Incubation Period Of Infection Research Articles

Weather conditions and legionellosis: a nationwide case-crossover study among Medicare recipients.

Legionellosis is a respiratory infection caused by Legionella sp. that is found in water and soil. Infection may cause pneumonia (Legionnaires' Disease) and a milder form (Pontiac Fever). Legionella colonizes water systems and results in exposure by inhalation of aerosolized bacteria. The incubation period ranges from 2 to 14 days. Precipitation and humidity may be associated with increased risk. We used Medicare records from 1999 to 2020 to identify hospitalizations for legionellosis. Precipitation, temperature, and relative humidity were obtained from the PRISM Climate Group for the zip code of residence. We used a time-stratified bi-directional case-crossover design with lags of 20 days. Data were analyzed using conditional logistic regression and distributed lag non-linear models. A total of 37883 hospitalizations were identified. Precipitation and relative humidity at lags 8 through 13 days were associated with an increased risk of legionellosis. The strongest association was precipitation at day 10 lag (OR = 1.08, 95% CI = 1.05-1.11 per 1 cm). Over 20 days, 3 cm of precipitation increased the odds of legionellosis over four times. The association was strongest in the Northeast and Midwest and during summer and fall. Precipitation and humidity were associated with hospitalization among Medicare recipients for legionellosis at lags consistent with the incubation period for infection.

Transcriptomic Profiling of Bean Aphid Megoura crassicauda upon Exposure to the Aphid-Obligate Entomopathogen Conidiobolus obscurus (Entomophthoromycotina) and Screening of CytCo-Binding Aphid Proteins through a Pull-Down Assay.

Prolonged periods of host-lethal infection by entomopathogenic fungi pose challenges to the development of biological control agents. The obligate entomopathogen C. obscurus, however, rapidly kills aphid hosts, warranting investigation. This study investigated the interaction between C. obscurus and a bean aphid Megoura crassicauda during the incubation period of infection, using transcriptome analysis to map host gene expression profiles. Results indicate C. obscurus-inoculated aphid activation of the wound healing immune responses, alongside suppression of the key molecules involved in Toll signaling, melanization, and metabolism. Furthermore, neuromotor system-related genes were upregulated, paralleling the intoxication observed in a nematode pest treated with C. obscurus-derived CytCo protein. To deepen interaction insights, a His-tag pull-down assay coupled with mass spectrometry analysis was conducted using CytCo as a bait to screen for potential aphid protein interactors. The proteins were identified based on the assembled transcriptome, and eleven transmembrane proteins were predicted to bind to CytCo. Notably, a protein of putatively calcium-transporting ATPase stood out with the highest confidence. This suggests that CytCo plays a vital role in C. obscurus killing aphid hosts, implicating calcium imbalance. In conclusion, C. obscurus effectively inhibits aphid immunity and exhibits neurotoxic potential, expediting the infection process. This finding facilitates our understanding of the complex host-pathogen interactions and opens new avenues for exploring biological pest management strategies in agroforestry.

Study of incubation period of infection with 2019-nCoV Omicron variant BA.5.1.3

Objective: To study the incubation period of the infection with 2019-nCoV Omicron variant BA.5.1.3. Methods: Based on the epidemiological survey data of 315 COVID-19 cases and the characteristics of interval censored data structure, log-normal distribution and Gamma distribution were used to estimate the incubation. Bayes estimation was performed for the parameters of each distribution function using discrete time Markov chain Monte Carlo algorithm. Results: The mean age of the 315 COVID-19 cases was (42.01±16.54) years, and men accounted for 30.16%. A total of 156 cases with mean age of (41.65±16.32) years reported the times when symptoms occurred. The log-normal distribution and Gamma distribution indicated that the M (Q1, Q3) of the incubation period from exposure to symptom onset was 2.53 (1.86, 3.44) days and 2.64 (1.91, 3.52) days, respectively, and the M (Q1, Q3) of the incubation period from exposure to the first positive nucleic acid detection was 2.45 (1.76, 3.40) days and 2.57 (1.81, 3.52) days, respectively. Conclusions: The incubation period by Bayes estimation based on log-normal distribution and Gamma distribution, respectively, was similar to each other, and the best distribution of incubation period was Gamma distribution, the difference between the incubation period from exposure to the first positive nucleic acid detection and the incubation period from exposure to symptom onset was small. The median of incubation period of infection caused by Omicron variant BA.5.1.3 was shorter than those of previous Omicron variants.

Bioinspired Plasmo-virus for Point-of-Care SARS-CoV-2 Detection.

Directly identifying the presence of the virus in infected hosts with an appropriate speed and sensitivity permits early epidemic management even during the presymptomatic incubation period of infection. Here, we synthesize a bioinspired plasmo-virus (BPV) particle for rapid and sensitive point-of-care (POC) detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) via a self-assembled plasmonic nanoprobe array on spike proteins. The BPV enables strong near-infrared (NIR) extinction peaks caused by plasmonic nanogaps. We quantify SARS-CoV-2 in viral transport medium (VTM) at low titers within 10 min with a limit of detection (LOD) of 1.4 × 101 pfu/mL, which is 103 times more sensitive than the current gold-standard method. The high-sensitivity and high-speed POC detection may be widely used for the timely, individualized diagnosis of infectious agents in low-resource settings.

Monkeypox: A Re-emerging Viral Zoonotic Infection

Context: Monkeypox virus (MPXV) infection is a zoonotic disease, endemic in sub-Saharan Africa, but recently has re-emerged outside Africa and caused some concerns. Evidence Acquisition: The current study aimed to briefly present a narrative mini-review on different features of MPXV. Data were gathered from Google Scholar, ScienceDirect, and PubMed databases and also WHO and CDC websites, using ''Monkeypox'', ''Variola'', ''Bioterrorism'', and ''Bioweapon'' keywords. Results: Monkeypox virus is categorized into two genetic clades with different outcomes. The incubation period of infection is 5 - 21 days, and infection by Central African clade may lead to a clinical representation similar to smallpox with about 10% mortality rate. Monkeypox virus can infect a wide range of mammals, and its natural reservoir is almost unknown. It is endemic in sub-Saharan Africa and is rarely seen outside Africa. Its most reliable detection is based on nucleic acid amplification tests (NAATs). Treatment is mainly supportive, and some selective drugs are developed for severe cases. Avoiding close contact with wild animals and infected patients is the first line of prevention. Prior vaccination with smallpox or MPX vaccines is also protective. Due to similar symptoms of human monkeypox and smallpox, it may be a candidate for bioterrorism. However, there is no evidence of recent intentional spread of MPXV. Conclusions: This study has tried to provide a summary of MPXV infection. Despite recent concerns, there is still a very low risk of the MPXV pandemic. However, it is recommended to be alert for such infection and provide essential readiness against it.

Heterogeneous epidemic modelling within an enclosed space and corresponding Bayesian estimation.

Since March 11th, 2020, COVID-19 has been a global pandemic for more than one years due to a long and infectious incubation period. This paper establishes a heterogeneous epidemic model that divides the incubation period into infectious and non-infectious and employs the Bayesian framework to model the ‘Diamond Princess’ enclosed space incident. The heterogeneity includes two different identities, two transmission methods, two different-size rooms, and six transmission stages. This model is also applicable to similar mixed structures, including closed schools, hospitals, and communities. As the COVID-19 pandemic continues, our mathematical modeling can provide management insights to the governments and policymakers on how the COVID-19 disease has spread and what prevention strategies still need to be taken.

COVID-19 MANIFESTATION IN A CHILD WITH LUNG METASTASES OF OSTEOSARCOMA: A CASE REPORT

Background: COVID-19 (Corona virus disease-19) is an infectious disease caused by a new type of corona virus which in the same group of the virus that causes Severe Acute Respiratory Syndrome (SARS), where the incubation period for infection is 1-14 days or up to 24 days, accompanied by symptoms of a respiratory tract infection and other organ systems. The number of recent cases in November 2020 was 59.8 million worldwide. Elderly patients and people with comorbid diseases are at high risk of developing severe manifestations of this viral infection. Osteosarcoma is a deadly bone cancer that often causes patients to die from metastases to the lungs Purpose: The purpose of this study is to report cases of COVID-19 in a 9-year old child patient with a history of osteosarcoma at Bethesda Hospital Yogyakarta. Case Description: A 9-year old female patient came to the emergency room complaining of fever, cough, severe chest pain, and shortness of breath since 3 weeks before being admitted to the hospital. The patient had a past medical history of osteosarcoma since 1.5 years before being admitted to the hospital and an amputation procedure on the right arm was carried out, no specific illness in the family history was found. The general condition of the patient appears to be moderate with delirium consciousness (E4V6M1). Vital sign examination showed a pulse rate of 130 beats per minute, an oxygen saturation of 85% and a breath rate of 30 beats per minute. CT scan without contrast shows a massive left pleural effusion, malignancy/metastatic mass of the left lung, with pneumonic opacity in the right lung. Conclusion: COVID-19 is an infectious disease caused by SARS-CoV-2 and causes severe manifestations in patients with comorbid diseases including pulmonary metastases. CT-Scan modalities are used as a basis for diagnosis other than RT-PCR. Management of COVID-19 is in the form of supportive therapy based on the degree of disease severity.

A simple statistical physics model for the epidemic with incubation period

Based on the classical SIR model, we derive a simple modification for the dynamics of epidemics with a known incubation period of infection. The model is described by a system of integro-differential equations. Parameters of our model are directly related to epidemiological data. We derive some analytical results, as well as perform numerical simulations. We use the proposed model to analyze COVID-19 epidemic data in Armenia.

Influence of Gamma Irradiated Steinernema carpocapsae on Some Physiological Aspects of Galleria mellonella Larvae

The physiological changes in G. mellonella larvae treated with unirradiated and 2 Gy gamma irradiated S. carpocapsae had been investigated. The results indicated that S. carpocapsae exhibited a significant decrease in the total body concentrations of proteins, lipids, carbohydrates and urea of 5th larval of G. mellonella with increasing the infection incubation period. Moreover, the decrease in the concentration of these total body metabolic products was greatly remarkable in larvae infected with gamma irradiated S. carpocapsae. In contrast, the results revealed that S. carpocapsae caused a significant increase in the acid phospatase and chitinase activity of the total body of 5th larval instar of G. mellonella with increasing the treatment time. Which was greatly remarkable in larvae treated with gamma irradiated S. carpocapsae. Protein bands at different time intervals for all tested treatments revealed the absence of some bands, appearance of new bands and changes in the intensity of the bands. Therefore, it could be concluded that gamma irradiation of S. carpocapsae increased it’s efficacy and can be used in pest control.

Predictive values of the postoperative neutrophil-to-lymphocyte ratio, platelet-to-lymphocyte ratio, and lymphocyte-to-monocyte ratio for the diagnosis of early periprosthetic joint infections: a preliminary study

BackgroundSeveral studies have been conducted to report diagnostic values of the neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), and lymphocyte-to-monocyte ratio (LMR) in the many diseases, such as oncological, inflammatory, and some infectious diseases. However, the predictive value of these laboratory parameters for early periprosthetic joint infections (PJIs) has not yet been reported. The aim of this study was to determine predictive values of the postoperative NLR, PLR, and LMR for the diagnosis of PJIs.MethodsIn this retrospective study, 104 patients (26 early PJI cases and 78 non-PJI cases) who underwent total joint arthroplasty were enrolled in this study. All the patients were then categorized into two groups: PJI group, patients with the diagnosis of PJI (26 patients; 14 males, 12 females; mean age = 65.47 ± 10.23 age range = 51–81 ) and non-PJI group, patients without PJI (78 patients; 40 males, 38 females; mean age = 62.15 ± 9.33, age range = 41–92). We defined “suspected time” as the time that any abnormal symptoms or signs occurred, including fever, local swelling, or redness around the surgical site between 2 and 4 weeks after surgery and before the diagnosis. Suspected time and laboratory parameters, including NLR, PLR, LMR, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP), were compared between both groups. The trends of postoperative NLR, LMR, PLR, CRP, and ESR were also reviewed. The predictive ability of these parameters at the suspected time for early PJI was evaluated by multivariate analysis and receiver operating characteristic (ROC) curve analysis.ResultsNLR, PLR, and LMR returned to preoperative levels within 2 weeks after surgery in the two groups. In the PJI group, NLR and PLR were significantly increased during the incubation period of infection or infection, and LMR was significantly reduced, although 61.5% (16/26) of the patients had normal white blood cells. Interestingly, ESR and CRP were still relatively high 2 weeks after surgery and were not different between the two groups before infection started (p = 0.12 and 0.4, respectively). NLR and PLR were significantly correlated with early PJI (Odds ratios for NLR and PLR = 88.36 and 1.12, respectively; p values for NLR and PLR = 0.005 and 0.01, respectively). NLR had great predictive ability for the diagnosis of early PJI, with a cut-off value of 2.77 (sensitivity = 84.6%, specificity = 89.7%, 95% CI = 0.86–0.97).ConclusionsESR and CRP seem not to be sensitive for the diagnosis of early PJI due to their persistently high levels after arthroplasty. The postoperative NLR at the suspected time may have a great ability to predict early PJI.

Art of prevention: Life in the time of coronavirus.

The novel coronavirus disease 2019 (COVID-19) has continued to progress since its discovery in December 2019. A cluster of patients with atypical pneumonia identified in Wuhan, China, served as the epicenter of this recent epidemic. This family of viruses is responsible for the common cold along with the infamous severe acute respiratory syndrome epidemic in 2002 and Middle East respiratory syndrome in 2012. The Southern China Wholesale Market reportedly has connections to the original 27 cases in Wuhan, China. The worldwide confirmed case total has eclipsed 1,450,000, with more than 83,000 deaths. Patient presentation ranges from mild respiratory illness to acute respiratory distress syndrome and subsequent death. Early epidemiologic studies of viral spread support the hypothesis that COVID-19 can remain latent with an extended and infectious incubation period. The U.S. government has issued level 3 precautions for most international travel, along with prohibiting entry to foreign nationals traveling from China, Iran, the United Kingdom, the Republic of Ireland, and the European Schengen area (e.g., France, Italy, Germany). Prevention remains the mainstay in treating and defeating the COVID-19 epidemic. Anyone infected or suspected of being infected should self-quarantine at home or admit themselves to a specified hospital with infrastructure to handle the situation. The combination of prevention and containment provides the best opportunity to stall the spread of COVID-19.

Assessment of Knowledge of Medical Students on an Important Health Issue Neagleria Flowri Infection at a Medical College of Karachi, Pakistan

Background: Since 2005 Neagleria Flowri infection appeared as a major health issue in Karachi, Pakistan. Most infections were acquired due to swimming in fresh water, ablution with fresh stagnant water. Our objective was to assess the knowledge of medical students regarding this important health issue and to highlight any deficiencies in medical education system. Material and methods: It was a prospective cross sectional study conducted at a medical college of Karachi, Pakistan. The sample size was calculated and sampling technique was randomized stratified sampling. Knowledge of the students was assessed through designed questionnaire. The data was recorded and analyzed on SPSS vs 21. Results: Our study included 250 medical students from five years of medical school. The highest response was recorded from final year regarding type of organism and habitat. Regarding treatment of Naegleria most correct response was from 4th year MBBS. Most final years answered correctly regarding the ablution as risk factor. The knowledge of medical students regarding incubation period of Neagleria was generally low. Conclusion: The knowledge of medical students regarding this significant medical issue appears low. The response of medical students was generally poor regarding treatment of infection, incubation period of infection and earliest presenting symptom of infection. Important measures should be taken to improve the knowledge of medical students regarding this significant health issue.

An age-structured SIR epidemic model with fixed incubation period of infection

This paper is devoted to the study of an age-structured SIR epidemic system on the basis of the model of polycyclic population dynamics of susceptible, infected and recovered individuals. This model was considered as a nonlinear competitive system of three initial–boundary value problems for the nonlinear transport equations with non-local integral boundary conditions and discrete time delay (fixed incubation period of infection). It was obtained the explicit recurrent formulae for computing the traveling wave solution of such system provided the model parameters (coefficients of equations and initial values) satisfy the restrictions that guarantee the existence and uniqueness of continuous solution. Using some insignificant simplifications the age-structured SIR model was reduced to the nonlinear autonomous system of delay ODE. It was studied the dimensionless indicators and conditions of existence of trivial disease-free equilibrium, two non-trivial endemic equilibriums for the incurable and curable infection-induced diseases, respectively. By carrying out an analysis of the local asymptotical stability of the solution of such system we obtain the restrictions for the time delay that guarantee the stability of solutions in the neighborhood of equilibriums. The numerous simulations of dynamics of SIR population illustrate the results of theoretical analysis.

Transmission of Foot-and-Mouth Disease Virus during the Incubation Period in Pigs.

Understanding the quantitative characteristics of a pathogen’s capability to transmit during distinct phases of infection is important to enable accurate predictions of the spread and impact of a disease outbreak. In the current investigation, the potential for transmission of foot-and-mouth disease virus (FMDV) during the incubation (preclinical) period of infection was investigated in seven groups of pigs that were sequentially exposed to a group of donor pigs that were infected by simulated-natural inoculation. Contact-exposed pigs were comingled with infected donors through successive 8-h time slots spanning from 8 to 64 h post-inoculation (hpi) of the donor pigs. The transition from latent to infectious periods in the donor pigs was clearly defined by successful transmission of foot-and-mouth disease (FMD) to all contact pigs that were exposed to the donors from 24 hpi and later. This onset of infectiousness occurred concurrent with detection of viremia, but approximately 24 h prior to the first appearance of clinical signs of FMD in the donors. Thus, the latent period of infection ended approximately 24 h before the end of the incubation period. There were significant differences between contact-exposed groups in the time elapsed from virus exposure to the first detection of FMDV shedding, viremia, and clinical lesions. Specifically, the onset and progression of clinical FMD were more rapid in pigs that had been exposed to the donor pigs during more advanced phases of disease, suggesting that these animals had received a higher effective challenge dose. These results demonstrate transmission and dissemination of FMD within groups of pigs during the incubation period of infection. Furthermore, these findings suggest that under current conditions, shedding of FMDV in oropharyngeal fluids is a more precise proxy for FMDV infectiousness than clinical signs of infection. These findings may impact modeling of the propagation of FMD outbreaks that initiate in pig holdings and should be considered when designing FMD control strategies.

Heterogeneous disease progression and treatment response in a C3HeB/FeJ mouse model of tuberculosis

ABSTRACTMice are the most commonly used species for non-clinical evaluations of drug efficacy against tuberculosis (TB). Unlike commonly used strains, C3HeB/FeJ mice develop caseous necrosis in the lung, which might alter the representation of drug efficacy in a way that is more like human TB. Because the development of such pathology requires time, we investigated the effect of infection incubation period on the activity of six drugs in C3HeB/FeJ and BALB/c mice. Mice were aerosol infected and held for 6, 10 or 14 weeks before receiving therapy with rifampin (RIF), rifapentine (RPT), pyrazinamide (PZA), linezolid (LZD), sutezolid (PNU) or metronidazole (MTZ) for 4-8 weeks. Outcomes included pathological assessments, pH measurements of liquefied caseum and assessment of colony-forming unit (CFU) counts from lung cultures. Remarkable heterogeneity in the timing and extent of disease progression was observed in C3HeB/FeJ mice, largely independent of incubation period. Likewise, drug efficacy in C3HeB/FeJ mice was not affected by incubation period. However, for PZA, LZD and PNU, dichotomous treatment effects correlating with the presence or absence of large caseous lesions were observed. In the case of PZA, its poor activity in the subset of C3HeB/FeJ mice with large caseous lesions might be explained by the pH of 7.36±0.09 measured in liquefied caseum. This study highlights the potential value of C3HeB/FeJ mice for non-clinical efficacy testing, especially for investigating the interaction of lesion pathology and drug effect. Careful use of this model could enhance the bridging of non-clinical results with clinical outcomes.

Development and validation of an integrated cell culture-qRTPCR assay for simultaneous quantification of coxsackieviruses, echoviruses, and polioviruses in disinfection studies

This study demonstrated the applicability of integrated cell culture-quantitative RTPCR (ICC-qRTPCR) for the simultaneous quantification of coxsackievirus, echovirus, and poliovirus in disinfection studies. Buffalo green monkey cells were inoculated with a 10-fold dilution series of mixed enteroviruses and incubated prior to qRTPCR quantification. Optimal assay conditions included three post infection washes and a 24-hour post infection incubation period based on successful differentiation between infectious and noninfectious viruses and significant and consistent viral replication rates. Ultraviolet disinfection studies were performed to validate the ICC-qRTPCR assay. Using the optimized assay, three-log microbial inactivation was achieved at UV doses of 30-44, 28-42, and 28-29 mJ/cm(2) for coxsackievirus B6, echovirus 12, and poliovirus 1, respectively. These results compare favorably to side-by-side assessments using conventional cultural techniques and values previously reported in the literature. This indicates that ICC-qRTPCR is a practical alternative for the simultaneous quantification of enteroviruses in disinfection studies.

Kuru in the 21st century—an acquired human prion disease with very long incubation periods

Kuru provides the principal experience of epidemic human prion disease. Its incidence has steadily fallen after the abrupt cessation of its route of transmission (endocannibalism) in Papua New Guinea in the 1950s. The onset of variant Creutzfeldt-Jakob disease (vCJD), and the unknown prevalence of infection after the extensive dietary exposure to bovine spongiform encephalopathy (BSE) prions in the UK, has led to renewed interest in kuru. We investigated possible incubation periods, pathogenesis, and genetic susceptibility factors in kuru patients in Papua New Guinea. We strengthened active kuru surveillance in 1996 with an expanded field team to investigate all suspected patients. Detailed histories of residence and exposure to mortuary feasts were obtained together with serial neurological examination, if possible. We identified 11 patients with kuru from July, 1996, to June, 2004, all living in the South Fore. All patients were born before the cessation of cannibalism in the late 1950s. The minimum estimated incubation periods ranged from 34 to 41 years. However, likely incubation periods in men ranged from 39 to 56 years and could have been up to 7 years longer. PRNP analysis showed that most patients with kuru were heterozygous at polymorphic codon 129, a genotype associated with extended incubation periods and resistance to prion disease. Incubation periods of infection with human prions can exceed 50 years. In human infection with BSE prions, species-barrier effects, which are characteristic of cross-species transmission, would be expected to further increase the mean and range of incubation periods, compared with recycling of prions within species. These data should inform attempts to model variant CJD epidemiology.

An outbreak of gastroenteritis and fever due to Listeria monocytogenes in milk.

After an outbreak of gastroenteritis and fever among persons who attended a picnic in Illinois, chocolate milk served at the picnic was found to be contaminated with Listeria monocytogenes. In investigating this outbreak, we interviewed the people who attended the picnic about what they ate and their symptoms. Surveillance for invasive listeriosis was initiated in the states that receive milk from the implicated dairy. Stool and milk samples were cultured for L. monocytogenes. Serum samples were tested for IgG antibody to listeriolysin O. Forty-five persons had symptoms that met the case definition for illness due to L. monocytogenes, and cultures of stool from 11 persons yielded the organism. Illness in the week after the picnic was associated with the consumption of chocolate milk. The most common symptoms were diarrhea (present in 79 percent of the cases) and fever (72 percent). Four persons were hospitalized. The median incubation period for infection was 20 hours (range, 9 to 32), and persons who became ill had elevated levels of antibody to listeriolysin O. Isolates from stool specimens from patients who became ill after the picnic, from sterile sites in three additional patients identified by surveillance, from the implicated chocolate milk, and from a tank drain at the dairy were all serotype 1/2b and were indistinguishable on multilocus enzyme electrophoresis, ribotyping, and DNA macrorestriction analysis. L. monocytogenes is a cause of gastroenteritis with fever, and sporadic cases of invasive listeriosis may be due to unrecognized outbreaks caused by contaminated food.

Kinetics of Duck Hepatitis B Virus Infection Following Low Dose Virus Inoculation: One Virus DNA Genome Is Infectious in Neonatal Ducks

Using pooled serum from congenitally duck hepatitis B virus (DHBV)-infected ducks as inoculum, we examined the effect of virus dose on the incubation period of infection and on the patterns of spread of virus infection in the liver. The pooled serum inoculum contained 9.5 × 109DHBV genomes per milliliter and had an infectivity titre (ID50) in newly hatched ducks of 1.5 × 1010per milliliter with a 95% confidence interval of 3.0 × 109to 6.3 × 1010ID50/ml, indicating the equivalence between one DHBV genome and one infectious unit within the limits of the assays. The incubation period of infection was inversely related to the dose of inoculum and the onset of viraemia ranged from Day 6 with the highest dose to Day 14 or 29 with the lowest dose inoculum. To study the spread of virus infection from a low percentage of initially infected cells we inoculated newly hatched ducks intravenously with sufficient DHBV (1.5 × 103ID50) to infect only ∼0.0001% of total liver cells. DHBV infection first reached detectable levels on Day 4 postinoculation (p.i.) and was detected in ∼0.035% of hepatocytes, most of which occurred as single cells or pairs of cells, indicating that a number of rounds of infection had occurred with the spread of virus both to adjoining cells, i.e., by cell-to-cell spread, and to cells located in other parts of the liver lobule. Despite some bird-to-bird variation in timing, the percentage of infected hepatocytes increased exponentially with a mean doubling time of 16 hr from Day 4 to Day 14 p.i., by which time replication was seen in >95% of hepatocytes. This rapid dissemination from a small number of infected hepatocytes suggests that, in neonatal ducks, there are no major delays in virus replication within the liver, that any innate and adaptive defence mechanisms operating during the first 10 to 14 days of infection are insufficient to contain virus spread, and that even a small number of infected hepatocytes produce enough progeny to rapidly infect the remaining hepatocytes.

Persistence of Anaplasma marginale (Rickettsiales: Anaplasmataceae) in male Dermacentor andersoni (Acari: Ixodidae) transferred successively from infected to susceptible calves.

The persistence of Anaplasma marginale Theiler in male Dermacentor andersoni Stiles ticks exposed to the organism as adults was studied as the ticks were successively transferred to five susceptible calves. All calves fed upon by these ticks rapidly developed clinical anaplasmosis; incubation periods of infection ranged from 19 to 26 d and did not change significantly with successive feedings. Development of A. marginale in tick midgut and salivary glands was followed daily during tick feeding (total, 35 d) with light microscopy and DNA hybridization. With microscopy, A. marginale colonies persisted in midgut cells throughout the experiment. Large colonies were observed in gut muscle cells on days 8 through 35 and were the predominant infected cell type during this part of feeding. Colonies were seen in salivary gland acini from day 2 throughout the 35-d experiment. The DNA probe confirmed the presence of Anaplasma DNA in midgut and salivary glands throughout the experiment. Quantitative estimates of infection intensity in tissues of individual ticks approximated 10(7) initial body equivalents, confirming heavy infections. A marginale in midgut tissues decreased with feeding time, whereas the estimated number of organisms in salivary glands remained constant. These data demonstrate that D. andersoni males are efficient vectors of A. marginale and may be potential reservoirs of infection for ruminants for extended periods.