Loa loa It is a species of roundworm that belongs to the phylum Nematoda. It is a parasite that affects humans, causing a disease known as loasis, which is also known as subcutaneous filariasis.
It receives that name because the parasite is lodged in the subcutaneous tissues of the host. Apart from Loa loa There are also other nematodes that cause filariasis, such as Onchocerca volvulus.
Loa loa it is an endemic parasite of the African continent, specifically in the west. It is native to Ethiopia. A large percentage of the population in this region is infected by the worm, but they do not show symptoms. Those who experience more serious clinical conditions are those who acquire the infection when visiting areas where it is endemic..
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Loa loa it is an animal that belongs to the Eukarya domain and is therefore a multicellular organism. Its DNA is packaged within a cell nucleus, constituting the chromosomes.
Likewise, from the point of view of its embryonic development, it is a triblastic animal, because it has three germ layers: ectoderm, mesoderm and endoderm. From these layers differentiate the different cells that will make up the tissues of each organ of the animal.
Loa loa It is also an animal that is characterized by its bilateral symmetry, which means that it is made up of two exactly equal halves, joined in the longitudinal plane of the parasite's body..
These parasites reproduce exclusively sexually and are viviparous, with indirect development. This implies that after fertilization occurs, the female releases larvae into the environment, which must undergo a metamorphosis process to reach adult morphology..
As said before, Loa loa it is a parasite, which means that in order to develop, it must be inside a host or vector. Its definitive host is humans, while its vector is a fly.
The taxonomic classification of Loa loa is the next:
-Domain: Eukaria
-Animalia Kingdom
-Subkingdom: Eumetazoa
-Phylum: Nematoda
-Class: Secermentea
-Order: Spirurida
-Family: Onchocercidae
-Gender: Loa
-Species: Loa loa.
Loa loa It is a nematode worm and as such has an elongated, cylindrical shape. They are dioecious, which means that the sexes are separate. They also present sexual dimorphism, so that the female and the male have certain differences that allow them to be distinguished.
The body of these worms are divided into three areas or zones: a simple head, a body and a tail that ends in a blunt point. In addition, they are made up of a kind of protective covering that is mainly made up of collagen..
In terms of color, they are mostly pale, whitish in color..
As with many parasites, female Loa loa they are larger than males. They can measure up to 8 cm in length. His tail is straight.
Internally, your reproductive system is made up of two ovaries, from which two oviducts come out that communicate with the uterus, which empties into the genital pore..
Males are smaller than females. They measure up to 3 cm. Its tail develops a characteristic ventral curvature. They also have two spicules.
Your reproductive system is made up of a testicle that empties into the seminal vesicle. From this comes the ejaculatory duct, which opens to the outside of the animal in the cloaca.
As is well known, parasites require certain conditions and elements for their life cycle to develop successfully. Among those elements, a host and a vector are of vital importance. Well Loa loa is no exception.
In the particular case of this parasite, the vector is represented by an insect, a fly belonging to the genus Chysops. This is hematophogenic, that is, it feeds on the blood that it obtains through the bite of individuals such as humans. This constitutes the host par excellence of this parasite.
This parasite has three larval forms: microfilariae (L1), labditiform (L2) and filariform (L3). Microfilariae are produced inside the human being and later undergo their metamorphosis within the fly.
Once this is cleared up, the biological cycle of Loa loa It is that humans who are infected by the parasite have microfilariae circulating in their bloodstream. When a fly bites you and sucks your blood, it also sucks those microfilariae.
In the fly's digestive tract, the microfilaria lose their protective capsule and move towards their thoracic muscles. There it undergoes a process of metamorphosis, passing through the L2 (labditiform) and L3 (filariform) stages..
The L3 larvae move from the thorax muscles towards the proboscis of the fly. The proboscis is an elongated organ that some invertebrates use to suck. In the case of flies, they use it to suck the blood of the animals they bite.
Once they bite a healthy human being, the filariform larvae (L3) take advantage of the wound made by the insect to enter the host's organism..
Inside the human body, the larva travels to the subcutaneous tissues. There they undergo a new metamorphosis and transform into an adult individual..
Adults mate and are capable of producing microfilariae (L1). In infected people, microfilariae have been collected in cerebrospinal fluid, urine, and lung. They also circulate in the blood during the day.
When a fly bites an infected person, it acquires the L1 larvae, starting the cycle again..
As already explained in the description of the biological cycle of Loa loa, this parasite is transmitted through the bite of flies of the genus Chysops. This occurs because when they bite the person, they deposit the larvae of the parasite there and they take advantage of entering the bloodstream.
There have been no cases of direct transmission from one human being to another, so this transmission mechanism is totally ruled out..
The disease that causes Loa loa It is known by the name of loasis. This is an infection that mainly affects the subcutaneous tissues of the body, since that is where the parasite reproduces.
The incubation period is approximately three months. After this time, the infected person begins to manifest certain symptoms and signs.
Among the most characteristic signs of this infection is the so-called Calabar edema. This is characterized by being an area in which there is edema (inflammation) without redness. This inflammation is subcutaneous and very extensive, and can measure up to 20 cm.
Also, before edema appears, you may experience pruritus (itching), burning, and pain. Calabar edema develops mainly on the face, wrists and ankles, specifically at the level of the joints. Its duration is variable, from hours to even weeks. When the edema disappears, it is very likely that it reappears but in another location.
At the blood level, the affected person suffers from eosinophilia. This means that eosinophils (a type of blood cell) increase their concentration in the blood. This occurs because these cells have, among one of their many functions, to fight infections by parasites..
Likewise, adult forms of the parasite tend to cause certain local reactions where they are found. One of the favorite tissues of these worms is the ocular conjunctiva. When this occurs, the person experiences tearing, tingling, and a foreign body sensation..
When the infection progresses, complications at the renal, neurological, pulmonary and cardiac levels are possible..
The severity of the infection depends mainly on the state of the immune system of the affected person and the degree of immunity to the parasite. For example, in regions where the loasis is endemic, it is possible to find microfilariae in the blood of its inhabitants, without these showing symptoms or signs..
The diagnosis of loasis can be given through several mechanisms:
The doctor may observe the adult form of the worm on the patient's conjunctiva or on the skin..
This is the most commonly used test to diagnose infection with Loa loa. To carry it out, it is necessary to take a blood sample from the patient. This should be done between 10:00 am and 2:00 pm, as this is the time when there is the highest concentration of microfilariae in the blood..
This is a highly specialized molecular diagnostic test. Thanks to this, it is possible to directly detect the DNA of the parasite, as well as to quantify the amount of parasites that there are. This is an extremely expensive exam that must be performed in specialized centers. It is uncommon for it to be done to diagnose infection..
The drug used to treat infections by Loa loa is diethylcarbamizine. This is nothing more than an anthelmintic (antiparasitic) that is used to treat infections caused by some nematodes such as Loa loa.
However, the treatment scheme for loasis is somewhat complex, since the behavior to be followed depends on several factors..
The most important factor is the number of parasites per milliliter of blood. In patients whose concentration is higher than 8,000 microfilariae per milliliter, it is not advisable to start treatment with diethylcarbamizine directly..
This is because parasites, when attacked, release certain substances that can trigger terrible reactions in the patient, such as encephalopathy..
In patients with a high level of microfilariae in the blood, it is common to undergo treatment with albendazole for a period of 21 days in order to reduce the number of parasites.
Once the parasite load has reached more manageable levels, then the treatment with diethylcarbamizine is applied, always with the required care and monitoring..
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