Six of seven Hawaii Amakihi (Hemignathus virens) with chronic malarial infections had no increases in peripheral parasitemia, declines in food consumption, or loss of body weight when rechallenged with the homologous isolate of Plasmodium relictum 61 to 62 days after initial infection. Five uninfected control amakihi exposed at the same time to infective mosquito bites developed acute infections with high parasitemias. Reductions in food consumption and loss of body weight occurred in all control birds and three of these individuals eventually died. When surviving birds were rechallenged >2 yr later with either the same parasite isolate or an isolate of P. relictum collected on the island of Kauai, all individuals were immune to superinfection. Chronically infected birds developed antibodies to a common suite of malarial antigens ranging in size from 22 to 170 kDa that were detectable as early as 8 days post infection on immunoblots of SDS-polyacrylamide gels. Antibodies to this suite of malarial antigens persisted as long as 1,248 days after initial infection and were consistently detectable at times when parasites were not easily found by microscopy on Giemsa-stained blood smears. The immunoblotting method that is described here appears to be an effective technique for identifying birds with chronic, low-intensity malarial infections when circulating parasites are not easily detectable by microscopy. Hawaiian honeycreepers that are capable of recovering from acute infections develop concomitant immunity to superinfection, making them functionally immune in areas where malaria transmission has become endemic.

Introduced avian pox virus and malaria have had devastating impacts on native Hawaiian forest birds, yet little has been published about their prevalence and distribution in forest bird communities outside of windward Hawaii Island. We surveyed native and non-native forest birds for these two diseases at three different elevations on leeward Mauna Loa Volcano at the Kona Forest Unit of Hakalau Forest National Wildlife Refuge. Prevalence of malaria by both serology and microscopy varied by elevation and ranged from 28% at 710 m to 13% at 1830 m. Prevalence of pox-like lesions also varied by altitude, ranging in native species from 10% at 710 m to 2% at 1830 m. Native species at all elevations had the highest prevalence of malarial antibody and pox-like lesions. By contrast, pox-like lesions were not detected in individuals of four non-native species and only 5% of Japanese White-eye (Zosterops japonicus) was positive for malaria. A significantly high proportion of birds with pox-like lesions also had serological evidence of concurrent, chronic malarial infections, suggesting an interaction between these diseases, dual transmission of both diseases by the primary mosquito vector (Culex quinquefasciatus) or complete recovery of some pox-infected birds without loss of toes. Results from this study document high prevalence of malaria and pox at this refuge. Development of effective disease control strategies will be important for restoration of remnant populations of the endangered ‘Akiapola‘au (Hemignathus munroi), Hawaii Creeper (Oreomystis mana), and Hawaii ‘Akepa (Loxops coccineus coccineus) that still occur on the refuge.Prevalencia de Lesiones del Tipo de la Viruela Aviar y Malaria en Comunidades de Aves de Bosque en el Volcán Leeward Mauna Loa, HawaiResumen. La malaria y la viruela aviar, ambas introducidas, han tenido un impacto devastador sobre las aves nativas de bosque, pero se ha publicado poco sobre su prevalencia y distribución en las comunidades fuera de la isla de Hawai. Muestreamos aves de bosque nativas y no nativas para determinar la presencia de estas dos enfermedades a diferentes elevaciones en el volcán Mauna Loa en la Unidad Forestal de Kona del Refugio de Fauna Silvestre del Bosque Nacional de Hakalau. La prevalencia de malaria determinada a través de serología y microscopía varió con la altitud entre un 28% a 710 m y un 13% a 1830 m. La prevalencia de lesiones del tipo de la viruela aviar también varió con la altitud, entre un 10% a 710 m y un 2% a 1839 m en especies nativas. Las especies nativas tuvieron la más alta prevalencia de anticuerpos contra malaria y lesiones del tipo de la viruela aviar. De modo contrastante, las lesiones del tipo de la viruela aviar no se detectaron en individuos de cuatro especies no nativas y sólo el 5% de los individuos de la especie Zosterops japonicus fue positivo para malaria. Una proporción significativamente alta de las aves con lesiones del tipo de la viruela aviar también presentaron evidencia serológica de infecciones crónicas de malaria simultáneas, sugiriendo una interacción entre estas dos enfermedades, transmisión dual de las enfermedades por el vector principal (el mosquito Culex quinquefasciatus) o recuperación completa en algunas aves infectadas con viruela aviar sin la pérdida de dedos. Los resultados de este estudio documentan altas prevalencias de malaria y viruela aviar en este refugio. El desarrollo de estrategias de control de estas enfermedades será importante para la restauración de las poblaciones remanentes de las especies en peligro Hemignathus munroi, Oreomystis mana, y Loxops coccineus coccineus que aún existen en el refugio.

We studied the effects of chronic avian malaria (Plasmodium relictum) infections on the reproductive success of a native Hawaiian honeycreeper, Hawaii Amakihi (Hemignathus virens). Chronic malaria infections in male and female parents did not significantly reduce reproductive success as measured by clutch size, hatching success, fledging mass, number of nestlings fledged, nesting success (daily survival rate), and minimum fledgling survival. In fact, nesting success of pairs with chronically infected males was significantly higher than those with uninfected males (76% vs. 38%), and offspring that had at least one parent that had survived the acute phase of malaria infection had a significantly greater chance of being resighted the following year (25% vs. 10%). The reproduction and survival of infected birds were sufficient for a per-capita population growth rate >1, which suggests that chronically infected Hawaii Amakihi could support a growing population. Efectos de las Infecciones Crónicas de Malaria Aviaria (Plasmodium relictum) en el Éxito Reproductivo de Hemignathus virens

Omao (Myadestes obscurus) from the Hawaiian Islands typically have very low prevalences of infection with avian malaria (Plasmodium relictum) and it is not clear whether they share the same high susceptibility to this parasite that has been documented in native Hawaiian honeycreepers. We exposed four captive Omao to single infective mosquito bites and measured parasitemia, serological responses, and mortality over time. All four birds experienced transient infections with low parasitemias and were immune when rechallenged with multiple infective mosquito bites. By contrast, three of four honeycreepers (Maui Alauahio, Paroreomyza montana) that were exposed to the same dose and parasite isolate succumbed to infection. All four Omao developed antibodies to a common suite of malarial antigens that were detectable on immunoblots of a crude red blood cell extract of P. relictum. We used this technique to screen plasma samples from wild Omao and endangered Puaiohi (Myadestes palmeri) that were captured at elevations between 900 and 1300 m on the islands of Hawaii and Kauai. We found that the true prevalence of infection at elevations where active malaria transmission occurs is much higher than estimates based on blood smears alone. Hawaiian thrushes appear to have a high tolerance for malaria, with most individuals developing chronic, low-level infections after exposure that cannot be diagnosed accurately by blood smears.

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