Lymphatic Filariasis in the Americas

Lymphatic filariasis (LF) in the Americas is restricted to infections by Wuchereria bancrofti which is transmitted by Culex quinquefasciatus. In general, it occurs in restricted areas where there is little basic sanitation and there are large bodies of water. That is rich in organic material and, propitious for vector breeding sites. In all countries where LF is found it is in localized foci of discontinuous distribution. These special circumstances which are found in certain places in the New World give LF a particular epidemiological picture, in that it is generally found in limited foci in countries where it occurs. In many areas, as sanitary conditions improve, the incidence of the disease declines, and in some cases, disappears completely. Due to these particular conditions, LF is relatively rare in the Region.

It is estimated that there are 6.5 million people living in endemic areas, and that as much as 300,000 are microfilaria-positive or have the disease. The low incidence of the disease, as well as the few resources available for combating it, usually gives it low ranking on the list of public health priorities. However, recent advances in control activities, as well as management of chronic cases (elephantiasis, hydrocoele, etc.), have made control and/or elimination programs more attainable.

LF occurring mainly in Brazil, Costa Rica, Dominican Republic, Guyana, Haiti, Suriname and Trinidad and Tobago.

In Brazil, the initial hemoscopic surveys, carried out in the 1950's, revealed the presence of lymphatic filariasis in at least six states (Alagoas, Amapá, Bahia, Maranhão, Pará and Pernambuco). Today, the FNS (National Health Foundation of the MOH) considers three foci as still being active with transmission; Belém (Pará State), Maceió, (Alagoas State) and Recife (Pernambuco State). Of these, the Recife focus, with important reemergence of transmission, is by far the most important, primarily due to the high incidence rates in several barrios, the expansion of the disease to neighboring municipalities within the metropolitan area, as well as a significant number of chronic manifestations in the affected population (elephantiasis, hydrocoele, etc.). Even though Belém had a high incidence rate in the past, it has been registering a gradual decrease in the number of cases over the years. This may be due to the gradual elimination of the disease, or possible deterioration of the surveillance and control program. The Maceió focus is more recent, and is restricted to only three barrios in that city.

Noteworthy are the results of the scientific work carried out by Dr. Gerusa Dreyer of the Instituto Ageu Magalhães, in Recife, Brasil. This pioneering research allows for effective treatment of elephantiasis. Proper clinical management and specific chemotherapeutical approach have shown marked improvement in elephantiasis, hydrocoele and other LF manifestations. Pathogenic mechanisms of these chronic lesions have also been revealed by this group, together with methods for close monitoring of patient recovery.

At present, the program in Brazil is largely a vertical program which, most of the activities being carried out by the FNS. The actions are almost solely restricted to active and passive case detection, blood sample collection for hemoscopic examination, and selected treatment of microfilaremic patients. The recent loss of staff by the FNS due to retirement and staff transfers to other control programs, has impeded the LFCP in attaining its annual goals and the desired coverage. In Recife, the program is now being carried out by the Municipal Secretary of Health with financial resources transferred through agreements with the FNS.

Since the Pan American Health Organization and the World Health Organization consider lymphatic filariasis as a disease that can be eliminated and potentially eradicated based on recent advances in treatment, the FNS has prepared a National Plan for the Elimination of Lymphatic Filariasis. This plan, which is based primarily in the municipalization of control activities, with all Municipal Secretaries of Health preparing individual plans of action, which propose the following activities:

• re-evaluation of the active foci of the disease;
• modification of the treatment scheme, going from selected treatment to mass treatment; and,
• use of supplementary vector control measures, when necessary.


Table 1 provides data that have been obtained for the past 10 years for the States of Pará.

Table 1.
Number of cases of microfilaremic reported from the States of Pará and Pernambuco, 1987-1996.

Pará				Pernambuco
Year	# examined	# infected	IPS*	# examined	# infected	IPS*
1987	301,342	113	0.04	144,989	1,743	1.20
1988	250,690	89	0.04	153,248	2,103	1.37
1989	241,306	71	0.03	173,832	3,174	1.83
1990	225,405	67	0.03	89,536	3,251	3.63
1991	322,721	51	0.02	134,289	4,337	3.23
1992	205,494	32	0.02	111,674	5,449	4.88
1993	301,160	21	0.01	221,121	3,586	1.62
1994	268,701	10	0.00	91,748	1,526	1.66
1995	252,390	6	0.00	103,048	2,151	20.9
1996**	52,755	0	0.00	174,124	4,119	2.37

 

* IPS = Index of Positive Slides.

** = preliminary data, subject to modification.

Source: FNS/GTEF

The microfilaremic index for Recife for 1975 to 1996 can be seen in the following graph:

 

Microfilaremic Index for Recife, 1975-1996

IPS=Index of Positive slides

Source: FNS/GTEF

In Costa Rica the focus of LF has traditionally been restricted to four barrios in the coastal city of Puerto Limón, on the Atlantic Coast. In the 1980’s microfilaremic has been found in all age groups and the incidence of the disease has been reported from 1.8% to 3.3%. No recent surveys have been conducted, but reports indicate that transmission has been interrupted. A survey to confirm this is strongly recommended.

In the Dominican Republic, the endemic foci are restricted to certain foci in Santo Domingo and other southern areas. The microfilarial rates, in the 1990’s, have been reported to be 7% to 26%. No recent surveys have been conducted.

The information available for Guyana suggests that all age groups are positive south of the City of Georgetown, close to the City of New Amsterdam. These data are fairly representative of the microscopically positive situation throughout the country where the disease is endemic, primarily in the coastal region. The incidence rate of microfilaremia in the 1990’s has been reported to be 6.4% in Georgetown.

Haiti is the only country in the Americas where LF appears to be present in much of the country. There are hyperendemic foci in some areas, and low rates of infections elsewhere. In a focus that is presently fairly well studied, 30% of people have microfilaremia, 50% have antigenemia, about 25% of men have hydrocoele, and about 3% of women have lymphodema of the leg. The infection rates in mosquitoes is about 2%. In forays in the rest of the country, it appears that transmission is very focal; conditions that bad for sampling, but good for control activities. Present activities include the "mapping" of Haiti so that filarial control efforts may be targeted to high-risk areas.

The situation in Suriname and in Trinidad & Tobago is similar to that in Guyana, yet with very low levels of transmission. The foci, if active, are located in the coastal region of the countries, and the incidence is low. No recent surveys have been conducted.

 

Source: National Health Foundation of the MHO (FNS) and the Division of Disease Prevention and Control, Communicable Diseases Program, HCP/HCT, PAHO.

 

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