Introduction

Overview of mansonellosis

Mansonellosis is a neglected tropical disease (NTD) that is mostly found in sub-Saharan Africa. The disease appears in people who have been infected by one 1 of 3 species of worms coming from the Mansonella genus. The species concerned are Mansonella perstans, Mansonella ozzardi and Mansonella streptocerca.¹ The worms are nematodes that get into the human bloodstream when female midges (genus Culicoides) bite in order to feed on the blood.¹ Important to note is that M. ozzardi is also passed on to humans by flies coming from the Simulium genus.¹ Since Mansonella species are nematodes, a mansonellosis infection can also be referred to as a filariasis. Even though M. perstans, M. ozzardi and M. streptocerca are the known agents of mansonellosis in humans, Mansonella rodhaini has also been found in skin samples of humans in Gabon. M. rodhaini is another species of Mansonella whose reservoir is chimpanzees in Central Africa.²

Mansonellosis is much more widespread than is currently acknowledged and is probably the most common parasitic disease in the tropical regions of Africa. Since the disease is mainly asymptomatic, the extent of its reach may severely be underestimated as 141 million people in 33 African countries are estimated to be infected with just M. perstans alone.³ Mansonellosis is also there in Central and South America where M. perstans and M. ozzardi infections have been found to take place.¹ In Africa, M. perstans infections are the most common cause of mansonellosis.^1,3 M. streptocerca infections have not been recorded outside of Africa.¹ All in all, M. perstans is the most common causative agent of mansonellosis.¹ Cases of M. perstans and M. ozzardi infections have also been reported in Papua New Guinea.¹ Recently, a seemingly new and unknown species of Mansonella has been identified from blood samples taken from feverish children in Gabon. This potentially new species, referred to as Mansonella sp. ‘Deux’, is very closely related to some strains of M. perstans strains.⁴

Initially, mansonellosis only referred to infections concerning M. ozzardi whereby the disease was referred to as mansonelliasis. The disease only came to be known as mansonellosis after the perstans and  streptocerca species were assigned to the Mansonella genus.¹ Prior to this classification, infections concerning M. perstans and M. streptocerca were referred to as perstans filariasis and streptocerciasis, respectively.¹ Regarding M. perstans which is the most prevalent causative agent of mansonellosis, the parasite has previously had different names, including Acanthocheilonema perstans. Other names that have previously been used to refer to M. perstans parasite are Filaria sanguinis hominis, Filaria sanguinis perstans, Tetrapetalonema perstans and Dipetalonema perstans. Worth noting is that mansonellosis is sometimes referred to using names that are derived from the previous names of M. perstans.³

This article will give you an understanding of mansonellosis, especially the impact of the disease on the skin.

Manifestation of mansonellosis

General symptoms of mansonellosis

In terms of the pathology of mansonellosis, very little has been established in order to specifically link certain symptoms to the disease. The symptoms that appear are not specific and can be found in other parasitic diseases that take place in Africa. These include skin itching (pruritus), hives (urticaria), joint discomfort (arthralgia), abdominal pain and fatigue.² The reason for the lack of knowledge about mansonellosis is the widely held belief that Mansonella infections do not result in any serious illness.¹ Taking M. perstans as an example, what is known about the parasite is derived from patients who have been simultaneously infected by M. perstans and other filarial parasites which are considered to be more relevant in terms of public health.³ The filarial parasites that are considered to be more important include Loa loa, Wuchereria bancrofti and Onchocerca volvulus and the diseases they cause.³ These parasites infect people to cause diseases called loiasis, lymphatic filariasis (elephantiasis) and onchocerciasis, respectively.

Despite infections with the Mansonella parasites being viewed as harmless, the disease may have some negative effects on the public health system. Mansonellosis may have an effect on the course of other infectious diseases such as HIV, tuberculosis and malaria which are also prevalent in Africa.³ Taking O. volvulus as an example, research into onchocerciasis has uncovered serious health effects of the disease that were previously unknown. Therefore, the same could be said about mansonellosis which to a large extent has been accepted to be an asymptomatic or mild disease without any serious health consequences.¹

Effects of mansonellosis on the skin

Even though there is not enough information regarding how Mansonella infections make people sick, there are some specific symptoms that may be linked to each of the 3 Mansonella species.¹ These include the effects of the parasites on the skin.

When it comes to M. perstans infections, most symptoms have been reported in USA-based tourists who had visited central Africa.¹ The reported symptoms are:³

• Calabar swellings are commonly reported in cases of loiasis. These are swellings in layers below the skin which usually occur in the face, hands and forearms
• Swelling of the eyelids, infection of the eyeball, proptosis and nodules appearing in the conjunctiva
• Pruritus which may be accompanied by a rash or ulceration on the skin
• Aching in the joints linked to the bursae or synovial membrane
• Aching in the liver area or serous cavities
• Unexplained fatigue, neuropathy and psychosis
• An increase in the number of eosinophils in a state referred to as eosinophilia
• Inflammation of the pericardium surrounding the heart and the pleural membranes surrounding the lungs

Symptoms associated with M .ozzardi infections include:¹

• Pruritus and swelling of the skin
• Respiratory illness
• Fatigue
• Appearance of lesions on the cornea of the eyes (keratitis)

The symptoms of M. streptocerca mirror those of onchocerciasis.² The reported symptoms mostly affect the skin around the shoulders and chest areas where the parasites are mostly present:¹

• Chronic papular eczema (dermatitis)
• Appearance of lesions known as macules
• Pruritus

Diagnosis

The symptoms that are seen in mansonellosis patients are not unique as they also occur in patients of other parasitic diseases. The other parasitic diseases being referred to here are also found in the same geographic regions as mansonellosis. Since the symptoms of mansonellosis are simply not enough to be used for diagnosis, laboratory techniques that involve parasitology and molecular biology are required.¹

In terms of parasitology, the perstans, ozzardi and streptocerca species of Mansonella differ in size and shape. In this way, they can be distinguished from amongst each other under the microscope. M. streptocerca are only found in the skin whilst M. perstans and M. ozzardi are present in the bloodstream.¹

Molecular biology techniques such as the polymerase chain reaction (PCR) have been developed for differential diagnosis. These techniques help in pointing to the exact species of Mansonella that is causing the disease. It also helps in eliminating other filarial infections such as O. volvulus and W. bancrofti as being the cause of illness.¹

Treatment

For the treatment of M. perstans infections, a few studies have been carried out on a very small number of European and North American patients travelling from endemic areas. What was found is that mixing diethylcarbamazine (DEC) and mebendazole results in a sizable decrease in the number of parasites in patients. Mebendazole also reduces the parasites. Thiabendazole was also found to be a good drug to use in treating mansonellosis patients who are infected by M. perstans. Another drug mixture of ivermectin and albendazole was also shown to result in a decrease in the number of parasites, albeit minor. In treating M. ozzardi infections, ivermectin has been proven to be very effective. On the other hand, ivermectin and DEC were shown to work well in dealing with M. streptocerca infections.¹

Another possible approach to treating mansonellosis is to kill the bacteria that live within the parasites. The bacteria being referred to here come from the Wolbachia genus and have a symbiotic relationship with the parasite. Treating M. perstans infections with doxycycline has been shown to be very good in eliminating the parasites.^1,5 The same could be realised for M. ozzardi infections as they also harbour the Wolbachia symbiont. In the case of M. streptocerca, it has not been ascertained if the parasite also carries the Wolbachia endosymbiont. As such, it is not known if treatments such as doxycycline may be effective.¹ There is also uncertainty as to whether all M. perstans strains possess the Wolbachia endosymbiont, begging the question of whether all M. perstans infections are eligible for treatment with doxycycline.¹

Summary

• Mansonellosis is a neglected tropical disease that affects people living in the tropical regions of Africa, as well as Central and South America
• Humans get the disease when they get bitten by midges and black flies. When the insects bite, they infect humans with worms that are called Mansonella perstans, Mansonella ozzardi and Mansonella streptocerca 
• Mansonella infections are generally accepted to be harmless and this has resulted in the disease getting neglected with very little research going into it. As such, there may be some unknown effects of the disease, some of which may be severe 
• Fatigue, joint discomfort and inflammation are some of the known symptoms that people with mansonellosis may experience
• The skin of people with mansonellosis also gets affected as it becomes itchy, sometimes developing rashes or sores
• Some of the skin symptoms depend on which species of Mansonella has infected that particular patient
• With Mansonella perstans infections, the layers below the skin of the forearms, hands and face get swollen. This condition is referred to as Calabar swellings
• With Mansonella streptocerca infections, affected people also get lesions that are known as macules as well as chronic eczema
• Despite there being known symptoms of mansonellosis, they are not enough when it comes to diagnosing. So the disease is diagnosed by placing blood samples of patients under the microscope in order to identify the parasite
• Mansonella may also be diagnosed by using PCR to see if the DNA of the parasites is present in the blood
• To treat the disease, a number of antiparasitic medications are given to patients. These include diethylcarbamazine (DEC), mebendazole, thiabendazole and ivermectin