Infectious Disease and Microbiology – Mansonella Species

Overview

Mansonella species are filarial nematodes that cause human infections collectively known as mansonellosis. Important human species include Mansonella ozzardi, M. perstans, and M. streptocerca.

Compared with several other filarial infections, Mansonella infections are generally milder and frequently asymptomatic. When symptoms occur, manifestations may include pruritus, dermatitis, hypopigmented skin lesions, edema, arthralgia, and nonspecific systemic symptoms.

Classification

Genus: Mansonella

Species:

• M. ozzardi

• M. perstans

• M. streptocerca

Type: Filarial nematode

Disease: Mansonellosis

Microbiologic Characteristics

Mansonella species are tissue-dwelling filarial nematodes.

Their life cycle involves:

Adult worms

↓

Production of microfilariae

↓

Microfilariae present in blood or skin, depending on species

↓

Uptake by an arthropod vector

↓

Development of infective larvae

↓

Transmission to another human during a subsequent bite

Incubation Period

The incubation period is:

Not clearly established

Because these infections may remain asymptomatic for prolonged periods, the interval between infection and recognizable disease can be difficult to determine.

Transmission

Mansonella species are transmitted by small biting insects.

Important vectors include:

Biting midges (Culicoides)

and, for some transmission cycles:

Blackflies (Simulium)

The specific vector differs according to the Mansonella species and geographic region.

Mansonella ozzardi

Epidemiology

M. ozzardi occurs primarily in:

• Central America

• South America

• West Indies/Caribbean

It is therefore predominantly a parasite of the:

New World

Clinical Manifestations

Many M. ozzardi infections are asymptomatic.

Symptomatic patients may develop:

• Fever

• Headache

• Pruritus

• Arthralgia

• Lymphadenopathy

• Eosinophilia

• Nonspecific skin manifestations

Microfilariae

The microfilariae of M. ozzardi circulate primarily in:

Peripheral blood

This makes examination of blood an important diagnostic approach.

Mansonella perstans

Epidemiology

M. perstans occurs predominantly in:

West and Central Africa

and has also historically been reported in parts of:

South America

Its true geographic distribution may be broader than recognized because many infections are asymptomatic or minimally symptomatic.

Clinical Manifestations

M. perstans infection is often asymptomatic but may produce:

• Pruritus

• Angioedema

• Fever

• Headache

• Arthralgia

• Abdominal discomfort

• Eosinophilia

Adult worms characteristically inhabit:

Serous body cavities and connective tissues

Microfilariae

M. perstans microfilariae circulate in:

Peripheral blood

Unlike Loa loa, their detection is not characterized by the same classic daytime periodicity.

Mansonella streptocerca

Epidemiology

M. streptocerca occurs predominantly in:

West and Central Africa

Clinical Manifestations

This species is particularly associated with:

Cutaneous disease

Possible manifestations include:

• Pruritic dermatitis

• Hypopigmented lesions

• Papular skin lesions

• Skin thickening

Because of its cutaneous manifestations, infection may resemble:

Onchocerca volvulus infection

Microfilariae

Unlike M. ozzardi and M. perstans, the microfilariae of M. streptocerca are primarily found in:

Skin

This distinction is especially important diagnostically.

Species Comparison

M. ozzardi

→ Central/South America and Caribbean

→ Microfilariae mainly in blood

M. perstans

→ Primarily Africa

→ Adult worms associated with body cavities

→ Microfilariae in blood

M. streptocerca

→ West/Central Africa

→ Cutaneous disease

→ Microfilariae primarily in skin

Clinical Infection

Overall, mansonellosis is generally considered:

Milder than many other filarial infections

A substantial proportion of infected individuals remain:

Asymptomatic

Dermatologic Disease

The source particularly emphasizes:

Hypopigmented pruritic dermatitis

This is especially relevant to M. streptocerca infection.

Patients may experience:

• Itching

• Hypopigmentation

• Papular eruptions

• Chronic localized dermatitis

Diagnosis

Diagnosis depends on the infecting species and may involve:

• Examination for microfilariae

• Skin biopsy or skin snip

• Peripheral blood examination

• Histopathology

• Serology

Blood Examination

For:

M. ozzardi

and

M. perstans

microfilariae can be detected in:

Peripheral blood

Microscopic examination of appropriately prepared blood specimens may establish the diagnosis.

Skin Examination

For:

M. streptocerca

microfilariae are primarily detected in:

Skin specimens

Histopathologic examination or examination of skin tissue can therefore be useful.

Serology

The source also lists:

Serologic testing

However, serologic assays may demonstrate cross-reactivity with other filarial infections and may not always identify the exact Mansonella species.

Treatment

The source describes a historical regimen of:

Diethylcarbamazine (DEC)

with:

50 mg on day 1

↓

100 mg on days 2 and 3

↓

50 mg every 8 hours for 3 weeks

Treatment response varies substantially among Mansonella species, so therapy should be considered species-specific rather than assuming that one regimen is equally effective for all mansonellosis.

Additional Treatment

The source identifies a possible role for:

Doxycycline

Doxycycline can be useful against filarial parasites that depend on intracellular bacterial endosymbionts called:

Wolbachia

Reduction of Wolbachia can impair the survival and reproduction of susceptible filarial worms.

Its usefulness varies among Mansonella species.

Prevention

Prevention primarily involves reducing exposure to biting insect vectors.

Measures include:

• Protective clothing

• Insect repellents

• Screening or other barriers when appropriate

• Avoiding heavy exposure to biting midges and blackflies in endemic areas

Mansonella vs. Loa loa

Mansonella

→ Biting midges/blackflies

→ Usually mild or asymptomatic

→ Blood or skin microfilariae depending on species

→ M. streptocerca causes pruritic dermatitis

Loa loa

→ Chrysops deer fly

→ Calabar swellings

→ Subconjunctival “eye worm”

→ Diurnally periodic blood microfilariae

Mansonella streptocerca vs. Onchocerca volvulus

M. streptocerca

→ Microfilariae in skin

→ Pruritic/hypopigmented dermatitis

→ Usually relatively mild

Onchocerca volvulus

→ Microfilariae in skin and ocular tissues

→ Severe pruritic dermatitis

→ Subcutaneous nodules

→ Ocular disease

→ River blindness

High-Yield Clinical Pattern

Patient from a filariasis-endemic region

• ●

Mild or asymptomatic infection

• ●

Pruritic or hypopigmented dermatitis

• ●

Microfilariae in blood or skin depending on species

→ Think Mansonella species

Exam Essentials

Genus: Mansonella

Type: Filarial nematode

Disease: Mansonellosis

Major species: M. ozzardi, M. perstans, M. streptocerca

M. ozzardi geography: Central/South America and Caribbean

M. perstans geography: Primarily Africa, with historical South American distribution

M. streptocerca geography: West and Central Africa

Vectors: Biting midges and, in some transmission cycles, blackflies

Typical severity: Usually mild or asymptomatic

Skin manifestations: Pruritus and hypopigmented dermatitis

M. ozzardi microfilariae: Blood

M. perstans microfilariae: Blood

M. streptocerca microfilariae: Skin

Diagnosis: Blood examination or skin examination depending on species, histopathology, supportive serology

Source treatment: Diethylcarbamazine

Additional treatment: Possible role for doxycycline

Prevention: Avoid bites from transmitting insects

Key clinical pearl: The most useful distinction among Mansonella species is where the microfilariae are found: M. ozzardi and M. perstans are primarily detected in blood, whereas M. streptocerca is primarily detected in the skin and can produce a pruritic, hypopigmented dermatitis resembling mild onchocerciasis.