What is Lymphatic Filariasis?
Lymphatic filariasis is a group of tropical helminth infections that affect the subcutaneous retina, serous membranes, eyes, lymphatic system.
Causes of Lymphatic Filariasis
The causative agents are Wuchereria bancrofti, Brugia malayi and Brugia timori. The diseases they cause, respectively, wuchereriasis and boliosis, can occur in the form of lymphatic filariasis and tropical pulmonary eosinophilia.
Mature helminths that have a filamentous form inhabit lymphatic vessels and lymph nodes. There they can remain viable for more than 20 years.
Pathogenesis during Filariasis Lymphatic
Pathological changes are due to inflammation of the lymphatic vessels and lymph nodes, which cause adult matured worms (and not microfilariae). Parasites live in bringing lymphatic vessels and the sinuses of the lymph nodes, causing dilatation of blood vessels and thickening of their walls. Infiltration of the walls of the lymphatic vessels and perivascular tissue by plasma cells, eosinophils and macrophages, proliferation of endothelial cells and proliferation of connective tissue are observed. All this leads to varicose lymphatic vessels and damage to their valves.
In the skin and subcutaneous tissue, lymphatic edema and chronic congestive changes develop in the form of pronounced tissue consolidation.
However, not only the parasites themselves are involved in the pathogenesis, but also the body’s immune response. Immune mechanisms are assigned a leading role in the development of granulomatous inflammation and sclerosis, which precede a complete blockade of lymphatic drainage. It is believed that the vessel remains passable as long as the helminth is alive, and after its death, granulomatous inflammation and sclerosis increase. As a result, there is an obstruction of the lymphatic vessels, which violates the limfoottok, despite the development of collaterals.
Symptoms of Lymphatic Filariasis
The clinical manifestations of the disease depend on its area of distribution, the type of pathogen, the immune response of the infected patient and the intensity of the invasion. Nonintense invasions can be completely asymptomatic. Symptoms can appear during the first 3 months of invasion, but usually the incubation period is from 8 to 12 months. Clinical signs fairly accurately reflect the pathological changes characterized by inflammation at the onset of the disease and obstructive phenomena in its final. The inflammatory process in filariasis occurs in a series of short bouts of fever over several weeks. Fever is usually low, but can reach 40.6 ° C and is accompanied by chills, increased sweating. Other symptoms include headache, nausea and vomiting, photophobia and muscle pain. With the defeat of the superficial lymphatic vessels, local symptoms predominate in the clinical picture.
The main manifestations of lymphatic filariasis are asymptomatic microfilariaemia, hydrocele, lymphangitis and obstruction of the lymphatic vessels. Microfilariaemia is noted in the majority of those infected. In men, the scrotum is often affected, primarily due to the presence of sexually mature worms in the lymphatic vessels of the spermatic cord. Hydrocele may develop, which in the later stages of the disease turns into the elephant’s scrotum. Acute lymphangitis and lymphadenitis with high fever are often accompanied by stunning chills and transient local edema. Attacks can be repeated at short intervals and usually stop on their own after 7-10 days. It is noteworthy that the inflammatory process spreads retrogradely – along the lymph node bringing the lymphatic vessel from the lymph node affected by the parasite to the periphery. Regional lymph nodes are usually enlarged, and lymph vessels are thickened and inflamed. Sometimes thrombophlebitis joins.
In boliosis, an abscess may form over the inflamed lymphatic vessel, which is subsequently opened.
The lymph nodes and vessels of the arms and legs suffer from both vukheririoze and brugiosa; genital organs – almost exclusively with vukererioze, which manifests itself as funiculitis, epididymitis, pain and tenderness of the scrotum on palpation. If damage to the lymphatic vessels leads to a blockade of lymphatic drainage, elephantiasis develops. First, there is swelling, leaving a hole with pressure, then – tight swelling. As the subcutaneous tissue thickens, hyperkeratosis, fissures and warty growths occur. Due to insufficient blood supply, bacterial infection often joins. When wuchereriasis occurs lymphatic swelling of the scrotum.
When the lymphatic drainage is blocked at the level of the lumbar lymph nodes, the pressure in the lymphatic vessels of the kidneys rises, which is fraught with their rupture and the appearance of chiliuria. Chyluria is usually intermittent and most pronounced in the morning.
In tourists and people who recently settled in endemic foci, the clinical manifestations of filariasis have a number of features. After a sufficient number of infected mosquito bites (usually after 3-6 months), they develop acute lymphangitis, lymphadenitis, or acute inflammation of the scrotal tissue, sometimes with urticaria and local Quincke edema. Inflammation of the ulnar, axillary, superficial and deep inguinal lymph nodes is often complicated by retrograde spread of the process through the lymphatic vessels. Attacks do not last long and, unlike filariasis in the indigenous population, are rarely accompanied by fever. With a long stay in an endemic focus, the attacks of the disease, if not treated, become more severe and lead to an irreversible blockade of lymphatic drainage.
Diagnosis of Lymphatic Filariasis
The final diagnosis is made only when parasites are detected, which is not easy. Adult parasites that inhabit the lymphatic vessels and nodes, almost inaccessible. Microfilariae can be found in the blood, fluid that accumulates between the egg shells during hydrocele, and sometimes in other biological fluids. The resulting material is examined under a microscope – immediately or after enrichment. Enrichment methods (filtration through a polycarbonate filter with a pore diameter of 3 μm; centrifugation after mixing with 2% formalin, known as the Knott method) can increase the concentration of parasites and increase the sensitivity of the study. The timing of blood collection is crucial and depends on the variety of the parasite living in the area. Many patients do not have microfilariaemia, which makes diagnosis difficult.
In some cases, the diagnosis has to be made on the basis of the clinical picture. During seizures, the differential diagnosis should include thrombophlebitis, infection, and trauma.
Retrograde inflammation is a sign that distinguishes filariasis from ascending lymphangitis of a bacterial nature. With the development of elephantiasis, lymphatic edema in malignant tumors, postoperative scars, injuries, malformations of the lymphatic vessels and internal diseases accompanied by edema are included in the differential diagnosis. Eosinophilia, an increase in serum IgE concentration and the presence of antibodies to filarias argue for lymphatic filariasis. However, cross-reactions with antigens of other helminths, including intestinal nematodes, are not uncommon. Therefore, it is not easy to interpret the results of serological studies. In addition, the population of the endemic focus, without being ill, can be sensitized to filarial antigens (due to the bites of infected mosquitoes).
Samples for Wuchereria bancrofti antigens make it possible to diagnose wuchereria, regardless of the presence of microfilariae in the blood.
Developed methods for detecting DNA of Wuchereria bancrofti and Brugia malayi using PCR.
Valuable data can be obtained using lymphoscintigraphy. For this, albumin or dextran, labeled with 99Tc (labeled dextran not yet approved by the FDA) is injected intracutaneously or sc with the use of a gamma camera.
For men with suspected lymphatic filariasis, an ultrasound of the scrotum is performed, which can reveal the dilatation of the lymphatic vessels and nodules formed around the dead worms. The use of high-frequency ultrasonic waves (7.5-10 MHz) and Doppler studies makes it possible to discern mobile helminths in the lymph vessels of the scrotum.
Treatment of Lymphatic Filariasis
Currently used diethylcarbamazine (6 mg / kg / day inside for 2-3 weeks, taken in one or several receptions). The drug eliminates microfilariaemia, its effect on adult parasites is less pronounced. If part of the sexually mature worms survives, which usually happens, within a few months after treatment, microfilariamia and clinical manifestations reappear. It was reported that a cure could be achieved by continuously taking low doses of diethylcarbamazine and carrying out several courses of therapy.
Passed the test, but was not approved by the FDA ivermectin (a drug used in onchocerciasis). A single dose of ivermectin on the effects on microfilariae was comparable to the course of treatment with diethylcarbamazine.
Side effects of diethylcarbamazine include fever, chills, arthralgia, headache, nausea, and vomiting. The severity of side effects directly depends on the degree of microfilariaemia, therefore, it is possible that they represent the body’s response to antigens released during the death of the parasites. In order to avoid side effects, they start taking the drug from a low dose, raising it to normal in a few days. Another way – the preliminary appointment of glucocorticoids.
It is difficult to fight lymphatic obstruction, but sometimes it is possible to achieve success. Elastic stockings, the elevated position of the affected limb and meticulous care of the skin of the feet bring relief to the patient. In severe limb lesions, surgical decompression is sometimes required with a lymphovenous anastomosis. With hydrocele, fluid aspiration or surgery is resorted to.
Chiluria is not amenable to surgical treatment or sclerotherapy (the introduction of sclerosing agents into the affected lymphatic vessels).
Prevention of Lymphatic Filariasis
The indigenous population of endemic foci are usually not able to protect themselves from mosquitoes, but visitors must use repellents and bedbirds.
Diethylcarbamazine causes the death of the developing larvae of filarias, so it can be used as a prophylactic agent. The optimal scheme of drug prevention has not been developed. Extensive use of diethylcarbamazine can reduce the incidence of microfilariaemia in the general population and thus halt transmission.