Understanding machupo virus: A neglected arenavirus with global health importance

Abstract

Machupo virus (MACV), classified within the Mammarenavirus genus of the Arenaviridae family, serves as the causative agent of Bolivian hemorrhagic fever (BHF), a life-threatening zoonosis primarily confined to rural regions of Bolivia’s Beni Department. First identified in 1959 during epidemics in San Joaquín, this bisegmented, ambisense, single-stranded RNA virus exhibits 20%-35% case-fatality rates, with highest lethality among children under 5 and adults over 55. The vesper mouse (Calomys callosus) acts as the principal reservoir, sustaining lifelong asymptomatic infections and shedding virus through excreta, facilitating human spillover via aerosol inhalation, contaminated food, or direct contact-predominant in agrarian settings. Clinically, BHF follows a 5-21 days incubation with initial nonspecific febrile prodrome (fever, myalgia, prostration) evolving into hemorrhagic diathesis (petechiae, mucosal bleeds), neurological signs (tremors, delirium), leukopenia/thrombocytopenia, and shock. Pathogenesis hinges on transferrin receptor 1-mediated endothelial tropism, type I interferon suppression (NP/Z), and cytokine storms, recapitulated in guinea pig/primate models. Designated Centers for Disease Control and Prevention Category A and biosafety level (BSL)-4, MACV constrains research; diagnostics demand reverse transcription polymerase chain reaction, enzyme-linked immunosorbent assay, or isolation in maximum containment. Supportive therapy prevails, augmented by off-label ribavirin (preclinical efficacy) and convalescent plasma; Candid 1 (Junín-attenuated) cross-protects informally. This review details MACV’s genomic organization (L/S segments encoding L/Z, NP/GPC), epidemiology, etiology, and advances: Reverse genetics for antivirals, GP-specific mAbs (100% guinea pig survival), multi-epitope vaccines, and high-throughput screening entry inhibitors. One health imperatives-rodent control, artificial intelligence surveillance, and Bolivian BSL-3 expansion-counter ecological drivers like deforestation. Amid climate, prioritizing global collaborations will forge resilient countermeasures, leveraging MACV as a sentinel for new world arenavirus threats.

Key Words: Machupo virus; Bolivian hemorrhagic fever; Arenavirus; Zoonosis; Vaccine development; One health

Core Tip: Machupo virus, the etiological agent of Bolivian hemorrhagic fever, remains a neglected yet highly lethal arenavirus with significant biosafety and outbreak potential. This review integrates current knowledge on viral biology, transmission ecology, pathogenesis, diagnostics, and emerging countermeasures including monoclonal antibodies, antivirals, and next-generation vaccines. Strengthening one health surveillance and global research collaboration is essential to mitigate future spillover risks and improve preparedness against new world arenaviruses.

INTRODUCTION

Machupo virus (MACV), a member of the Arenaviridae family in the Mammarenavirus genus, stands out among New World arenaviruses for triggering Bolivian hemorrhagic fever (BHF), a severe zoonotic illness confined mainly to Bolivia. First isolated in 1963 from a fatal human case in Bolivia’s Beni region-named after the nearby Machupo River-this bisegmented, ambisense, single-stranded RNA virus has caused recurrent outbreaks since its initial recognition in 1959. With case-fatality rates reaching 30%-35%, sporadic re-emergence, and potential for human-to-human spread in healthcare settings, MACV poses an ongoing public health challenge, despite its geographic limitation[1].

Its designation as a category A bioterrorism agent by the United States Centers for Disease Control and Prevention (CDC) and requirement for biosafety level (BSL)-4 containment underscore its high virulence and research constraints. These factors position MACV as a critical model for studying arenavirus pathogenesis, rodent-host interactions, and hemorrhagic fever mechanisms-insights applicable to related pathogens like Junín, Guanarito, Sabiá, and Lassa viruses[2].

The primary reservoir, the vesper mouse Calomys callosus (C. callosus), maintains persistent, asymptomatic infections, shedding virus lifelong through urine, feces, and saliva. In endemic rural areas of Bolivia’s Beni Department, up to 25% of these rodents carry MACV. Neonatal C. callosus develop immune tolerance upon infection, fueling silent transmission cycles. Humans acquire the virus mainly via inhalation of aerosolized excreta or direct contact during agricultural activities or in rodent-infested homes, with rare nosocomial spread mirroring Lassa fever dynamics[3].

Clinically, BHF unfolds after a 1-2 weeks incubation with initial flu-like symptoms-fever, myalgia, and prostration-progressing to neurological signs (tremors, encephalopathy), hemorrhagic diathesis (petechiae, mucosal bleeding), and shock. Historical outbreaks illustrate this severity: From 1959-1962, Bolivia recorded about 470 cases with 142 deaths; a 1963 epidemic in San Joaquín exceeded 400 cases; and a 1971 Cochabamba nosocomial cluster highlighted interpersonal risks. The 1994 Magdalena family outbreak (7 cases, 6 fatal) involved ages 10 months to 50 years, with virus isolation and seroconversion confirming MACV via enzyme-linked immunosorbent assay (ELISA) and BSL-4 assays[4].

Diagnosis demands BSL-4 facilities, relying on virus isolation, antigen detection, or serology (IgM/IgG ELISA, neutralization tests). Rodent population surges and household incursions often precede outbreaks, though drivers remain incompletely defined. No licensed vaccine or antiviral exists, though convalescent plasma curbed early epidemics. As a neglected tropical disease with bioterrorism potential, MACV warrants renewed focus on surveillance, rodent control, and cross-protective countermeasures to avert wider threats[5].

This review aims to provide a comprehensive and updated overview of MACV, focusing on its epidemiology, transmission dynamics, molecular pathogenesis, clinical features, diagnostic approaches, and emerging therapeutic strategies (Figure 1). By integrating recent scientific advances with public health perspectives, this article highlights key research gaps and future directions necessary to improve preparedness and response against MACV and related arenaviruses.

Figure 1 Overview of Bolivian hemorrhagic fever. BSL: Biosafety level.

To provide a well-rounded overview of MACV and BHF, a systematic and transparent literature review strategy was adopted. Scientific articles were retrieved from major databases such as PubMed, Scopus, and Web of Science, along with relevant guidelines and technical reports issued by international health organizations including the World Health Organization (WHO) and CDC. The search encompassed publications spanning 1960 through 2025, allowing inclusion of both early outbreak reports and recent developments in arenavirus research. Search terms were carefully selected to capture diverse aspects of the topic, including MACV, BHF, arenavirus biology, diagnostic approaches, genomic features, and treatment strategies. Priority was given to peer-reviewed studies, comprehensive reviews, and epidemiological investigations directly related to MACV transmission, pathogenesis, clinical features, and control measures. In addition, reference lists from key articles were examined to identify further relevant sources. This structured approach enabled integration of molecular, clinical, and public health perspectives into a cohesive synthesis of current evidence.

MACV remains endemic to the Beni Department of Bolivia, where it circulates silently within its primary rodent reservoir, the vesper mouse (C. callosus) (Figure 2). Human infection typically occurs through inhalation of aerosols contaminated with rodent excreta or through direct contact with contaminated food, water, or household materials, particularly in rural agricultural settings. Although secondary transmission between humans has been documented, especially in healthcare environments, it is relatively uncommon and usually requires close exposure to infected bodily fluids. Environmental and ecological changes-including deforestation, expansion of agriculture, and seasonal increases in rodent populations-continue to influence spillover events and outbreak risk. Since its emergence, BHF has shown case-fatality rates ranging from 20% to 35%, with clinical patterns frequently characterized by hematological abnormalities, neurological manifestations, and progression toward circulatory shock[6].

Figure 2  Vesper mouse Calomys callosus.

A notable example illustrating these transmission dynamics occurred during the 1994 Magdalena outbreak in Iténez Province. Seven members of a single household developed severe febrile illness accompanied by hemorrhagic and neurological symptoms, resulting in six fatalities. Laboratory confirmation under high-containment conditions demonstrated active viral infection through antigen detection and serological conversion. Additional suspected cases included a laboratory worker exposed to aerosolized blood samples and two individuals from nearby communities, highlighting the potential risks associated with occupational exposure and delayed clinical recognition. Importantly, prompt antiviral intervention in one patient was associated with improved survival, emphasizing the potential value of early therapeutic management. Rodent surveillance conducted during the investigation reflected the complexity of identifying reservoir infection despite ongoing transmission, reinforcing the role of ecological monitoring in outbreak prevention[7].

Since the 1960s, BHF episodes have yielded 20%-35% fatality rates, with leukopenia, thrombocytopenia, and neurological involvement (tremors, delirium in about 50% of cases) as hallmarks amid progressive shock[8]. BSL-4 confirmation involved virus isolation/antigen detection from five deceased patients’ samples and IgM/IgG seroconversion in the survivor[9].

Three secondary suspects emerged: A 37-year-old Santa Cruz lab technician exposed to centrifuged blood aerosol (August 18); symptoms (fever, arthralgia, conjunctivitis) began August 29. Prompt ribavirin averted hemorrhage; pre-treatment serum was MACV-negative, with no seroconversion at 3 months. A 41-year-old Magdalena man (no known contacts) progressed rapidly from fever/chills (August 28) to death (September 5) in Cochabamba; serum confirmed via isolation/antigen. A 52-year-old Poponas farmworker showed hemorrhagic fever (September 3), hospitalized in Trinidad (September 11), and survived ribavirin started September 13; antigens/virus isolated.

No secondary cases arose among monitored contacts. Rodent trapping (1811 trap-nights, August-September) yielded 84 animals, including 9 C. callosus, all antibody-negative (isolation pending). These patterns highlight MACV’s rodent-driven epidemiology, with human incursions amplifying risk, and underscore ribavirin’s potential in early intervention.

MACV, the causative agent of BHF, belongs to the genus Mammarenavirus within the family Arenaviridae. It is an enveloped virus possessing a bi-segmented, ambisense, single-stranded RNA genome of approximately 10.7 kb. Phylogenetically, MACV is closely related to other South American arenaviruses such as Junín, Guanarito, and Sabiá viruses, which share similar ecological niches and pathogenic characteristics. The virus maintains persistent infection within rodent hosts without causing apparent disease, facilitating continuous environmental circulation. Human infection represents an incidental spillover event driven by ecological interactions between rodents and agricultural communities. Understanding these ecological and molecular relationships is essential for designing targeted surveillance strategies and developing effective countermeasures against future outbreaks[10].

VIRAL STRUCTURE AND REPLICATION

MACV’s virions (about 50-300 nm) feature a pleomorphic envelope studded with glycoprotein precursor complex (GPC) spikes, housing the RNA-dependent RNA polymerase (L), nucleoprotein (NP), glycoprotein precursor (GP), and matrix protein (Z) encoded by the large (L) and small (S) segments. GPC cleaves into GP1 (receptor-binding) and GP2 (fusion), with GP1 engaging human transferrin receptor 1 (TfR1) for cellular entry via clathrin-mediated endocytosis. Post-fusion, replication in cytoplasmic inclusions disrupts endothelial integrity, triggers cytokine storms, and impairs platelet function-hallmarks of BHF’s vascular pathology[11].

RESERVOIR AND ZOONOTIC SPILLOVER

The vesper mouse (C. callosus) sustains MACV as its natural reservoir through lifelong, asymptomatic persistence, with chronic shedding via urine, feces, saliva, and bite wounds. Infected neonates develop T-cell tolerance, perpetuating enzootic cycles in Bolivia’s Beni savannas.

Humans encounter MACV incidentally in peridomestic settings: Inhaling aerosols from dried excreta, ingesting contaminated food/water, or cutaneous/mucosal exposure during rodent control or harvests. Nosocomial human-to-human transmission-via blood splashes or fomites-occurs rarely but amplifies outbreaks when infection control lapses, as in 1971 Cochabamba.

RISK FACTORS AND PATHOGENIC CASCADE

Rural agrarian lifestyles heighten exposure, yet BHF rarity stems from inefficient human transmission (R0 < 1). Infection culminates in immune evasion, monocyte/macrophage targeting, and type I interferon suppression, yielding high viremia and multiorgan failure. This zoonotic triad-reservoir-virus-human interface-defines MACV’s etiology, demanding integrated ecological surveillance[12].

GENOMIC STRUCTURE AND VIRAL PROTEINS

Ambisense coding

MACV possesses an ambisense genomic arrangement, a characteristic feature of arenaviruses in which each RNA segment carries coding regions in opposite orientations. This configuration enables a sequential pattern of gene expression during infection. Proteins essential for initiating replication are produced early, whereas additional regulatory or structural components are synthesized only after the formation of complementary RNA intermediates. Such staged expression allows the virus to optimize replication efficiency while adjusting to intracellular conditions and partially avoiding early host immune detection[13].

Z-mediated host shutoff

In addition to its structural role in virion assembly, the arenaviral Z protein acts as a key regulator of host–virus interactions. It can suppress cellular protein synthesis and interfere with antiviral signaling pathways, thereby shifting the cellular environment in favor of viral replication. By limiting host translational activity and weakening interferon-mediated defenses, Z reduces the production of antiviral factors and supports sustained infection. This functional suppression of host responses is commonly described as a host-shutoff mechanism.

Genome organization

MACV possesses a bisegmented, negative-sense RNA genome organized into two ambisense segments that form ribonucleoprotein (RNP) complexes. The large (L) segment encodes the RNA-dependent RNA polymerase and the small matrix protein Z, which together regulate viral replication, transcription, and particle assembly. The small (S) segment encodes the NP and a GPC that is cleaved into GP1 and GP2. GP1 mediates attachment to the human TfR1, promoting cellular entry, while GP2 facilitates membrane fusion within endosomes (Figure 3). NP binds viral RNA to form the nucleocapsid and contributes to immune evasion, whereas Z coordinates virion budding and host translation control. The coordinated interaction of these structural and non-structural proteins enables efficient viral propagation, zoonotic transmission, and pathogenicity.

Figure 3  Strucutre of machupo virus.

The genome comprises two circularized RNPs: Large (L) segment (7.2 kb): Encodes RNA-dependent RNA polymerase (L; 250 kDa) for transcription/replication and zinc-binding matrix protein (Z; 11 kDa) for assembly/budding. Small (S) segment (3.5 kb): Encodes (NP; 63 kDa) for genome packaging/immune evasion and GPC; 75 kDa, cleaved by SKI-1/S1P into GP1 (26 kDa; receptor binding) and GP2 (37 kDa; fusion) (Table 1)[14].

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.

Key viral proteins and entry mechanism

GP1/GP2: Surface trimers drive entry; GP1 binds human TfR1, enabling endothelial tropism, while GP2 mediates low-pH fusion in endosomes.

NP: Multimerizes along RNA, shields from RNases, and suppresses interferon via ZAP inhibition.

L: Forms RNP-associated complex for cap-snatching and mRNA synthesis.

Z: RING domain oligomerizes, interacts with L/NP for egress, and disrupts host translation[15].

This architecture underpins MACV’s efficient zoonotic adaptation, persistent rodent infection, and human pathogenesis, informing therapeutic targets like GP2 fusion inhibitors.

Notable outbreaks

MACV outbreaks underscore its sporadic yet lethal epidemiology, driven by C. callosus population irruptions in Bolivia’s Beni Department. Highest case-fatality rates (about 40%) afflict children < 5 years and adults > 55, with transmission via aerosolized/ingested rodent excreta; interpersonal spread is rare.

The 1959-1963 San Joaquín epidemic marked BHF’s debut, with about 400-500 cases and 142 deaths (30%-35% case fatality rate) in a village of about 1500. CDC-led efforts identified MACV, deploying rodenticide campaigns (C. callosus eradication) and convalescent plasma, halting spread until 1971’s Cochabamba nosocomial cluster exposed human-to-human risks via fomites/blood.

In 1994, Magdalena saw 7 family cases (6 fatal) plus 3 suspects (2 fatal, 1 ribavirin survivor); no secondary transmission occurred despite monitoring. The 2007-2008 Beni resurgence yielded about 220 cases/14 deaths (about 6% CFR), mitigated by surveillance and control amid ecological shifts (Table 2)[16].

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.

Pathogenesis entails respiratory/gastrointestinal entry, endothelial replication, viremia, and hemorrhage-elucidated mainly via guinea pig models given BSL-4 constraints and case rarity. Misinformation endures, such as the debunked 2023 WhatsApp hoax claiming MACV in Indian paracetamol. These episodes affirm intervention success while flagging rodent-driven vulnerabilities, advocating one health vigilance[17,18].

PATHOGENESIS AND CLINICAL MANIFESTATIONS

MACV infection results in BHF, a severe zoonotic disease with reported case-fatality rates of approximately 20%-35%, particularly affecting young children and older adults. Following exposure to contaminated excreta of C. callosus, the virus undergoes an incubation period of about 5-21 days before clinical symptoms appear. The disease typically progresses through two major phases that reflect the underlying viral replication dynamics and host immune responses, which may be effectively illustrated using a timeline-based schematic[19,20].

Early febrile phase

During the first week of illness, patients develop nonspecific influenza-like symptoms, including high fever, chills, headache, retro-orbital pain, muscle and joint discomfort, fatigue, anorexia, and sore throat. This stage corresponds to initial viral replication within monocytes, macrophages, and reticuloendothelial tissues, leading to systemic viremia and early immune activation.

Hemorrhagic and neurological phase

Between days 7 and 14, disease severity increases as viral dissemination triggers endothelial dysfunction and immune dysregulation. Neurological features such as tremors, confusion, or seizures may develop, accompanied by mucosal and subcutaneous bleeding, hypotension, and cardiovascular instability. Laboratory findings often include leukopenia, thrombocytopenia, elevated liver enzymes, and proteinuria. In severe cases, uncontrolled inflammation and vascular leakage contribute to shock and multi-organ failure involving hepatic, renal, and central nervous systems (Figure 4).

Figure 4  Pathogenesis and clinical progression of Machupo virus infection.

RECOVERY OR FATAL OUTCOME

Patients who survive the acute phase may enter a prolonged recovery period marked by gradual resolution of fever and increased urine output, although complications such as hearing impairment or orchitis may occur. Fatal outcomes are typically associated with extensive viral replication, cytokine dysregulation, and coagulation abnormalities during the peak viremic phase[21].

Underlying pathogenic mechanisms

At the molecular level, MACV exploits the TfR1 to infect host cells, suppresses interferon signaling through NP and Z-protein functions, and induces excessive cytokine release, including interleukin-6 and tumor necrosis factor-alpha. Experimental animal models demonstrate that replication within immune and endothelial cells drives systemic viremia, vascular damage, and coagulopathy. These mechanisms highlight potential therapeutic targets, including glycoprotein-focused vaccines and inhibitors of viral polymerase activity[22]. This cascade highlights MACV’s immune subversion, fueling research into GP-targeted vaccines and RdRp inhibitors.

TRANSMISSION AND OCCUPATIONAL RISK

Humans acquire MACV primarily through zoonotic spillover from C. callosus reservoirs: Inhaling aerosolized urine/feces/droppings in peridomestic settings, ingesting contaminated food/water, or percutaneous/mucosal contact during farming or cleaning. Vertical transmission occurs in rodents (neonatal persistence) and rarely in gravid women, with transplacental fetal infection documented.

Person-to-person spread proves inefficient (limited secondary cases) yet manifests nosocomially-via blood splashes, fomites, or needlesticks-as in 1971 Cochabamba. High-risk occupations include: Agrarian workers (rodenticide applicators, harvesters). Veterinarians and field biologists trapping C. callosus. BSL-4 lab personnel handling isolates. Stringent personal protective equipment, barrier nursing, and environmental decontamination mitigate risks; no traveler cases reported, confining threat to endemic Bolivia[23].

Early and accurate detection of MACV is essential for effective clinical management and outbreak control of BHF. Because the initial clinical presentation is nonspecific, laboratory confirmation using molecular, serological, antigen-based, or virological techniques is required. Diagnostic strategies vary depending on the stage of infection, sample availability, and biosafety infrastructure, with most confirmatory procedures performed under high-containment conditions. Recent advances in rapid molecular assays and point-of-care platforms are improving field diagnostics in endemic regions (Table 3).

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.

THERAPEUTIC AND PREVENTIVE INTERVENTIONS

Therapeutic approaches

Supportive therapy dominates: IV fluids/electrolytes for shock, transfusions for hemorrhage/coagulopathy, and mechanical ventilation for respiratory failure. Ribavirin (IV, 30 mg/kg loading then 16 mg/kg for every 6 hours for 4 days, 8 mg/kg × 6 days) shows preclinical promise (guinea pigs, nonhuman primates) and anecdotal success (1994 survivor), akin to Junín hemorrhagic fever, but randomized controlled trial lack-use off-label in severe acute cases.

Convalescent plasma curbed 1960s outbreaks (via hyperimmune Bolivian donors) yet faces supply/Logistics hurdles. Pipeline candidates target L polymerase (favipiriravir analogs), GP-TfR1 (monoclonals), and host factors [interferon (IFN) inducers].

Recent advancements in the treatment of MACV infection

BHF management stays supportive-fluids, shock reversal, complication control-absent approved antivirals/vaccines. Yet, post-2020 preclinical surges target MACV vulnerabilities[24,25].

Monoclonal antibodies: GP1-specific humanized monoclonal antibodies (mAbs) (e.g., MR191 analogs) neutralize TfR1 binding, achieving 100% guinea pig survival post-challenge (2022 studies); bispecifics vs clade B arenaviruses advance to investigational new drug.

Small-molecule antivirals: High-throughput screens yield L polymerase inhibitors (e.g., galidesivir derivatives, IC₅₀ < 1 μM in Vero cells) and entry blockers (GP2 helix mimetics); non human primate (NHP) efficacy trials ongoing (2024).

Ribavirin/favipiravir optimization: Dose-regimens refined via pharmacokinetic/pharmacodynamic modeling; combo with IFN-α boosts survival 80% in models, bridging to human compassionate use.

Reverse genetics platforms: Tri-segmented reassortants dissect Z-mediated shutoff, pinpointing RNAi triggers; Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) screens validate NP as host-directed target.

Immunomodulators: Epitope vaccines elicit antibody-dependent cellular cytotoxicity; checkpoint inhibitors (anti-PD-1) enhance T-cell clearance in persistent models. These pipelines signal Phase I readiness by 2027, prioritizing at-risk Bolivians.

Emerging therapeutic strategies for MACV

Neutralizing antibodies: National Institutes of Health initiatives engineer prefusion-stabilized GP trimer monoclonal antibodies to sterically hinder TfR1 engagement; guinea pig prophylaxis yields 90%-100% protection, paving Phase I paths akin to Ebola mAbs cocktails[26].

Polyclonal therapies: Hyperimmune guinea pig/equine sera mirror 1960s convalescent plasma success (80% survival boost); scaled IgG purification advances post-exposure prophylaxis for lab/Bolivian exposures.

Reverse vaccinology/multi-epitope designs: Immunoinformatics pipelines fuse GP/NP/L CTL/HTL/B-epitopes into chimeric immunogens; in silico human leucocyte antigen coverage > 95% predicts pan-population responses, with DNA/viral vector delivery in rodent trials.

Entry inhibitor screens: High-throughput screening libraries (e.g., National Center for Advancing Translational Sciences) uncover GP2 fusion peptides and TfR1 decoys (EC50 < 10 nM vs MACV pseudotypes); structure-guided optimization targets clade-shared sites for broad New World protection. These converge on prophylaxis-first paradigms, complementing ribavirin. No United States Food and Drug Administration/European Medicines Agency-approved antivirals or prophylactics exist for MACV; management hinges on supportive care and rodent control.

Prevention and control

Rodenticide campaigns slashing C. callosus densities halted 1960s epidemics and quelled 2007-2008 resurgence. Community measures: Home sealing, food storage, trapping, and education in Beni/La Paz[27].

Candid 1-a live-attenuated Junín vaccine-cross-protects against MACV (90% efficacy in primates); deployed off-label for Bolivian high-risk workers since about 2000s, though not formally licensed for BHF. Surveillance counters travel risks (no imported cases), with 2019 La Paz incursion signaling geographic creep. BHF’s triphasic course (febrile → hemorrhagic → convalescent) demands vigilance; MACV research bolsters arenavirus preparedness.

Vaccine development

No licensed MACV vaccine exists, but platforms leveraging arenavirus genetics advance toward high-risk immunization. Preclinical successes emphasize GP/NP immunogens for neutralizing antibodies (nAbs) and CD8+ T-cells.

Live-attenuated: Recombinant tri-segmented r3MACV (lassa GPC reassortant) elicits sterilizing immunity in guinea pigs (100% survival, no viremia); stable attenuation suits BSL-3 production.

Viral vectors: Adenovirus (Ad5) or modified vaccinia ankara expressing MACV GP/NP induce potent nAbs and T-cell responses in rodents/NHPs, with heterologous boosts enhancing durability.

Nucleic acid/peptide: DNA plasmids or mRNA encoding GP ectodomains, plus immunoinformatics-designed multi-epitope constructs (CTL/HTL/B-cell), promote balanced Th1/Th2 immunity; nanoparticle delivery boosts potency.

Cross-protective platforms: Candid 1 (Junín-attenuated) offers about 80% heterologous protection vs MACV in models; pan-new world arenavirus designs (e.g., GPC consensus) target Junín/Guanarito/Chapare/Machupo clade. Challenges include BSL-4 trials, maternal/fetal safety, and duration (> 5 years needed). Phase I human studies loom for r3MACV/vectors.

BIOSAFETY AND PUBLIC HEALTH CONSIDERATIONS

Laboratory biosafety

MACV’s aerosol transmissibility, > 30% CFR, and lab-infection history (e.g., 1969 Marburg analog) mandate BSL-4 protocols: Positive-pressure suits, class III cabinets, using high-efficiency air filters to discharge waste, and inactivated surrogates for downstream work. CDC/WHO categorize it as Risk Group 4; select-agent status restricts access.

Integrated one health tactics curb BHF

Rodent management: Carbamate rodenticides, traps, and habitat modification (C. callosus exclusion) slashed 1960s cases 90%.

Environmental interventions: Rodent-proof housing, elevated storage, sanitation in Beni villages.

Community education: Campaigns on excreta avoidance, early reporting-reduced 2008 outbreak scale.

Surveillance/diagnostics: Syndromic alerts, reverse transcription polymerase chain reaction networks, serosurveys in La Paz/Beni; mobile BSL-3 labs for edge detection. Intersectoral human-animal health synergy, plus tourism advisories, fortifies against emergence.

SUPPORTING TOOLS FOR THERAPEUTIC RESEARCH

Reverse genetics systems

The development of reverse genetics platforms for MACV enables researchers to construct recombinant viruses and minigenomes. These tools accelerate antiviral drug testing, allow functional studies of therapeutic targets, and facilitate preclinical evaluation of candidate treatments.

Despite encouraging progress in experimental therapeutics and vaccine platforms, the development of countermeasures against MACV faces significant practical barriers. As a BSL-4 pathogen, research is restricted to a limited number of high-containment laboratories, which slows preclinical testing and international collaboration. Ethical challenges also arise because BHF occurs sporadically and affects small populations, making large-scale randomized clinical trials difficult to conduct. In addition, manufacturing and commercialization of vaccines or antivirals for rare zoonotic diseases remain economically challenging, as limited market demand reduces industry investment. Regulatory complexities, logistical constraints in endemic rural regions, and the need for specialized cold-chain infrastructure further complicate the translation of promising laboratory findings into accessible clinical interventions. Addressing these barriers will require coordinated global funding mechanisms, flexible trial designs, and strengthened regional research capacity.

FUTURE DIRECTIONS FOR MACV RESEARCH

Breakthroughs in cryo-electron microscopy structures, artificial intelligence-immunoinformatics, and metagenomics accelerate MACV countermeasures. One health fusion of rodent genomics, eco-epidemiology, and host transcriptomics will unlock interventions, illuminating arenavirus-wide threats[28].

Reverse genetics systems

Reverse genetics approaches allow the reconstruction of infectious arenaviruses from engineered DNA copies of their genomes under controlled laboratory conditions. Using this strategy, researchers can introduce defined mutations into viral genes and analyze how these changes influence replication dynamics, virulence, and immune evasion. For MACV and related pathogens, reverse genetics platforms have become indispensable tools for mechanistic studies, antiviral target discovery, and rational vaccine design, especially given the limitations associated with handling high-containment viruses.

Key priorities

Vaccine innovation: Engineer mRNA, self-amplifying RNA, and nanoparticle platforms for durable, clade-spanning protection against BHF.

Targeted therapeutics: Screen host-directed (IFN boosters) and direct-acting (RdRp/GP inhibitors) agents via organoids and humanized models.

Pathogenic mechanisms: Elucidate replication/IFN antagonism using spatial multi-omics in disease-relevant NHPs.

Rapid diagnostics: Field-ready CRISPR/nanosensors for < 30-minutes RNA/antigen detection in Beni outposts.

One health surveillance: AI-modeled C. callosus spillover risks amid climate shifts and land-use change.

Infrastructure enhancement: Scale BSL-3 networks in Bolivia with virtual training/simulations.

Global partnerships: CEPI-like alliances for equitable trials, data commons, and bench-to-bedside translation.

CONCLUSION

MACV, the causative agent of BHF, remains a significant yet underrecognized zoonotic threat characterized by high case-fatality rates, persistent rodent reservoirs, and the need for high-containment laboratory facilities. Although historically restricted to Bolivia’s Beni region, environmental changes, human expansion into wildlife habitats, and increased mobility continue to elevate the risk of future spillover events. The clinical progression from early febrile illness to severe hemorrhagic manifestations underscores the importance of early recognition; however, limitations in rapid diagnostics and the absence of widely approved therapeutics continue to challenge effective management.

Recent advances in molecular virology and immunology have deepened our understanding of viral entry mechanisms, immune evasion strategies, and endothelial dysfunction, providing a foundation for next-generation vaccines and antiviral approaches. Despite this progress, research remains constrained by biosafety requirements and limited infrastructure in endemic regions. Moving forward, five priority actions are critical: (1) Accelerating vaccine and antiviral development through international collaborative trials; (2) Expanding rapid diagnostic capacity and genomic surveillance in endemic areas; (3) Strengthening BSL-3/4 laboratory infrastructure and workforce training; (4) Implementing integrated one health strategies focusing on rodent ecology, environmental monitoring, and community engagement; and (5) Enhancing global data sharing and coordinated outbreak preparedness. By prioritizing these strategic actions, MACV research can evolve from reactive outbreak response toward proactive prevention, offering valuable insights for managing other arenaviruses and emerging zoonotic hemorrhagic fevers worldwide.

ACKNOWLEDGEMENTS

I sincerely acknowledge Maharajah’s College of Pharmacy, Vizianagaram for its continuous support and cooperation in the completion of work.