Can An. Mosquitoes Co-transmit both Malaria & LF?
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Definition of some key terms
LF: This is the abbreviated form of ‘lymphatic filariasis’, a disease characterized by swollen feet (elephantiasis). The
disease is popularly known as ‘elephantiasis’, although that is not the
accurate name for it. This is because the condition, elephantiasis is only a
symptom of LF.
Wuchereria
bancrofti: this is the causative organism
for LF.
Anopheles mosquito: This is a particular grouping of mosquitoes
commonly involved in the transmission of a number of insect-borne diseases.
Endophagic: Indoor biting
behaviour of mosquito.
Exophagic: Outdoor biting
behaviour of mosquito.
Researcher: D.I.
Introduction
In 2006 and 2008, respectively, an estimated 8.3 million and 3.2 million malaria cases were reported for Ghana (WHO, 2009).
Prevalence of LF is between 9.2 –
25.4% along the coast (Dunyo et al., 1996) and 20 – 40% in the northern
regions (Gyapong et al., 1996).
In 2006 and 2008, respectively, an estimated 8.3 million and 3.2 million malaria cases were reported for Ghana (WHO, 2009).
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LF prevalence in Achowa was
estimated to be 30 – 50 %, whilst that in Butre to be 10 – 30 %; an estimated
malaria prevalence of 10 – 30 % for Achowa and > 0 – 10 % for Butre
(Kelly-Hope et al., 2006).
Work done by Dunyo et al.
(1996) along the coast of Ghana revealed the presence of Anopheles gambiae
s.s., which Gyapong et al. (2005) reported to be involved in the
phenomenon of limitation, despite deployment of mass drug administration in the
area.
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The vectors that play major roles
in malaria and LF transmission in Ghana are: Anopheles gambiae Giles,
and An. funestus Giles (Appawu et al., 1994 and Dzodzomenyo et
al. 1999).
Work done by Muturi et al.
(2006b) along the Kenyan coast revealed that Wuchereria-infected An.
gambiae s.l. had significantly higher Plasmodium falciparum
sporozoite rates than uninfected mosquitoes suggesting that filarial parasites
may enhance malaria transmission.
There is therefore the need to
study if concomitant infections of the two diseases in Anopheles vectors
is transmittable to the human hosts living in those areas so that appropriate
integrated vector control strategies that target both diseases simultaneously
may be designed and implemented.
Objective
To determine if concomitant
infections of the two diseases, malaria and lymphatic filariasis (LF) in Anopheles
vectors is transmittable to the human hosts living in those areas.
Key
Findings
Morphological identification
showed that anophelines were the predominant mosquito species in Butre, whereas
in Achowa culicines predominated (Fig 2).
PCR revealed that in both study sites, Anopheles melas was the most dominant followed by An. gambiae s.s. This may largely be due to the abundance of saltwater in both study sites, as both sites are coastal villages. Anopheles melas is not known to transmit P. falciparum in Ghana.
Occurrence of both W. bancrofti
and P. falciparum infections in Anopheles mosquitoes was
found to be nil. Wuchereria bancrofti prevalence rate in Anopheles mosquitoes
was 0.12 %. Only Anopheles gambiae s.s.
from Butre harboured Wuchereria bancrofti larva, indicating its
ability to pick parasites even at
low densities.
There was no significant
correlation between the nocturnal biting cycles of Anopheles mosquitoes
in Achowa and of those in Butre (r = 0.31; p > 0.05) (Fig. 3).
In both study sites, indoor biting
anophelines were more associated with the part of the community closest to the
coast, whilst outdoor biting anophelines were more associated with that part of
the community which was away from the coast. The part of the community closest
to the coast was more windy by virtue of its proximity to the sea, accounting
for this trend.
Abstract
Africa
accounts for about 33 and 90 % of the world’s burden of lymphatic filariasis
(LF) and malaria respectively. This study set out to investigate if
co-infections of Wuchereria bancrofti and Plasmodium falciparum, the
causative agents of LF and malaria, in Anopheles mosquitoes was transmittable
to the human populations living in areas co-endemic for the two diseases. The
study was conducted in Achowa and Butre, both in the Ahanta West District of
Western Region of Ghana using human landing and pyrethrum spray catches to
collect adult mosquitoes.
Using morphological identifications, and Polymerase
Chain Reactions (PCR), it was found that Anopheles gambiae s.l. was the
most dominant mosquito species in Ahanta West District, with a frequency of
68.63 %. There was no occurrence of concomitant infections of Wuchereria
bancrofti and Plasmodium falciparum in the Anopheles vectors,
probably because female Anopheles mosquito populations collected were not old
enough to carry the individual infections, much less both infections.
Only Anopheles
gambiae s.s. harboured Wuchereria bancrofti microfilaria, an
indication of its ability to pick the parasites even at low densities.
Anopheles mosquitoes at the study sites were found to be more endophagic than
exophagic, and their peak biting times were observed to be towards and after
midnight. Wuchereria bancrofti infection rate in the Anopheles
mosquitoes was found to be 0.12 %. No clear-cut relationship could be
established between malaria and filariasis transmission indices. Eighty-nine
per cent (89.7 %) of the Anopheles mosquitoes collected were parous, and 78.5 %
of them were not older than 6 days.
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Some References
Appawu, M. A.;Baffoe-Wilmot, A.; Afari E. A.; Nkrumah, F. K. and Petrarca, V. (1994). Speciescomposition and inversion polymorphism of the Anopheles gambiae complexin some sites of Ghana, West Africa. Acta Tropica, 56: 15 – 23.
Appawu, M. A.;Dadzie, S. K.; Baffoe-Wilmot, A. and Wilson, M. D. (2001). Lymphatic filariasisin Ghana: entomological investigation of transmission dynamics and intensity incommunities served by irrigation systems in the Upper East Region of Ghana. TropicalMedicine and International Health, 6: 511 – 516.
Dunyo, S. K.; Appawu, M. A.; Nkrumah, F. K.;Baffoe-Wilmot, A.; Pedersen, E. M. and Simonsen, P. E. (1996). Lymphaticfilariasis along the coast of Ghana. Transactions of the Royal Society ofTropical Medicine and Hygiene, 90: 634 – 638.
Dzodzomenyo, M.;Dunyo, S. K.; Ahorlu, C. K.; Coker, W. Z.; Appawu, M. A.; Pedersen, E. M. andSimonsen, P. E. (1999). Bancroftian filariasis in an irrigation project communityin southern Ghana. Tropical Medicine and International Health, 4:13 – 18.
Gyapong,J. O.; Adjei, S. and Sackey, S. O. (1996). Descriptive epidemiology oflymphatic filariasis in Ghana. Transactions of the Royal Society of TropicalMedicine and Hygiene, 9: 26 – 30.
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