Emerging Infectious Diseases is a high impact factor journal (> 8 );
Parasite and Vectors is also a good option but they take APC but provide waivers for low income countries(https://www.biomedcentral.com/getpublished/article-processing-charges/open-access-waiver-fund).
Bulletins of World Health Organisation ( 2016 impact factor: 4.939 ) is completely free of charge journal.
Infectious diseases of poverty provide waivers for member institutions.
Biomed Research International is also good with 2 + impact factor also provide waivers for both mid and low income countries
PeerJ (https://peerj.com/about/how-it-works/) has a limited cost APC, or none from some institutions, and a lifetime membership for a one-off fee that allows publication of one paper a year (https://peerj.com/pricing/#apc-membership-pricing). It also operates a free to submit pre-print server that can act as a jump-off point for a full publication in the PeerJ journal or is acceptable to many other journals.