Year : 2009 | Volume
: 52 | Issue : 1 | Page : 122--124
Subperiodic, asymptomatic microfilaremia in an adult male from Mysore: A nonendemic area
MN Sumana1, K Jayashree2, BJ Subhash Chandra3, M Girish1,
1 Department of Clinical Microbiology, JSS Hospital, Mysore, India
2 Department of Pathology, JSS Hospital, Mysore, India
3 Department of Medicine, JSS Hospital, Mysore, India
M N Sumana
Department of Clinical Microbiology, JSS Medical College, #1088, 6th Main, E and F block, Ramakrishna Nagar, Mysore - 570 022
Wuchereria bancrofti is found throughout tropics and subtropics like Asia, Pacific islands, Africa, areas of South America and Caribbean basin. In all these areas, except Pacific islands, microfilaria occurs in the periodic form, in which case the microfilaria are found in large numbers in the peripheral blood during night. In the Pacific islands, they occur in the subperiodic form, i.e., microfilaria are present in the peripheral blood at all times and reach the maximum level of parasitemia in the afternoon. Microfilaria of Wuchereria bancrofti and Brugia malayi occurring in India displays a nocturnal periodicity, appearing in large numbers at night. This is the biological adaptation to the nocturnal biting habits of the vector mosquitoes. The maximum density in blood is reported between 10 PM and 2 AM. Here is a case report of asymptomatic microfilaremia showing subperiodicity, which is very unusual in India.
|How to cite this article:|
Sumana M N, Jayashree K, Subhash Chandra B J, Girish M. Subperiodic, asymptomatic microfilaremia in an adult male from Mysore: A nonendemic area.Indian J Pathol Microbiol 2009;52:122-124
|How to cite this URL:|
Sumana M N, Jayashree K, Subhash Chandra B J, Girish M. Subperiodic, asymptomatic microfilaremia in an adult male from Mysore: A nonendemic area. Indian J Pathol Microbiol [serial online] 2009 [cited 2021 Jul 31 ];52:122-124
Available from: https://www.ijpmonline.org/text.asp?2009/52/1/122/44993
Wuchereria bancrofti is found throughout tropics and subtropics like Asia, Pacific islands, Africa, areas of South America and Caribbean basin. In all these areas, except Pacific islands, microfilaria occurs in the periodic form in which case microfilaria are found in large numbers in the peripheral blood during night; while in the Pacific islands, they occur in the subperiodic form, wherein they are present in the peripheral blood at all times and reach the maximum level of parasitemia in the afternoon. 
Microfilaria of Wuchereria bancrofti and Brugia malayi occurring in India displays a nocturnal periodicity, i.e., they appear in large numbers at night and retreat from the peripheral blood stream during the day. This is the biological adaptation to the nocturnal biting habits of the vector mosquitoes. The maximum density in blood is reported between 10 pm to 2 am.  In asymptomatic microfilaremia, the patients remain asymptomatic for months and in some for years. They are an important source of infection in the community. These carrier states are usually detected by night blood examination. 
Filarial endemicity rate is obtained by filarial survey - night survey of 5%-7% of population at random (representative unbiased sample) and clinical survey to determine number of people with the disease. 
There are a number of screening tests and investigative modalities in the form of serological techniques using indirect immunofluorescent assay, adult worm antigen detection using monoclonal antibodies and specific DNA probes to detect filariasis. But the essential, efficient, rapid, definitive and cost-effective method for diagnosis of filariasis remains the finding of the parasite in the peripheral blood by microscopy and the identification of the species based on morphology. Microscopic examination is the primary diagnostic modality for a few agents such as Plasmodium species, Babesia, Ehrlichia, Microfilaria, Trypanosome and Borrelia . Special techniques like quantitative buffy coat (QBC), where a centrifugal stratification of the parasite is done, aids in enhancing their visibility. This enables a rapid and sensitive method to detect the parasites. In addition, examination of the Romanowsky stained film confirms the diagnosis and helps in confirming the species. Concentration techniques like thick blood films, stained with Giemsa (modified Romanowsky stain) is of immense help in appreciating the various morphological characteristics of the parasite that assists in identification of the genus to the species level.  Filariasis is common in the coastal areas of India; Mysore not being a coastal region is a nonendemic area.
This is the case report of a subperiodic asymptomatic microfilaremia in a nonendemic area.
A 22-years-old male from Ittigegoodu area of Mysore city presented in the month of May 2006 with history of abdominal pain, in the right hypochondriac region. Pain was intermittent in nature. The patient also had history of mild on and off fever, vomiting and diarrhea of 2 days duration. Fever was not associated with chills and rigors. Clinical examination revealed the patient to be febrile (101°F) with other vital data within normal limits. (pulse - 78 per min, BP - 110/80 mm of Hg). Per-abdominal examination revealed tenderness in the right hypochondrium with no organomegaly. Cardiovascular and respiratory systems were normal. No lymph node enlargement was noted. A provisional clinical diagnosis of acute gastroenteritis was made.
Stool microscopy revealed Vibrio cholerae-like organisms showing darting motility, which was confirmed by culture. The Vibrio cholerae isolated was of Ogawa serotype. The patient was treated for cholera with oral rehydration salts (ORS) and tetracycline. Simultaneously peripheral blood drawn was sent in EDTA (ethylene diamine tetra acetic acid) bulb for QBC examination and other routine hematological investigations.
Evaluation and clinical course
The QBC capillary tube was filled with the blood (collected at 9 am) and centrifuged for 10 min. The capillary tube was observed under ultra violet (UV) microscope. The buffy coat showed plenty of live microfilariae, showing motility amidst the blood cells. The same was confirmed by the wet mount preparation of the blood sample in which live parasites agitating groups of blood cells was noted. Thick and thin blood films were prepared and stained with Romanowsky stain.
Repeat blood samples were collected from the patient (at 2 am and 11 pm) to confirm Microfilaremia. The samples collected at different times did not show any alteration in the degree of parasitemia. The dehemoglobinized thick films helped in identifying the species of microfilaria to be that of Wuchereria bancrofti, which were sheathed and measured approximately 400-450 µm. The nuclei were seen extending along the whole length of their body sparing the tip of the tail [Figure 1] and [Figure 2].
A detailed evaluation of the patient revealed no signs of filarial infection. There was no lymphadenopathy or organomegaly.
The patient was a resident of a nonendemic area and by occupation a flower vendor. None of the family members had any complaints suggestive of filariasis nor were residing in the endemic area.
On further enquiring, it was learnt that the patient had visited Nellore, an endemic area for filariasis in the state of Andhra Pradesh 8 months back.
The case was reported to the District Health Office, Mysore. A survey of microfilaremia was carried in the locality of the patient's residence. But no cases of microfilaremia were detected.
The patient with asymptomatic microfilaremia was treated as per the recommended dosage of diethyl carbamazine citrate [DEC] to contain the spread of filariasis in and around Mysore district. After treatment, repeat examination of the peripheral blood by wet mount, Leishmann staining of the thick and thin smear and QBC did not reveal the parasites.
To the best of our knowledge, very few reports illustrate the possibility of asymptomatic microfilaremia in nonendemic areas. The present study deals with one such case. It also highlights the relevance of special techniques like QBC for rapid identification of the parasite with due importance to routine staining, which enables the morphologic characteristics in categorizing the proper species.
No reports of subperiodic microfilaremia cases from tropical countries like India were found in the literature. All the blood samples collected at different times of the day showed the same degree of parasitemia. Hence, this is one of the rare cases of subperiodic asymptomatic microfilaremia.
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