Mansonella ozzardi is a parasite in the phylum of Nematoda. This filarial nematode is one of two that causes Serous Cavity filariasis

Filariasis

Filariasis is a parasitic disease and is considered an infectious tropical disease, that is caused by thread-like nematodes belonging to the superfamily Filarioidea, also known as "filariae"....

 in humans. The other filarial nematode that causes Serous Cavity filariasis in humans is Mansonella perstans. Mansonella ozzardi is an endoparasite that inhabits the serous cavity of the abdomen in the human host. It lives within the mesenteries, peritoneum, and in the subcutaneous tissue.

Morphology

Like other nematodes, Mansonella ozzardi is a cylindrical and bilaterally symmetrical worm. It is an organism with a pseudocoel, or a false body cavity. The exterior of the parasite is called the cuticle. The cuticle is a protective layer that can withstand the harsh environment in the digestive tracts of the human host.

M. ozzardi and other nematodes have longitudinal muscles that run along the body wall. They also have dorsal, ventral, and longitudinal nerve cords connected to these longitudinal muscles.

In the adult stages of Mansonella ozzardi, the females are larger than the males.

Reproduction

This is a dioecious species. It is believed that the female releases a pheromone to attract males (Prior 2003). The male that finds the female will coil around the female over the genital pore. The male has spicules that are used to hold the female during copulation. The females are ovoviviparous. The sperm of a nematode lacks a flagellum. Its motility is due to its amoeboid-type cell.

Geographic Range

This is a New World parasite. It is prominent in the subtropical, tropical, and temperate regions of Central America, South America (Mexico, Panama, Brazil, Colombia, and Argentina), and the Caribbean (Medeiros 2009).
The prevalence of Mansonella ozzardi in Brazil is very high. About 44-52% of Brazilian farmers are infected. It is also prevalent with the American Indian population (Rozendaal 1997).

Life cycle

1. An arthropod (black fly or biting midge) will take a blood meal from a human and will insert its third-stage filarial larvae into the human host.
2. The larvae will then become an adult and will inhabit the subcutaneous tissues.
3. The adults will mate and produce unsheathed microfilariae. These microfilariae will go to the blood stream.
4. An arthropod will not take a blood meal from an infected human and ingest the microfilariae.
5. In the arthropod, the microfilariae will travel from the midgut to the thoracic muscles.
6. In the thoracic muscles, the microfilariae will develop into the first-stage larvae.
7. Later, the microfilariae will further develop into the third-stage larvae.
8. The third stage larvae will travel from the thoracic muscles to the arthropod's proboscis. This is the stage where the arthropod can infect a human when it takes a blood meal.

Transmission

M. ozzardi is transmitted by two types of arthropods that feed on the blood of humans: biting midges (genus Culicoides) and blackflies (genus Simulium). In the Caribbean, M. ozzardi uses the biting midge as its intermediate host. The blackfly serves as the intermediate host for the filariae parasite in the Amazon Basin and mainland South America.

Biting Midge

The biting midge are small flies that breed on sandy beaches near the sea. Some species also lay their eggs on decaying leaf litter, humus, manure and semi-rotting vegetation, in tree holes, and the cut stumps of banana trees. They feed on the blood of mammals, birds, reptiles, and humans. Their short mouthparts prohibit them from biting through clothing. As a result, they prefer to drink from the head or other exposed body parts. Blood meals occur throughout the day and night, but biting activity peaks during the early evening. Since individual bites can be painful, they are a cause of concern because they tend to attack in swarms of hundreds or thousands. Due to their small size, they can pass through mesh mosquito nets (Rozendaal 1997).

Blackfly

The blackflies are larger blood-sucking flies that breed in fast-flowing streams and rivers. Their larvae can be found attached to submerged vegetation and stones of infected waterways. Blood meals occur during the day in the outdoors, especially along riverbeds. After a meal, the flies rest for 2–3 days on trees and other vegetation to digest the blood. Like the biting midges, blackflies attack their victims in swarms and their bites are painful. The bites may cause swelling, inflammation, and irritation that may last for weeks (Rozendaal 1997).

Symptoms

The pathogenicity of Mansonella ozzardi needs further research. Although the adult worm lives in the body cavities and the mesentery, they seem to cause little or no harm to their human hosts. As a result, infected people rarely present any symptoms.
However, a few clinical manifestations have been reported:

1. Moderate fever
2. Coldness in the legs
3. Joint pains, like articular pain or arthralgias
4. Headaches
5. Pruritis (itchiness)
6. Skin eruptions
7. Pulmonary symptoms
8. Lymphadenitis - inflammation of the lymph nodes
9. Adenopathy - enlargement of the lymph nodes
10. Hepatomegaly - enlargement of the liver

Diagnosis

Microscopic examination is the most practical diagnostic tool used to identify the M. ozzardi microfilariae in blood samples from infected patients. Blood smears are usually stained with haematoxylin or Giemsa to visualize the worms under the microscope (WHO 1997).

Diagnosticians must not rely entirely on blood samples since microfilariae have also been detected in the skin. Ultrasound may be used to detect the presence of the adult worms. Researchers are currently developing a polymerase chain reaction

Polymerase chain reaction

The polymerase chain reaction is a scientific technique in molecular biology to amplify a single or a few copies of a piece of DNA across several orders of magnitude, generating thousands to millions of copies of a particular DNA sequence....

(PCR)-based method of detecting the parasites in skin biopsies (Ewert et al., 1981).

Treatment

Ivermectin is the treatment of choice for M. ozzardi infections. It is a potent macro-cyclic lactone that binds to chloride channels, which then open and allow chloride ions to enter the affected cells. These cells hyperpolarize, resulting in muscle paralysis in the M. ozzardi microfilariae. This allows host immune cells to adhere to the microfilariae surface and facilitate their elimination. Ivermectin is unable to kill the adult worms (Richard-Noble 2003).

Another drug that has been used in treating filarial infections is diethylcarbamazine (DEC). While DEC works well against many filarial parasites, it is not effective in treating M. ozzardi infections. Research has shown that DEC is unable to kill the M. ozzardi microfilariae (Bartholomew et al., 1978).

Disease Control

Aside from Ivermectin, preventive measures can be taken by individuals living in areas endemic to Mansonella ozzardi. Since biting midges cannot bite through clothing, those living in the Caribbean should wear long-sleeved shirts and pants to decrease the amount of body parts exposed. Insect repellents could also be used to cover body parts not protected by clothing (Rozendaal 1997). Communities should also maintain the natural vegetation around them to decrease the possible breeding grounds for the biting midges.

In South America, the best way to control the population of blackflies, and the transmission of M. ozzardi, is to apply insecticides specific for blackfly larvae to streams and rivers. It has been shown that application of insecticide to a specific breeding site also kills larvae in breeding sites up to 10 km downstream (Rozendaal 1997). Extensive networks of waterways must be treated with insecticide since blackflies have the ability to fly with the wind for several hundreds of kilometers. Individuals should also avoid the waterways whenever possible.