Mansonellosis or Mansonelliasis, as it is also known, is infection with parasites of the genus Mansonella. There are three species of these nematodes and they are three of the eight members of the filarial parasites. These roundworms are unsheathed and have a round, enlarged anterior end and a smooth cuticle. They are mainly found in central and western Africa, South America, and the Carribean and transmitted by Culicoides midges or Simulium blackflies. Unlike infection with some of the other filarial parasites, Mansonellosis does not cause lymphatic filariasis, so it is much less pathogenic.
The three types of mansonellosis are M. ozzardi, M. perstans, and M. streptocerca. Adult Mansonella worms live in tissues, body cavities, or in the dermis and the females produce microfilaria which migrate in the blood or skin and can survive there for 3-36 months. When the vector takes a blood meal, it injests microfilarae, which go on to develop into infective filariaform in the vector and can infect the next blood meal victim.
M. ozzardi is the only one of the three that is specifically a human parasite and has two vectors and thus two biological forms. It was the first described and found in Guyana in the late 19th century. This parasite lives in subcutaneous tissues.
M. perstans (African fever, filariasis hives) adult parasites live in body cavities and larval forms are released into the blood. It is found in humans, apes, gorillas, and chimpanzees but is usually nonpathogenic. However, some symptoms may occur and are described below. This mansonellosis is also known as Acanthocheilonema perstans, Dipetalonema perstans, and Filaria perstans.
M. streptocerca (African fever, skin swillellings) is found in people and in chimpanzees in the skin. Since the microfilariae are found both in the blood and skin and causes skin rashes, it is sometimes confused with Onchocerca volvulus. However, the eye is never affected in M. streptocerca. The disease is also known as Acanthocheilonema streptocerca and Dipethalonema streptocerca.
Knowing how to differentiate the mansonella parasites from lymphatic filariasis like W. bancrofti, L. loa, and O. volvulus is important since all of these parasites overlap in geographical areas and it is important to treat the more pathogenic ones appropriately.
TaxonomyKindgom: Animalia Phylum: Nematoda Class: Secernentea Subclass: Spiruria Order: Spirurida Suborder: Spirurina Superfamily: Filarioidea (filards)
Family: Filariidae Genus: Mansonella Species: ozzardi, perstans, or streptocerca
Morphology
M. ozzardi microfilaria: This microfilaria was identified with a blood smear. M. ozzardi microfilaraie are 170-240 mm long, unsheathed, and have a slender, clear, tapered tail called a "button hook." The nuclei do not extend to the end of the tail. The microfilaria are distinguished from M. perstans by their sharp, pointed tail.
M. perstans microfilaria: The microfilaria measures about 100-200 mm long and 3.5-4.5 mm wide. It is unsheathed and has a blunt tail with nuclei extending through the end of the tail. Adults are white and thread-like. Females adults are longer and can grow up to 8 cm long. The tail is half a coil in females and a full coil in males.
M. streptocerca microfilaria: This microfilaria (180-240 micrometers long) is pictured after a skin snip. Microfilariae are numerous in the upper dermis. It is unsheathed, has a linear body, a "sherperd's crook" coiled tail, and nuclei extending in a single row to the end of the tail. Adult worms live in dermal collagen and are thin, with females being longer than males (27 and 17 mm, respectively). The tip of their tail is bifid, not blunt and they make shimmering and stretching movements.
Transmission
Culicoides Midges: These vectors transmit M. ozzardi, M. perstans, and M. streptocerca in Central and South America and in the Caribbean islands. The primary vectors are C. austeni and the day biting C. grahamii.
Cedar Creek Natural History image http://cedarcreek.umn.edu/insects/album/029022005ap.html
Symptoms
Mansonelliasis is difficult to diagnose because it is usually asymptomatic. When symptoms are noticeable they are variable and only seen when worms or microfilariae die. Often encountered symptoms include headache, coldness of the legs, pruritus, and articular swelling. In most cases eosinophilia is present, but this characteristic is not specific for Mansonelliasis. The specific symptoms possible for each type of mansonellosis are described below (emedicine.com).
M. ozzardi is associated with joint pains, headaches, coldness of the legs, adenopathy, pruritic and maculopapular skin lesions, fever, pulmonary symptoms, hematomegaly, and peripheral eosinophilia. The clinical symptoms are nonspecific, so a person is unlikely to know infection is present and the diagnosis is difficult.
M. perstans symptoms depend on location. In Africa it is associated with subcutaneous swellings of the arms, shoulder, and face, including periorbital edema called "Kampala" or "Ugandan eye worm" that is found when the adult worm invades and degrades in the periorbital connective tissues, causing edema and granulomas (Bregani 2002). Abdominal pain, pruritus, hives, fever, headaches, and intense eosinophilia are also common. It may cause arthralgias and fever. In South America bone and joint pains, lymphadenitis, and hydrocele are seen. *Image belongs to emedicine and can be found at http://www.medicine.mcgill.ca/tropmed/txt/lecture5%20filaria%20and%20schisto.htm
M. streptocerca symptoms are similar but less severe than those seen in onchocerciasis. When the worm is alive it is asymptomatic, but when it dies the most common skin manifestation is chronic itching dermatitis and skin thickening in the torso. Hypopigmented macules (1-3 cm in diameter, see picture), dizziness and inguidnal adenopathy also occur. Adult worms do not cause a skin reaction while alive, but when they die there is abscess formation or granuloma that leads to a pruritic rash. *Image belongs to emedicine.com and can be found at <www.emedicine.com/derm/topic888l.htm>
Life CyclesWhen the appropriate vector (black fly or midge), takes a blood meal from an infected person, it ingests microfilarie, which develop into infective larvae in the vector's gut. When the larvae reach infective stage (1-2 weeks) they migrate to the vector's head or proboscis. During the next blood meal, the infective larvae enter the skin through the bite wound. They then develop to adults (about 1 year) and reside in a person's subcutaneous tissues (M. ozzardi), a body cavity (M. perstans), or the dermis (M. streptocerca) where female worms release nonperiodic microfilaria into the bloodstream (M. ozzardi and M. perstans) or skin (M. streptocerca). The illustrations below explain the lifecycles in more detail.
M. ozzardi adults live in the mesenteries and visceral fat, releasing unsheathed microfilariae into the blood. Humans are the only known definitive hosts.
The microfilarae of M. streptocerca are found primarily in the skin but also in the blood.The incubation period after infection is about 3-4 months. These images belong to the CDC Division of Parasitic Disease. They can be found at http://www.dpd.cdc.gov/DPDx/HTML/Filariasis.htm
Laboratory Diagnosis is the most practical method of diagnosing the three types of Mansonelliasis. By using a microscope to examine a blood sample, the microfilariae of M. ozzardi and M. perstans can often be identified. Since the microfilariae are not periodic, periodicity is not a factor in taking the blood sample. To perform this technique a thick smear stained with Giemsa or hemtoxylin and eosin may be used.
Another method of laboratory diagnosis includes examining a skin snip, which is particularly helpful in finding the dermis-residing M. streptocerca. The skin snips can be taken with a corneal-scleral punch or a scalpel and needle. The snips are then incubated in saline or an appropriate medium and then examined for microfilarae. With either laboratory technique, the parasites must be identified correctly, so close examination by an expert who can differentiate microfilaria is necessary for proper diagnosis.
In a recent study, M. streptocerca was detected in skin biopsies by molecular diagnosis using a nested PCR Assay (Fischer 1998).
Antibody detection is useful in detecting parasitic infection since some filaria and helminths have cross reactivity, but the test does not differentiate between past or current infection or type of parasite (CDC 2004).
Finally, travel history and eosinophilia count are also useful in diagnosing parasitic presence, but this information is also not specific to Mansonellosis.
TreatmentBecause Mansonellosis is often asymptomatic, only those who present with symptoms (usually due to adult worm) have treatment options. However, because infections often remain untreated or are non-pathogenic, there is no set standard, and studies do not agree on doses. Thus, general information is described below.
Diethylcarbamazine (DEC) has no effect on M. ozzardi, while Ivermectin has worked in a single 200 mcg/kg (Abramowicz 2004). However, prognosis is good even without treatment.
When M. perstans is treated, the drug of choice is Albendazole (400 mg twice a day for ten days) or Mebendazole (100 mg twice a day for 30 days). DEC and ivermectin are ineffective, though DEC will kill microfilarae over a prolonged treatment.
M. streptocerca does not have a standard treatment, but in persons 9 years of age or older DEC (6 mg/kg/day for 14 days) is effective. However, a skin reaction similar to the Mazzotti reaction in onchoceriasis may develop due to the dying worm. Ivermectin (150 mcg/kg once) is also an option. *Both DEC and Ivermectin may cause mild to severe pruritus. Cutaneous papules containing worms are also described with DEC.
**Doses described above are only for adults.
*Image belongs to emedicine.com and can be found at http://www.emedicine.com/derm/topic888.htm#section~mansonelliasis
EpidemiologyM. ozzardi infection prevalence rate varies from a few percent to 96% in endemic areas such as Trinidad, Guyana, and Columbia. There is no morbidity directly related to infection. M. perstans infection is common in Africa, but prevalence rate are also highly variable, from 2% to 86% depending on the location in Africa. People at greatest risk are those residing in endemic areas for a long time and American Indians (WHO 1997). Tourists have a low risk, but if they do get infected symptoms are usually worse (CDC 2004).
Geographic Distribution
M. perstans is found in central Africa in high proportions and in Central and South America, such as Venezuela, Trinidad, Guyana, northern Argentina, and the Amazon. *images can be found at <http://www.med1.de/Laien/Krankheiten/Tropen/Mansonelliasis/#04>
Public HealthAttempts at controlling Mansonelliasis have been few, since the infection causes little or no harm. Most people do not complain or notice symptoms so infection is often undetected. Both Culicoides and Simulium vectors are small, so mosquito nets are often ineffective, but vector control is an option, especially in areas where lymphatic filariasis and vectors overlap. Residents of endemic areas usually have high immunity against these parasites and visitors can protect themselves with insect repellents. DEC and Ivermectin campaigns would be a possible strategy, but those resources would best serve a more pathogenic infection (World Health Organization, 1997).
References
P. Fisher, D.W. Buttner, J. Bamuhiiga, and S.A. Williams. Detection of the Filarial Parasite Mansonella streptocerca in Skin Biopsies by a Nested Polymerase Chain Reaction-Based Assay. American Journal of Tropical Medicine and Hygiene, 58: 816-820, 1998.Center for Disease Control and Prevention, Division of Parasitic Diseases. Laboratory identification of parasites of public health concern: Parasites and Health: Filariasis. 2004. <http://www.dpd.cdc.gov/dpdx/HTML/Filariasis.htm>
Vector Control: Methods for Use by Individuals and communities. World Health Organization: Water Sanitation Health Resources. 1997. <http://www.who.int/docstore/water_sanitation_health/vectcontrol/begin.htm>
Abramowicz et al. On Drugs and Therapeutics. The Medical Letter. 2004.
<www.medicalletter.org effective. http://www.medletter.com/restricted/articles/w1189c.pdf>
Bregani et al. Case report: intraocular localization of Mansonella perstans in a patient from south Chad. Transactions of the Royal Society of Tropical Medicine and Hygiene (2002) 96: 654.
Filariasis. Emedicine. 2003. <http://www.emedicine.com/med/topic888.htm>
Cedar Creek Natural History. <http://cedarcreek.umn.edu/insects/album/029022005ap.html>
