5. Toxocariasis, Onchoceriasis, Histoplasmosis - Systemic Disease Fall 2026

What are the FUNGAL/PARASITIC infections learned this semester?

-Toxoplasmosis

-Toxocariasis

-Onchocerciasis

-Histoplasmosis

Toxocara canis is a roundworm in ____

dogs

Toxocara cati is a roundworm in ___

cats

What is the mode of transmission of Toxocariasis?

-Ingestion of dirt contaminated with parasite eggs from dog or cat excrement

-Ingestion of food from infected soil

Toxocariasis is more common in what areas?

warm, humid, climates where eggs can survive longer in the soil

____% of the population has evidence of Toxocariasis infection

6.5

_____% of children have evidence of Toxocariasis infection

30

____ are particularly susceptible to infection (80%)

Puppies

Epidemiology of Toxocariasis (Pic)

Epidemiology of Toxocariasis (Pic)

The systemic infection of Toxocariasis is known as what?

visceral larva migrans

What is the avg age of infection of visceral larva migrans?

under age 2yo

Describe the affect of visceral larva migrans

Many organs are affected but often benign and subclinical.

Fever, cough, wheezing, enlarged spleen/liver

What are the ocular signs/symptoms of Toxocariasis (Ocular larva migrans)?

-unilateral

-white focal granuloma

-peripheral inflammatory mass

-retinal folds

When do children typically develop ocular larva migrans?

around age 7 yo

What is the diagnosis of Toxocariasis based on?

-Clinical signs

-Hx of exposure to dogs

____ test can be used to detect Toxocara antibodies in the blood and confirm infection

ELISA

What is the treatment for toxocariasis?

-Antiparasitic drug: Albendazole, Mebendazole

-Corticosteroids

-Systemic steroids & Antiparasitic therapy for ocular cases

-Deworming pets

-Good hygiene

Onchocerciasis is a ____ infection

parasitic

What is the parasite responsible for Onchocerciasis infection?

Onchocerca volvulus

What is the mode of transmission of Onchocerciasis?

-Vector borne and spread through bite of infected female blackflies

-Flies breed near fast flowing rivers and streams "river blindness"

-Larvae migrate to subcutaneous tissues and eyes and mature

Is there any person to person transmission of Onchocerciasis?

No -- requires the blackfly as a vector of transmission

Where is Onchocerciasis endemic to?

-Sub-Saharan Africa (99% of cases)

-Central and South America

Who is infected by Onchocerciasis?

People living or working near fast-flowing rivers where blackflies breed. Rural farming or fishing communities

What are the signs/symptoms of Onchocerciasis?

-Subcutaneous nodules (onchocercomas)

-Severe itching

-Chronic dermatitis

-Lymphadenopathy

-Fever, malaise, and weight loss in chronic disease

What do the cutaneous nodules (onchocercomas) of Onchocerciasis contain?

adult worms, often on the scalp, trunk, neck, or limbs

What is the appearance of chronic dermatitis?

Thickened, depigmented "leopard skin" appearance of the skin

What is the cause of ocular signs/symptoms of Onchocerciasis?

Live larvae in the cornea, vitreous, and anterior chamber

What are the ocular signs/symptoms of Onchocerciasis?

-Keratitis

-Anterior uveitis

-Chorioretinitis/Optic neuritis/Atrophy

-VF defects and blindness

-Bilateral involvement common in long-standing cases

What is the appearance of punctate keratitis d/t Onchocerciasis?

snowflake opacities

What is the appearance of sclerosis keratitis d/t Onchocerciasis?

Progressive scarring ---> corneal opacification and vision loss

What is the treatment for Onchocerciasis?

-Ivermectin 12mg (every 6-12 months to prevent reoccurrence)

-100 to 200mg Doxycycline

-Nodulectomy (Remove the onchocercomas to reduce larvae load)

-Manage the signs/symptoms with topical corticosteroids and cycloplegics for uveitis

-Manage pruritis

Histoplasmosis is a ____ infection

fungal

What is the fungus responsible for Histoplasmosis?

Histoplasma capsulatum

Histoplasma capsulatum is a ____ fungus

dimorphic (mold, yeast)

What is the mode of transmission of Histoplasmosis?

-Carried by birds or bars and grows in soil enriched with bird/bat droppings

-Inhalation of spores after contaminated soil or droppings are disturbed

Is there any person to person transmission of Histoplasmosis?

No -- only environmental

Transmission of Histoplasmosis

Fungus will pass through ___ and ___

birds and bats

Transmission of Histoplasmosis

Bird and bat ___ will contain the fungus

droppings

Transmission of Histoplasmosis

Fungus will grow into mold in the soil which will produce ____

spores

Transmission of Histoplasmosis

Disruption of the soil will cause what?

The spores to become aerosolized

Transmission of Histoplasmosis

Where are the spores inhaled into?

The lungs of humans

Transmission of Histoplasmosis

In the lungs, what do the spores convert into?

yeast

Transmission of Histoplasmosis

Yeast will spread where in the body?

through the lymphatic system and blood

Transmission of Histoplasmosis

Can Histoplasmosis remain dormant?

Yes for years

Histoplasmosis is endemic to where?

The Ohio-Mississippi River Valley

Histoplasmosis Epidemiology Worldwide (Pic)

Histoplasmosis Epidemiology Worldwide (Pic)

More than 90% of cases of Histoplasmosis is ______

asymptomatic

Describe Asymptomatic Histoplasmosis

-Positive skin test or chest Xray

-Incidental finding

-Dormant in the lungs

Is Primary Acute Histoplasmosis Common?

No -- infants/children and immunocompromised

What are the symptoms of Primary Acute Histoplasmosis?

Flu like symptoms that resolve in 2-3 months with no residual effects

Who is affected by Disseminated Histoplasmosis?

Immunocompromised individuals

Describe Disseminated Histoplasmosis

-Multiple organ involvement

-Pulmonary inflammation, inflammation of lymph nodes and spleen, adrenal gland insufficiency, anemia, ulcerations of the tongue and mouth, and meningitis possible

Disseminated Histoplasmosis will be ____ if untreated

fatal

What is the classic triad of Presumed Ocular Histoplasmosis Syndrome?

-Histo spots

-Peripapillary atrophy

-Maculopathy

What are Histo spots?

multiple small chorioretinal scars throughout the retina

What is the cause of vision loss in Presumed Ocular Histoplasmosis Syndrome?

Maculopathy (+/- CNV)

You will need ___/3 of the classic triad to diagnose Ocular Histoplasmosis

2

POHS - Histo Spots and PPA (Pic)

POHS - Histo Spots and PPA (Pic)

Maculopathy with Histoplasmosis will occur in ____% of patients with POHS

< 3

When does maculopathy occur in patients with POHS?

When the fungus is inhaled early in life

Describe Maculopathy of Histoplasmosis and how it can lead to vision loss over time...

Macular lesions reactivate 10-30 years later in life within the choriocapillaris and grow through existing breaks in Bruch's membrane --> subretinal hemorrhage ---> vision loss

What are the symptoms of maculopathy of POHS?

-Metamorphopsia

-Blurred/decreased vision

-Scotoma

What are the tests used in the diagnosis of Histoplasmosis?

-Histoplasma antigen detection

-Serology testing

-Culture

What does Histoplasma antigen detection test for?

Active disease

What does serology testing for Histoplasmosis test for?

prior exposure

Culture of what tissue can be used for Histoplasmosis testing?

sputum, lungs

What is the gold standard test for Histoplasmosis testing?

culture from respiratory sample

What is the downside of using culture from respiratory sample for diagnosis of histoplasmosis?

slow (5days - 6 weeks)

Histoplasmosis is a _____ diagnosis

Clinical -- the systemic tests will supplement the clinical dx

What are the tests that can detect CNV?

OCT/OCTA/FA

Most of the time Histoplasmosis is _____

self limiting

What are the treatment options for Histoplasmosis?

-Antifungal agents (Oral Itraconazole, IV Amphotericin B)

-Corticosteroids to reduce inflammation in the lungs and other tissues

What is the eye exam schedule for a patient with Histoplasmosis?

-Monitor annually with DFE if no macular changes (get baseline fundus photos)

-Monitor every 6 months if there are macular changes and consider OCT/OCTA

Can anti-VEGF injections be used for patients with CNV d/t Histoplasmosis?

yes

Patients with macular changes d/t Histoplasmosis should be provided with what?

Amsler grid