Optimal control analysis of a tuberculosis model with exogenous re-infection and incomplete treatment

A new mathematical model of tuberculosis (TB) featuring exogenous re-infection and incomplete treatment is presented and analyzed. The model divides total population into susceptible, latently infected, actively infected (uninformed and enlightened), and treatment classes. The model with or without incomplete treatment exhibits backward bifurcation phenomenon, which is caused by the presence of exogenous re-infection. However, further investigation reveals that the absence of incomplete treatment has the potential to reduce the backward bifurcation range significantly. The global dynamics of the TB model without exogenous re-infection is completely determined by the basic reproduction number under certain modifications on parameters. Furthermore, the model is extended to include three time-dependent control functions, such as public awareness campaign, treatment effort, and preventive control against incomplete treatment. The existence of the optimal control for the nonautonomous model is proven and the three controls are characterized using Pontryagin's maximum principle. Numerical simulations are performed to show the significance of singular implementation of each of the controls and combination of the three controls in minimizing the TB burden in the population.     

Prevalence of different skin conditions in an outpatients' setting in north-western Nigeria

BACKGROUND: Information on skin diseases in north-western Nigeria is scanty. We therefore conducted a prospective survey of 2611 new patients seen between August 1999 and July 2001 at the consultant medical/dermatology clinics of Usmanu Danfodiyo University Teaching Hospital, Sokoto, Nigeria. METHODS: The personal bio-data of all consecutive patients with skin diseases were documented. They were examined and the diagnoses, which were based on the history of presentation and physical examination, were recorded. Bacteriologic, mycologic, and histologic confirmations were obtained as appropriate. RESULTS: Seven hundred and forty-six patients (28.6%) had skin diseases. There were 407 male and 339 female patients aged between 0.17 and 90 years; the median age was 27 years. The median ages for male and female patients were 28 and 25 years, respectively. There were 900 skin diseases seen in the 746 patients. The majority of skin diseases were found amongst the younger age group, which represented over 85% of the patients. Infectious and parasitic skin diseases accounted for 44.4% of cases; eczema, acne, papulosquamous, and pigmentary skin disorders were observed in 14.1%, 7.0%, 6.4%, and 6.0% of cases, respectively. CONCLUSIONS: Preventable skin diseases are common in north-western Nigeria and predominantly affect individuals in the highly productive age group. Health education is therefore necessary to curb their spread, reduce the associated morbidity, and improve the health status of the population. A concerted effort should be made to train health workers in the diagnosis and treatment of the more common dermatologic conditions.     

Dermatology in Nigeria: evolution, establishment and current status

The history of dermatology in Nigeria can be summarized by listing the "first events and people" who played major roles. The first dermatologist to work in Nigeria was George HV Clarke in the mid 1950s. He was based in Lagos. Organized training/teaching and research in dermatology was first established at the University of Ibadan in the western region of Nigeria, in collaboration with the Institute of Dermatology, London. The first set of dermatologists from the Institute on secondment who established dermatology as a discipline at the University of Ibadan were Roger RM Harman as lecturer and GC Wells as the Visitor/supervising consultant in 1962. The first indigenous dermatologist was Anezi Okoro. The first female dermatologist was Yetunde M Olumide. The first (and still the only) Department of Dermatology was at the Obafemi Awolowo University in Ile-ife in the western region of Nigeria, started by a German trained dermatologist: F. Soyinka, the junior brother of Nigeria's first (and only) Nobel Laureate. The first leprologist in Nigeria was George Stanley Browne, a medical missionary. He worked briefly as an associate lecturer (1963-65) under Professor Alexander Brown at the University of Ibadan. Most of the events in Nigeria's dermatology history as well as the greatest concentration of dermatologists in the country have been around the south-western part of the country: Lagos, Ibadan, and Ile-ife. The military coup and the political events that occurred thereafter had a great negative impact on the development/growth of dermatology in Nigeria. The documentation by Ryan as of 1990 indicates that many African countries still do not have a single trained dermatologist.     

Effect of proguanil interaction on bioavailability of cloxacillin

METHODS: To investigate a potential drug-drug interaction between proguanil (PG) and cloxacillin (Clox). Seven healthy adult volunteers received a single oral dose of Clox plus coadministration of single oral doses of PG and Clox in a simple cross-over manner after a wash-out period of 1 week. Total urine voided was collected at predetermined time intervals over 12 h. Amount of Clox in urine was determined by a reversed-phase high-pressure liquid chromatography method. RESULTS: The mean maximum excretion rate [(dDu/dt)max] of Clox when taken alone was 16.13 +/- 2.92 mg/h at tmax of 1.86 +/- 01.07 hours, whereas in the presence of PG, it was 7.72 +/- 3.24 mg/h at tmax of 2.43 +/- 00.98 hours (P < 0.0001). The total amount of Clox excreted in urine (Du infinity) in 12 h was markedly reduced by coadministration with PG by up to 48% with Du infinity of 49.57 +/- 8.16 mg after Clox alone and 25.81 +/- 8.46 mg in the presence of PG (P < 0.0001). The tmax and t1/2-values obtained from the excretion rate plot were lengthened by 23 and 34%, respectively, in the presence of PG but the differences were not statistically significant (P > 0.05). CONCLUSION: These pharmacokinetic values indicate slowed and diminished absorption (bioavailability) of Clox when concurrently administered with PG. The clinical implication is unknown. However, concomitant administration of the two drugs during antibacterial therapy should be done with caution so as to avoid subtherapeutic levels of Clox, which can lead to treatment failure and facilitate drug resistance.