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Research Article

The discovery of human Plasmodium among domestic animals in West Sumba and Fakfak, Indonesia

[version 1; peer review: 2 not approved]
PUBLISHED 23 Jul 2021
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Abstract

Background: In Indonesia, malaria incidence is at a high rate despite maximum preventive efforts. Therefore, this study aims to determine the possibility of a Plasmodium reservoir among domestic animals in malaria-endemic areas.
Methods:  Animal blood was collected using EDTA tubes, then smeared and stained with Giemsa for Plasmodium microscopic identification. About 10 µl of blood was dropped on to a filter paper to capture Plasmodium DNA. Nested PCR was used for parasite molecular detection, while Plasmodium species were identified using the sequenced DNA.
Results: A total of 208 and 62 animal blood samples were collected from Gaura village, West Sumba and Fakfak village, West Papua, Indonesia respectively. In total, 32 samples from Gaura contained P. falciparum or P. vivax, while the Plasmodium percentage in buffalo, horse, goat, and dogs were 20.7%, 14.3%, 5.8%, 16.7%, respectively. P. knowlesi was not found in any of the samples, and no other species were detected in 18 pig blood samples.
Conclusion: Human Plasmodium existence among domestic animals in Indonesia partly explains the high prevalence and persistence of malaria in some endemic areas due to a reservoir host presence. Therefore, future studies need to ascertain the cause.

Keywords

Plasmodium falciparum, Plasmodium vivax, malaria, animals, host reservoir, PCR.

Introduction

Malaria is transmitted by the Plasmodium vector Anopheles mosquitoes. Four Plasmodium types, namely P. falciparum, P. vivax, P. ovale, and P. malariae cause pathologic conditions in humans. Recently in Southeast Asia, P. knowlesi infection cases have also been reported.13

Before molecular diagnostics development, only humans were assumed to be the primary host for Plasmodium. However, studies in the last two decades on Plasmodium reported that the parasites originated from animals. Further stating that P. falciparum originated in the gorilla4 and chimpanzee,5,6 P. vivax was from African apes,7 P. malariae was from chimpanzees6 and P. knowlesi was from monkeys,8,9 while P. ovale in humans and chimpanzees are genetically identical.10 The factors hypothesized to explain this situation include primate’s habitat loss and human’s aggressiveness in exploring forest.11 A study from South Kalimantan reported the contribution of forest workers to malaria incidence.12

East Nusa Tenggara and West Papua are known as malaria-endemic areas in Indonesia as their annual parasite incidence (API) in 2015 was 31.29% and 7.04%, respectively,13 while in 2018, according to the health office in both the districts, the API rate in Fakfak, West Papua and East Nusa Tenggara, West Sumba was 4.85% and 12.9%, respectively.(unpublished data) Due to this situation, we aimed to explore the presence of human Plasmodium among domestic animals that are a potential reservoir host.

Methods

Study area and population

This study was conducted in October 2018 in Gaura village, West Sumba Regency, an area 29.96 km2 in size inhabited by 9,584 people, and Fakfak, West Papua Province, in August 2019 with an area of 11,036 km2 inhabited by 84,692 people (Figure 1). The residents’ main occupation is farming, while livestock such as goats, horses, cows, pigs, and buffalos are commonly found in their enclosures located around the owner’s residence. Furthermore, they also own pets such as dogs and cats.

031bb7c5-ab35-4af8-8d95-624f767bfc55_figure1.gif

Figure 1. Study area: Map of Gaura Village, West Lamboya, West Sumba, Indonesia and Fakfak Regency, West Papua, Indonesia.

Sample collection

Sampling was carried out by the veterinarian and staff from West Sumba and Fakfak Animal Husbandry Office. The buffaloes, goats, pigs, and horses’ blood samples were collected in 5 ml EDTA tubes from the jugular vein located in the ventrolateral area of the neck using vacutainer needles, size 16–18. Meanwhile, the dog’s blood was drawn from the cephalic antebrachial vein in the leg using a size 21 vacutainer needle. By using a micropipette, approximately 10 ul of EDTA blood was dropped onto a microscope slide, then smeared and stained with Giemsa (MERCK Millipore, Germany) for Plasmodium microscopic identification, while the remaining was dropped onto a filter paper (Whatman CAT No. 1442-090) until it absorbed to about 1.5 cm in diameter. The dry filter paper was put on a sterile plastic clip and stored at room temperature for a maximum of 10 days.

DNA extraction

A dried blood spot (DBS) isolation kit for DNA extraction on filter paper (Cat. no. 36000) from Norgen Biotec was used. A 6 x 3 mm piece of blood-stained filter paper was put into a 1.5 ml tube containing 100 μl of digestion buffer B. It was vortexed and incubated at 85°C. Afterwards, 20 μl of proteinase K and 300 μl of lysis buffer B were added to the tube and then vortexed before incubation at 56°C for 10 minutes. About 250 μl of 95% ethanol was added to the tube and then vortexed, while the DNA content was washed by adding 500 μl of WN wash solution and centrifugated for one minute at 8,000 rpm. Washing was carried out again using 500 μl of WN wash solution and centrifugated at 14,000 rpm. For DNA elution, 90 μl of elution buffer B was put into the tube and centrifuged at 8,000 rpm for one minute, and the purified DNA was stored at -20°C.

DNA amplification and electrophoresis

DNA amplification of nested PCR and qPCR were performed as directed by Tiangen Biotech (Beijing). Plasmodium DNA amplification was carried out using the nested PCR method with a 2× Tag Plus PCR mix enzyme (Tiangen). The final volume of 12.5 μl contained 6.25 μl enzyme, 2.25 μl ddH2O, 1 μl forward primers, 1 μl reverse primers, and 2 μl DNA sample. For sequencing, the PCR mixture’s volume was doubled, with the final volume being 25 μl, while the primer sequences of P. falciparum, P. vivax14 and P. knowlesi15 can be seen in Table 1.

Table 1. Primer sequences for nested PCR.

Nested PCRSpeciesSequences primersSize (bp)
Nested 1PlasmodiumrPLU6: 5′-TTAAAATTGTTGCAGTTAAAACG-3′
rPLU5: 5′-CCTGTTGTTGCCTTAAACTTC-3
1200
Nested 2P. falciparumrFAL1: 5′-TTAAACTGGTTTGGGAAAACCAAATATATT-3′
rFAL2: 5′-ACACAATGAACTCAATCATGACTACCCGTC-3′
205
Nested 2P. vivaxrVIV1: 5′-CGCTTCTAGCTTAATCCACATAACTGATAC-3′
rVIV2: 5′-ACTTCCAAGCCGAAGCAAAGAAAGTCCTTA-3′
120
Nested 2P. knowlesiKn1f: 5′-CTCAACACGGGAAAACTCACTAGTTTA-3′
Kn3r: 5′-GTATTATTAGGTACAAGGTAGCAGTATGC-3′
296
Other primersP. falciparumrPF1: 5′-AGAAATAGAGTAAAAAACAATTTA-3′
rPF2: 5′-GTAACTATTCTAGGGGAACTA-3′
918
Other primersP. vivaxrPV1: 5′-CCGAATTCAGTCCCACGT-3′
rPV2: 5′-GCTTCGGCTTGGAAGTCC-3′
714

The nested one DNA amplification temperature was set at 94°C denaturation (one minute), 55°C annealing (one minute) and 72°C extension (one minute) for 35 cycles. For nested two, denaturation was carried out at 94°C (30 seconds) and extension was at 72°C (30 seconds) in 35 cycles. There was a difference in the annealing temperature for each species in nested two, namely 55°C (one minute) for PCR multiplex P. falciparum and P. vivax, but 56°C (one minute) for P. knowlesi. Nested one products were used as templates for nested two and both were run on agarose gel 1.5% and 2%, respectively, while qPCR was analysed using agarose gel 1.5% for electrophoresis. Molecular work was not performed for P. ovale and P. malariae due to difficulties in finding the positive control, and according to the local health office these species have never been reported from Sumba and Fakfak.

Considering the possibility of contamination, DNA was re-extracted from blood from the same filter paper. PCR was performed using the primers, rPF1 and rPF2, as well as rPV1 and rPV216 to detect P. falciparum and P. vivax, respectively. The same extraction and amplification method were used as described above.

Sequencing and alignment

To determine the Plasmodium species, in the second round of nested PCR, products having positive band targets were sent to the 1st BASE, Axil Scientific Pte Ltd Singapore for sequencing. The DNA sequence result was adjusted using multiple alignments found in the BioEdit 7.0 application17 and then read by the BLAST program from the NCBI website.

Ethical clearance

This study was approved for ethical clearance by the ethics committee of the Faculty of Medicine, Hasanuddin University (734/H4.8.4.5.31/PP36-KOMETIK/2018). All efforts were made to ameliorate any suffering of animals. To prevent stress, animals were comforted by their owners while blood samples were taken, and sampling was performed by experienced officers. Second and third blood samples were taken if there was a failure in the first sample and only if the animals were cooperative. About 20% of animals were sampled more than once.

Results

A total of 208 and 62 animal blood samples were collected from Gaura and Fakfak villages, respectively. These consisted of 92 buffalos, 21 horses, 121 goats, 18 dogs, and 18 pigs. Using the nested PCR method, 32 of the 270 animals were found to be P. falciparum and P. vivax positive. The percentage of Plasmodium positive animals included 20.7% buffalo, 14.3% horse, 5.8% goat, and 16.7% dog with one buffalo having a mixed infection (P. falciparum and P. vivax). There was no P. knowlesi found in any of the samples and no other Plasmodium was found in 18 pig blood samples. PCR gel products, DNA sequence results, and the sample’s quality can be seen in Figures 2, 3 and 4, respectively.18 Plasmodium distribution in the animals’ blood samples from Gaura and Fakfak are presented in Table 2, and it shows that blood containing Plasmodium was only found in Gaura. The results of the qPCR using rPF1–rPF2 and rPV1–rPV2 primers were similar to the nested PCR

031bb7c5-ab35-4af8-8d95-624f767bfc55_figure2.gif

Figure 2.

Gel view of PCR product from Plasmodium vivax and Plasmodium falciparum in domestic animals in Gaura, West Sumba (LD = DNA ladder, PS = positive samples, CN = control negative, CP = control positive) by nested PCR (multiplex PCR). 120 bp for positive Plasmodium vivax, 205 bp for positive Plasmodium falciparum.

031bb7c5-ab35-4af8-8d95-624f767bfc55_figure3.gif

Figure 3.

Plasmodium DNA sequence alignments from blood samples taken in Gaura village, West Sumba, Indonesia by ClustalW multiple sequence alignment.

031bb7c5-ab35-4af8-8d95-624f767bfc55_figure4.gif

Figure 4.

Example of Plasmodium PCR product quality from a blood sample taken in Gaura village, West Sumba, Indonesia.

Table 2.

Distribution of animal blood samples and Plasmodium species found in Gaura village, West Sumba, Indonesia and Fakfak, West Papua, Indonesia.

NoDomestic animalsNumber of samplesPositive PlasmodiumTotal positive
Gaura
(2018)
Fakfak
(2019)
PfPvPkMix Pf & Pv
1Buffalos (Bubalus bubalis)9201530119
2Horse (Equus caballus)21030003
3Goat (Capra aegagrus hircus)724961007
4Dog (Canis lupus familiaris)10821003
5Pig (Sus scrofa domesticus)13500000
Total20862265-132

Microscopically, trophozoites, schizonts, and gametocyte forms at 100× magnification can be seen in Figure 5. P. falciparum gametocytes found in buffaloes were sausage and crescent-shaped (a, b), while schizonts found in horses were smaller or the same size as the red blood cells (c). The P. vivax gametocyte was larger than the red blood cells found in buffalo (d). P. falciparum gametocyte and trophozoites (ring-shaped) with one or two nuclei was found in goats (e) and P. falciparum trophozoite found in horses had one nucleus (f).

031bb7c5-ab35-4af8-8d95-624f767bfc55_figure5.gif

Figure 5.

Morphology of Plasmodium in animals from Gaura village, West Sumba, Indonesia. Gametocytes (a,b,d) in buffalo, schizont in horse (c), gametocyte and trophozoite in goat (e) and trophozoite in horse (f) with magnification 1000 ×.

Discussion

The presence of Plasmodium was suspected in domestic animals because malaria cases in these two villages remained high despite maximum preventive efforts having been applied including insecticide-treated bed nets. About 32 of the 270 blood (11.9%) samples contained human Plasmodium parasites, and this is the first data report and further study is therefore needed.

Previous studies found Plasmodium relictum in avian species,19 P. cephalophi in ungulates,20 P. traguli in mousedeer,21 P. brucei in gray duiker,22,23 P. bubalis in water buffalo,24 and P. odocoilei in white-tailed deer.25,26 Other parasites found included P. caprae in goats (ruminant),27 P. bergei in Rodentia,28 and P. cynomolgi, P. inui, and P. fragile in primates.29 The five Plasmodium species that infect humans were originally parasites in primates.1,3,69 In this study, P. falciparum was found in buffalos, goats, dogs, and horses, while P. vivax was in buffalos, goats, and dogs. Initially, the presence of Plasmodium in these animals’ erythrocytes was not certain. However, the nested PCR showed the same results for all positive samples. The sequencing results of the positive bands in the nested PCR two analysis showed the bands were P. falciparum and P. vivax (Figure 3). This is the first investigation reporting human Plasmodium in domestic animals (ruminant, ungulate, and carnivore).

Plasmodium discovery among domestic animals in malaria-endemic areas raises the following questions. How do P. falciparum and P. vivax live in these animals? Are they intermediate hosts for this parasite? Did these Plasmodium species evolve to live in ruminants, ungulates, and carnivores? As a result of repeated exposure, have these animals become more permissive to Plasmodium, which generally lives in humans? Is this parasite pathogenic in animals? P. knowlesi is a commensal microbe in primates but pathogenic in humans13 and its migration from primates to humans is caused by forest loss or human invasion of primate habitat.11 There is a possibility that animal and human proximity aids easier cross parasite transfer between both groups by mosquitoes.

Despite high API in Fakfak and Gaura village, West Sumba, only the animals from West Sumba had human Plasmodium. This difference is possibly due to the distance between the residents’ houses and animal enclosures as the enclosures are located approximately 50–500 meters from the main houses in Fakfak. Meanwhile, in Gaura, residents live in stilt houses where the ground floor functions as an animal shelter, allowing microbial transfer between humans and animals by mosquitoes. In Fakfak, the sampling locations were not easily accessible, and the steep geographical conditions made it difficult to collect many samples compared to Gaura.

Although Plasmodium can be detected microscopically due to erythrocyte size, which is smaller in animals than humans, molecular methods become significant in detecting Plasmodium presence. The nested PCR was used to detect Plasmodium because its sensitivity was equally as high as Real-Time PCR and the cost was relatively lower.30,31 The microscopic method of double fluorescent dye utilization with Giemsa stain is recommended for further studies.32

Conclusion

In this study we found human Plasmodium in domestic animals. It is still not clear whether the animal had malaria, but this finding may be used as a reference for conducting malaria surveys in domestic animals in endemic areas. Human Plasmodium was only found in Gaura where the location of the animal enclosures is integrated with the residents’ houses. Local communities need to be educated about the possibility of malaria transmission due to the integration of animal enclosures and peoples’ homes. The discovery of human Plasmodium in domestic animals in this study may partly explain the persistence of the high prevalence of malaria in some endemic areas.

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Munirah M, Wahyuni S, Wahid I and Hamid F. The discovery of human Plasmodium among domestic animals in West Sumba and Fakfak, Indonesia [version 1; peer review: 2 not approved]. F1000Research 2021, 10:645 (https://doi.org/10.12688/f1000research.53946.1)
NOTE: If applicable, it is important to ensure the information in square brackets after the title is included in all citations of this article.
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ApprovedThe paper is scientifically sound in its current form and only minor, if any, improvements are suggested
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Not approvedFundamental flaws in the paper seriously undermine the findings and conclusions
Version 1
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PUBLISHED 23 Jul 2021
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Reviewer Report 22 Dec 2022
Jaishree Raman, UP Institute for Sustainable Malaria Control, WRIM,, University of Pretoria, Pretoria, Gauteng, South Africa;  National Institute for Communicable Diseases, University of the Witwatersrand Johannesburg, Johannesburg, Gauteng, South Africa 
Not Approved
VIEWS 40
This manuscript describes the interesting finding of human malaria parasites in domestic pets and farm animals in Indonesia. While this finding has potential implications for countries trying to stem residual transmission with the aim of being certified malaria free, this ... Continue reading
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HOW TO CITE THIS REPORT
Raman J. Reviewer Report For: The discovery of human Plasmodium among domestic animals in West Sumba and Fakfak, Indonesia [version 1; peer review: 2 not approved]. F1000Research 2021, 10:645 (https://doi.org/10.5256/f1000research.57382.r156443)
NOTE: it is important to ensure the information in square brackets after the title is included in all citations of this article.
  • Author Response 20 Mar 2023
    Sitti Wahyuni, Hasanuddin University, Indonesia
    20 Mar 2023
    Author Response
    This manuscript describes the interesting finding of human malaria parasites in domestic pets and farm animals in Indonesia. While this finding has potential implications for countries trying to stem residual ... Continue reading
COMMENTS ON THIS REPORT
  • Author Response 20 Mar 2023
    Sitti Wahyuni, Hasanuddin University, Indonesia
    20 Mar 2023
    Author Response
    This manuscript describes the interesting finding of human malaria parasites in domestic pets and farm animals in Indonesia. While this finding has potential implications for countries trying to stem residual ... Continue reading
Views
63
Cite
Reviewer Report 06 Jan 2022
Alfred Amambua-Ngwa, Medical Research Council Unit, The Gambia at London School of Hygiene and Tropical Medicine, Fajara, The Gambia 
Not Approved
VIEWS 63
The authors present data showing microscopically identified Plasmodium species in non-primate domestic animals in a region of Indonesia. They followed on to confirm infections with Plasmodium species with molecular methods targeting human malaria parasites P. falciparum, P. vivax, and P. ... Continue reading
CITE
CITE
HOW TO CITE THIS REPORT
Amambua-Ngwa A. Reviewer Report For: The discovery of human Plasmodium among domestic animals in West Sumba and Fakfak, Indonesia [version 1; peer review: 2 not approved]. F1000Research 2021, 10:645 (https://doi.org/10.5256/f1000research.57382.r101607)
NOTE: it is important to ensure the information in square brackets after the title is included in all citations of this article.
  • Author Response 16 Feb 2023
    Sitti Wahyuni, Hasanuddin University, Indonesia
    16 Feb 2023
    Author Response
    Thank you for the suggestions and corrections. The corrections and suggestions were compiled and a revised version of the document is written. We believe that the method used has followed ... Continue reading
COMMENTS ON THIS REPORT
  • Author Response 16 Feb 2023
    Sitti Wahyuni, Hasanuddin University, Indonesia
    16 Feb 2023
    Author Response
    Thank you for the suggestions and corrections. The corrections and suggestions were compiled and a revised version of the document is written. We believe that the method used has followed ... Continue reading

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Alongside their report, reviewers assign a status to the article:
Approved - the paper is scientifically sound in its current form and only minor, if any, improvements are suggested
Approved with reservations - A number of small changes, sometimes more significant revisions are required to address specific details and improve the papers academic merit.
Not approved - fundamental flaws in the paper seriously undermine the findings and conclusions
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