Screening of Rodents from Rural Communities of Lagos and Ogun State Nigeria of Lassa Virus RNA

Background: In recent times, there has been an increase in the number of Lassa fever cases resulting from the several episodes of Lassa fever epidemics ravaging Nigeria and other West African countries. The presence of Lassa virus in rodents other than the major reservoir (Mastomys natalensis) has been a public health concern as to the actual burden of the disease. It is therefore of a public health necessity to explore the LASV RNA habouring potential of several species of rodents in endemic as well as non-endemic areas for proper prevention of emergence of outbreaks in non-endemic areas. Objectives: The aim of this study was to detect the presence of LASV RNA in different species of rodents in Ikorodu, Lagos state and Abeokuta, Ogun state. Methods: A total of ninety one (91) rodents were captured from Ikorodu, Lagos State (61 rodents) and Abeokuta, Ogun State (30 rodents), euthanized, bled, and plasma obtained for the detection of LASV RNA by Reverse Transcriptase Polymerase Chain Reaction. Results: A total of 91 rodents consisting of 77 Rattus rattus and 14 Crocidura spp. The S segment of LASV RNA was not in any of the 91 rodents’ plasma samples. Conclusion: The rodents captured within the rural communities of Ikorodu, Lagos State and Abeokuta, Ogun State were found not to habour the LASV RNA. This study is limited by the relatively small sample size. Similar studies should be encouraged both in endemic and non-endemic areas in order to understand the actual burden of Lassa fever as well as put into check future epidemics.

Lassa Fever: Patients Profile and Treatment Outcomes at Benue State University Teaching Hospital Makurdi, North-Central Nigeria

Lassa fever is a viral haemorrhagic fever found mostly in West Africa where it is endemic but generates periodic outbreaks in the dry seasons. The virus is spread by the rat species named mastomys natalensis. While the illness is minor in most cases, the mortality is significant in hospitalized patients. Few completely equipped treatment centers existed in Nigeria previous to current increase in frequency requiring demand for new treatment centers without the full complement of essential capabilities. Aim: To analyze the profile and treatment outcome in patients hospitalized in one of such new resource-constrained centers at the Benue State University Teaching Hospital Makurdi, Nigeria. Methodology: This was a retrospective, descriptive hospital-based research encompassing January 2020 to March 2023. Medical records of those admitted to the isolation center were reviewed. The relevant data was coded and analyzed using IBM SPSS version 23. Results: One hundred and ten (110) individuals were hospitalized for probable or suspected Lassa fever throughout the research period. A total of 35 confirmed patients satisfied the inclusion criteria and were included as the study subjects. There were 23 (65.7%) men and 12 (34.3%) females. Their mean age was 35.36 ± 12.21 years (range 15-61 years). The treatment outcome showed that 24 (75%) survived and were discharged, 5 (15.6%) were referred out of the facility for dialysis and 3 died, providing a mortality of 8.6%. The causes of mortality in study patients were acute kidney injury and encephalopathy. Conclusion: Lassa fever is endemic in Benue state with all types of individuals afflicted. The outcome of treatment was good despite resource difficulties. Lassa fever can be successfully managed even in resource-challenged situations typically encountered in developing countries.

Lassa Fever Case Report: Challenges in Making Early Diagnosis

Introduction: Lassa fever is a disease of public health importance because of the associated morbidity and high case fatality rate among hospitalized patients. Even after recovery, there may be residual problems such as sensorineural hearing loss. The initial presentation of Lassa fever may be with non-specific symptoms similar to what is seen in the more common febrile illnesses such as malaria or typhoid fever. In such a setting therefore, timely diagnosis of Lassa fever may be difficult. Case Report: We report a case of Lassa fever that presented to our institution. She was a middle aged woman who had non-specific symptoms of febrile illness and who died in less than 48 hours of admission. She had a subtle bleeding on the lip just before death which was what raised the suspicion for Lassa fever. Laboratory confirmation of Lassa fever was made retrospectively. Conclusion: When the presenting symptoms are non-specific, a high index of suspicion is required for timely recognition of Lassa fever. Early diagnosis is important for prompt therapeutic intervention as well as for limiting the spread of the disease. This is the second case of Lassa fever presenting to our hospital, but the first published case of Lassa fever from our hospital.

Clinical Presentations of Lassa Fever in Non-Endemic Parts of the World: A Systematic Review

Background: Lassa fever cases outside Africa are seen as imported cases of Lassa fever. Timely diagnosis of imported Lassa fever is important for timely intervention necessary to reduce the morbidity and mortality associated with Lassa fever, and this requires the knowledge of the clinical manifestations of Lassa fever. Purpose: This review was done to see how clinical diagnosis of imported Lassa fever can be facilitated based on the clinical presentations of imported cases of Lassa fever in Lassa fever non-endemic region. Methods: The relevant articles for the review were obtained from the databases of PubMed and Google Scholar. Results: The clinical presentations of the imported Lassa fever cases consisted of multisystem involvement and were similar to those of Lassa fever patients who were treated in the Lassa fever endemic region. Conclusions: History of recent travel to, or residence in, Lassa fever endemic region is an important clue for clinical diagnosis of Lassa fever. The 2011 CDC surveillance case definition and the modified Khan case definition for Lassa fever may aid clinical diagnosis of Lassa fever. Any clinically suspected case of Lassa fever should have a laboratory confirmation.

From Social Determinants of Health Actions to Fight against the Lassa Virus Hemorrhagic Fever Epidemic in Tchaourou Commune in Benin, 2018

Background: Lassa Hemorrhagic Fever (LHF) is endemo-epidemic in West Africa with seasonal outbreaks raising a major public health issue. Nigeria borders Benin by the Tchaourou Commune. Since 2016, Tchaourou commune has been affected every year by this epidemic. Objective: To study how an action on the health social determinants can contribute to ending this epidemic in Tchaourou commune, Benin. Methods: This cross-sectional study was conducted in Tchaourou commune. All of the cases of LHF occurring in 2016-2018 were retrospectively tracked throughout the commune. The health workers and 172 participants of the general population of villages of the cases were enrolled. We used absolute frequency to describe the LHF cases because of their small number. The descriptive analyses were performed using EPI-INFO 7.1.14. Results: Overall, 27 cases of LHF occurred in Tchaourou. In these 27 cases, 12 were Laboratory-Confirmed. All 4 probable cases died while 42% and 18% died in the confirmed and suspected cases, respectively. Most (75%) of the cases were female. By direct observations, the commune had a weak health-promoting environment for fighting against LHF outbreak. According to the health care staff in the commune, the interventions were for controlling the outbreak and not the promoting interventions to preventing further outbreaks. Conclusion: To fight effectively against the Lassa fever, it is necessary to act on different social determinants of health with community participation, empowerment and health control. The fight against Lassa fever remains a major challenge facing developing countries like Benin.

Prognosis and Evolution of Lassa Virus Infected Persons during the 2017 Epidemic in Togo

Introduction: Lassa viral hemorrhagic fever is common in West Africa. Almost 300,000 persons are affected each year with 5000 deaths. The mice of the genus mastomys is the wild tank. Objective: The aim of our study is to describe clinic, therapeutic and evolution of the affected patients during February-March 2017 epidemic that occurred in the north of Togo. Methodology: Our study is a record review study from patients’ record, who were hospitalized from February, 1st to March, 31st 2017 at Mango hospital. Lassa diagnosis was performed by PCR. They patients have received Ribavirin and blood transfusion when necessary. Results: We have reported 5 clinical observations of Lassa viral hemorrhagic fever. Patients came from Benin (03 cases), from Burkina-Faso (1 case), from Togo (1 case) and were 25, 34, 60, 52 years old and a premature baby of 13 days. External hemorrhage and abdominal pains were the main symptoms. Fever was observed for all the cases. Complications were marked by hemorrhages and shocks. Only 3 patients had benefitted of Antiviral therapy with Ribavirin. The other 2 patients did not benefit from the treatment because the diagnosis of Lassa fever was done the day they dead before the treatment started. Lethality was 80% (4 cases) with a highly secured burial. Effective management of contacts was done. Conclusion: Diagnostic and therapeutic delays of patients are responsible of the bad prognosis of the disease.

The Lassa Virus Epidemic in Mango, Togo: Therapeutic Route of the First 4 Cases

Introduction: Lassa viral hemorrhagic fever is caused by the Lassa virus. The aim of our study is to describe the therapeutic itinerary of the 4 cases of Lassa virus hemorrhagic of February-March 2017 epidemic that occurred in Mango. Methodology: Our study is a transverse retro-prospective and descriptive study from February, 1st to March, 31st 2017 that dealt with 4 confirmed Lassa fever cases declared positive on the PCR basis;hospitalized or deceased at the hospital “Esperance” of Mango;support center of Lassa viral hemorrhagic fever. Results: we reported 4 clinical observations of Lassa viral hemorrhagic fever diagnosed on the PCR basis during the Lassa fever epidemic. Patients came from Benin (2 cases) or from Burkina-Faso (1 case) and were 25, 60, 52 years old and a premature baby of 13 days. The reasons for admission were external hemorrhage, a pultated tonsillitis and abdominal pains. Fever was observed for all the cases. Complications were marked by hemorrhages and shocks. Only two patients benefitted from Antiviral therapy with Ribavirin and were declared healed. The other two patients did not benefit from the treatment due to diagnostic and therapeutic delays. Lethality was 75% (3 cases) with a highly secured burial. Effective management of contacts was established. Conclusion: Diagnostic and therapeutic delays of patients are responsible of the Dark Prognosis of Lassa fever during the epidemic.

Hearing Loss in Lassa Fever: A Systematic Review

Background: Lassa fever is a viral haemorrhagic fever associated with several complications which include hearing loss. Hearing loss in Lassa fever may become residual with its negative impact on the quality of life. Purpose: This paper is a review of various studies on Lassa fever related hearing loss. Methods: Systematic literature review was done on articles on Lassa fever patients and Lassa fever survivors. Relevant articles published in English between 1969 and 2021 were searched for using Google Scholar and PubMed databases. Eight studies which met the inclusion criteria were finally selected and included in the review. The variables of interest were extracted from the full-text articles. Results: Lassa fever related hearing loss occurs in both sexes and in all age groups. The incidence of self-reported hearing loss ranged from 12.5% to 30% with a mean of 17.6%. The incidence of audiometrically determined sensorineural hearing loss ranged from 13.5% to 29% with a mean of 22.1%. Hearing loss persisted in 64% of those that were followed up. Cases of hearing loss varied in severity, ranging from mild to profound. No successful specific treatment for Lassa fever related hearing loss was reported apart from hearing rehabilitation. Conclusion: Hearing loss among Lassa fever patients remains a major challenge. Lack of effective treatment for Lassa fever related hearing loss is a serious gap in the management of Lassa fever patients which should be addressed in future research.

Epidemiological Pattern of Lassa Fever Outbreak in Ondo State, Southwest Nigeria, 2014 to 2019

Introduction: Annual outbreak of Lassa Fever (LF) has been reported in Ondo State over the years. We analyzed LF surveillance data from January 2014 to December 2019 to describe the epidemiological pattern of the outbreak. Method: Lassa fever dataset from January 2014 to December 2019 was obtained from the State Ministry of Health. Variables analyzed include date of onset of symptom, age, gender, place (Local Government Area, LGA) and outcome of laboratory test. Data were summarized using frequencies, proportions, chart and maps. Results: From January 2014 and December 2019, 2141 suspected LF cases were reported. Of these, 551 cases were laboratory confirmed with 134 deaths recorded. The LF cases (suspected vs. confirmed) reported increased in 2016 (73 vs. 19), 2017 (207 vs. 76), 2018 (452 vs. 159) and 2019 (856 vs. 285) respectively. Most of the confirmed cases (89.5%) were ≥15 years while more than half (53.7%) were males. Prior to 2016, only two LGAs (Owo and Ose) recorded continued transmission of the disease. However, between 2016 and 2019, the disease had spread to 8 neighboring LGAs (P < 0.001) with the CFR declining from 67% in 2015 to 20% in 2019. Conclusion: We found an unusual increase in the suspected LF cases reported between January 2016 and December 2019 with a corresponding increase in the confirmed cases and high annual case fatality rates. Hence, we recommend intensified surveillance activities to enhance timely reporting of cases and laboratory confirmation to ensure early commencement of treatment to reduce the case fatality rate.

Seasonal Changes in Vegetation and Land Use in Lassa-Fever-Prone Areas (Kenema and Kailahun Districts) in Eastern Sierra Leone

Lassa Fever is endemic to the eastern region of Sierra Leone. It is a haemorrhagic disease that is often transmitted from rats to humans and then human to humans. Ecological disturbances such as changes in land use involving conversion of natural ecosystems to agriculture, mining or for urban expansion are reported to bring humans into close contact with animals such as the Mastomys rat that carries the Lassa Fever virus thereby posing health problems.The nature and extent of such ecological disturbances or land use changes within areas known to be endemic to Lassa Fever are not clearly understood from a research context in Sierra Leone. This study was therefore undertaken to identify the pattern of changes in land use and cropping practices and their potential to bring humans into close interactions with the Mastomys rat that is the host for the Lassa Fever virus. Four communities were chosen for the study, two rural (Lalehun and Majihun) and two urban (Lambayama section in Kenema City and Largo Square section in Segbwema Town). Different vegetation and land use/cropping practices were identified and observations were made on the pattern of changes at different times in the cropping year. There were four common vegetation and cropping practices found in all communities: upland rice intercropping, old fallow, young fallow, and swamp rice cultivation. The study revealed the variations in land use patterns and cropping practices between urban and rural settlements. Agro-forestry practices such as perennial cash crops cacao and rubber plantations were more common in rural communities. The study also revealed that while fallow vegetation persisted in rural areas there had been expansion of settlements into old fallow vegetation indicating a greater threat to the persistence of natural ecosystem in urban than in rural settlements. These disturbances resulted in habitat fragmentation and increased the likelihood of contact between humans and animal species (e.g. Mastomys rat) associated with various habitats.

Understanding the transmission pathways of Lassa fever:A mathematical modeling approach

The spread of Lassa fever infection is increasing in West Africa over the last decade.The impact of this can better be understood when considering the various possible transmission routes.We designed a mathematical model for the epidemiology of Lassa Fever using a system of nonlinear ordinary differential equations to determine the effect of transmission pathways toward the infection progression in humans and rodents including those usually neglected such as the environmental surface and aerosol routes.We analyzed the model and carried out numerical simulations to determine the impact of each transmission routes.Our results showed that the burden of Lassa fever infection is increased when all the transmission routes are incorporated and most single transmission routes are less harmful,but when in combination with other transmission routes,they increase the Lassa fever burden.It is therefore important to consider multiple transmission routes to better estimate the Lassa fever burden optimally and in turn determine control strategies targeted at the transmission pathways.

Deletion of the first glycosylation site promotes Lassa virus glycoprotein-mediated membrane fusion

The Lassa virus(LASV)is endemic in West Africa and causes severe hemorrhagic Lassa fever in humans.The glycoprotein complex(GPC)of LASV is highly glycosylation-modified,with 11 N-glycosylation sites.All 11 N-linked glycan chains play critical roles in GPC cleavage,folding,receptor binding,membrane fusion,and immune evasion.In this study,we focused on the first glycosylation site because its deletion mutant(N79Q)results in an unexpected enhanced membrane fusion,whereas it exerts little effect on GPC expression,cleavage,and receptor binding.Meanwhile,the pseudotype virus bearing GPC_(N79Q)was more sensitive to the neutralizing antibody 37.7H and was attenuated in virulence.Exploring the biological functions of the key glycosylation site on LASV GPC will help elucidate the mechanism of LASV infection and provide strategies for the development of attenuated vaccines against LASV infection.

Identification of the dietary supplement capsaicin as an inhibitor of Lassa virus entry

The limited treatment options for the increasing occurrence of Lassa hemorrhagic fever in West Africa poses an urgent need for the discovery and development of novel therapeutics.Dietary supplements,especially natural products that are edible and safe for human use,are a good source of drug discovery with potential for uncovering novel applications,In this study,we tested 40 natural products of dietary supplements and identified capsaicin,a common dietary supplement abundant in chili peppers,as an inhibitor of Lassa virus(LASV)entry with EC5,of 6.9-10.0μmol/L using an HIV based pseudo virus platform.Capsaicin inhibits the entry of five LASV strains but not against the Old World arenavirus lymphocytic choriomeningitis virus(LCMV),showing a preferential activity against LASV.Capsaicin inhibits LASV entry by blocking the pH dependent viral fusion through affecting the stable signal peptide(SSP)-GP2 transmembrane(GP2TM)region of the LASV surface glycoprotein.Mutational study revealed the key residues Ala25,Val431,Phe434 and Val435 in SsP-CP2TM region in capsaicin’s antiviral effect.This study for the first time reveals a direct acting antiviral effect of capsaicin against the hemorrhagic fever causing LASV,providing detailed interaction hot spots in the unique SSP-GP2TMinterface of LASV glycoprotein that is crucial in fusion inhibition,and offering a new strategy in discovering and developing antivirals from natural products that are safe for human use.

Fatal case of newborn Lassa fever virus infection mimicking late onset neonatal sepsis: a case report from northern Nigeria

Background:Lassa fever is a zoonotic viral infection endemic to the West Africa countries.It is highly fatal during pregnancy and as such reports of neonatal onset Lassa fever infections are rare in scientific literature.We report a fatal case of Lassa fever in a 26-day-old neonate mimicking the diagnosis of late-onset neonatal sepsis.Case presentation:The patient is a 26-day-old neonate who was admitted with a day history of fever,poor feeding,pre-auricular lymphadenopathy and sudden parental death.He was initially evaluated for late onset neonatal sepsis.He later developed abnormal bleeding and multiple convulsions while on admission,prompting the need to evaluate for Lassa fever using reverse transcription polymerase chain reaction(RT-PCR).He died 31 h into admission and RT-PCR result was positive for Lassa fever.Conclusions:Neonatal Lassa fever infection is highly fatal and can mimic neonatal sepsis.High index of suspicion is needed particularly for atypical presentations of neonatal sepsis in Lassa fever endemic areas.

Analysis of Lassa hemorrhagic fever model with non-local and non-singular fractional derivatives

In this paper, we investigate a possible applicability of the newly established fractional differentiation in the field of epidemiology. To do this, we extend the model describing the Lassa hemorrhagic fever by changing the derivative with the time fractional derivative for the inclusion of memory. Detailed analysis of existence and uniqueness of exact solution is presented using the Banach fixed point theorem. Finally, some numerical simulations are shown to underpin the effectiveness of the used derivative.

Characterizing the Lassa Virus Envelope Glycoprotein Membrane Proximal External Region for Its Role in Fusogenicity

The membrane-proximal external region(MPER)of Lassa virus(LASV)glycoprotein complex(GPC)is critical in modulating its functionality.Till now,the high-resolution structure of the intact GPC,including MPER is not available.In this study,we used alanine substitution to scan all 16 residues located in LASV MPER.Western blotting and quantification fusion assay showed that the residues located at the C terminus of the HR2(M414 and L415)and N terminus of the MPER(K417 and Y419)are critical for GPC-mediated membrane fusion function.Furthermore,cell surface biotinylation experiments revealed that M414 A,K417 A and Y419 A expressed similar levels as WT,whereas L415 A mutant led to a reduction of mature GPC on the cell surface.Moreover,substitution of these residues with the similar residue such as M414 L,L415 I,K417 R and Y419 F would partly compensate the loss of the fusion activity caused by the alanine mutant in these sites.Results from this study showed that several key residues in the MPER region are indispensable to promote the conformational changes that drive fusion events and shed light on the structure analysis of LASV GPC and anti-LASV therapeutics.

Re-emerging Lassa fever outbreaks in Nigeria:Re-enforcing“One Health”community surveillance and emergency response practice

We evaluated the impact of man-made conflict events and climate change impact in guiding evidence-based community“One Health”epidemiology and emergency response practice against re-/emerging epidemics.Increasing evidence of emerging and re-emerging zoonotic diseases including recent Lassa fever outbreaks in almost 20 states in Nigeria led to 101 deaths and 175 suspected and confirmed cases since August 2015.Of the 75 laboratory confirmed cases,90 deaths occurred representing 120%laboratory-confirmed case fatality.The outbreak has been imported into neighbouring country such as Benin,where 23 deaths out of 68 cases has also been reported.This study assesses the current trends in re-emerging Lassa fever outbreak in understanding spatiogeographical reservoir(s),risk factors pattern and Lassa virus incidence mapping,inherent gaps and raising challenges in health systems.It is shown that Lassa fever peak endemicity incidence and prevalence overlap the dry season(within January to March)and reduced during the wet season(of May to November)annually in Sierra Leone,Senegal to Eastern Nigeria.We documented a scarcity of consistent data on rodent(reservoirs)-linked Lassa fever outbreak,weak culturally and socio-behavioural effective prevention and control measures integration,weak or limited community knowledge and awareness to inadequate preparedness capacity and access to affordable case management in affected countries.Hence,robust sub/regional leadership commitment and investment in Lassa fever is urgently needed in building integrated and effective community“One Health”surveillance and rapid response approach practice coupled with pest management and phytosanitation measures against Lassa fever epidemic.This offers new opportunities in understanding human-animal interactions in strengthening Lassa fever outbreak early detection and surveillance,warning alerts and rapid response implementation in vulnerable settings.Leveraging on Africa CDC centre,advances in cloud-sourcing and social media tools and solutions is core in developing and integrating evidence-based and timely risk communication,and reporting systems in improving contextual community-based immunization and control decision making policy to effectively defeat Lassa fever outbreak and other emerging pandemics public health emergencies in Africa and worldwide.

Effects of N-Linked Glycan on Lassa Virus Envelope Glycoprotein Cleavage,Infectivity,and Immune Response

Lassa virus(LASV)belongs to the Mammarenavirus genus(family Arenaviridae)and causes severe hemorrhagic fever in humans.The glycoprotein complex(GPC)contains eleven N-linked glycans that play essential roles in GPC functionalities such as cleavage,transport,receptor recognition,epitope shielding,and immune response.We used three mutagenesis strategies(asparagine to glutamine,asparagine to alanine,and serine/tyrosine to alanine mutants)to abolish individual glycan chain on GPC and found that all the three strategies led to cleavage inefficiency on the 2nd(N89),5th(N119),or 8th(N365)glycosylation motif.To evaluate N to Q mutagenesis for further research,it was found that deletion of the 2nd(N89Q)or 8th(N365Q)glycan completely inhibited the transduction efficiency of pseudotyped particles.We further investigated the role of individual glycan on GPC-mediated immune response by DNA immunization of mice.Deletion of the individual 1st(N79Q),3rd(N99Q),5th(N119Q),or 6th(N167Q)glycan significantly enhanced the proportion of effector CD4+cells,whereas deletion of the 1st(N79Q),2nd(N89Q),3rd(N99Q),4th(N109Q),5th(N119Q),6th(N167Q),or 9th(N373Q)glycan enhanced the proportion of CD8+effector T cells.Deletion of specific glycan improves the Th1-type immune response,and abolishment of glycan on GPC generally increases the antibody titer to the glycan-deficient GPC.However,the antibodies from either the mutant or WT GPC-immunized mice show little neutralization effect on wild-type LASV.The glycan residues on GPC provide an immune shield for the virus,and thus represent a target for the design and development of a vaccine.

Lassa hemorrhagic fever model using new generalized Caputo-type fractional derivative operator

In some of the previous decades, we have observed that mathematical modeling hasbecome one of the most interesting research fields and has attracted many researchers.In this regard, thousands of researchers have proposed different varieties of mathematicalmodels to study the dynamics of a number of real-world problems. This research workis framed to analyzing the structure of the well-known Lassa hemorrhagic epidemic;adangerous epidemic for pregnant women, via new generalized Caputo type nonintegerorder derivative with the help of a modified Predictor–Corrector scheme. Lassa hemorrhagic disease is an epidemical and biocidal fever, whose negative impacts were initiallyrecognized in the countries of Africa. This virus has killed many pregnant women ascompared to the Ebola epidemic. It was noticed that Lassa virus was isolated in Verocell cultures from a blood pattern, and after 12 days it was ejective, after the climb ofthe sickness. In this research study, necessary theorems and lemmas are reminded toprove the existence of a unique solution and stability of given fractional approximationscheme. All necessary results are reminded to confirm the effectiveness of the proposedapproximation algorithm by graphical observations for various fractional-order values.In our practical calculations, we plotted the graphs for two different values of naturaldeath rate along with various values of given fractional-order operator. Our major target is to show the importance of the proposed modified version of the Predictor–Correctoralgorithm in epidemic studies by exploring the given Lassa hemorrhagic fever dynamics.

班公湖-怒江缝合带同碰撞海沟盆地砂岩物源分析及其大地构造意义

同碰撞海沟沉积可为重建板块缝合带大地构造演化、约束陆块初始碰撞时间提供重要信息。本文对班公湖-怒江缝合带西段的改则县亚多组和日土县多仁组进行了沉积学、岩相学、碎屑锆石年代学、重矿物研究。沉积学分析表明,多仁组、亚多组沉积于海底扇环境。最年轻的碎屑锆石年龄限制了最早沉积时代为晚侏罗世。多仁组、亚多组砂岩Q:F:L分别为52:4:44、32:8:60,均以丰富的沉积岩和酸性火成岩岩屑及少量的变质岩屑为特征;重矿物以磷灰石、锆石、电气石等稳定重矿物为主。多仁组和亚多组具有相似的碎屑锆石年龄分布模式,主峰分布在350~200 Ma、550~450 Ma、900~750 Ma、1900~1800 Ma、2550~2450 Ma范围内。这些数据表明,亚多组、多仁组碎屑物质来源于沉积区北侧的班公湖-怒江缝合带增生杂岩及南羌塘岩浆岩。多仁组、亚多组出现的大量沉积岩岩屑,表明物源区经历了广泛的构造缩短作用,导致沉积岩和同期岩浆岩被剥蚀,因此多仁组、亚多组是拉萨-羌塘同碰撞的产物。据此推断,沿班公湖-怒江缝合带改则-日土区域拉萨-羌塘初始碰撞发生在晚侏罗世多仁组、亚多组沉积之前。