Filariasis: Pathogenicity, Diagnosis, Treatment and Prevention
Posted on : 23-11-2017 Posted by : Admin

PATHOGENECITY OF FILARIASIS

Wuchereria causes the disease called filariasis or elephantiasis or wuchereriasis in man. When these filarial worms reside in the lymphatic vessels of the man and obstruct the flow of the lymph, it causes a severe condition known as elephantiasis or filariasis. In this condition, the limbs and other body parts grow into enormous size.

When the infection mild it results in filarial fever, headache and mental depression. Inflammation is the main symptom of the infection of filarial worms. Lymphangitis is the condition which results due to the inflammation of lymph vessels and lymphadenitis is the condition which results due to the inflammation of lymphatic glands.

When the infection is serious, there is every chance that the dead worms get accumulated in the lymph vessels and glands. This accumulation will completely block the lymph vessels and glands, this result in immense swelling of limb extremities, scrotum of males and mammary glands in females. This kind of swelling is termed as lymphedema

Sometimes, the infection results in the increased permeability of the wall of lymph vessels thereby leading to accumulation of lymph in the tissues. Consequently, fibroblasts get accumulated in the oedematous tissues resulting in fibrosis.  In much severe cases, the sweat glands of the skin of affected parts disintegrate to become rough and dry, resulting in the condition called as elephantiasis.

Other manifestations of filariasis are

• Lymphangiovarix (dilation of lymph vessels in inguinal, scrotal and abdominal regions)
• Lymphorrhage ( deposition of lymphocytes and rupture of lymph vessels)
• Hydrocele (accumulation of fluid due to obstruction of spermatic cord)

DIAGNOSIS OF FILARIAL WORM

Demonstration of the filarial worm at laboratory can be of two types,

Direct demonstration: Either the organism itself or the components of the organism are demonstrated by this method. This includes identification of the organism through microscopic examination.

The standard diagnosing method to identify active infection is microfilariae in a blood smear by microscopic examination. The microfilariae that cause lymphatic filariasis circulate in the blood at night. And hence, blood sample collection should be carried out at night to overlap with the appearance of the microfilariae. A thick smear should be made and stained with Giemsa or hematoxylin and eosin.

Indirect demonstration: In this method the response to organism is demonstrated. This could be either nonspecific or specific response. This includes identification of the organism through serological tests.

Apart from microscopic examinations, serologic tests also provide an effective screening to diagnose lymphatic filariasis. Patients with active filarial infection have elevated levels of anti-filarial IgG4 in blood. Because lymphedema may develop many years after infection, lab tests are most likely to be negative for the patients with lymphedema.

Though the standard diagnosis includes identification and study of microfilariae different species are identified based on their specific shape and morphological characters. The following are the specimens to be collected,

• Blood sample
• Chyluric urine
• Exudate of lymph
• Hydrocele fluid
• Lymph node biopsy
• Ultrasound examination

TREATMENT AND PREVENTION OF FILARIASIS

There is no vaccine for filariasis, moreover a complete satisfactory treatment is not yet known hence, preventive measures must be carried out religiously. The disease can be reduced or eliminated by eradication of microfilariae from blood circulation by administration of heterazan and compounds of antimony and arsenic.

The following are the control measures for filariasis,

Control with Diethyl Carbamazine

• Diethyl Carbamazine is still the only drug available for chemotherapeutic control of filariasis. The administration of Diethyl Carbamazine can be carried out in various ways:
• Mass drug administration of Diethyl Carbamazine or Diethyl Carbamazine along with Albendazole to all the people in a community irrespective of infection was tried in the late 1950s and also this the method opted as a part of National Roadmap for Elimination of Lymphatic Filariasis (NRELF).
• This is an expensive approach and relies on the compliance of the people to take the medicine and non–compliance was one of the reasons for its failure in 1955. This approach also requires intensive health education of the general public to comply.
• Currently, the approach is based on detection and treatment of human carriers. The recommended dose in the Indian program is 6 mg of Diethyl Carbamazine /kg of body weight daily for 12 doses, to be completed in two weeks. In endemic areas, treatment must be repeated at specified intervals, usually for every two years.
• Addition of DEC to salt for mass treatment has been tried in the Island of Lakshadweep and has been quite successful. It is also a cheap and safe method.

Mosquito control measures

• The adult mosquitoes are controlled by spraying insecticides like organochlorides like DDT and BHC in the houses. Insecticides are used in the breeding places to kill the larvae.
• Fumigation in the human dwellings is also effective in killing mosquitoes.
• Use of mosquito nets is the safest method to avoid the mosquito bite.
• Spraying of kerosene or pyrethrum oil on the waters of sewage gutters and ditches is recommended to kill mosquito larvae.
• Biological control using larvivorous fishes such as Gambusia is also in practice. These fish feed on mosquito larvae.

1. What are the other manifestations of filariasis.
   
2. Diffrentiate between direct and indirect demonstration of filaria worm in infected human
3. Write about the drug regime to be followed to control filariasis.
   
4. What are the ways in which mosquitoes controlled to prevent filariasis?