loa loa, is a parasitic nematode worm that can infect the eyes and subcutaneous tissues of humans. It is primarily found in tropical regions of West and Central Africa and is transmitted by the biting mango fly.
Granulomatous amebic encephalitis: Granulomatous amebic encephalitis (GAE) is a rare and severe infection of the brain caused by free-living amoebas, primarily Acanthamoeba species and Balamuthia mandrillaris. It typically affects individuals with compromised immune systems and can lead to progressive and often fatal inflammation of the brain and central nervous system.
Ivermectin: Ivermectin is a broad-spectrum antiparasitic medication used to treat various parasitic infections, including those affecting the skin and eyes, as well as helminthic infections of the gastrointestinal tract. It works by disrupting the nervous system of parasites, leading to their paralysis and eventual death.
Trophozoite: A trophozoite is the active, feeding, and replicating stage of a protozoan parasite that infects a host. It is the form of the parasite that is responsible for causing disease and symptoms in the infected individual.
Cyst: A cyst is a closed, membrane-bound structure that contains liquid, gaseous, or solid material. Cysts can develop in various parts of the body and are commonly associated with parasitic infections, particularly in the context of unicellular eukaryotic parasites, protozoan and helminthic infections of the skin and eyes, and protozoan infections of the gastrointestinal tract.
Albendazole: Albendazole is a broad-spectrum anthelmintic (antiparasitic) drug primarily used to treat infections caused by various types of parasitic worms, including those that can infect the skin, eyes, and gastrointestinal tract. It works by interfering with the structural integrity and function of the parasites, leading to their death and expulsion from the host's body.
Pathogenesis: Pathogenesis refers to the biological mechanisms by which a disease or disorder develops and progresses within a host organism. It encompasses the complex interplay between the pathogen and the host's immune system, leading to the manifestation of clinical symptoms and the establishment of the disease state.
Epidemiology: Epidemiology is the study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to the control of health problems. It is a fundamental science of public health that investigates the patterns, causes, and effects of diseases and other factors related to health in defined populations.