Malaria - Bahamas (Exuma Islands)(02)

International Society for Infectious Diseases
<http://www.isid.org>

Source: MMWR 22 Sep 2006 / 55(37);1013-1016 [edited]
< http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5537a1.htm?s_cid=mm5537a1_e.


Malaria --- Great Exuma, Bahamas, May-June 2006
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In the Caribbean region, malaria has been eliminated from all islands
except Hispaniola, the island consisting of Haiti and the Dominican
Republic. Caribbean islands where malaria is no longer endemic remain
at constant risk for reintroduction of the disease because of their
tropical climate, presence of competent malaria vectors, and
proximity to other countries where malaria is endemic. This
susceptibility was underscored by the recent outbreak of malaria on
the island of Great Exuma in the Bahamas; during May-June 2006, a
total of 19 malaria cases were identified. Four of the cases, in
travelers from North America and Europe, are described in this
report; such cases of imported malaria can signal the presence of a
malaria problem in the country visited and thus assist local health
authorities in their investigations.

On 19 Sep 2006, after 3 months with no report of new cases, CDC
rescinded its previous recommendation that U.S.-based travelers take
preventive doses of the antimalarial drug chloroquine before, during,
and after travel to Great Exuma.*

Case 1. On 24 May 2006, a man aged 33 years from the United States
received a diagnosis of malaria in a hospital emergency department in
Virginia. The patient had intermittent fever, sweats, abdominal
discomfort, nausea, and vomiting, which had begun during a 4-7 May
visit to Great Exuma, where the patient had stayed in a resort hotel.
The patient had no history of exposure to malaria. Blood smears on 24
May indicated _P. falciparum_. After outpatient treatment with
chloroquine, changed later to quinine and doxycycline, the patient
recovered uneventfully.

Case 2. On 6 Jun, a woman aged 29 years from Germany received a
diagnosis of _P. falciparum_ malaria in a hospital in Germany. She
had experienced fever, headache, nausea, and vomiting since 30 May,
near the end of an 18-31 May visit to Great Exuma. After her return
to Germany, she was hospitalized on 6 Jun with high fever and neck
stiffness. A blood smear revealed _P. falciparum_. She was treated
with artemether-lumefantrine and recovered.

Case 3. On 16 Jun, a man aged 20 years from Canada had _P.
falciparum_ malaria diagnosed. The man had been born in the Bahamas
and had visited friends and relatives there during 19 Apr -- 11 Jun,
spending most of his time in Georgetown, the most populous city on
Great Exuma. On 14 Jun, the man experienced fever and chills, and the
diagnosis of _P. falciparum_ malaria was confirmed by blood smear on
16 Jun. He was treated on an outpatient basis with chloroquine
followed by atovaquone-proguanil and recovered uneventfully.

Case 4. A man aged 66 years from the United States, who lived on a
boat, received a diagnosis of _P. falciparum_ malaria on 19 Jun. The
man, who had not recently visited any area that was endemic for
malaria, stayed in Great Exuma from late April to late May. In early
May, he began experiencing fever, chills, sweats, headaches, and
fatigue but did not seek medical care; he left Great Exuma to sail to
other Bahamian islands. On 18 Jun, on his return to Great Exuma, the
patient learned of the outbreak and went the next day to the district
medical clinic, where he received a diagnosis of _P. falciparum_
malaria. He was treated with chloroquine and primaquine and recovered
uneventfully.

After report of the 1st case in Virginia, the Bahamian Ministry of
Health (MOH) initiated epidemiologic and entomologic investigations
with the technical assistance of the Pan American Health
Organization. MOH also heightened mosquito-control activities that
were already being conducted on Great Exuma in conjunction with the
Bahamian Department of Environmental Health Services.

Active case detection was conducted on Great Exuma during 6-30 Jun;
however, no case of malaria was diagnosed later than the 19 Jun
diagnosis in case 4. Persons examined at primary-care clinics who had
a history of fever and a temperature of >99.0 F (>37.2 C) and
contacts of persons who received diagnoses of malaria were screened
using thick and thin blood smears stained with Wright's stain. On
Great Exuma, 15 persons were determined infected with _P.
falciparum_. Ages ranged from 16 to 66 years (median: 36 years); 84
percent were males. Most of these patients were residents of the
Bahamas, clustered around the areas of Georgetown and Bahama Sound,
and living in close proximity to a community of immigrants from
Haiti; most said they had not recently traveled to Haiti or any other
area endemic for malaria. All patients were initially treated with
chloroquine and doxycyline; the latter was subsequently replaced by
primaquine to eliminate gametocytes and thus prevent further
transmission. All 15 patients recovered.

A parasite prevalence survey was conducted on Great Exuma in a
community of immigrants from Haiti, from whom anecdotal reports of
illness had been received. Of 159 persons who consented to testing,
29 adults were determined to be infected with _P. falciparum_. This
finding prompted mass treatment with chloroquine and primaquine of
203 persons within that community. Entomologic surveys were conducted
in multiple sites near bodies of fresh water identified by ground and
air surveys in Great Exuma. Human bait and CDC light-trap collections
yielded large populations of mosquitoes, of which only 5 were adult
_Anopheles albimanus_. Surveys of potential breeding sites indicated
few areas favorable for breeding of An. albimanus larvae, with 5
confirmed _An. albimanus_ larvae collected from 3 breeding sites.
Mosquito-control interventions were intensified beginning on 30 May.
These measures included spraying 1) at all potential breeding sites,
2) within a 1/4-mile radius of patients wi!
th confirmed cases, and 3) within a 1/2-mile radius of patients
detected through contact tracing, initially with a water-based
pyrethroid insecticide, and later with malathion 96.5 percent. In
addition, all bodies of fresh water on Great Exuma, neighboring
Little Exuma, and surrounding cays (reefs) were treated with temephos
to eliminate larvae.

As of 19 Sep, no additional cases of malaria had been identified on
Great Exuma or any other island in the Bahamas, despite intense
epidemiologic surveillance. Mosquito-control measures were being
continued throughout the Bahamas.

Reported by:
M Dahl-Regis, MD, Ministry of Health, Bahamas.
C Frederickson, PhD, Caribbean Epidemiology Centre;
K Carter, MD, Y Gebre, MD, Pan American Health Organization, World
Health Organization.
B Cunanan, Arlington County Dept of Human Svcs, Arlington, Virginia.
C Mueller-Thomas, MD, Klinikum rechst der Isar, Munich, Germany.
AE McCarthy, MD, Ottawa Hospital--General Campus, Ottawa; M
Bodie-Collins, Public Health Agency of Canada.
P Nguyen-Dinh, MD, Div of Parasitic Diseases, National Center for
Zoonotic, Vector-Borne, and Enteric Diseases (proposed), CDC.

MMWR Editorial Note:
The Bahamas is an archipelagic nation in the northern Caribbean Sea,
consisting of approximately 700 islands and 2400 cays stretching
between Florida and Haiti [Figure at URL above]. Persons from
Hispaniola and other countries have emigrated to the Bahamas, where
malaria is not endemic and only one imported case was reported in
2005. However, because of frequent travel and relocation among
countries, health-care providers in the Bahamas and other countries
where malaria is not endemic should remain alert to the risk for this
disease, especially in travellers and immigrants. Introduced malaria
is much less common than imported malaria but of greater
epidemiologic significance. Imported malaria usually occurs when
travelers acquire the infection while visiting areas where malaria is
endemic. Introduced malaria typically occurs when infected travelers
return home and transmit the infection to local Anopheles mosquitoes,
which subsequently transmit it to local residents. Left unchecked,
this process can result in reestablishment of endemic malaria in
countries that have previously eliminated the disease because these
areas have climatic conditions favorable to transmission and
Anopheles species that are receptive to malaria parasites. In the
United States, 1320 cases of imported malaria were reported in 2004
(1), and 63 episodes of introduced malaria were detected from 1957 to
2003, the year when the latest episode occurred in Florida (1-3).

Available evidence indicates that during May-June 2006, Great Exuma
experienced an outbreak of introduced malaria that was successfully
contained and terminated. The observations that all cases were caused
by _P. falciparum_ and a substantial proportion of patients were
immigrants from Haiti suggest that malaria was introduced by those
immigrants. All patients treated with chloroquine responded to the
treatment, which is a further suggestion that the parasites
originated from Haiti, where _P. falciparum_ has remained sensitive
to chloroquine. _P. falciparum_ causes 99 percent of malaria cases in
Haiti and the Dominican Republic (MD Milord, Ministry of Public
Health and Population, Haiti, and JM Puello, National Center for
Control of Tropical Diseases, Dominican Republic, personal
communication, 2006), which share the only Caribbean island still
endemic for malaria. Conversely, _P. vivax_ causes 94 percent of
cases in Mexico and Central America (4).

The successful containment of this malaria outbreak is attributable
to several factors. The 1st identified case, detected in a foreign
tourist returning from the Bahamas, was promptly reported to the
Bahamian MOH, which responded with several complementary
interventions, including identification and treatment of patients and
asymptomatic parasite carriers and institution of mosquito-control
measures. Fewer than 30 days elapsed between diagnosis of the first
identified case in Virginia and diagnosis of the last case on Great
Exuma. Since 19 Jun, no additional cases have been noted, despite
intensive ongoing surveillance among febrile patients.

In view of these findings, CDC has rescinded recommendations made on
16 Jun 2006, that travelers take preventive doses of chloroquine
before, during, and after travel to Great Exuma. As of 19 Sep, CDC no
longer recommends that travelers to Great Exuma take antimalarial prophylaxis.

This malaria outbreak illustrates the importance of vigilance by
health-care providers and rapid response by public health authorities
for successful containment (2) and also might provide incentive for
measures to eliminate malaria from all Caribbean islands, including
Hispaniola. Recently, the International Task Force for Disease
Eradication recommended that Haiti and the Dominican Republic work
jointly to eliminate from Hispaniola both malaria and lymphatic
filariasis, 2 vectorborne parasitic diseases that have been
eliminated from all other Caribbean islands (6). Agreements reached
in July 2006 between the ministries of health of Haiti and the
Dominican Republic represent a first step toward achieving this goal.

References
1. CDC. Locally acquired mosquito-transmitted malaria: a guide for
investigations in the United States. MMWR 2006;55(No. RR-13):1--9.
2. CDC. Preventing reintroduction of malaria in the United States.
Atlanta, GA: US Department of Health and Human Services, CDC; 2005.
Available at < http://www.cdc.gov/malaria/features/prevent_reintroduction.htm>.
3. CDC. Multifocal autochthonous transmission of malaria---Florida,
2003. MMWR 2004;53:412-3.
4. Pan American Health Organization. Regional strategic plan for
malaria 2006--2010. Washington, DC: World Health Organization, Pan
American Health Organization; 2006. Available at
< http://www.paho.org/English/ad/dpc/cd/mal-reg-strat-plan-06.pdf>.
5. International Task Force for Disease Eradication. Summary of the
ninth meeting of the  ITFDE (II), May 12, 2006. Atlanta, GA.
International Task Force for Disease Eradication;
  2006. Available at
<http://www.cartercenter.org/documents/2435.pdf#search=%22itfde%20haiti%22>.