Understanding machupo virus: A neglected arenavirus with global health importance

Table 1 Genome segments, viral proteins, and functional interactions of Machupo virus

Genome segment	Viral protein	Primary role	Key functional interactions
L segment (approximately 7.2 kb)	L (RNA-dependent RNA polymerase)	Viral genome replication and transcription	Associates with NP to form RNP complex; mediates cap-snatching during mRNA synthesis
	Z (matrix protein)	Virion assembly, budding, and regulation of replication	Interacts with L and NP; modulates host translation and virion release
S segment (approximately 3.5 kb)	NP (nucleoprotein)	RNA encapsidation and nucleocapsid formation	Binds viral RNA; suppresses interferon pathways; stabilizes RNP structure
	GPC → GP1 + GP2	Host cell entry and membrane fusion	GP1 binds TfR1 receptor; GP2 drives low-pH-dependent fusion in endosomes

RNP: Ribonucleoprotein; NP: Nucleoprotein; TfR1: Transferrin receptor 1; GPC: Glycoprotein precursor complex; GP: Glycoprotein precursor.

Table 2 Comparison of Machupo virus structure with other arenavirus

Feature	Machupo	Junín	Lassa	Guanarito	Sabiá	Chapare	Lujo	LCMV
Genus group	New world	New world	Old world	New world	New world	New world	Old world lineage	Old world
Geographic region	Bolivia	Argentina	West Africa	Venezuela	Brazil	Bolivia	Zambia/Southern Africa	Worldwide
Disease	Bolivian haemorrhagic fever	Argentine haemorrhagic fever	Lassa fever	Venezuelan haemorrhagic fever	Brazilian haemorrhagic fever	Chapare haemorrhagic fever	Lujo haemorrhagic fever	Aseptic meningitis/encephalitis
Genome type	Bi-segmented ambisense ssRNA	Same	Same	Same	Bi-segmented ambisense ssRNA	Bi-segmented ambisense ssRNA	Bi-segmented ambisense ssRNA	Bi-segmented ambisense ssRNA
Genome segments	L (L polymerase, Z) S (NP, GP)	Same	Same	Same	L (L polymerase, Z) S (NP, GP)	L (L polymerase, Z) S (NP, GP)	L (L polymerase, Z) S (NP, GP)	L (L polymerase, Z) S (NP, GP)
Reservoir host	Calomys callosus	Calomys musculinus	Mastomys natalensis	Zygodontomys brevicauda	Suspected rodent	Suspected rodent	Suspected rodent	Mus musculus
Primary transmission	Rodent excreta	Rodent exposure	Rodent + human-to-human	Rodent exposure	Rodent exposure	Rodent + healthcare spread	Rodent + nosocomial	Rodent; vertical; transplant
Cell receptor	Transferrin receptor 1	Transferrin receptor 1	α-Dystroglycan	Transferrin receptor 1	Transferrin receptor 1	Likely Transferrin receptor 1	Unclear (distinct usage suspected)	α-Dystroglycan
Pathogenesis pattern	Immune suppression; vascular leakage	Similar to Machupo	Immune suppression; high viremia	Similar to Machupo	Limited data; similar NW pattern	Hemorrhagic; immune dysregulation	Severe systemic inflammation	Immune-mediated CNS inflammation
Case fatality rate (untreated)	20%-30%	15%-30%	1%-20%	20%-30%	Limited; high reported	High in outbreaks	Approximately 80% (2008 outbreak)	< 1% in healthy adults
Human-to-human spread	Rare	Limited	Common	Rare	Rare	Confirmed	Confirmed	Rare
Outbreak profile	Rural agricultural	Rural argentina	Endemic seasonal	Rural venezuela	Sporadic	Small outbreaks (2004, 2019)	Single major outbreak (2008)	Sporadic global cases
Vaccine	No	Candid 1 (live attenuated)	No widely licensed vaccine	No	Not available	Not available	Not available	Not available
Biosafety level	BSL-4	BSL-4	BSL-4	BSL-4	BSL-4	BSL-4	BSL-4	BSL-3 (BSL-4 high risk)

GP: Glycoprotein precursor; NP: Nucleoprotein; CNS: Central nervous system; BSL: Biosafety level.

Table 3 Diagnostic methods

Diagnostic method	Principle	Specimen	Optimal timing	Advantages	Limitations
RT-PCR	Detects viral RNA by reverse transcription followed by amplification	Whole blood, serum, plasma	Early acute phase (first 1-10 days of illness)	High sensitivity and specificity; rapid; confirms active infection	Requires specialized laboratory (BSL-4 for handling live virus); expensive; limited availability in endemic regions
Real-time RT-PCR (qRT-PCR)	Quantifies viral RNA in real time using fluorescent probes	Whole blood, serum	Early acute phase	Fast; quantitative; highly sensitive; useful for monitoring viral load	Same biosafety and infrastructure requirements; costly
Virus isolation (cell culture)	Growth of live virus in susceptible cell lines	Blood (acute phase)	Early acute phase	Definitive diagnosis; allows further characterization	Requires BSL-4 containment; slow; high biohazard risk
Antigen detection (ELISA)	Detects viral proteins using specific antibodies	Serum, plasma	Acute phase	Faster than culture; useful when PCR unavailable	Lower sensitivity than PCR; cross-reactivity possible
IgM ELISA	Detects virus-specific IgM antibodies	Serum	Late acute to early convalescent phase (after about 5-7 days)	Indicates recent infection; safer than virus isolation	Not useful in very early phase; possible cross-reactivity with other arenaviruses
IgG ELISA	Detects virus-specific IgG antibodies	Serum	Convalescent phase	Indicates past exposure or recovery	Cannot confirm acute infection alone
Immunohistochemistry	Detects viral antigens in tissue using labeled antibodies	Tissue samples (biopsy or autopsy)	Severe/fatal cases	Useful in post-mortem diagnosis	Invasive; requires specialized labs
Next-generation sequencing	Detects and sequences viral genome directly from specimen	Blood, tissue	Acute phase	Comprehensive; detects variants; useful for outbreak investigation	Expensive; limited access; requires advanced bioinformatics

PCR: Polymerase chain reaction; RT-PCR: Reverse transcription polymerase chain reaction; ELISA: Enzyme-linked immunosorbent assay; BSL: Biosafety level.